Thursday, 3 September 2015

RT-320 trailing counterpoise?

Out today at the local park since Tom wanted to go and play now he's feeling better, and with an hour or so to spare before my blood appointment, I decided to take the Clansman along so I could play too. Using just the 2.5m whip, I perched the radio atop one of the metal picnic tables, and noted that it seemed to receive a little better. It might just have been my imagination, and anyway, I hadnt checked the battery, which was all but flat!

Once home, I wondered about counterpoise wires. The official CES counterpoise consists of a spool of four 10m wires, but these are selling for rediculously silly money. It occurred to me that I didnt know what had happened to the vertical wire element that came with my first 5.4m mast. I'd removed it from the end adapter when I fitted the securing bolt modification to allow me to mount and turn small beam antennas on it. Perhaps if I could find it, I could use it as a single counterpoise wire? I also didnt know if my second 5.4m mast even had one of these antenna wires.

So I sat on the floor an hoiked all the pegs and guys out. It turns out the second mast is complete with the antenna wire. And it also turned out that the first masts wire was bundled up in the bottom of the pouch! These wires are 5.5m long and have the proper connecting pin for the radio.

With the wire attached, although I couldnt tell much difference by ear, the antenna match certainly changed somewhat. I did try a few calls, but didnt get anything, I suspect mostly because im on a small whip inside a garage!

Since i'd been using the radio a fair bit, I decided to give it a bit of a health check on the Marconi 2955, testing the output power, AM modulation, and receive sensitivities. Power in HP mode is a tad below 30w, dropping to 10w after a short while of continuous transmission (a feature of these radios), which is spot on. In  LP mode it was about 1.5w, I think that might be low, but thats probably an adjustment point out of calibration. AM with 100% mod was about 10w carrier. Oddly, unmodulated the AM carrier was the full 30w, something I hadnt expected. Modulation was nice and clean. CW, both the wide and narrow, were also good. Two things though surprised me. First, the receiver sensitivity. Working by ear, I could still make out a usable AM signal (75% mod) at -128dBm, and the CW I could still hear plainly when the test set signal generator topped out at -135dBm. The second surprise was the frequency error - there wasnt any! At most, after a few seconds to stabilise, 3-4Hz difference between what the radio said it was doing and what the test said said it actually was!

I also checked the tuning extremes. No problem at all at 29.9999MHz. Now these radios are spec'd for 2-30MHz. After some trial and error due to hysteresis, I found that this one would lock up and work from 1.855MHz.

Tomorrow i'll give her a bit of a clean, as theres dust around the knobs.

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