H

Height Above Average Terrain (HAAT)
A measurement used by the FCC in conjunction with station power to determine the antenna contour of a broadcasting FM radio station.  Expressed as the antenna height above an elevation average, which is  calculated by determining the average ground elevation in all directions from the transmitter site between 1.5 and 10 miles away. 

Hertz (Hz)
One complete cycle of the radio wave per second

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Heterodyne (het)
A high-pitched whistling sound caused by two carriers interfering with each other.  The pitch of the whistle depends on the frequency difference between the two carriers.  On AM radio, a het is a fantastic way to identify trans-atlantic and trans-pacific signals.  This is because stations in North and South America are separated by 10 kHz while Europe, Asia and Africa all use 9 kHz spacing.  Because of this difference in spacing, stations that are within 1-3 kHz from each other will normally cause a het to be heard, alerting you that a station is being received on a “split” frequency outside of your normal frequency spacing.  An example of this for US DXers is 890 kHz and the het produced by Algeria’s Chaine 1 on 891 kHz.  An example of this for European DXers would be 1089 kHz, which is normally TalkSPORT in the United Kingdom, however U.S. stations on 1090 kHz such as WBAL in Baltimore, Maryland can cause a distinct het to be heard. Hets are fantastic propagation markers to know when DX is coming in from across the ocean!

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High Frequency (HF)
The portion of the radio spectrum that lies above the mediumwave bands.  Generally speaking, HF starts at 1.8 MHz (1800 kHz) and runs through 30 MHz (although some consider the 50-54 MHz frequencies of the amateur radio 6-meter band to be part of HF as well, while others contend it classifies as VHF).  On HF, you will find heavy usage from amateur radio, international shortwave broadcasters, the ‘tropical bands’, utility communications (essentially anything that is not broadcast or amateur including military communications, transoceanic airline communications, maritime communications, some satellite communications (including weather fax) and much, much more), time stations (such as WWV in the United States and CHU in Canada)

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I

Identification (ID)
Normally, this will consist of the call letters of the station (for those that use them) and are most frequently noted at the top of the hour.  In the United States, all radio stations are required by law to provide a full “legal ID” in English which consists of their Call Letters, immediately followed by the community or communities identified in the station’s license.  The only thing allowed to be presented between the call letters and location is the frequency and/or the licensee information.  This must be presented on-air as “close as possible” to the top of the hour” in a “natural break in program offerings.”  A legal ID in the United States might read:  “This is 680 WAAA, Anytown.  An Anytown Radiocasting radio station.”  Most DXers consider it to be in poor form to add a radio station to one’s logbook without hearing some form of positive identification (normally, the call letters).

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Impedance
The opposition against the flow of electronic current and radio energy that an electronic component or circuit presents.   Impedance is measured in ohms.  For optimum performance, the impedance of a receiving antenna, the feedline and the antenna connector on the radio should be approximately equal.  Impedance mismatches will degrade the performance of the receiving equipment.

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Ionosphere
Electrically charged and Ionized layers forming a portion of the upper atmosphere of Earth (can be found between 40 to 400 miles or 50 to 600 km above the Earth’s surface), where it merges with the magnetosphere.  It is also the portion of the atmosphere which has the most interaction on radio signals in either absorbing, refracting or reflecting them back to the surface.  Composed of multiple layers, each with their own characteristics.

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J

Jamming
Intentional interference caused to radio signals to prevent the intended audience from receiving the signal.  This is commonly played out when there are adversarial political relationships such as between Cuba and the United States, between North and South Korea, etc.  This can also be done to block programming a government considers contrary to their broadcasting standards such as in the 1960s and 70s the efforts of the British government to jam the transmissions of offshore pirate radio stations.

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JJ
Radio station programming/content that is in Japanese.

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K

Kilohertz (kHz)
A unit of measuring frequency equal to 1000 hertz; Frequencies for stations in the AM/mediumwave bands are usually expressed in kHz. 

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Kilowatt (kW)
A unit of measuring power equal to 1000 watts; The transmitter power of AM and FM radio stations are usually stated in kilowatts and in watts for very low-power stations.

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K-Index (K)
A measure of short-term changes in geomagnetic activity with values that range from 0 to 9; the mid-latitude K-Index is released every three hours.  Since K-index is a much more short-term measurement than the longer term A-index, a high K-index is usually a predictor that that A-Index will be going up soon. Like with the A-Index, there are many web sites which gather this and other solar indicator values as an aid to DXers (see the General DX>Solar Conditions area of the DX Central Links page).

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Kiwi SDR
A specific type of SDR that is commonly used by DXers for their online capacity, as they are able to be streamed online.  This permits a DXer to stream a Kiwi SDR from anywhere around the world to observe radio conditions at that location.  This is especially helpful when trying to hone-in on a particular station by trying to find a Kiwi SDR located near the target station.  As an example, one night, I was trying to tune in a station located in Venezuela on 780 kHz.  By using a Kiwi SDR located on the island of Bonaire (right next to Venezuela) I was able to verify that the programming content I heard on my radio was indeed coming from the Venezuelan station.  The proliferation of streaming online receivers has made it possible for DXers to DX virtually from anywhere both as a research and DX aid as well as to answer the age-old question, “I wonder what DX would sound like from….”!

KK
Radio station programming/content that is in Korean.

