Sunday, May 10, 2015

Learning to Dig Deeper for DX

The body of this post was written a few months ago as part of a planned longer biographical look at DX-ing.  It refers to the early days when I first became aware of reference materials for helping to identify DX and the first steps beyond casual, random tuning of the bands and just listening to what I found.

In those days I was still using my very first receiver, a semi-homebrew thing consisting of  a six-tube broadcast receiver with one RF and one IF stage with a single tube converter in front of it to tune roughly 6-18 mhz. It had been part of a series of kits that came with a radio-tv repair correspondence course my dad was taking in the early fifties. In about 1959,  I was entrusted with it, finished the receiver construction and built the HF converter.

The receiver had no real frequency calibration...just a 0-100 logging scale.  The selectivity was very broad and on the shortwave bands, the image rejection was all but nil. That brings us to this episode. This refers to an era in the late fifties and early 1960's.

After the first few months of listening and after getting my first copy of the World radio TV Handbook, I started listening beyond the “easy” targets. I began spending some time trying to identify some of the weaker signals and some of those in different languages.

The way the Voice of America ID'ed in those days actually helped. They would identify the transmitter site and language about the be transmitted. For example : “ This is Voice of America transmitter KNBH in Dixon, California. The following program is in Thai.”( or Russian, or Polish, or Swahili...) It was not long until I was able to identify languages by their basic sounds, even if I could not understand what was being said.

The WRTH ( World Radio TV Handbook) helped in another way. They included phonetic spellings of station identifications in the various languages.( “transmite Radio Atlantco”,”Ici Bamako”, etc). Sometimes the station identity could be confirmed by what band, what time and what language was being transmitted, sometimes with other clues such as locations or city names being repeated a lot.

There were also the Interval Signals. In the days of analog dials and stations seeking listeners they knew often had simple receivers, the stations would help listeners find the stations before programs started by transmitting these signals. Often they were a phrase of a tune, or a short musical excerpt repeated over and over again. The Voice of America used “ Columbia, the Gem of the Ocean” and “Yankee Doodle”. Radio Moscow used a short phrase played on chimes. The BBC World Service used three tones played over and over. Radio Australia used a music box version of “Waltzing Matilda”. The WRTH and many of the DX articles in the magazines of the time would list these Interval Signals. The WRTH went one step further in publishing the actual musical notes under the listings for the stations with the name of the musical piece from which it was taken.

Between these clues and a development of the ability to listen intently through noise and interference, the percentage of stations being identified began to improve. The big thrills came with the logging of the first African stations. My first were the Voice of America Relay in Monrovia, Liberia. In those days each transmitter site identified itself before the programming began " This is the Voice of America Relay Station in Morovia. the following program is in Arabic".  But there was something particularly exotic about hearing the VOA relay from Tangier. Then there was the second station in the log: ELWA, a missionary station that was really weak here. I finally realized that it was probably beaming away from us and toward the center of the continent. It was a true disappointment years later when both of these sites were destroyed in the war that swept that West African nation.

During that same period Radio Brazzaville from the Congo had strong signals here, as did the South African Broadcasting Corp. For many of these, it was a matter of learning what the best times for receiving the signals would be. It was also about this time that I found the VOA station from Rhodes, which was not a land based station, but broadcast from the vessel “ Courier”. The QSL card depicted a blimp like balloon holding an antenna aloft. I never knew if that wire was the one that the short wave transmitters used or if it was just for the medium wave outlet the ship also carried.

I had not logged any Asian stations at all by this time, but again it was a matter of learning when to listen. I think I shocked my parents when I began getting up early and no longer had to be drug out of bed to get ready for school. It was on one of those early morning forays where I first heard NHK from Tokyo on 25 meters. I don't know why I had so much trouble finding them the first time, unless it was just some quirk in the directional pattern of my antennas. I know I never heard any Japanese hams on that particular wire after I got my ham license, either.

