Saturday, July 6, 2013

Into The Short Waves

The step into short wave listening began with a gift and a construction project. The basis for the receiver was a six tube broadcast receiver that had been part of my dad's radio repair correspondence course. The short wave part came with the construction of the next external hf converter that would transform the range from about 6.5 to 16 mc/s to about 1600 kc/s, hence to be detected in the bigger receiver.

The base receiver was a six-tube superhet with a tuned RF stage and untuned converter with a single 455 kc IF. The HF converter used a single 12k8 and did not have an RF stage. Normally this would have led to unacceptable image response problems, but the 1600 kc first IF stage would place the image some 3200 kc away from the desired frequency. Even a very broadly tuned input stage would attenuate something over 3 mc away pretty well.

The project did not go well at the beginning. The receiver project had been built as a kit several years before and was not working. With the help of a gentleman running a local radio repair shop, the problem was solved. The repairman was an early technical mentor who deserves his own complete story. He had been a teacher and occasional supplier of part for various projects and was a great help in understanding many of the things I was reading at the time.

The construction of the HF converter took longer for me than would normally be the case. While my soldering technique had come along quite a bit, the instructions were not very detailed and many of the kit parts had been scattered among several boxes when the correspondence course materials had been stored. My mentor at the repair shop supplied some of the capacitors and resistor values that I could not find amongst the “debris”.

The receiver was of the same AC/DC variety as my Watterson broadcast receiver with the exception of an extra tube in the broadcast section. The lineup was 12SK7 RF amplifier, 12SA7 pentagrid converter, 12SK7 Intermediate Frequency amplifier ( 455 kc) 12SQ7 detector/AVC/First Audio amplifier, 35L6 Audio Output amplifier and 35Z4 rectifier. The filaments were all in series across the power line.

The 12K8 converter in the HF section had a 25 watt light bulb in series with the filament across the power line for voltage dropping. The high voltage for the plate was taken from the power supply for the basic radio.

Even for a simple receiver, this one had an S-meter of sorts. It consisted of a milliammeter in series with the plate lead of the 455 kc IF stage. The automatic volume control voltage applied to the control grid of the 12SK7 controlled the gain of the stage by supplying negative bias to the grid. The stronger the signal, the move negative bias. This resulted in a reduction in plate current. Therefore the plate current meter reading was inversely proportional to signal strength. With no signal, the meter read almost full scale. The stronger the signal, the lower it read. The meter thus read in reverse. However, by mounting the meter upside down, it appeared to swing upward rather than downward with increasing signal strength.

Firing up the receiver and getting it set up for its “ new mission” was a two step process. First, the outside antenna was connected to a clip connector input for the broadcast receiver section ( there was no band switch...this was a demonstration project kit designed to teach circuit design and operation, not necessarily for regular use!) The broadcast receiver was then turned on. I managed to find a local station that was fairly strong and did a quick alignment of the 455 kc IF for maximum signal. I then tuned the receiver up to the top of the dial to find at least the general area of 1600 kc.

Luckily there was station licensed to McKinney near Dallas that operated on 1600 and it was audible. I peaked the front end tuning capacitor trimmer for maximum signal on it. I wasn't too much worried about making the front end alignment track properly on the whole band because I did not plan to use it for broadcast reception anyway. I just wanted it to have the best performance on the frequency that the HF converter would feed in. I also figured I could cheat a little on the frequency that it would feed in to a bit above 1600kc to avoid any broadcast station feed through. The dial for the receiver was only calibrated 0-100 and I estimated about 20 kc spacing and set the tuning capacitor there.

Then it was time to try the HF converter. I did not know if it would even work, how critical the alignment would be or if I would be able to hear anything at all if the alignment was off. The only adjustment that would really matter would be the trimmers on the section of the variable capacitor that tuned the mixer input. I was not too concerned about where the local oscillator hit or what the tuning range would be, at least in the beginning.

To switch to the shortwave mode, the antenna lead had to be disconnected from the clip leading to the broadcast receiver input and moved over to another clip on the chassis for the HF converter. That second chassis was bolted onto the end of the broadcast receiver. The output of the HF converter was connected under the chassis to the input of the broadcast receiver. The only other thing that had to be done to complete the switch was to screw in the lightbulb that served as the filament voltage dropper for the 12K8 tube.

I got that done and waited. I was soon rewarded by a noticeable increase in noise coming from the radio speaker as the 12K8 filament came up to temperature. The heartbeat of a now 11-year-old DX-er was picking up speed about this time.

Now realize that the tuning dial for the converter was also calibrated only 0-100 ( separate dials for the two receiver sections) I had absolutely no idea where in the HF spectrum I was, other than somewhere between 6 and 18 mc.

I had set the tuning on the converter to “50” or mid scale for some reason. There was no signal there at all. I had no idea what to expect, not having tuned shortwave at all prior to this ( other than the 160 meter ham band just above the top of the broadcast band on the Watterson broadcast set). I had some idea of what the shortwave broadcast bands would be in the range of the converter, that they would include at least the 31 and 25 meter bands, and depending on where the upper and lower edges landed maybe 49 meters or 19 meters. Also the 40 and 20 meter ham bands should be in there somewhere.

A little gentle tuning back and forth of the tuning dial of the brought a few strange signals that I now know were teletype or multiplex signals. Then I ran into a signal with a tone and ticking sounds. I waited a minute ( or less ) and heard my first shortwave ID: “National Bureau of Standards, WWV, Ft Collins, Colorado”. My first logging on shortwave was WWV!

