SDR & Red Devil

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Re: SDR & Red Devil

Postby m0lsx » Mon Jan 07, 2019 3:55 pm

xxjondoexx wrote: I have that cable while I wait for my RG58 50 Ohm coax cable, it was all I had laying around that gave me the distance I required. It was left over from an old ISP installation, it came from the demarcation point which I've re-purposed.


RG-58 Coax is acceptable in short runs on the lower parts of VHF, but at UHF it is going to be no better than RG-6 & if it's cheap stuff from a CB supplier then potentially worse.

100 feet of average RG-58.

150 mhz, loss of just under 55%.
500 mhz just under 80%.

With antennas we use compromise antennas for broadband coverage.
And although the antennas you link to are in some respects correct there are things to take into account.
The polarisation is important & if you get it wrong you will loose 3dB (50% of the signal.) Almost all VHF & UHF radio traffic is Vertically polarised. Satellite & amateur radio SSB traffic being the two most common non vertical polarised signals.
Edited to add. Long distance signals bouncing off the ionosphere are not as polarity important as the polarity is not stable on these signals.
For some satellite work you need a antenna that is adjustable both for elevation as well as compass direction. As not all satellites are low to the horizon.
Also to account for doppler effect on the signal, dual polarisation in a rotational pattern is used on some antennas. As doppler effect causes a signal to rotate, which is why you see some very strange looking antennas used on satellites at UHF. But the direction of rotation is important too, so it needs to be correct.
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Re: SDR & Red Devil

Postby Chris P » Mon Jan 07, 2019 4:37 pm

having said the abovein my reply regarding cable if you intend to transmit on your antenna (assuming you have the appropriate licence) the more you spend on the coax the better so if budget is not an issue then go for 50 ohm westflex or heliax with the appropriate connector (specific to the cable) and your transmitting equipment you choose . I would not recommend RG58 for anything above 30 Mhz. RG213 would be OK up to 500Mhz but it is quite inflexible and difficult to run through walls and ceilings
Regards Chris aka G8FFF nipper or tazmin88
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