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January 10th 15, 01:55 AM
posted to rec.radio.amateur.equipment
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Field Strength Meter for VHF. Android-based?
Vigilant1 wrote:
;833309 Wrote: An external instrument will tell you very little and the cheapest inline instrument that would be useful (a SWR meter) is going to cost at least $50 to buy, which is getting close to the $100 shop fee without having done anything. . . . Jim Pennino Jim, Thanks. So, do what I can to improve the integrity of the most obvious/easily fixed failure points external to the radio. An SWR can be used to see if what I'm doing is improving things, at least as far as the antenna, then it's just a check of the physical condition of that piece. Seems simple enough. A SWR meter will tell you about the integrity of the cable and antenna as a system. Of course the SWR won't tel me anything about the integrity of the signal itself (am on on frequency, is it spilling over, am I overmodulating, etc). That will take a bunch of rather expensive equipment for a one off fix. And if any of those things are bad, you will HAVE to send the radio somewhere as there is nothing you can do about any of those things without the maintenance manual, a pile of test equipment, and an appropriate piece of paper from the FAA. Can I learn anything by checking the cable's (cable and connector's) resistance? It's 50 ohm cable and about 12 feet long. Not much; if the resistance between the center conductor and shield is less than infinity you have a short/grundge/corrosion problem. Again, I appreciate your patience and support. Mark One other thing to look at if the problem is transmit audio; check the mic/headset connector. It too should be clean and shiny. Mandatory war story... Back when I worked at the avionics shop, about twice a year some guy (not the same guy every time) would come in with some piece of avionics in a cardboard box that was partially disassembled. My first question was "Engineer at General Dynamics?", which was nearby. The guy would either nod or mumble yes and I would give him the paper to fill out and tell him we would call when it was working. The moral here is that for other than simple stuff, test equipment and skill are not enough, you also need the manufacturers maintenance manual. However, a large portion of flaky/intermittant issues were due to loose/dirty/corroded connections, so start there. And if you do find the antenna or cable to be toast, you will at least save the labor of the tech discovering that. -- Jim Pennino |
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