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L

LA
Shorthand abbreviation for Latin America

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Legal ID
In the United States, every radio station is required by law to provide a ‘full legal ID” at the top-of-the-hour (as close as possible to the beginning of the hour, during a natural programming break).  This legal ID must be in English and must include the station call letters and city of license with nothing else between them (with the exception of the operating frequency).  During sports broadcasts, network announcers usually indicate they are going to “pause for 10 seconds for station identification, this is the _______ radio network”.  This is when you should hear the station ID (hopefully, unless the person running the board at the station is not paying attention).  Outside of the US, there are varying requirements for providing identification (if there are any at all). 

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Longwave (LW)
In a general sense, refers to any frequencies below the MW band (below 530 kHz). Many non-directional beacons used for aircraft and ship navigation can be found here.   There are an increasingly smaller number of broadcasters that can be found here from 153 - 279 kHz, primarily originating n Europe, the Middle East, Central Asia and Siberia. However due to the high costs of transmitter and antenna maintenance, these stations are becoming increasingly less common.

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Longwire antenna
An antenna made up of traditionally copper wire (though other wire can be used) and of varying lengths.  The longer the better to achieve sufficient signal strength and directionality.  Differs from a Beverage in that there is no grounding or terminating resistor at the terminating end of the antenna.  Shorter antennas are much more unidirectional however less efficient.  For most DXers, including the author, this is the first antenna many of us were able to use, stretching a run of copper wire (can be found at most hardware stores in the wire section) out of a window and into and through a nearby tree. 

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Loop antenna
A directional antenna consisting of loops of antenna wire forming a round or rectangular figure.  Sizes can vary from small, indoor desktop loops, larger 4-6 foot (1-2 meters) loops on a stand (can be used indoors or outdoors) and larger outdoor loops (such as the W6LVP or Wellbrook ALA-1530 magnetic loops).  Loop antennas can either be tuned (which involves tuning the loop to the desired frequency to provide adequate amounts of gain to the inbound signal) or untuned (for more broadband use, though usually requires some sort of pre-amplifier to boost signal strengths to a usable level).  Due to the figure-8 receiving pattern found on loop antennas, the main benefit of a loop antenna is the ability to turn the loop to achieve acceptable boost in signal strength from desired stations or (and this can be the more effective option) to “null” or eliminate undesired signals (including local stations, routinely heard stations and noise).  Loop antennas receive along their axis and null to their broadside.  So, a loop antenna which is oriented to the north and south would favor signals from those directions while attenuating signals from the east and west.  Magnetic loops especially are susceptible to having their antenna pattern altered by anything metal so it is best to have them mounted as far from your home as possible. 

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Lower sideband (LSB)
Used widely in AM/mediumwave DX, this is the lower sideband of a transmitter’s carrier. Many communications receivers, software-defined radios (SDR) and even some portable radios have this feature.   If you were looking at a signal on a spectrum display or waterfall on a software-defined radio (SDR), this would be the signal to the left of the carrier frequency of an AM radio station.  Can be used to great effect to reduce or eliminate co-channel interference from stations above the desired frequency.  For instance, if you have a local station on 1450 kHz, and are trying to DX on 1440 kHz, you can engage the radio’s LSB to narrow the bandwidth of the received signal to only the part of the signal found below the carrier frequency.  In many cases, this can greatly or entirely reduce co-channel interference. 

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LPFM
Shorthand abbreviation for a low power FM radio station.  These are specifically licensed radio stations in the United States and many other countries that serve very specific location/regions.  Often referred to as microbroadcasting.   Coverage areas of LPFM can sometimes not extend past a few blocks in a city environment. 

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Local Sunrise Time (LSR)
Defined as the time in a given location which constitutes sunrise.  Used in the application of Pre-Sunrise Authority and Critical Hour privileges for radio stations in the United States.  Also used in determining sign-on times for stations that are Daytime-only.  In the United States, since sunrise times can change daily, the FCC uses the sunrise time from the 15th of the month, adjusted to the nearest quarter hour.  So, a local sunrise that occurs at 07:41 on the 15th of the month, the actual LSR of the station would be 07:45. 

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Local Sunset Time (LSS)
Defined as the time in a given location which constitutes sunset.  Used in the application of Post-Sunset Authority and Critical Hour privileges for radio stations in the United States.  Also used in determining sign-of times for stations that are Daytime-only.  In the United States, since sunset times can change daily, the FCC uses the sunrise time from the 15th of the month, adjusted to the nearest quarter hour.  So, a local sunset that occurs at 5:41 on the 15th of the month, the actual LSS of the station would be 5:45. 

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M

Maximum Usable Frequency (MUF) Based on propagation, represents the highest frequency allowing for DX reception/transmission.  For FM DX, it is a reflection of band openings especially as it relates to Sporadic Es skip.  As an Es opening intensifies, the MUF increases, eventually reaching the FM band.

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Mediumwave (MW)
Radio frequencies found between 530-1700 kHz (in the Western hemisphere) or 531-1611/1702 kHz (in the Eastern hemisphere).  Only stations licensed by their country’s government body for radio licensing are permitted to transmit on these frequencies.  Mediumwave (or Medium Wave by some) is the more commonly used terminology used outside of the United States.  Within the United States, this band is most commonly referred to as the “AM” or “AM Radio”. 

