By Timothy Raneyâ€¦Bald Engineer Guy with Glasses
Glad you asked. Iâ€™ll tell you a little about hamfests today, the one I just visited in my area and what I found. And I always find cool stuff tooâ€¦at least to me. So, whatâ€™s a â€œhamfestâ€ anyway? Wait! Before you get too excited, it has nothing to do with Virginia ham or our famous annual â€œpork festâ€ in Emporia.
Â Well, I tell folks itâ€™s an electronics flea market. Though many of you will know its origins better than I â€“ as a venue for amateur radio enthusiasts or â€œhamsâ€ to swap/sell all manner of communications equipment. Youâ€™ll also find just about everything youâ€™d need to build your own ham radio or almost anything else. For some background, visit the American Radio Relay League website (www.arrl.org) and youâ€™ll find a wealth of information, to include the dates and locations of hamfests nationwide. As the ARRL website mentions, it was founded in 1914 and is the national association for amateur radio in the USA with more than 158,000 members. Itâ€™s the largest organization of radio amateurs in the US. Go visit ARRL and see what youâ€™ll find â€“ itâ€™s a great resource. Back to the hamfest now.
Ah, it was another great hamfest. In this case, the hamfest is the Richmond â€œFrostfest sponsored by the Richmond Amateur Telecommunications Society (www.frostfest.com). So, I got to the Frostfest before the doors opened at 7:30 am – I was the fifth guy in the â€œearly birdâ€ ticket holderâ€™s line. What a deal. You get a jump start before everyone else arrives at 8:30 am. I spent a stupendous $118.00 in an hour â€“ the most Iâ€™ve spent at a hamfest in years. Of course, I have to include a photo of all these cool things – shown above.
What is all this cool stuff anyway? Well, I found a brand new IET Labs decade resistance box for $60 â€“ great deal since they list for $174.00 (photo below). And once tested, it was within 1% per its specifications. I also found two X-band 10GHz gain horns for $20 each â€“ intended for a future microwave radar demonstration. More about that topic later. Along with the horns, the same guy had a 10GHz Gunn diode transmitter assembly for $5.
Other items included new/surplus Irwin HSS twist drills â€“ I bought eight (8) for $1 a piece â€“ another great deal. The drill bit sizes ranged from 9/64â€ to 27/64â€. I would have spent about $7 at a home center for the 27/64â€ bit alone. I then found a dealer with hardware packaged in little plastic bags â€“ 6-32 and 3/16â€ stainless steel stand-offs, along with nylon Â¼-20 bolts â€“ a dollar a bag â€“ 10 pieces in each bag. Sure, it doesnâ€™t sound too exciting, but these items are very handy have on-hand. If I bought the stainless steel 6-32 stand-offs from an electronics supplier, theyâ€™d cost about $0.75 per piece. Lastly, just check some of the prices for aluminum gain horn X-band (8 to 12 GHz range) antennas at various manufacturersâ€™ websites. Though you can find some deals elsewhere, like eBay. However, you might be hard pressed to find one for $20.
Iâ€™ve been going to hamfests for over 20 years now. I donâ€™t buy as much anymore, since Iâ€™ve built up my stock. Though you can always find something unusual, industrial or military surplus electronics and of course, ham radio gear and test instruments of every description. You will also see many computers, their accessories and the like. I saw big bin with dozens of keyboards â€“ just a dollar each. Unless itâ€™s a new item from a distributer, most of what youâ€™ll find has no guarantee. You just need to know what youâ€™re buying. If I buy a vacuum tube, Iâ€™ll check the filament on-the-spot with an ohmmeter. The physical appearance is a good indicator in many instances, but itâ€™s always a â€œlet the buyer bewareâ€ atmosphere. Iâ€™d say this phrase in Latin, i.e., caveat emptor, but I donâ€™t know Latin.
Now itâ€™s time to digress a bit since I tested the Gunn diode assembly. Golly gee, the Gunn diode worked! At its rated 10V input, it drew ~0.38 amperes. A World War II vintage 1N23 crystal diode in a waveguide picked up a ~160mV signal at 18-inches. It will make a good, basic radar principles demonstration. And with one of the horn antennas attached to another 1N23 diode, it produced a 27mV signal at 42-inches. And no, I did not use an old cow bell as the other horn antenna. Well, maybe it was calf bell or even a goat bell – itâ€™s kind of small. Iâ€™m really happy now.
Using the horns I just bought (photo at left), the setup produced a 35mV signal at 42-inches. However, depending what horn was used, the system would produce a signal up to 80mV at 42-inches. Distances were arbitrary â€“ I wanted get an idea of the practical range.
Moreover, I used millivolts (mV) as a measurement of signal amplitude merely because the multimeter is conveniently located just above the experiment bench. What a coincidence! Iâ€™ve also done this kind of demonstration before with an analog micro-ammeter â€“ a vintage galvanometer in fact. And the signal was then measured in micro-amperes. Iâ€™ve certainly digressed a bit and didnâ€™t do what I had planned today. Where have we heard that before? However, I learned a little something about Gunn diodes. I now have plans to make a basic radar demonstrator. Though weâ€™ll have to get back to the high power rocket project now. Until next time, go to a hamfest and find cool stuff.Â
Find a hamfest! The season is just starting.