Amateur Radio
A Lemmy Community to share links about and for amateur (ham) radio to advance the technology, and promote communication and international goodwill. This community IS NOT for CB, GMRS, MURS, FRS, etc topics unless they are related to ham radio in some way.
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If it has trouble hearing you then it's likely there's something near by producing lots of noise. Maybe cellular antenna. Look up cavity filters and maybe install one on it.
I found out they were using a 3 foot jumper of RG-316 cable and I'm betting on 900 megahertz that the antenna is not really getting any other power and that the cable is acting as the antenna.
Likely.. What a waste for a node that someone went through the trouble of putting high up.
Well, that's just what it came with. Once I found that out and mentioned it, they are ordering a low-loss cable so that should no longer occur.
I had a similar experience with RG58 and UHF. I guess the good old tech support wisdom is true: when in doubt, check the cable..
According to something I saw on the internet, RG-316 has 47 dB worth of loss at 3 GHz. So even if it's a third of that at 1 GHz, that's still 15.6 dB per foot, which considering the transmission is only 30 dB or 1 watt, that means that the entire power would be lost after 2 feet of cable.
Late reply, and forgive me if I am over-explaining. I found some random datasheets that say RG-316 has 26-29 dB per 100 ft at 1 GHz. So in the worst case, 3 ft would be 0.87 dB. Doesn't sound like much, but 30 dBm - 0.87 dB = 29.13 dBm = 818 mW, so he is losing 182 mW to the cable. Not great, not terrible.
It definitely should not make that much of an impact. Maybe look into antenna tuning / SWR? Or broken connectors / pinched cables? If my past IT jobs have taught me anything that that it's always the cable, unless it's the plug :)
No prob. Thanks for that info
Have you considered the Fresnel zone? You know, the ellipse between sender and receiver where most of the signal power is located? If you are 200+30 feet up, at 17.5 miles, my back of the napkin map says you are barely having a line of sight, so much of the Fresnel zone is probably obscured by the earth.
Some random online calculator says that at 433 MHz, you have a Fresnel zone radius of 230 ft, (145 MHz has 395 ft, 866 MHz has 161 ft). So half of the signal path is blocked at 433 MHz, and apparently the rule of thumb is it should be at least 60% free. I am too lazy to do actual math right now, but that might be a reason.
Well, the frequency we are working at is 900 megahertz, so that might explain a lot of it. Also, I think the coax might be part of the problem because he is using three feet of RG316, which appears like it's very lossy, and so I'm not even sure if power is making it to the antenna or if the cable basically is the antenna