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Megahertz (MHz)
A unit of measurement of frequency equivalent to 1,000,000 Hz or 1,000 kHz.  This is the primary frequency unit used for FM radio frequencies. 

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Megawatt (MW)
A unit of measurement of power equivalent to 1,000,000 watts.  There are some stations in Europe and Asia that have powers in this range, though they are not as common as they once were. 

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Meteor Scatter (Ms) 

A propagation commonly found in VHF frequencies​ and therefore used with FM DX, by which FM signals are refracted through the ionized trails of meteors entering the Earth's atmosphere.  Can last anywhere from milliseconds to several minutes.

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Mode
Can refer to the transmission method of a transmitted signal (such as AM or FM) but also can refer to the receiving mode within a communications receiver, software-defined radio (SDR) or portable radio (AM, FM, LSB, USB, SSB). 

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Modulation
The term used for the addition of information to an electronic signal by changing the carrier.  In AM and FM radio, this is through changing the amplitude of the carrier (Amplitude Modulation or AM) or the frequency of the carrier (Frequency Modulation or FM).  This additional information is the actual programming content of the station and can include music, voice and sounds/tones.

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Morning Drive
Like Afternoon Drive, this is one of the most listened to periods of time for a radio station and typically runs from roughly 6am to 9am local time.  Coined as this is the period of time that most listeners are in their vehicles commuting to their jobs.  Depending on the format of the radio station, this can be an excellent time to be able to pull an identification for received stations – especially since this usually also coincides with local sunrise enhancement.  Stations that are formatted primarily in News/Talk (especially those with high power) are more likely to have regular traffic/weather updates and these almost always contain some sort of identifying information (“traffic and weather together on the 8s” or “traffic and weather every 10 minutes” are common marketing tools used by stations to lure listeners – but it also works for DXers!)   

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Mountain Daylight Time (MDT)
Time zone in North America that is UTC -6 (six hours behind UTC time).  Only used during “daylight savings” periods from early spring to late fall.

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Mountain Standard Time (MST)
Time zone in North America that is UTC -7 (seven hours behind UTC time).  Only used outside of “daylight savings” periods from late fall to early spring.  

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Mx
Shorthand abbreviation to refer to music. 

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N

Na
Shorthand abbreviation for the continent of North America.  Can also refer to National Anthem (NA).  In the United States and many other countries, radio stations will sometimes play their national anthem at signoff, at sign-on or sometimes both.  Hearing a national anthem is a really fantastic way to help identify a station that you are hearing. 

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Network
A grouping of radio stations around common programming content.  This can be anything from a music station that is part of a news network (national or sometimes state/provincial networks), a station whose format is entirely reliant upon a network (such as a sports formatted station carrying ESPN or other nationally syndicated network content), it can be a sports network that carries a particular sports teams’ games/matches (such as Premier League, National Football League, etc.) or it can even be a network that delivers a specific radio program (Coast-to-Coast AM, Rush Limbaugh, Focus on the Family) that a radio station can broadcast on their channel.  Networks usually will have “network” breaks which consist of a combination of network advertisements (carried to all stations down “the line”) and slots for local advertisements (so that a station can sell advertising time on those specific programs).  Network content can be tricky to navigate for a DXer, as being that they are often nationally or regionally syndicated, and can go for long stretches without any chance for the carrying station to provide an identification,  a DXer can spend a large amount of time on a single frequency, chasing a single station waiting for them to ID.  This is especially true during overnight and weekend periods.  The proliferation of software-defined radios (SDR) has helped to circumvent this issue by allowing DXers to fast-forward/rewind through content that does not contain identifying information. 

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Noise blanker (NB)
A feature found in many communications receivers, software-defined radios (SDR) and some portable radios that helps to reduce or eliminate electric pulse noise from a frequency. 

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NOS
Shorthand abbreviation that refers to Nostalgic programming on a radio station. Similar to EZL, although the genre has shifted a bit to include softer hits from The Beatles (think Yesterday), Michael Buble, Pat Boone, Tony Bennett, Louis Armstrong, Harry Connick Jr.  Often referred to as “Adult standards”.

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Notch filter
A feature found in many communications receivers, software-defined radios (SDR) and some portable radios that allows a DXer to filter certain frequencies that are unwanted from the signal path.  This can include heterodynes or even specific frequencies within the programming content (low frequencies, for example).  Some receivers/SDRs even have what is known as an Auto Notch Filter (ANF) which will try to eliminate unwanted signals on its own.  Many a DXer tuned to a frequency looking for heterodynes from trans-oceanic DX only to find none were there and only later realizing it was because they had their Auto Notch Filter on and it was suppressing those hets from being heard!

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NWS/NX
Shorthand abbreviation for News programming content on a radio station.  This can either be the primary format of the station (as in a News/Talk station) or simply a news update on any station (such as a primarily music formatted station that is doing top-of-the-hour network news). 

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O

Oc
Shorthand abbreviation for the continent of Oceania. 

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OLD
Shorthand abbreviation that refers to Oldies programming on a radio station.  This is often music from the late 1950s to late 1970s from such artists as The Beatles, The Beach Boys, The Rolling Stones, Buddy Holly, Motown artists, etc.  There can be some crossover between this format and NOS or CLR in some stations.  Oldies stations will often brand as such (“Oldies 92.5”) or carry verbiage such as “Good time oldies”. 

