Post
by Albert H » Wed Feb 05, 2025 11:37 pm
I was pleased to be able to help Stephen out when Hollings tried to shut him down. He asked me if I had any way to make his products significanly different to the ones from "down the road", I improved his Pro II stereo coder into the Pro III. For the first time, the coder audio input sockets could be labelled "left" and "right", because the 4013 bistable would always start in the correct phase (I used the other half of the 4013 as a monostable to guarantee the starting phase of the bistable that was driving the multiplexing switches). I also added the facility to switch it to mono - with a single pole switch! It also gained mono / stereo indication with a couple of LEDs which looked good. I also modified the pre-emphasis circuit so that 50µs, 75µs or none could be selected with little push-fit jumpers.
Stephen upgraded the Pro II exciter from 1 Watt to 4 Watts and eliminated the output stage trimmers by designing a properly broadband two-stage amplifier. One evening, we discovered that it was possible to develop a "conjugate" match situation in the final stage by adding resistors to reduce the voltage available to the final transistor, and develop exactly 1 Watt out (and some warm resistors!) instead of the full 4 Watts.
I suggested the use of the 74HC4059, to allow BCD programming of the output frequency. There were plans to move to BCD-coded rotary switches for frequency selection, but Stephen had stock of tens of thousands of those little DIP switches, so we stayed with those, with the BCD option for a future upgrade. The use of the '4059 made frequency setting much easier than the old "Look-up" table - if you knew about binary representations of denary numbers, you could easily work out the settings.
Stephen had developed the Out-Of-Lock Powerdown circuit several years before and it was always fitted as a little board beneath the exciter in the rigs that were used for RSLs. I took the EasyPC files for the PCB and added the OLPD circuit as a permanent feature (without increasing the PCB size), so that - unlike the competitor product - it wouldn't ever transmit on the wrong frequency.
There were a number of things that made the product stand out from the crowd: much more power, effective harmonic suppression, no in-band spurs whatsoever, and even little details like the inclusion of plastic pillars and nylon screws that allowed the use of the "naked" PCD by standing it off the surface, and a small, screw-in dummy load containing a pair of 1 Watt carbon 100Ω resistors and a note to warn against using this with the board set to 4 Watt output!
"Down the Road", the clown H****ngs had tried to make his board "no tune", by saturating the driver and output stages in an effort to get his paltry 1 Watt right across the band. It didn't work, of course, and generated a huge amount of wideband noise. He also tried to "simplify" the VCO by removing the "unneccessary" balance transistor - ensuring lots of ½f and 1½f breakthrough. The clown also removed many of the "excessive" decoupling capacitors. Just for amusement, we bought one of these worthless kits anonymously, and assembled it according to the instruction sheet. The "performance" of the thing was a sick joke - it was a wideband noise generator with a bit of carrier on the chosen frequency!
"Why is my rig humming?"
"Because it doesn't know the words!" 
