Another Bird View Comes Back To Life!!!

[pendragon]

I'm just not getting it. If the measurements were properly made in a Faraday cage, the only incoming source of RF leakage would be the control cables that crossed the boundary. Given the control pulses probably were below the kHz region and the RF was around a MHz, it should be quite straightforward to filter out the RF. Is it possible the cables entering the cage were re-radiating inside, thus nullifying the whole point of the Faraday cage? Nevertheless I do understand the necessity of getting something to work, even if you have to use a cannon when a spit ball would do.

Regarding ham licenses, long long ago when I was a physics undergrad, I handled the classical music shifts at a community FM station. One evening when the chief engineer got torqued and walked out, the station manager freaked. Back then stations had to have someone listed with a First Phone license, or go dark until they did. Being as I was the only one there with a technical background, I was dispatched on the bus to Denver the following morning to take the First Class Radiotelephone Operator exam.

This was no big deal, and given that I had to wait until evening for a bus back, I discovered I could take an amateur license exam during the interim. The only problem was I really didn't know Morse anymore, having largely forgotten it from my SWL experiences as a kid. So I hoofed it over to the library, and as a good college student does, started cramming. The examiner was awfully sympathetic with my klutzy code, and let me walk out with an Amateur General Class license to boot.

I never used the amateur license and didn't bother to renew it. Three jobs and school were just too much. I did renew my First Phone until it got reclassified. To be honest, I eventually wanted that one to slip because even though I had long moved to Denver with a real job, the stations I had worked at always kept my phone number by the boards, even when I begged them to strike it off. So when a station's transmitter conked out at 4:00 in the morning and they couldn't raise their chief engineer, I got calls out of the blue from strangers. As much fun and as rewarding an experience I had in the broadcast world, I'm glad it's over.

 

[nicknjen]

Scott, Just wanted to let you know that the board is still working great!!! It got a bit of a workout this past weekend and will get one again today. Also get a hold of me on Jim's issue, I was doing some brainstorming and was thinking that we could keep using high volatage on his from the encoder and back and then drop it once it was back inside the box with the solid state circuit

also pendragon I was totaly shocked about the "voltage in the air" and couldn't believe it till I saw it.. but when you are less than 50' from 5000 watts of RF emitted from a 199' AM tower I am convinced that there is current in the air!

 

[pendragon]

I'm not quibbling about whether there is a potential difference between the antenna and ground plane. And with the relatively low frequency of an AM transmitter, it will definitely affect measurement devices with high impedances and measurement leads. Depending on the particulars one can light fluorescent bulbs and play other parlor tricks - all of that is real. What is not real is applying an ordinary meter with standard test leads to a circuit and assuming that what it reads is what is happening just in the circuit. Not only will the leads and meter potentially be measuring something completely different, but the leads may be injecting AC and/or DC into the circuit. Troubleshooting in a high RF environment goes by a more stringent set of rules than with ordinary circuit design.

I recall one case where a concert was being held a couple of miles away from one of my stations' transmitters and they wanted to carry it live. There was no possibility for a telephone hookup and their remote gear was so horrible the sound would have been like a wax cylinder's. Moving the STL to the concert wasn't that practical, so I dragged a couple of miles of shielded two-pair microphone cable. By matching the inherent low impedance of the cable (I recall it was less than 10 ohms), there was very little practical rolloff on the highs, but the peak signals were only a few hundred millivolts. The line was the perfect antenna for RF, but with some very strong multi-order filtering, there was nothing that fed back into the modulators of either the AM or FM transmitters. High voltages can help solve some problems, but it's not the only way.