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In our August column we discussed the difficulty in find a suitable
speaker to match the 600 ohm output of the popular surplus classic, the Collins
R390 receiver. We suggested a make-do approach with inexpensive audio output
transformers. But Chuck Rippel, an expert in R390 restoration, has an even
better answer.
A custom transformer made with the R390 in mind is available for $18.35
(stock number P-T119DA) from Antique Electronic Supply (phone (480) 820-5411).
The 1.8 lb. transformer is a perfect match for the 600 ohm audio output of the
radio, and can be used with either 4 or 8 ohm speakers. It is capable of 12
watts of audio, and has a flat 30-20,000 Hz frequency response. Now that's a
transformer!
For more information on Chuck's restoration services, visit his web site
at http://www.avslvb.com/R390A/index.html,
and to see some of Chuck's nice restorations, visit http://www.avslvb.com/R390A/html/shackhamktour.htm.
Thanks, Chuck.
In our September issue, a reader asked what a number of radio
abbreviations meant; one was DCS. While this is commonly heard among members of
the Defense Communications System, sharp-eyed reader Brain Cathcart suggested
it's more likely digital coded squelch since the inquiree was using mostly
VHF/UHF references. I agree.
Q.
I’m situated between several NOAA weather stations and would like to erect
three identical beam antennas so I can home in on SAME alerts of my selection.
Any suggestions for home-brew antennas? B. Williams, Peoria, IL)
A.
Sounds like an easy task if you’re handy with simple tools and have some
aluminum around; I’d suggest old TV antennas for elements and insulators.
Let’s make a three-element Yagi. The elements will all be in a vertical plane,
equally separated from one another.
The center of the three is the driven element – the one to which the
coax will be connected. It must be insulated from the mast, and the two halves
insulated from each other, just like on a TV antenna. Make the two halves 17”
each, or a total, tip-to-tip span for both halves of about 34”.
The reflector should be about 37-1/2” long, and it can be mounted right
against the metal boom, 17” behind the driven element. The forward director,
30” long, can also be mounted right against the boom, 17” ahead of the
driven element.
You should get about 6 dBd gain with this home-made antenna, and if
it’s made durably, it should withstand strong winds and heavy ice for many
years. If you wish another dB or two of gain and slightly sharper directivity,
mount a second director in front of the first, length and separation the same.
Q.
If a car radio is turned on during a lightning storm, does this increase the
likelihood of being hit by lightning? (Donald Michael Choleva, Cleveland, OH).
A.
No. The small shift in electrical charge which the radio causes is
inconsequential when compared to the enormous voltage developed between the
earth and clouds. The conductivity, height, and resistance to ground of the
vehicle are the determining factors.
Q.
I recently felt a shock when I was touching a “hot” wire and my elbow
brushed a gas pipe. Was the pulsating feeling due to the AC? What would I have
felt if it had been DC? (Mark Burns, Terre Haute, IN)
A.
Yes, the “buzzing” sensation was the 60 Hz repetition rate of the
alternating current, successively contracting and releasing the muscles; it is
also the sensation of the 60 Hz firing the pain receptors of your nervous
system. Had this been DC, you would have felt a strong “clamping” sensation.
But I wouldn’t keep on experimenting if I were you!
Q.
According the signal-strength meter, shortwave reception on my Sony ICF-2010 is
strong, but I get a lot of background noise which interferes with the signals.
Is this a sign of an ineffective antenna? (Gerald Silver, Tamarac, FL)
A.
It certainly is a sign of electrical interference, either from nearby
appliances or the power line. If you are using the built-on whip, you need to
change the location of your radio; take it outside on battery power and see if
the noise goes away. This will let you know if the noise is locally generated.
If you are using an outside antenna, you may not be connecting it with
coaxial cable to the radio; this shielding is necessary to avoid – or at least
reduce – the unwanted pickup referred to above.
After you determine the source of the noise, it is easier to determine
the steps to take to reduce it.
Q.
Is Project HAARP in Alaska likely to be jamming signals around the globe? Is
there any connection between this project and Area 51 in Nevada? (Donald Michael
Choleva, Cleveland, OH)
A.
No and no. The transmissions are carefully timed so as not to interfere with
busy frequencies, and the powerful beams are directed overhead, not toward the
horizon. Any effects on the ionosphere are temporary.
And the HAARP project isn’t even remotely connected to experimental
flight tests at Area 51.
Q.
If I accidentally insert AA cells into a radio with the wrong polarity on the
contacts, am I likely to cause damage?
A.
No. Modern silicon transistors have a reverse breakdown voltage well
in excess of what they would experience from such reversed polarity. And if such
an occurrence could cause problems, engineers include what they call an “idiot
diode,” a simple rectifier diode in series with the battery wiring to prevent
such accidental misalignment from allowing reverse current to flow.
