Antenna feed line length question

Useful information regarding antennas for SDR products.
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Antenna feed line length question

Post by Greg33 » Wed Jan 10, 2018 8:20 pm

Hi All,

I'm new to the world of SDRplay (just ordered the RSP2). My questions mostly relate to the distance of the feed line I can potentially use between the SDRplay and my external antenna.

The only listening post available to me is not ideal - a room inside a concrete structure, approximately 5 meters from the nearest door/window and the eventual external antenna. Is this distance going to be too excessive? I mainly plan to listen to signals below 20MHz to begin with (MW & SW), but eventually would like to have an antenna for VHF as well (primarily to receive aviation broadcasts).

Would I be better off trying to place to RSP2 closer to the external antenna and getting a longer USB cable or would that be a drawback? I've successfully used USB devices up to a distance of 3 meters in the past, but not sure if that sort of distance would be too detrimental for the RSP2.

Thanks, Greg
Last edited by Greg33 on Thu Jan 01, 1970 12:00 am, edited 0 times in total.
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Re: Antenna feed line length question

Post by g1hbe » Wed Jan 10, 2018 10:31 pm

With just 5 or 10 metres of feeder on HF you'll be fine, even with standard RG58. The loss will be quite small. However, if you plan to listen on VHF/UHF at a later date, the situation becomes more complicated. Your HF antenna will not do for VHF/UHF so you'll need two antennas (at least!) and a feeder for each one. Feeders for VHF/UHF need to be somewhat better than RG58. I use satellite coax type CT100 for all my listening duties as it is cheap, low-loss up to the low GHz bands and easy to work with. It is also well-screened.

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Re: Antenna feed line length question

Post by CaptainNemo » Tue Jan 16, 2018 11:26 am

I live on the second floor of a five floors concrete building.
Antennas are on the roof and I have no less than 30 meters of RG6-like coax from the local tv/sat shop.
I have a lot of fun from 77 k (time signal) to 260 M (milsat pirates)
With this kind of rig sensitivity is not an issue. The problem is noise...

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