Recommended outdoor antenna for SDR?

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Tom41
Posts: 7
Joined: Sun Dec 30, 2018 8:23 pm

Recommended outdoor antenna for SDR?

Post by Tom41 » Fri Jan 18, 2019 11:22 pm

Now that I've got into SDR, I'm considering getting some kind of outdoor antenna to improve reception with less interference from devices inside the house. From what I can make out, most antennas are tuned to certain frequency ranges and have very poor performance at other ranges.

So what I really need is a nice wideband antenna that doesn't break the bank, and doesn't make the house look 'ugly' (like with a Discone). When I was younger we mounted an old car aerial to the guttering on top of the house to use with a CB radio, but that got ripped off in a storm and I lost interest for quite a while.

With the advent of SDR it's reawakened my interest in radio. I'm most interested in picking up Air band signals, and Shortwave radio with the Ham it Up converter. Can you recommend a decent antenna for me?

rtlsdrblog
Site Admin
Posts: 1955
Joined: Mon Nov 19, 2012 11:54 pm

Re: Recommended outdoor antenna for SDR?

Post by rtlsdrblog » Sat Jan 19, 2019 5:52 am

You won't find an antenna that can do both VHF/UHF and HF at the same time. There's just too much of a difference wavelength wise.

For VHF/UHF look for discone antennas.

For HF look at long wire, dipole antennas (large) or magnetic loop antennas (small).

snn47
Posts: 128
Joined: Tue Dec 27, 2016 11:00 pm

Re: Recommended outdoor antenna for SDR?

Post by snn47 » Sun Jan 20, 2019 6:48 am

There are active antennas that provide the frequency range you want, e.g. like the R&S®HE700 with the Rod antenna but than the price is also quite high, since with the other antenna elements it works up to 18 GHz (thats 18 000 MHz).

Models Frequency range
R&S®HE700 10 kHz to 18 GHz
R&S®HE700 Rod antenna 10 kHz to 100 MHz
R&S®HE700 Dipole antenna 100 MHz to 1500 Hz
R&S®HE700 Spiral antennas 1.5 GHz to 18 GHz

You might try an active antenna the cheapest form is a short whip with an associated pre-amplifier. For starter from an old active car antenna could do, since it had to work for AM and FM (~600 kHz up to ~108 MHz).
If you search the internet you will find ideas and some background how to DIY active antenna here http://www.pa3fwm.nl/technotes/tn07.html or http://www.g8jnj.net/activeantennas.htm.

Comercial active antennas come in price ranges from a few hundred up to and exceeding 10 000 € (e.g. like the R&S antenna above), but then you get several GHz of Bandwidth and all the bells and whistles you could possibly wish for.

For SW and below just put 5 or more meter of wire horizontally up for FM and above simple groundplanes will do, since for receive you can get away with a lot and still receive signals. You can always improve with time.

PS.: The disadvantage of having a very broadband antenna with preamplifier is that without filter/frequency selective antenna the receiver and or the preamplifier in the antenna may be overloaded. This means the active components cannot process all signals with the same factor, e.g. weak and stong signals by 10 dB. This is called Intermodulation or IM, which will produce additional signals that are not present at the antenna (e.g. IM 3rd order 2*f1 +f2 and 2*f2 -f1 in case you have only IM of 2 strong sigals). You can identify this if you add a 10 or 20 dB attenuator. If you have IM than all signals that were at least a bit stronger than 10 or 20 dB in signals strength are gone you have IM.

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