Winter 2010 Issue

Beginning Experiments
on the VHF
Amateur Bands


In this issue of CQ VHF we welcome Rick Campbell, KK7B, one of the most prolific  writers of amateur radio related technical articles and designers of amateur radio projects. Here he gives us a peptalk of sorts concerninng our mandate to build,  modify, and experiment.
He then describes using a 6-meter to
40-meter converter to operate QRP CW
on the 6-meter band.

By Rick Campbell,* KK7B


Photo A. A 10-milliwatt CW source available as a kit from Kanga US.

I have been experimenting on VHF since I discovered as a young teen that I could spread coil turns in an FM transistor radio and tune in signals above the FM broadcast band. In those days, the VHF ham bands were populated by experimenters. Everyoneís station had some homebrew gear, and my beginnerís questions were welcomed by gentlemen who were willing to put down the soldering iron long enough to help me get a station on the air. Those early days led me to degrees in physics and electrical engineering and a long and varied career in basic research, university teaching, and designing the microwave radios inside cell phones.

Over the years the VHF bands evolved from the playground of experimenters to something else. Homebrew gear is now rare, and gentlemen with soldering irons who understand the inner workings of radio technology are not as visible. However, they are still around, often retired from careers in electronics and radio. Iím not ready to retire yet, but Iíd like to re-create some of those early VHF games that I played and observed in my early years. There is still no better place to explore the magic of radio than the VHF bandsówith small antennas, low power, slow CW, easy modulators, simple test equipment, and basic receivers. This series of articles will introduce basic experiments and experimental gear for the VHF amateur. Weíll start with a low-power signal source, and then progress through receivers, modulators, more capable antennas and stations, portable operation, etc.

Our amateur radio license is more than permission to transmit; it is also a license to build, modify, and experiment with transmitters, antennas, and signals. For a large and very interesting group of amateurs, experiments are the focus of amateur radio and often result in spin-off technology for other services. Amateur experiments are different from simply operating a radio to make contacts, and require different equipment as well. Fortunately, we can get started exploring radio science at very little expense.

The most basic radio experiment is generating and radiating a signal, picking it up on an antenna, and listening to it. We need a receiver, which you may already have, and a low-power VHF signal source. Low power is essential for several reasons: You want to pick up the signal across the room without overloading your receiver; you want to connect experimental modulators and amplifiers to the output; and you donít want to interfere with other amateurs while experimenting.

CW is a good choice for many reasons, but the obvious one is that CW provides a constant frequency and amplitude to make repeatable measurements. Your signal source isnít just a low-power transmitter; itís a signal generator for your bench as well. You donít need to learn to communicate using Morse code to operate a CW signal generator. However, if you are going to radiate it on the air connected to an antenna, you need to be able to send your own amateur callsign to identify the transmissions. You donít even need a key; a push-button switch will do, and you can write the dots and dashes on a piece of paper until you have your own callsign memorized. Fast CW is for HF; VHF experimenters use slow CW. It is more effective when signals are weak, and we are more interested in making one difficult contact than racking up a large number of contest points per hour.

Photo A is a 10-milliwatt CW source available as a kit from Kanga US for $27. It has a few chip components and some toroids to wind, so if you havenít done any construction you will need some guidance. One of the most interesting experiments is to find out how far away you can hear a 10-milliwatt 50.100-MHz signal, and for that goal you will need a friend. Find one who has a magnifying glass and a fine-tip soldering iron. The complete schematic and other construction details are on the Kanga website: <http://www.kangaus.com/>.

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