Now that things are happening on the HF bands, it's a good time for those of us (and that's probably most of VMARS) whose body clocks stopped at 1947, to indulge in some real Ham Radio, and enjoy the high quality AM on 29MHz, with all the W's coming in loud and clear on their Johnsons, Gonsetts and Heathkits, etc.
My "Minimitter" station (see below) works well into the 80m doublet but most of the telephones in the area also receive my signals rather well. So some form of portable set up seemed to be the answer. Although the Alinco DX70 "Rice Box" puts out some very nice AM, where is the fun in that? Some form of "vintage" gear would be better, and my attention turned to a pile of old CAMBRIDGE AM10 transceivers, bought for 50p each, at Picketts Lock for spares. Luckily I had left a couple intact.
Hardly "real" vintage, but these sets were originally very popular in the early days of AM on 2M - crystal controlled Tx and "carefully tuning the band for a reply" on the station receiver. Some models were, in fact, made to cover 28 MHz, but I have never seen them on the surplus market, so a conversion from the Low Band set would be the best bet. A rewind of the RF coils was fairly easily achieved, as these sets are very simple to work on, the boards being very large and accessible.
With the addition of a simple 18MHz VFO, the receiver tuned nicely on 29.0 - 29.1MHz, and with a crystal for 29.03MHz, the (VALVE!) Tx section produced a nice little 9 watts at the aerial socket. To make it fully transceive, it was a simple matter to take a buffered output from the VFO to the original oscillator, tune that to 18MHz as an amplifier, and replace the 6BA6 tripler stage with a 6BE6 mixer (almost a direct replacement), self oscillating with a 10.7MHz crystal. The output now follows the receiver (closely enough for AM!), and many contacts have been made with this odd little set-up! I originally designed it to be used with a quad loop, but am actually getting some respectable contacts with my four foot mobile whip, and at least there are no phones around!
10m has now closed efectively for AM for the Summer but should be back next Autumn. You have to be persistent and be prepared to wait for the right moment, it is not as "cast iron" as SSB on 28.5 Mhz etc. but when the signals come through they are really amazing, some of the guys have big beams and of course nearly a KW of AM although the more modest powers are also impressive.
The band is 29.00 to 29.20 but the main activity is centered around 29.03 the "calling" frequency and the best time is approx 3.00 p.m. our time (best on weekends).
This comprises a "Minimitter De-Luxe Table topper" 150W transmitter (actually under the table). 2x 807, modulated by 2x 807 and the forerunner to the "Mercury 200 Tx (the same rig but in a new box).
The receiver is the "Minimitter MR44, a slightly later double conversion superhet, veryunstable but OK for 10m AM, with the matching "Cats Eye" speaker.
As all of us in VMARS know, you don't have to spend a fortune to get on the air.
© G4BXM April 2000
The Minimitter Station
(amen to that-G4DDI)