It was during one of those morning sweeps that I found one of my long time friends on the dial for the first time: Radio Australia. The first time I heard it was on 9580 and it became a morning fixture to listen to while dressing for school. It seems that 9580 was the morning spot for that station for many, many fact until just a few years ago. I was really surprised to find when I got a QSL from them that some of the hours that I would hear it were not the actual North American service, but the Pacific Service and the power for the time I sent the report in was just 10 kw! Though I spent many mornings hunting, I did not hear their band mate, radio New Zealand, at all during that period. I remember wondering if it was because of their power. In those days, the WRTH had them listed as having just two transmitters with 7.5 kw each. To this day I am not sure if I just missed them or if perhaps their antennas were beaming a path not favorable to the US.

The 31 and 25 meter bands were very interesting in the mornings in those days. It was the first time and place that I heard that unique, fluttery sound that marks that Asia/Pacific path on those bands in the morning. I first heard the multi-path, echo signals during that period also. I often wondered ( still do ) if perhaps I was hearing signals both long and short path at the same time. It was during that period that I first heard the VOA relays from the Philippines and from Okinawa. They were loaded with echos to the point that the first few times, it was difficult to understand them and pick out the ID!

There was one other thing that sometimes made them difficult to identify. It was the first time I heard jamming signals and actually figured out what they were. They were most often heard on the VOA relay station frequencies. After I figured out what they were, I realized I had been hearing some of that on the 31 meter band, too, mostly during the evening hours. In those cases, I was not able to hear the station beneath the sounds at all and could not even tell what was being jammed.

It was during this period that my parents found they had traded one morning difficulty with me for another. Instead of trouble dragging me out of bed, they had trouble dragging me away from the radio to catch the school bus on time!

About this time I began to start “targeting” stations. I would read the DX columns in Popular Electronics and concentrate on the loggings at the ends of the columns. I would pick out a few, look at the times they were being heard and “lie in ambush” for them. Of course with this receiver, that was particularly difficult because of the total lack of frequency readout, but I began using the usual suspects on the bands like beacons just as I had before on the broadcast band. I would look for the interval signals.

I also figured out that it might be easier to find the “out of band” or “edge of band”stations more easily because they would not be in the thick pack. It was that way that I found Cairo and Israel at the lower extremes of 31 meters. I think Tel Aviv held forth on 9009 kHz at the time, if memory serves.  ( that is a good technique for finding some good DX even today!If you have a simple receiver without a lot of selectivity, hunt away from the big packs!)

Tuning the home built receiver was always difficult at best and often the tuning rate was a bit fast for trolling for the weak ones. I tried putting a larger knob on the tuning shaft and that helped some. I also developed a two-handed tuning technique that helped overcome the less than smooth operation of the dial-string-and-drum tuning arrangement.

The big problem that was coming to the fore was the lack of selectivity of the receiver with its single IF stage and no filters. A bit of reading in an older Radio Amateurs Handbook at the Waco Public Library gave a few clues on things to try. There was an article in one of the books about coupling between tuned circuits in IF amplifiers that gave me an idea. I probably shouldn't have done it, but being a kid, did not think about the possible consequences, but I removed the shield cans from the IF transformers and saw that the coils for primary and secondary were wound pie fashion on a horizontal wood dowel and were fairly close together. After reading about the effects of coupling on selectivity, I decided to try to loosen the coupling and see if that would help.

Luckily the glue on the windings was not too tight and they both sprang free with out much twisting. I was probably very lucky I did not break the tiny wires leading to the windings. I moved them as far apart as possible, out to the ends of the horizontally mounted dowel. That was for the input transformer to the IF stage. I did the same for the output transformer and replaced the shield cans.