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Online SDR
Refers to a software-defined radio (SDR) that has been made available to stream online.  One of the more popular SDRs for this is the Kiwi SDR and one of the more popular sites to browse available streams is SDR.HU.  With this technology, it is possible for a DXer to pull up a receiver that is located close to a station they are trying to target for reception to confirm programming details.  It also allows a DXer to take a virtual DXpedition around the world any time they want!  The proliferation of SDR technology and online streaming has been one of the biggest advances in DXing in the last 30 or more years!

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Opening
Refers to a period where there is better than usual propagation conditions to a certain area.  For instance, on the East Coast of the United States, one can have an opening into locations such as Europe, Africa, South America, etc. 

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P

Pacific Daylight Time (PDT)
Time zone in North America that is UTC -7 (seven hours behind UTC time).  Only used during “daylight savings” periods from early spring to late fall.

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Pacific Standard Time (PST)
Time zone in North America that is UTC -8 (eight hours behind UTC time).  Only used outside of “daylight savings” periods from late fall to early spring.  

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Parallel (//)
When a station’s programming is simulcast on more than one frequency at a time, a DXer can use those other transmissions to establish a parallel to confirm receipt of the original station.  This is commonly used when identifying Cuban radio stations as their national networks will often transmit on many different AM radio frequencies.  For instance, Radio Progresso transmits on 640 kHz as well as 890 and 900 kHz as well.  Therefore, if you are hearing Spanish programming content on 640, you can check to see if you are hearing that same content on 890 and/or 900 kHz.  If so, you have established that the 640 content is parallel to 890 and 900 kHz (written as //890 and 900).  This can also be used when comparing a transmitted signal’s programming with that of an online Web stream of a station’s on-air programming.  Web streams are often delayed from the on-air signal anywhere from 2 seconds to a minute or more, but you can still use this method to great effect to confirm the identity of the station being received.  A word of caution, though.  Syndicated network content does not make for a good source of confirmation, as that same content can be found on any station carrying that particular network.  For instance, a station running ESPN sports programming would sound like any other station on that frequ3ncy that is also running ESPN sports programming.  Also, note that many stations will run special web stream-only advertising during commercial breaks, so advertising may sound different on on the Web stream when compared to the on-air signal. 

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Phaser
A device that combines the signals received on two different antennas, and then allows the user/DXer to adjust the level (or amount of signal) and the phase of the incoming signals in order to develop a steerable null.  What these means for the DXer is that by using a phaser, you can null out strong local stations to DX what is left on the frequency without them, or to reduce or eliminate co-channel interference to allow for better DX on those adjacent frequencies.  You can also use a phaser to null or boost desired signals on a frequency (even those that are not overly strong), in effect allowing you to steer the antenna pattern created by the combination of the two antennas. 

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Pirate
An illegal, unlicensed and otherwise unauthorized broadcasting station, usually broadcasting music.  Also commonly referred to as a clandestine. 

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Polarization
Refers to whether an antenna transmits/received from a horizontal or vertical position.  If a transmitting antenna is in one polarization and the receiving antenna is in the opposite polarization, the receiving end will notice a significant loss of signal strength.  There are antennas that are ‘circularly polarized” which contain both horizontal and vertical polarized elements to rectify this situation.

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Portable Radio
A smaller receiver that can be used portably.  Often will have an option to allow it to run on batteries.  Some portable radios only cover AM and FM frequencies only, while others can include shortwave frequencies and even VHF aircraft frequencies.  Most will have a built-in ferrite rod antenna that is used for AM radio reception.  These antennas are normally mounted within the radio so that it is parallel to the horizontal orientation of the radio.  As such, you can turn a portable radio along this horizontal axis and it will act in a manner similar to a loop antenna.  However, the signals come in to the ferrite rod broadside to the antenna.  That is to say, if the radio is oriented horizontally, the two ends are the nulls, while the signals are coming in perpendicular to the radio itself.  For shortwave, FM/VHF reception, most portables will include a telescopic whip antenna.  Many DXers, this author included, have used portable radios to great effect in logging large numbers of AM and FM radio stations including non-domestic ones!  They are a great balance of price and performance for any DXer, especially those new to the hobby!

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PP
Radio station programming/content that is in Portuguese.

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Preamp
Short for: pre-amplifier.  A feature found on some communications receivers, software-defined radios (SDRs), some receiving antennas, and is sometimes found in external equipment that can be purchased separately.  A preamp boosts weak signals, however it is important to remember it will also amplify noise and interference

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Preselector
Normally found in an external unit that can be put in-line between an antenna and a radio, it allows a DXer to tune a receiver’s amplifying circuitry for increased sensitivity on a desired frequency range.  Much like the tuning function on a tunable loop antenna, a preselector allows you to essentially add an additional “tuning” to the receiver to the desired frequency, which boosts its ability to pull in weak signals.

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Propagation
The process by which a radio wave or radio signal travels between the transmitting location and the receiving location.  There are many different methodologies by which this can occur in both AM and FM DX. 

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Pre-Sunrise Service Authorization (PSRA)
Authorization from the FCC for daytime-only stations in the United States to sign on at 6 AM local time, even if this is prior to their local sunrise time.  This is due to the fact that during certain times of the year, sunrises happen later, thereby cutting short the amount of time – especially during morning drive – that a station can be operational.  PSRAs are a way around this for stations to provide programming content to their communities outside of the time that would be normally allotted to them, due to varying sunrise times in winter.

