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| Telescopic mag mount antenna question | |
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| Tweet Topic Started: Tuesday, 1. September 2015, 22:35 (408 Views) | |
| AlphaWere | Tuesday, 1. September 2015, 22:35 Post #1 |
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hi all i hope this does not seam a dumb question i have a SDR dongle and i am looking to pick up 70cm repeaters for monitoring for activity it has two antenna 1x 6cm to 20cm and 1x 20cm to 1.5m The question is what hight should the antenna be at and what size metal ground plane should i use this is for both home and portable usage hopefuly this a simple thing any advice given is welcome 73 alphawere Edited by AlphaWere, Tuesday, 1. September 2015, 22:36.
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My Equipment Transcevier Radios Misuta UV-5R, Misuta UV-82, Baofeng BF-888s Motorola XTR446 Antenna Nagoya NA771, SainSonic INF-661, Diamond SRH805S x2 SDR RTL-SDR Dongle (RTL2832U) from RTL-SDR.com, 1x 6cm to 20cm , 1x 20cm to 1.5m telescopic antennas and 1x 4.5cm diameter magnetic | |
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| Northern Crusader | Thursday, 3. September 2015, 13:16 Post #2 |
26 Charlie Tango 1760
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OK so you want the antenna to be a quarter wave at the frequency you're listening to. The formula for doing it in feet is 234/frequency (in MHz). To do it in metres its 300/frequency in MHz then divide that by 4. So for 145MHz, the 2m amateur radio band you get 300/145=2.07 - divide by 4= 0.5 or 50cm. So for listening to the 2 metre amateur band you want your antenna 50 centimetres long. Do the same for the 70cm band you end up at 17cm. Height wise as high as you can possibly get. VHF and higher is effectively a line of sight form of communications. For a groundplane you want a circle basically the same as the height of the antenna. You can get away with less and for receive it won't make much of a difference. Personally though with a SDR dongle I'd look at one of the wideband discone type antennas. The Standard Discone from Knights is £32.50 and is very portable. Discone antennas don't need a ground plane as its all part of the antenna design. http://www.kcb.co.uk/shop2/contents/en-uk/d153_Page_73.html Edited by Northern Crusader, Thursday, 3. September 2015, 13:16.
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| 26CT1760 / M0GVZ | |
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| AlphaWere | Thursday, 3. September 2015, 18:12 Post #3 |
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Thank for the advice |
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My Equipment Transcevier Radios Misuta UV-5R, Misuta UV-82, Baofeng BF-888s Motorola XTR446 Antenna Nagoya NA771, SainSonic INF-661, Diamond SRH805S x2 SDR RTL-SDR Dongle (RTL2832U) from RTL-SDR.com, 1x 6cm to 20cm , 1x 20cm to 1.5m telescopic antennas and 1x 4.5cm diameter magnetic | |
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