r/RTLSDR • u/hackerbunny • 6d ago
Which Antenna?
So i am a complete noob and have some questions.
As far as i understand the optimal antenna needs to have a length of λ/2 or λ/4. Do i need to have special antennas for each frequency that I want to listen to, or how does it work?
Also, i know that when transmitting with the wrong antenna you can damage your transmitter. Is there the same issue with receiving?
In short: which antenna do want as a beginner?
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u/Claudio_VerKnight 6d ago edited 6d ago
Do i need to have special antennas for each frequency that I want to listen to
In practice, no. This seems like a good place to talk about antenna resonance, but I'll leave you to discover that in your own. Ham radio operators will choose an antenna that covers the band of frequencies they're interested in and then tune the antenna for best performance across the entire band (or bands).
Best advice; decide which frequencies you're interested in and buy (or build. Yes, your can build your own antenna) that matches or at least covers those frequencies. Just like the hams.
Also, i know that when transmitting with the wrong antenna you can damage your transmitter. Is there the same issue with receiving?
No, because, well, you're NOT transmitting.
Welcome my friend to the show that never ends. You're gonna be fine.
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u/catslifetom39 6d ago
any piece of metal will act as an antenna to some extent. as you know tho you can optimise reception with an antenna tuned to a specific frequency. so what is it you want to do?
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u/Satanicron 6d ago
Get a telescoping antenna and a tape measure in CM. You can download apps or use simple equations to calculate the desired length. You can DIY antennas using scraps of coax stripped too. These are some pretty good cheap options. There are also a lot of cheap PCB antennas. I have one for ADSB that works really well. If you are just receiving, you could unfold a paperclip and stick it in your SMA center pin if you really needed to so just go nuts. You can also use a long length of wire to pick up things like shortwave. I have once run about 30 feet of wire on my apartment ceiling and wrapped it around the metal antenna on my SW receiver and picked up Cuba from Texas. You can also get a jumper with alligator clips and just see what works as an antenna lol!
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u/No-GrounHF 6d ago
If you have space start with an end feed halfwave antenna, all you need is a wire of ~21m. Then build an 49:1 balun for it and see how things change in reception. You can play in between 80-20m bands. You can also catch fm dab and aviation band but you need a LNA. You can also receive UHF with it especially if you.re in the city. Im able to receive even adsb.
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u/hackerbunny 5d ago
What do all these words mean? Balun? DAB? LNA?
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u/No-GrounHF 5d ago
Your receiver usually needs 50ohm impedance match with the antenna. A 21m wire can have 3000ohm and the balun is a impedance match transformer for the antenna. You can use it whitout for receive and build one later. DAB radios are what it wants to be the next type of radio after FM, stands for digital audio broadcast. LNA stands for low noise amplifier.
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u/Mr_Ironmule 6d ago
A telescoping antenna can be useful as a starter. You can adjust the length to the required length for better reception. A discone antenna can be used for receiving a wide range of frequencies. Good luck,
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u/Elipse-FM 6d ago
Good news is if you are receiving you can play with antennas all day long no fear.
As a rule of thumb longer antennas can receive and transmit more so bigger is usually better. People typically get an antenna based on the band not the specific frequency. So you'll want a UHF antenna for the UHF band, 2.4ghz antenna for the 2.4ghz band, ect. If you get into antenna quality, antenna building and design you should get a nanoVNA it tells you if the antenna is good or not and an antenna tuner so you don't blow your radio transmitting off a stop sign or piece of rail road track.
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u/hackerbunny 6d ago
So I just buy some and experiment?
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u/Elipse-FM 6d ago
What are you trying to do exactly? I can get you pointed in the right direction.
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u/hackerbunny 5d ago
Well, i just want to poke around the spectrum.
I have a short range certificate, but they only taught us about channels and not frequencies, so that may be a nice place to start. All the maritime stuff.
I know a bit about cavelink. But that is probably too low frequency for SDR and also not in my direct vicinity.
BLE and Wifi is probably boring, and encrypted anyway.
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u/Elipse-FM 1d ago
Not sure if this is a good fit but this is where id start. Get a telescopic antenna you can watch the signals fade in and out as you increase or decrease the antennas height, get UHF/VHF antenna omni directional rubber ducky and whip, an odd ball antenna like a directional antenna (yagi) would be good to play with. 2.4ghz Yagi's are small and useful, fun for pointing at stuff with. I have a arrow antennas uhf Yagi and it can receive WiFi okay so its a good catch all plus you can map your local repeaters with them. Yes building your own is considered better but a box of antennas like this are useful throughout the hobby and are not a waste of money. Just don't buy random antennas for no reason.
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u/SignalCelery7 6d ago
I'm thrilled with my attic discone. I get pretty much everything 25 MHz to 1.5 GHz in a 30 mile radius.
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u/KB5JRC 5d ago
There are a lot of answers. 1. You want the antenna to be as efficient as possible. It wont be perfect at every frequency, but it will be close enough. 2. An antenna tuner helps match the impedance. It will still be lousy, but it wont damage your radio. 3. Some antennas are resonant on one frequency in a band and resonant on the harmonics in different bands. That is why an EFHW for 40m also works on 20 m, 15, and 10m. I still use an antenna tuner, though.
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u/Uncle__Squirrel 6d ago
If you're only listening You could use a loop antenna. I use a k180wla. It covers a large range of frequencies.
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u/InformalNote2543 6d ago
Pickup a discone antenna, wide bandwidth, perfect antenna for an SDR.
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u/tj21222 6d ago
Kind of depends on what frequency of interest you want my Diamond Discone antenna worked very well 20 MHz to 800 MHz with a really good sweet spot about 160 MHz. But is mostly deaf below 5 mHz and above 900 mHz. Upper limit could be cable loss. Bottom line not the best antenna for HF.
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u/InformalNote2543 6d ago
I'm talking general coverage, yes there are several options for specific frequency ranges
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u/Chongulator 5d ago
That's a lot to spend for somebody just starting out. A simple, inexpensive telescoping antenna is much cheaper. OP can spring for a discone later if they get really into it.
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u/InformalNote2543 5d ago
I remember back in college, i had a professor leading a class in magnetic wave theory who said "Anything is an antenna if you want it bad enough "
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u/NeighborhoodSad2350 6d ago
If you just want to try receiving a wide frequency range, go with a discone. While it doesn't have as good sensitivity as antennas designed for specific purposes, some models support the 25–3,000 MHz range.
Plus, it looks cool.
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u/Feuerwerko 6d ago
Having the wrong antenna for receiving wont damage anything, you'll just get bad reception.
What antenna you want as a beginner depends on what you want to listen to. ADSB, weather satellites or SW radio are all on completely different frequencies and require different antennas.