Tuesday, September 26, 2017

Full Military Power

Back in the late nineties, Apple Computer released their Power Mac G4.  Based on Motorola's new then PowerPC G4 processor, it was the first personal computer that was capable of processing speeds in excess of 1 gigaflop or the ability to complete 1 billion floating-point math operations per second.  This put it into a category of computers that faced export restrictions imposed by the US government.  Not too many years earlier, computers with that kind of horsepower were the only ones capable of simulating nuclear explosions and, for obvious reasons, sales to certain countries were restricted.  Once the realm of nuclear scientists, the continuous advancement of technology meant that "super" computers like the Mac G4 could now be had by just about anyone.  Apple took advantage of the odd situation by airing a TV ad showing their new Mac guarded by tanks with the tagline "For the first time in history, a personal computer has been classified as a weapon."

Apple G4 Mac print ad from back in the day.

Around the same time, RF digital signal processing (DSP) was also the realm of cutting-edge technolgy and top-secret military programs. When Mackay Radio developed it's new then 5000 Series military HF radio system, it had state-of-the-art DSP receivers and transmitters.  Purchased shortly thereafter by the Thales Group, part of their new line was a computer-controlled kilowatt HF amplifier.  The TMR1090 was a rather conventional, solid-state amplifier design built with all modular components (including switching power supplies) and a built-in testing system which would, in theory, allow any faults to be diagnosed quickly in the field and replaced by simply swapping modules.  It was also (again, in theory) meant to fail "gracefully" so any module failure would only cause a reduction in power output instead of a total shutdown.  It was a smashing success for the military-industrial complex.  Any detected "fault" would have the failed module pulled and sent back to the manufacturer for servicing.  Hundreds of these systems were deployed, mostly by the US Navy and Coast Guard, where they still serve to this day.  And don't bother looking for them on the surplus market.  Even though every $25 Chinese handheld radio now puts more DSP processing power in the palm of your hand than the original DSP technology in the Series 5000 radios, in the USA the entire system including the amplifier was tagged with a DEMIL code D which means "destroy item and components to prevent restoration or repair".  Also, the installed base still needs to have its voracious appetite for spare modules fed and any that are decomissioned certainly get stripped for parts.

For about $75,000 you, too, could have added a TMR1090 to your Series 5000 HF radio system.

There are, however, a couple (maybe a few?) that have inadvertantly been surplused intact and are being re-purposed for amateur radio use.  Getting it to work with a transceiver, though, is a very difficult proposition.  The amplifiers are only designed to operate with the Series 5000 exciter/receiver pair and all the direct controls are via a serial data link from the exciter.  Furthermore, any public documentation beyond the catalogue page above just isn't available.  The unit I have was given to me by a friend who decided after a few years of it taking up storage space that trying to reverse engineer the control data set was beyond his abilities.  When I first got it I put it on the workbench and powered it up but the interfaces were completely opaque and it was soon pushed into the corner.  I might never have been able to do anything with it either except for a chance encounter at a coffee shop one day in another city.  Through sheer happenstance, I ran into what could probably be the only other ham in the world with one of these amplifiers! His was also waiting for the opportunity to become useful and he had something I didn't: the control software for the exciter.  I had no use for the exciter but it needed to be present and operational to reverse engineer the amplifier command protocols.  He also had a pdf copy of the manuals which, while not overly technical, did contain a few useful tidbits of information.

Once I was able to control the exciter, the datalink to the amplifier came alive and in short order the most important commands were deciphered and duplicated in some rudimentary control software.  The next step after that was RF interfacing.  The amp is designed for a 50mW input from the exciter and there is a separate output for a receiver.  After considering options I decided the best course of action was to build a complete transmit/receive relay with built-in attenuation and full bypass for receiving and operating barefoot.  I utilized Omron G2RL relays which, although designed for AC power switching, have a flat SWR up to VHF with reasonable isolation and RF power handling.  The output side has a high-power SPDT G2RL-1 and the input side a DPDT G2RL-2 which also isolates and sequences the amplifier keying.  The built-in attenuator knocks a 15 watt output from the radio down to 50mW for feeding the driver stage of the amp. 

Conveniently, the amp has bias power available on the output connector to drive a remote antenna tuner so that was used to power the relays.

Operation is very smooth and I've found that the ability to quickly switch output levels between 125/250/500/1000 watts without any other adjustments is beyond convenient.  Now that the amplifier control is integrated into my station's master control software, it operates automatically from 160m through 10m and all I have to do is pick the desired output level.

Sure glad I thought of removing all the power supply and RF modules before trying to hoist it into the rack!

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