// Tools
SDR tools
A few handy calculators and references. Type a frequency to see what lives there and which app to use, work out how long to cut an antenna, and look up any RF term at your level.
// Frequency finder
What's on this frequency?
// Antenna calculator
How long should my antenna be?
Full wave (λ)69.1 cm · 27.2 in
Half wave (λ/2)32.8 cm · 12.9 in
Quarter wave (λ/4)16.4 cm · 6.5 in
Quarter-wave is the usual whip length · cut long, trim to tune
// Glossary
RF glossary
Switch the header toggle to read each definition simply or technically.
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- SDR (Software-Defined Radio)
- A radio where software does the work, so one device can be many kinds of radio.
- Frequency
- The 'address' of a radio channel — how fast the wave wiggles, measured in Hz.
- Hz / kHz / MHz / GHz
- Ways to count wiggles: kilo = thousand, mega = million, giga = billion per second.
- Wavelength
- How long one wave is; higher frequency means shorter waves (and shorter antennas).
- Modulation
- How information is 'painted' onto a radio wave — by changing its size, speed, or phase.
- AM / FM
- AM changes how big the wave is; FM changes how fast it wiggles.
- SSB (USB/LSB)
- An efficient voice mode that sends only half the wave to save space.
- OOK / ASK
- The simplest signal: turning the wave on and off to send 1s and 0s.
- FSK / GFSK
- Sending data by switching between two (or more) tones.
- IQ samples
- The pairs of numbers that describe the exact shape of a radio wave.
- Bandwidth
- How much frequency space a signal takes up — like how wide a lane is.
- Waterfall
- A scrolling picture showing where signals are; bright means a strong signal.
- Spectrum
- A view of how strong the signal is at each frequency, right now.
- Squelch
- A gate that stays quiet until a signal is strong enough — mutes the hiss.
- RSSI
- A number for how strong the signal is — bigger means closer/stronger.
- Gain (LNA/VGA)
- How much the radio 'turns up' the signal; too much makes it crunchy.
- Antenna
- The wire that catches or sends radio waves; its length should match the channel.
- Half-duplex
- It can listen or talk, but not both at the exact same time.
- Carrier
- The plain wave that carries your information once you add it.
- Demodulation
- Getting the message back out of a radio wave.
- TCXO
- A very steady clock inside the radio so channel numbers stay accurate.
- ISM bands
- Free-to-use radio bands where lots of gadgets chatter (like 433 & 915 MHz).
- ADS-B
- The signal planes shout to say where they are.
- AIS
- The signal ships use to say where they are.
- POCSAG / FLEX
- The languages old pagers (beepers) use to send messages.
- Rolling code
- A secret code that changes every press, so copying one press is useless.
- FHSS
- A trick where a signal hops between channels so it's hard to block.
- Dummy load
- A device that soaks up a transmit signal so it doesn't go on the air.
- Baud
- How fast data is sent — symbols per second.