The trimmer capacitors for aligning the IF's on this rig were on the bottom and had to be reached with a screwdriver from the bottom of the chassis. I had a feeling the movement of the coils might change the tuning, so I peaked those trimmers on a steady local broadcast signal. There was some improvement, noticeable right away. The peaks seemed a little more well defined. I was afraid that the decreased coupling would reduce the gain of the stages too much, but that fear quickly disappeared. There was a just noticeable drop in signal level. I found the improvement noticeable in trying to separate some of the close packed signals on 31 and 41 meters the first night.There were some new loggings right away, and looking back at my “ stations heard list” from those days, I found a note where the modification was made, so even years later its easy to tell the difference it made. Some of the stations had been covered by strong VOA or Radio Havana signals. I was able to dig out Vatican Radio, Radio Prague. Austria and Deutsche Welle ( the latter might have been audible but just not identified before). It might have been frightening to know just how broad the tuning might have been on that thing before the change!

I also found the idea of “targeting” stations by looking up their schedules and frequencies was productive for finding “ new “ stations I had not heard before. Some of these were not really buried in the crowd, but had just been missed because I was stopped during band sweeps listening to a program that sounded interesting. Looking back, it seems almost odd that it was only after several months of listening that I found Radio Nederland from Hilversum, Holland given how strong it was. The same for Italy's RAI.

One disappointment to this day are the Scandanavian countries that are now absent from the bands and cannot be heard today. They were on the air then, but even though I lay in wait for them, I never did not log the stations from Denmark, Sweden, Norway or Finland during those glory days of short wave listening.

The improved selectivity of the receiver also made listening in the amateur bands much more enjoyable. Previously the crowded bands filled with predominately AM signals were a cacophany of whistles and squeals of carriers beating against one another with high pitched heterodynes making listening difficult. The narrower tuning began to make many weaker signals audible and tuning the 40 and 20 meter phone bands became much more pleasant and I began spending more time there. I was soon logging stations from all over the country, and from Canada and Mexico. Soon there were DX stations from the Caribbean and South America in the log for the first time.

Of course, improvements always lead to a desire for more improvements. I had read about another technique for further tightening up the tuning and providing additional gain: regeneration. This involved introducing a little intentional feedback in the IF amplifier. I was already somewhat familiar with the idea from my little one tube “ little howler” receiver I had built from a kit a couple years before. Soon the receiver chassis was once again turned over and this time the soldering iron was out. I had read about a simple method for introducing regeneration by soldering a short piece of insulated wire onto the plate pin of the IF amplifier tube and moving it close to the grid pin. The article cautioned about not getting it too close or full oscillation would take place.

The soldering job did not take long and soon a one inch piece of wire with insulation still in place on the free end had appeared on the bottom of the 12SK7 tube socket. Firing up the receiver soon showed what the author had meant about oscillation. Wild squeals burst from the speaker of the radio!. It took careful movement of the wire away from the grid lug using a pencil ( receiver was on and high voltage present on the plate lug!!) to reach the point where there was some feedback, but not enough to break into oscillation on weak signals. ( I learned later that the automatic gain control bringing the gain up on weak signals would increase the possibility of oscillation, just like turning the gain up on a public address system will do the same with audio).

Once again, peaking the IF tuning adjustment was done. The results were amazing. Just tuning the IF's made the change very obvious. The peaks were very sharp, with only a fraction of a turn resulting in a peak being found or lost. There was also what would later become a familiar sound, the swishing in the audio as the peak was swept past.

This turned out to be the biggest improvement made in the receiver to that point. Tuning was noticeable sharper and any gain lost by decreasing the coupling before was more than made up. Now we were getting somewhere.

But something else came of the experience. I found that by moving the coupling wire back and forth to intentionally get the receiver into oscillation, cw signals were suddenly audible. I had just begun to study the Morse Code with an Ameco course on a record and had been wondering how long it would be before I could afford an actual amateur receiver to hear code on the air. There would be no wait. It turned out that a plan to improve my existing radio led to something totally unexpected of it: the ability to hear cw. A major door had opened.

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