Antennas for getting started with SDR

Useful information regarding antennas for SDR products.
sdrplay
Posts: 624
Joined: Wed Jan 07, 2015 7:58 am

Re: Antennas for getting started with SDR

Postby sdrplay » Wed Jan 07, 2015 11:48 am

As Dr. Milazzo implies, at higher frequencies it may be advantageous to minimize coax losses by attaching the RSP as close to the antenna as possible, and using a longer USB cable to connect it to the computer.\n\nI found this contribution of interest:\n\n From: "Carol F. Milazzo" <kp4md@cfmilazzo.com>\n Date: Sun, 16 Mar 2014 19:01:10 -0700 (PDT)\n \n Here are my plans for a wideband discone antenna that covers 100-1300 MHz \n for $15 \n https://picasaweb.google.com/1140326408 ... neAntenna#\n It works well with RG-6/U 75 ohm cable. Get the antenna outdoors in a \n clear spot and use the shortest length of coaxial cable possible.\n To minimize loss I''ve also connected the RTL-SDR dongle directly onto the \n antenna and run a USB extension to the computer.\n \n Carol\n\nhttps://lh3.googleusercontent.com/-otoCrZPX-t8/UTPur3hg7II/AAAAAAAAErQ/Pug1g-elzoo/s720/discone1.jpg\n---------------------------------------------------------------------------\nDr. Milazzo is quite an impressive person:\n\n https://plus.google.com/114032640816757126398/about\n http://www.qsl.net/kp4md/\n http://www.qsl.net/kp4md/kp4mdnec2.htm\n http://www.youtube.com/user/kp4md\n\n

sdrplay
Posts: 624
Joined: Wed Jan 07, 2015 7:58 am

Re: Antennas for getting started with SDR

Postby sdrplay » Wed Jan 07, 2015 11:51 am

Yes, Dr Milazzo has a point. Especially at 1GHz and above when the use of RG6 will introduce significant losses if you have a long length of coax. There''s a useful WIKI page on http://en.wikipedia.org/wiki/RG-6 which indicates 100 feet of coax at 1GHz adds about 6dB of loss. Additionally - with the crude kind of long wire antenna I was suggesting for lower frequencies - then any length of antenna wire inside the building will also be picking up all sorts of noise which gets coupled-in by way of electrical interference from the house mains electricity wiring. So even here you may want a longer USB cable such that the antenna socket of the RSP is closer to free space and an antenna closer to being in the open air. If people would find it useful I will try to add some links to practical antenna designs. \n

jon
Posts: 311
Joined: Tue Jan 06, 2015 10:48 am

Re: Antennas for getting started with SDR

Postby jon » Mon Jan 12, 2015 2:44 pm

This is a re-posting of the earlier post with the urls updated...

Because the RSP from SDRplay covers the radio spectrum from 100Kz to 2GHz for best results it''s worth taking time to rig up an appropriate antenna. Many of the people I''ve spoken see the SDRplay RSP as an ideal platform for just exploring ''radio'' or TV in general - as yet they don''t know what aspect of it will become their ''thing''. Some are lapsed radio amateurs; others are computer code wizards who have noticed there''s a lot happening on the radio airways which a) is not available on the internet and b) is location dependent. So to get started, here''s a suggestion for truly cheap but ''good enough to hear stuff'' antennas:

For 100KHz up to 30 MHz - ground the outer of the F-type antenna socket on the RSP. (a crocodile clip with PVC covered wire to the ground pin of a mains plug is one way to do this) Connect the centre pin of the the F-type antenna socket to as long a length of insulated wire as you can practically string up outside. Try to get it as high as possible - where it ties to a handy support (a drain pipe, a tree, another building, use plastic coated or nylon line for added insulation during rain. Worst case something which looks like a washing line will give you some useful results below 30MHz. Now you''re set-to-go for LW and MW broadcast and the whole of the Shortwave spectrum. For LW and MW make sure you select AM and for the amateur bands select LSB below 10MHz and USB above 10MHz. The amateur bands frequencies are listed on http://en.wikipedia.org/wiki/Amateur_ra ... llocations There are plenty of sites with information on other interesting things to look for - weather maps, HF fax, intercontinental aircraft channels, emergency frequencies and so on.

For 50MHz up to 300MHz (this covers broadcast VHF (FM/HD Radio), private mobile (taxis, emergency services etc.), DAB radio, aircraft bands, amateur radio 144-150MHz and so on) then something like a mobile ''whip'' antenna as high as possible is what we''re trying to achieve. Actually a wire coathanger straightened out will actually be a reasonable length for the ''whip''. You''ll need to connect to the RSP using an F-type plug with a a couple of metres of coax (same as a typical satellite dish antenna plug and cable). At least try to reach from the RSP to a window sill. You can improvise how you mount the coathanger - e.g. tape to a giant plastic ''bulldog'' clip which can fix to the window sill Strip back and connect the centre wire conductor of the coax cable to the coathanger by wrapping it firmly round a few times and taping. Then to create a ''ground plane'' connect the outer conductor of the coax cable to a sheet of aluminium cooking foil which should cover the whole of the window sill (say 1 metre one way by 15cm the other way)

Above 300MHz: Actually the coathanger will also work well in strong UHF TV reception areas (i.e. on up to 800MHz) - try it and see. Otherwise a traditional TV yagi antenna pointing in the right direction will guarantee results. Another trick is to prune your coathanger to approximately 1/4 of the wavelength you''re interested in. There''s a handy calculator on http://www.csgnetwork.com/antennagpcalc.html which works it out for you - it also suggests optimised dimensions for ground plane ''radials'' which might work better than the tin foil approach!

Let us know how you get on.

jon
Posts: 311
Joined: Tue Jan 06, 2015 10:48 am

Re: Antennas for getting started with SDR

Postby jon » Tue Feb 10, 2015 10:37 am

To see how the RSP performs with a G5RV wire antenna you can try one remotely by following the instructions on v2.sdrspace.com


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