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An old HT becomes new

posted Mar 25, 2013, 4:57 PM by Charles Boling   [ updated May 14, 2013, 5:54 PM ]

After KF7ZIM's Baofeng UV-3R (Mark II) HT was dropped and lost, laid out in the rain for several days, and run over by at least one vehicle, it didn't want to work any more. (Imagine that!)  Lacking funds to buy a new radio, he appealed to his parent.  I offered him an old Alinco DJ-160 I'd acquired.  The DJ-160 was a nice radio when it appeared 20 years ago, and it's still a solid rig with features not found on many cheap radios.  This one was only lacking a couple of things -- a working battery pack and an antenna.  I offered to buy him some batteries if the price was right.

Alexander ignored the warning label and opened the battery pack (voiding the warranty?) and was pleased to find that it was composed of AA cells -- cheap and easy to find.  Someone had already
replaced a couple of cells, but didn't do a very good job, and after abusing the old cells for a while and then sitting around for a few years, the
whole pack was a mess from leaked electrolyte.  Rather than trying to solder consumer batteries (Why do cells with solder tabs have to be so much more expensive than "finished" cells? Grrrr...) I found a new pre-assembled NiMH pack (for remote controlled cars) at a good price, and ordered it for him.
charging circuit
Once it arrived, Alex cut the connector off, and we cleaned up the old voltage regulator board and soldered the new pack to it.  He then managed to fit the whole thing back in the casing (double the capacity of the original NiCad cells!) and fastened together, and was delighted to find that the radio worked as advertised.  But for how long?  We had this fancy new NiMH battery pack, and nothing to charge it with!

A bit of research on battery chemistry, some Ohms Law calculations, and a look through the junk box, and he was in business.  He found a suitable wall wart and used a resister pack to limit the current to an appropriate amount for a nice "dumb" 24-hour charge cycle.  We stuck an ammeter in the circuit so I could keep an eye on things -- this was experimental, after all -- and left it charging until the next day, when we deemed the operation a success.

After printing a copy of the user manual, we only lacked an antenna.  While I would like to find a low-cost "rubber duck" for him, I loaned him a BNC-to-RCA adapter and helped him build a temporary antenna that, while not as rugged, lets his radio outperform all of our HTs!  I found a scrap of 10ga solid copper wire from some Romex, stripped one end and pounded it to spread it until it fit snugly into the RCA jack (this is the same design that I used with a 1.25m HT for a while), and we used a combination of frequency-vs.-wavelength calculations, error measurement, and cut-n-test w/ my network analyzer to get the perfect length for a 1/4-wave element.  Good enough for beginners, and it provided a good opportunity to let principles of antenna design, complex impedance & resonance sink in through practical application.

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