Tuesday, October 10, 2017

Get Busy Living

I try to eat healthy foods and get plenty of exercise. I quit smoking years ago and drink in moderation. I follow news on longevity and try to stay out of the sun. The reason is simple: I want to get my 5-Band DXCC award before I die. At the rate I have been going, to work 100 countries on the 80-meter band from this far North, I will need to live to the ripe old age of 122 years.

Aside from the usual issues everyone has with the lower bands (room for large antennas, noise, etc.) I have a few things that make working 80m from up here particularly difficult. The first is the aurora, or more specifically, the absorption caused by geomagnetic activity.

Since the auroral oval is directly overhead it absorbs signals in all directions!

It takes at least two days with little or no geomagnetic activity before the absorption decreases enough to make DX on 80m possible. That limits the opportunities to only once or twice a month during the bottom half of the solar cycle. The second issue is the ground. At this latitude, the ground is permanently frozen. Only the top few feet thaws in the summer. It also doesn't get dark here during the summer so most of our nightime 80m operating is during the winter months when the ground is completely frozen and blanketed with snow. This makes for very high ground resistance and lousy fresnel zone reflectivity. Antenna ground radials will help with the near-field ground losses but there is nothing you can do about the far-field losses except try to operate when they are minimized by the ground being wet. The only time that coincides with darkness here is in the late fall right before the surface freezes again. The third problem is lack of 80m activity. It takes a decent station, usually working CW, to be able to push through the absorption and it seems the only time the "big guns" get on 80m is during contests. Having long since worked their fill of 80m, the old-timers seem to spend most of their nights obsessing over the 160-meter "top-band". On the other hand, DXPeditions will be active on 80m, just not very often at times that are convenient for a station like mine that, in addition to being quite far North, is also significantly far West (almost on the border with KL7).

So, DX can be worked on 80m from here, but for the most part only during a contest or DXpedition that happens to occur in the late fall, at the bottom half of the solar cycle, during exceptionally quiet geomagnetic conditions. With only 35 countries confirmed so far on 80m, picking up one or maybe two new ones every year will take me a very, very long time to earn 5-Band DXCC...

There are, however, a couple of things that might allow me to possibly eat a hamburger and skip a workout once in a while. My 80m half-sloper antenna on the new tower seems to work OK. I've been trying hard to reduce common-mode noise and the investment in ferrite is starting to pay off. A planned pennant receiving antenna will also help but the biggest cause for optimism is the new FT8 digital mode. Introduced a few months ago as a much faster version of JT65, this new digital mode has taken the HF bands by storm. Every band has a segment with FT8 activity and more and more stations are joining the fun every day. This past weekend was one of those rare "sweet spots" for Arctic low-band propagation. Very little geomagnetic activity for several days in a row, darkness during "prime-time" operating hours, soaking wet not-quite-frozen ground, and lots of activity on 80-meters. Friday night saw good 80m conditions and in addition to working VK, JA, and LA on FT8 I also picked up the RI1F expedition on several bands, including 80m. I have Franz Josef Land worked and confirmed on several bands from many years ago but never thought to get a QSL for 80m. RI1F says they will upload to LoTW so hopefully that one is now in the bag. Conditions were even better on Saturday night. I was thrilled to work F5UKW on FT8 for a new one (and a new zone for him!). Once I made it over the pole the FT8 window had my full and undivided attention. With France coming through I knew that probably every one of the 65 more countries I needed were within range. What happened next, though, was not even within the realm of what I thought possible. Not too long after working F5UKW, I saw a KL7 station calling ZS1A. I laughed out loud and said "good luck, buddy!". Most of the active KL7 stations are a thousand miles south of me and I will often hear them calling stations that I can't hear. It looked like he didn't get an answer from the South African station and a few minutes later I saw a QSO sequence on the screen with someone else working ZS1A. That's when I did a double-take because the callsign on the right hand side of the sequence was ZS1A. In other words, I wasn't hearing someone else working him, I was receiving his signal directly! Not strong, only -22dB SNR on the display, but the next sequence came through as well. I switched the amplifier to full afterburner and as soon as he finished his QSO I double-clicked on his callsign. I was wide-eyed when I first started receiving his transmissions but nearly fell out of my chair when he answered my call! We completed the QSO and I sat back to ponder what that meant. Looking at my grey-line display I could see it was sunrise at his QTH near the West coast of South Africa. I've worked Argentina on 80m before and recently I've been working Australia more-or-less regularly. The addition of South Africa means that when conditions are right I must be able to work pretty much anywhere in the world on 80-meters. That might seem like a no-brainer to some but from up here it never seemed possible before. The farthest I had ever been able to reach over the top on 80m was Azores and Cape Verde which are both paths that skirt quite far to the south of the pole. 




With the addition of H40GC last week that makes FOUR new ones on 80m. At this rate, maybe I won't have to save quite so much for retirement now...

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!

Wednesday, April 12, 2017

A Full Duplex Transverter/Receiver for Satellite Operation

A few years ago I went looking for a dedicated radio to use for mobile and portable operations.  I was very specific about what I wanted: a low-cost, all-mode, HF/VHF/UHF rig, with 100 watt output (at least on HF) and the ability to operate in cross-band, full-duplex mode for working satellites.  After realizing that such a radio doesn't exist, I decided that the only option was to build my own.

I opted to start with a Flex-1500 SDR radio with outboard transverters and amplifiers.  This kept the cost down and after using a Flex-3000 at home as my main HF radio for many years there was no way I was going back to playing "radio blind-man's bluff" with old-school knobs and buttons again.  It's a shame that as of this writing Flex has ended production of the 1500 but it had a nice 12-year run and I expect it will hold its value for quite some time.

The little Flex has a low-power IF port specifically for driving transverters and software support which makes it easy to add other bands.  I found that UT5JCW sells a nice lineup of low-cost transverters through his web site and on eBay.  They fit nicely with my 'low-cost' requirement and I ordered up one each of his 144-28 and 432-28 transverter boards.  Since the transverter boards would be doing all the heavy-lifting as far as gain and front-end filtering goes, I was able to meet my 'full-duplex' requirement simply by adding a little RTL-SDR USB dongle as a sub-receiver.  A toggle switch and a couple of relays to handle the 28MHz IF switching, a few LEDs, a little box to stuff it all into and I'm almost ready to go.

 
View from the rear with the internal shielding removed showing the transverter boards.  The rear panel jacks are for 28MHz IF, KEY in/out, V/U key-out, 12VDC, VHF and UHF.  The slot above the SO-239 connector is for the male USB of the RTL-SDR dongle to stick out.
With the internal shielding in place and the RTL-SDR dongle connected.
The finished product strapped onto the Flex in the portable station.
The transverter boards put out a modest signal (10 watts on VHF and 3 watts on UHF) but since I will be mainly using this with a dual-band vertical antenna the next bit will be to build an 80-watt VHF/UHF brick amplifier to complete the project.  Stay tuned!