From reading in various magazines and the Radio Amateurs Handbook, I knew the frequencies transmitted by WWV in 1960 were 2.5, 5, 10,15, 20, and ( then) 25 mc. It may have been a bit of an assumption, but knowing that the HF converter was supposed to tune roughly 6-18 mc, this must be the 10 mc WWV, almost dead center in the dial. That would mean the 31 meter band would have to be clockwise from that a bit. At least that would be direction for increased meshing of the variable capacitor plates.

Tuning in that direction brought more of the strange signals, then a Spanish speaking station or two, then an English speaking voice reading the news. It did not take long to figure out that I had found a Voice of America station. As luck would have it, it was near the end of a program and the English broadcast was about to end. There was the VOA theme music of the day “ Columbia, the gem of the Ocean”, then Yankee Doodle and the full ID the transmitters used to run: “ This is Voice of America Transmitter WLWO in Bethany,Ohio, following program is in ( I forget the language)” followed by Yankee Doodle and the beginning of the next program.

That was the beginning of logging many of the Voice of America transmitter sites. At that time, the big Greenville, North Carolina site was still under construction and many of the sites used dated back to pre-World War II days and were actually used originally by commercial broadcasters. They had been expanded over the years and built up, but many contained older transmitters that were less efficient and used more power than the newer designs. They would soon be replaced, but in those days they were a boon to the SWL. Each site would identify by location and call letters and announce what the following program would be.

In the coming few days, I would log all of the domestic sites and learned through some magazine articles to look for some of the overseas relay sites. Those, too, at the time identified themselves at the beginning of each program and announced the actual frequencies in use. For example the Tangier relay would announce “this is the Voice of America relay station in Tangier, Morocco. The following program is in Swahili.”

The VOA stations with call letters logged in those first few days included KCBR in Delano California, WLWO in Bethany, Ohio, KNBH in Dixon, California, WBOU in Bound Brook, New Jersey, WDSI in Wayne, New Jersey and WGEO in Schenectedy, New York. The others would come later.

Tuning the receiver was a bit touchy. This was not a receiver designed for real use, but one designed to teach how things worked and to introduce servicing techniques. The dial string could never be tightened completely. The tuning system consisted of a loop of string that went around a short axle mounted through the front of the chassis and went around a three inch diameter drum on the front shaft of the two gang variable capacitor. The string was looped twice around the short shaft axle, then went around the drum a turn and a half and terminated through a tensioning spring through a hole in the drum on one end of the string, the other end tied to a fixed lug on another part of the drum after making the loop around the tuning shaft.

Cutting the string and tying it was an approximate deal. After trying several times, I got close but it was still loose. I finally settled on a plan to tie knots in the string near the spring tie-down until it got tight enough. I finally got it to the point after adding several knots where there was some stretching going on with the tension spring and determined that that was going to be the best it was going to be.

The shaft for the tuning knob itself went through a hole in the front of the chassis and had two grooves in it about the thickness of the panel apart with two spring clips to hold it in place. It was a little floppy, but putting some extra washers between one of the clips and the chassis tightened it up a bit. Tuning still resulted in a little delay or slack or backlash when changing directions, but it was something that as a kid I just decided had to be put up with. After all, there were no real calibrations for reading frequencies anyway, and besides: I was listening to short wave!

During that first hour of so of tuning through what I had determined was the 31 meter band, all I heard were the VOA stations in English and a few other languages and some Spanish language stations I could not identify. I had not yet learned to identify languages by sound other than English, Spanish, German, French and Czech. ( the German and Czech I knew about from hearing family members speak those languages).

It was time to do a little further exploring. Going to the left on the dial, past WWV and going higher in frequency yielded other strange sounds before I ran into the 25 meter band. There were thumps from cw signals not readily audible because the receiver had no Beat Frequency Oscillator. There were sounds like propeller driven airplanes that were multi channel multiplex teletype signals.

The 25 meter band appeared as expected but it being near midday, there was not a lot on it. There were several Spanish language stations of varying strengths, but that was about all. The entire 31 meter band had only taken up about an inch of dial space, the 25 meter band even less.

The trip up frequency continued with the basic plan trying to figure out just how far up the tuning range would extend. After more strange airplane sounds and unintelligible ( at least to me at that time) cw signals, I ran into voice signals of the 20 meter ham band. There was not a lot there, or perhaps I expected more than I heard. I noted callsigns of a dozen or so stations and heard some in Spanish and some “Donald Duck” sounds that I took for single sideband signals. The entire phone band was about quarter inch of dial space. Continuing upward, there was not a lot between there and the top of the range of the radio. I did not run into another WWV, so I assumed that the range did not extend past 15 mc.

That noted, I ran the dial back down toward the low end, going past the 31 meter band hoping to find the 40 meter ham band. Success! About three-quarters of the way around, I ran into a gaggle of AM ham stations. I had stumbled across the afternoon session of the 7290 Traffic Net and spent about an hour transfixed at the net operation and the handling of messages among the stations. I had not even heard of traffic nets at the time and it took awhile to figure out what was going on. There were stations of varying strength from all across Texas, Oklahoma and Louisiana.

Tuning down the band from there, I found tuning had to be very careful because the tuning rate was quite high and the stations close together. I found myself listening to various ham radio roundtables, with voices and callsigns that would become very familiar in the years to come. Some of the stations heard that first day would be heard many times, and years into the future would end up in my own ham log after I got my license. A few would become close friends many years later when I moved to West Texas for a time. But on this afternoon, it was simply a new, magical time getting to know a whole new world.

The time flew by that afternoon and it was soon supper time. After I got the call, I took a quick tune down the band to the edge looking for the lower end frequency. I could not tell what it was but did determine that it did NOT extend down to the 49 meter shortwave band.

That would be the end of the my very first foray into short wave. It was also the first of many feelings of frustration at something as mundane as eating getting in the way of the DX adventure. But still ahead would be the first adventure into night time DX that evening.

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