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Post-Sunset Service Authorization (PSSA)
Authorization from the FCC for daytime-only stations in the United States to sign off at 6 PM local time, even if this is after to their local sunset time.  This is due to the fact that during certain times of the year, sunsets happen earlier, thereby cutting short the amount of time – especially during afternoon drive – that a station can be operational.  PSSAs are a way around this for stations to provide programming content to their communities outside of the time that would be normally allotted to them, due to varying sunset times in winter.

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Public Service Announcement (PSA)
A commercial aired by a radio station for a non-profit organization or for a government program.  Normally “public service announcement” will be explicitly mentioned, most will also mention “the ad council” as well.  PSAs can be national, regional and even local in nature.  If you hear a PSA that mentions a specific US State, for instance (i.e “the Missouri Association of Broadcasters,” “the South Carolina Department of Transportation” ) that can be a huge help in identifying which station you are hearing.

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PX
Shorthand abbreviation for ‘program’.  This will usually refer to a specific program within a block of programming (i.e. the Rush Limbaugh Program, the Bill Davis Coach’s Show, etc.). 

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Q

Q-Codes
A series of 2-3 letter codes, each starting with the letter Q, that began in use with the telegraph industry.  The codes are used as shorthand for commonly used phrases.  Examples include QTH for location, QRM for man-made interference and QSO for conversation. 

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Quarter Hour
In addition to top-of-the-hour and bottom-of-the-hour, the quarter hour periods (at :15 and :45 after the hour) are also when many stations will take an advertising break and therefore can be a time when a station may identify.  Even if the station does not complete a full ID with call letters, they may present some other sort of identifying information such as a branding slogan, local advertisements (with local business names, phone numbers and addresses) or weather forecast.  In addition, since the FCC rounds sunrise and sunset times to the nearest quarter hour, stations that are daytime-only may be noted signing on/off during these times which can also present a fruitful opportunity to try to catch an identification. 

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QRM
A Q-code which dates back to the days of the telegraph, which stands for man-made interference.  For AM/FM DXers this can be things such as television, electrical noise, etc.

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QRN
A Q-code which dates back to the days of the telegraph, which stands for natural interference.  For AM/FM DXers, this can be things such as lightning (which AM radio is much more susceptible to), atmospheric noise and noise created by the sun (especially during summer months).

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QSL
A Q-code which dates back to the days of the telegraph, which stands for “I confirm reception.”  For AM/FM DXers, a QSL is a written confirmation received from a radio station in exchange for a reception report sent by the DXer that contains programming details.  This QSL serves as verification that the DXer did in fact hear that station.  DXers have collected these QSLs since the early days of radio.  Though not as common as in past years, stations can and do still send station stickers, coverage maps, advertising rate sheets and other promotional materials to DXers who send reception reports.

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QTH
A Q-code which dates back to the days of the telegraph, which stands for location.  For AM/FM DXers this will normally mean their home location where their commit the majority of their DX.  It can also refer to the location of a DXpedition or other non-home location where DX can occur.  Also, it can refer to the location of the transmitting station.

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R

Radio Data System (RDS)

Digital text information that is embedded in the transmitted signal of an FM radio station.  Radios that have RDS-enabled will display this information to the listener.  Each station has a unique PI Code (which is searchable on sites such as the WTFDA database for North American stations) which will display with other RDS information sent by the station.  Each station is different but usually will send data such as call letter/slogan or other identifying information, title/artist of the song playing or program information.  Can be a HUGE help in rapidly identifying an FM DX station that is being received.  

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Reception report
A written description of program details gathered by a DXer and sent to a broadcast radio station in hopes that the station will verify those details in the form of a QSL card or letter.  Reception details should include specific information about programming content, specific verbiage used and any other identifying characteristics that will demonstrate reception of the station in question (phone numbers, addresses, local business/advertiser names, weather forecasts and especially any station branding or verbiage during identifications).

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REL
Shorthand abbreviation that refers to Religious programming on a radio station.  This is a very broad term that can encompass many different variations of programming.  It can be used to indicate content that is educational in nature (bible teachings and other discussion-based programming), call-in religious shows, sermons and music.  However, in most cases, there is a distinct difference between REL and GOS content.

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Radio Frequency (RF)
The oscillation rate of electrical or electromagnetic energy that is found between approximately 20 kHz and 300 GHz.  These frequencies are the rate at which an oscillating current (created by information from a transmitter) can radiate from a conductor (antenna) and into the surrounding air (and into the ionosphere) in the form of radio waves.

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RF gain
A control within a communications receiver, software-defined radio (SDR) or portable radio that controls the amount of sensitivity of the radio.  The more sensitive it is, the more it is capable to pull in weak signals.  However, in the presence of strong signals (such as a single local station or multiple strong stations) it can be beneficial to reduce the sensitivity of the receiver in order to allow signals to rise and fall individually and make them easier to decipher.

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RR
Radio station programming/content that is in Russian.

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Rx/RX
The shorthand abbreviation for receiver/receive. 

