RF getting into my test equipment?

Were you actually transmitting (through an antenna) during these tests?

If so, does the problem recur if you install a proper RF dummy load in place of the whip antenna?

My guess is that when you transmit through a whip, the whole chassis is going to be RF-hot (it's the "ground" or "counterpoise" side of the antenna system), and a lot of the RF is going to propagate back down the power cables. There's likely to be enough RF getting into the metering electronics (whether digital or analog) to cause rectification in diodes/transistors in the measurement circuitry... hence the rather bogus readings you're getting.

An old-style "hot wire" ammeter might be your best bet for evaluating DC current draw in this situation.

), ex military portable FM back pack radios on the bench that I'm checking out. These units tune 950 channels between 30 and 75 MHZ and output between one and two watts depending on frequency. Admittedly these circa 1968 radi os are no longer very practical, but fun to put on six meters and bring to Ham fests. The radios operate on 14.4 volt battery packs.

tors from them, soldered 9.0 foot 14 AWG. leads on them and connected these to two bench power supplies. I was trying to measure the voltage and note the current during transmit. I had my 265 set to the 60.0 volt range and co nnected at the power supply. The power supplies were both set to 14.0 volts as noted on my meter. Every time I keyed the transmitter the meter readin g dropped to slightly below zero. At first I thought that the power supplie s might be current limiting but that didn't make sense because the squelch remained open, clearly indicating the presence of a carrier on the scanner.

d to 4.80 volts and the fluke's power supply, (apparently) for whatever rea son broke the squelch on my scanner, so I wasn't able to use that meter at all. Interestingly the only meter that was "almost" impervious to the anoma ly was my old RCA Senior Voltohmyst. The meter fluttered very slightly but remained pretty steady. I seem to recall in the specs for that meter that t he upper limit was something like 3.50MHZ.

of the meter and confirmed the presence of an RF carrier superimposed on th e DC level every time I keyed. I tried using "HF REJ" on the scope hoping t hat would eliminate the carrier but surprisingly it made no difference.

pacitor, values unknown at this point. The configuration is as follows: Eac h lead of the scope is in series with a choke, then the cap is across the o ther side of the two chokes, and the line then goes to the radio, and then the power supply.

switched over to the 265, not enough to effect the problem with it very mu ch. However when this filter was placed ahead of the Senior Voltohmyst ther e were no anomalies present on it. Yay for old technology!

ke shift filter to read this voltage. But then in theory to use my other eq uipment such as the scope it would seem like I need to design a filter havi ng a resonant frequency equal to every frequency I want to check. That's no t very practical.

The 77's have a BNC jack on the top panel as well as a threaded mount for e ither a short or long whip antenna. At the time I had my watt meter connect ed to the BNC jack with a dummy load off the other side of that. However I did have the whips installed on both radios. I didn't want to key without a n antenna in place, but that probably wasn't necessary since I had the dumm y load on there. I'll repeat everything with the antennas removed and repor t back. Thanks. Lenny

I did QA testing on those at Cincinnati Electronics, in the '70s, after I got out of the US Army. The bench supplies we used for final testing only had 18" leads, and used remote sensing. Try wrapping the wire through some large ferrite torroids at the power supply, and at the radio. We had to do most of the testing in well shielded, RF tight screen rooms. That was a 1970 RCA design, a so called improvement on the PRC-25. It was built with obsolete Germanium transistors that we had to have Motorola make in large batches, and buy untested. They sent what they hoped were enough extras, for the fallout at incoming inspection. The subassembly work was done in Mexico, and required a lot of rework to meet specifications. I had real fun, reassembling one of the tuning gearboxes that an assembly worked took apart by mistake, as well as teaching them how to solder the audio output transformers to the circuit boards, for rework.