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WSQT Guerilla Radio
WSQT has installed a new 40 watt tube final rig inputting into our low antenna that yields enough signal to receive for miles but is damned hard to DF.
As you go up and down a block, a direction finder antenna swings wildly from all the multipath. There is little or no direct wave in most places, which is why so much power is needed to get any range.
The signal is clean and there have been no interference complaints, but we now cover a major part of DC with limited vulnerability to direction finding attack.
The rig has a solid state exciter using a "premix" VFO on 14 MHZ adding to a 74MHZ crystal oscillator in a balanced mixer, followed by a buffer, a two stage transistor amp, a 12by7a predriver, 6V6 driver and two 6146B final running on only 370 volts. All amp stages but the buffer are higly selective tuned circuits and the driver will not make even a single volt of output on, say, the crystal frequency.
The amp can be loaded as high as 45-50 watts, but heat considerations forced it down to 40 in use. Tube life on old tubes is an issue here, of course. It shoudl have made 70, but tuned circult losses even with minimum C are substantial. Just puttign the lid on the plate compartment seemed to eat 3 watts even after retuning!
A larger chassis(about 2 FEET long) would allow the use of a 1 inch copper pipe transmission line tuned circuit instead of a lumped inductor, but would have been hard to transport for less than a 3dB difference.
All design info has been recorded, so it can be quickly duplicated if need be.