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S

Software-Defined Radio/Receiver (SDR)
A device that contains the necessary circuitry to decode inbound radio signals, often over a large frequency range, that is then interfaced with a computer and special software.  SDRs will have connections for at least one antenna and require an interface software (much of which is available at no cost) to act as an interface with the SDR device. Most SDRs simply connect via USB connection to a laptop, tablet or desktop computer.  SDR pricing can range cost-effective options to much more sophisticated and expensive systems with integrated software.  Some of the benefits of using an SDR over a traditional communications receiver or portable radio include:  the ability to record or schedule recordings of part of or even entire radio bands, extensive filtering and digital signal processing, radio signal visualizations through waterfalls and spectrum displays, the ability to stream SDR receptions over an Internet connection for remote listening capability, the ability to grab screen captures of SDR receptions for documentation or even posting online.  The SDR community Is an ever-growing one and new uses and capabilities are being discovered and implemented all the time.  Just in recent years, the technology has advanced to allow the performance of smaller, low-cost SDRs to actually rival that of much more expensive and less flexible communications receivers. 

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Selectivity
Refers to the ability of a receiver to reject signals that are being received on frequencies adjacent to the desired frequency. Measured in decibels (dB).  The more selective a receiver is, the more capable it will be at rejecting co-channel interference, as well as being less subject to spurious signals caused by overload from strong local stations.

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Sensitivity
Refers to the ability of a receiver to receive weak signals and measured in microvolts (mV).  With sensitivity, the lower the number, the more sensitive the receiver is.  Receiver sensitivity is only part of the equation though when trying to pull in weak signals. The sensitivity of your antenna, the noise at your location, co-channel interference and ground conductivity are just some of the other factors that can impact the ability

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Shack
Colloquial term used by DXers and amateur radio operators to refer to the room where they house their radio equipment.

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Shortwave (SW)
Generally speaking, it is the part of the radio spectrum located anywhere between mediumwave and VHF (most commonly 1.8 MHz to 30 MHz).  It also is commonly used to refer to the portion of the HF frequencies where one would typically find international shortwave broadcasters (or specifically, the DX of international shortwave broadcasters).

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Shortwave Listener (SWL)
Another commonly used term/abbreviation (the abbreviation is the more commonly used) for a shortwave DXer.

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Shortwave Listening (SWLing)
Another commonly used term/abbreviation (the abbreviation is the more commonly used) for shortwave DXing.

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Sideband
In Amplitude Modulation, where the carrier wave is at the center of the signal, there are two sidebands on either side of that carrier wave.  These sidebands essentially contain half of the information contained within the radio signal (half of the voice, music, sounds, etc.).  As such, a sideband refers to a portion of the modulated carrier that is either above or below the center carrier wave.  The portion above is referred to as upper sideband (USB) while the portion below is the lower sideband (LSB).  By switching to USB or LSB, one can often reduce or even eliminate entirely co-channel interference from local and other strong radio stations.

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Single sideband (SSB)
Modulation that removes one sideband and the carrier and transmits only the remaining sideband.   This is opposed to an amplitude modulation (AM) transmission in which both sidebands are used to carry a message.  SSB (either upper or lower) is a popular transmission method of Amateur Radio operators as well as maritime and aviation transmissions over HF frequencies.

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SINPO
A system used in reception reports by DXers to indicate signal strength (S), interference (I), noise (N), propagation (P) and overall quality (O) of the reception on a scale from 1 (lowest) to 5 (highest).  More commonly used by shortwave DXers, but the principles can be applied for AM and FM DXers to better understand the characteristics of the signals they are receiving. 

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SIO
A more simplified version of SINPO to rate reception quality in reception reports. Values are given for signal strength (S), interference (I) and overall quality (O)

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Sister Station
A radio station that is in the same or nearby market and owned by the same owner/licensee.  Some sister stations will relay/re-broadcast programming on a part or full time basis.  This can also be referred to sometimes as a “station group”, especially when there is a combination of AM and FM translators being used.

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Skip
Used by DXers in general to talk about long distance propagation.  Specifically, refers to when a signal travels from the transmitter up to the ionosphere and back down to the Earth.  It is called skip because the signal “skips” off the ionosphere and over the area between the transmitter and where the signal can be received again. 

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Sky wave propagation
The type of propagation being described when radio signals are propagated by refraction in the ionosphere, making one or more “skips”.

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S-meter
What DXers call the meter on a receiver which indicates signal strength.

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Solar Activity
When there is activity on the surface of the sun, such as solar flares or sunspots, these can cause high levels of radiation to leave the solar surface and travel through space.  This activity can have impacts on radio frequency propagation through the interaction of the energy with the Earth’s ionosphere.

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Solar cycle
An 11-year cycle in the frequency and number of solar active events and sunspots. The downward period of the solar cycle which leads to the solar minimum, is when geomagnetic activity is at its lowest.  The upward period of the solar cycle, which leads to the solar maximum, is when solar activity is at its lowest.  After several very active solar cycles, Cycle 24 which began in 2008 and has now technically ended, was known for being largely one of very quiet solar activity.  There are signs that the transition to Cycle 25 was underway as of late 2019/early 2020.

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Solar flux
Measurement of the radio emission from the sun, used as an indicator of overall solar activity.

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Solar maximum
The period during the 11-year solar cycle in which the highest amount of solar activity occurs.  Cycle 24 had a “double peak” maximum in 2011 and again in 2014. The maximum for Cycle 25 should occur sometime between 2023-2026.

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Solar minimum
The period during the 11-year solar cycle in which the lowest amount of solar activity occurs.  In Cycle 24, this occurred in 2009 and again near the end of the cycle in 2017-2019.  For Cycle 25, you can likely expect Solar Minimum conditions from 2020-2023 and again from 2027-2030.

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Sporadic-E (Es)
In the upper portion of the HF bands and into VHF/UHF frequencies, Sporadic E (or E-Skip as it is most commonly referred) is a phenomenon of random areas of ionization (commonly referred to as clouds) occurring in the E-layer of the ionosphere that allows refraction of frequencies much higher than would normally behave in this way.  The summer months are the peak time of the year for E-skip propagation, with a second, smaller peak in early winter.  For locations at or very near the equator, equatorial E-skip can last throughout the year peaking around mid-day.  This propagation method is used by FM DXers for long-distance FM reception, with reception distances often approaching or exceeding 1,000 miles (1600 kilometers).

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SPT
Shorthand abbreviation that refers to Sports programming on a radio station.  This can refer to a station that is carrying sports programming at the time (such as a game or match) or a station whose primary format is sports.  For sports-formatted stations, this can take the form of call-in sports talk shows, host-driven sports discussion shows, live sports broadcasts and replays, and team specific sports content (coach’s shows, pre and post-game shows).  In the United States, most sports stations will primarily use syndicated network content (such as that offered by ESPN, Fox Sports, CBS Sports, etc.), though there are some stations that host their own full schedule of self-created sports content (bigger stations such as WFAN-660 New York, for example).  Sports stations that carry syndication will usually air sports news/highlights at the top of the hour and randomly throughout the hour.  Often during sporting events in the U.S., stations will “pause 10 seconds for station identification” at least once an hour (usually as close to the top-of-the-hour as they can). 

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Squelch (SQL)
A feature found in most communications receivers, software-defined radios (SDR) and in some portable radios that mutes the receiver until the signal strength exceeds a predefined level.  This level is set by adjusting the ‘squelch knob.’  For the purposes of AM/FM DX, it is usually something that a DXer would use, it is more often used in the VHF/UHF frequencies on scanner radios (those that are used for monitoring police, fire and EMS transmissions).
 

SS
Radio station programming/content that is in Spanish.  In the United States, even those stations that are formatted entirely in Spanish are required to provide a legal ID at the top-of-the-hour in English. 

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Sunrise Skip
The period of time starting two hours prior to and lasting until two hours after local sunrise when there is enhancement for signal propagation due to the grayline of the rising sun.  This is also when daytime-only stations are signing back on for the day.

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Sunset Skip
The period of time starting two hours prior to and lasting until two hours after local sunset when there is enhancement for signal propagation due to the grayline of the setting sun (this is because of the erosion of the D and E-layers of the ionosphere as well as the merging of the F1 and F2 layer into a single F-Layer that radio signals are now able to bounce off of for greater distance reception).  This is also when daytime-only stations are signing off for the day.

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Sunspot
A visible area of darkness on the surface of the sun because it is cooler than the surrounding surface.   Sunspots can be a visual indicator of solar activity.  The more visible sunspots, the more active the sun is, generally speaking (during a solar maximum is when one would generally see the highest concentration of sunspots).

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Sunspot number
A daily measurement of sunspot activity (R), defined as R = k (10 g + s) where s = number of individual spots, g = number of sunspot groups, and k is an observatory factor.

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T

Time Check/Time Announcement (TC)
Term and abbreviation/shorthand used for when a radio station will verbally give the time on the air.  This is most commonly done during the top-of-the-hour and during morning/afternoon drive periods.  An example would be “You’re listening to 680 WAAA, Anytown. It’s four o’clock.” or “It’s 4:15, time for a check of traffic and weather together every 15 minutes on newsradio 680 WAAA.”

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Television Interference (TVI)
Interference/noise noted on the mediumwave frequencies (FM is less prone) due to oscillations within nearby televisions.  Older Cathode-ray-tube (CRT) TVs were much more prone to creating this type of interference than newer televisions are, although plasma screen TVs are still notorious for creating this noise. 

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Tentative (Tent)
When a DXer did not during their DXing session hear a definitive station identification or other definitive information to positively identify a station they are receiving, but they believe they have narrowed down the station, they will mark the log as ‘tentative’ in their logbook.  This usually appears as “WAAA (Tent)”.  It is often recommended for a DXer to keep a list of these tentative stations handy so they can revisit them at a later time to try to pull a definitive identification so they can update their logbook.
 

TLK
Shorthand abbreviation that refers to Talk programming on a radio station.  This can refer to a station that is carrying talk programming at the time (such as a call-in show or talk radio program) or a station whose primary format is talk.  While there are exceptions, talk-formatted radio stations are almost always marketed as a News/Talk station.  This means that in addition to the talk radio programming, they also provide news updates at the top-of-the-hour and likely throughout the hour (most would even have a news staff at the station to provide local news as well).  The vast majority of talk radio programming is syndicated nationally or at least regionally, though there are some stations that have their own local talk show hosts that deal with local news/issues.  Great times to try to find an ID from one of these stations is at the top and bottom-of-the-hour and during the quarter hour advertising breaks. 

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Top-of-the-Hour (TOH)
The beginning of a new hour, in DX terms this usually starts 5 minutes prior to and ends 5 minutes after the new hour begins. This is when the vast majority of radio stations will self-identify, normally with their call letters (if they use them) and any other branding information.  In the United States, stations are required to provide a full “legal ID” that consists of a station’s call letters and city of license (must be together, although they can provide the frequency between these two, but that is pretty much it).  The legal ID in the US must be completed in English and must occur “as close as possible” to the start of the new hour (during a ‘natural programming break”).  Outside of the US, there are varying dfegrees of requirements for identification (if there is any at all) but the top-of-the-hour is usually the best bet for hearing a station ID.  This is also when stations will generally include news updates, weather forecasts, traffic updates, sports headlines, etc.  All of these will normally include some sort of station branding to aid in identifying the station.

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Tourist
Shorthand abbreviation used for the traveler’s information programming content of a radio station.  This can refer to Traveler’s Information Stations (TIS) which provide traveller’s advisory information (often near airports or theme parks, for example), stations formatted exclusively for tourists with information on tourist destinations (similar to what you might find on the TV in a hotel) or specific content oriented towards tourists (tourist attraction promotion, discussion, etc.). 

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Transequatorial Propagation (TEP)

A ​form of FM DX propagation by where signals cross between locations across the equator.  Most prevalent during periods of high solar activity in the evenings, allows for reception of stations 3000-4000 miles (4800-6400 km) from the reception location.

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Traveler’s Information Station (TIS)
In the United States, these are stations usually found new airports, theme parks or other tourist attractions or on stretches of highway.  They are typically using very low power (sometimes, anywhere from a couple of hundred milliwatts up to no more than about 10 watts) that provide recorded loops of traveler’s information.  This can be “highway advisory radio” with information on highway conditions (such as ramp closures, rest area information, etc), relayed NOAA weather radio forecasts, tourist attraction information (hours of operations, parking information, etc.) and other information directed entirely to travelers.  Normally, these can be found on either 530 or 1610 kHz, although they are able to be on other frequencies.

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Tropospheric Ducting (Tropo)
The propagation of frequencies above 30 MHz via bending through temperature inversion layers and along weather fronts in the troposphere, the lowest part of the atmosphere.  This type of propagation happens regularly in coastal regions but can happen inland as well.  FM DXers can use Tropo (sometimes called Tropo enhancement) to receive stations from 200 miles away or more, but rarely approaching or exceeding 1,000 miles (except in rare very strong tropo events). 

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U

UHF
Shorthand abbreviation for ultra-high frequencies (300-3000 MHz)

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Unidentified (UNID)
Used by a DXer when they have programming details but were unable to identify the station they were receiving.  Unlike Tent, a DXer will use UNID when they have no lead on which station it could be.  An example one might see/use would be “580 – UNID – 3/16 at 0100 UTC – Heard fast-talking man in SS mentioning “Radio Victoria” several times at the top-of-the-hour before going to SS mx.  Can find no Radio Victoria or anything close on 580 anywhere online.”

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Upper sideband (USB)
Used widely in AM/mediumwave DX, this is the upper sideband of a transmitter’s carrier. Many communications receivers, software-defined radios (SDR) and even some portable radios have this feature.   If you were looking at a signal on a spectrum display or waterfall on a software-defined radio (SDR), this would be the signal to the right of the carrier frequency of an AM radio station.  Can be used to great effect to reduce or eliminate co-channel interference from stations below the desired frequency.  For instance, if you have a local station on 1450 kHz, and are trying to DX on 1460 kHz, you can engage the radio’s USB to narrow the bandwidth of the received signal to only the part of the signal found above the carrier frequency.  In many cases, this can greatly or entirely reduce co-channel interference. 

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Utility stations
Radio stations or transmission other than broadcasting or amateur stations.  These are not transmissions targeted or serving the general public but are very popular among DXers such as marine, air traffic and military communications.

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V

VHF
Very high frequencies (30-300 MHz)

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v/s
Shorthand abbreviation for a verification (QSL) signer

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W

Wavelength
Known as the distance between identical points in adjacent cycles of a waveform radio signal.  Wavelength is inversely related to the frequency so the higher the frequency of the signal, the shorter the wavelength.  Wavelength and frequency can be counted as follows: divide 300,000 by the frequency in kilohertz and you get the wavelength in meters (e.g. 300,000 / 1700 kHz = 176 meters).

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WRTH
Shorthand abbreviation for the World Radio TV Handbook. Published annually, this is one of the gold standard publications for DXer use.  Has information on radio stations from around the world including those found on both mediumwave and shortwave.  Also has equipment reviews and feature articles of interest to DXers and broadcasters alike.

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WX
Shorthand abbreviation for weather.  This is most often used by DXers to indicate when a station gives a weather forecast on the air or talks about weather during programming content.

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X

X-band
Another term used to indicate the “Expanded Band” of the mediumwave band.  This is an addition to the traditional AM radio band introduced in some countries in the mid-to-late 1990's (1610-1700 kHz in the Western hemisphere, 1611-1702 kHz in the Eastern hemisphere).

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Y

Yagi
Highly directional antenna type used by FM DXers consisting of a dipole connected to the receiver and two additional elements, a slightly longer reflector and a slightly shorter director.  Directionality is in the direction of the director.

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OTHER

73
An amateur radio abbreviation for "best regards" however it is widely used among all DXers.

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Shorthand abbreviation for indicates a parallel frequency (see Parallel)