I am thrilled to see that there were
four very informative and very well
written articles on radio.
For J.W. Koebel's article, "Fix Up
That Old Radio," I saw the mention
of the fact that pre-WW II radios had
DC power provided by the radio to
the speaker to energize the
electromagnet in the speaker.
A bit of a warning here. About
20 years ago from the "School of
Hard Shocks," I learned these radios
have a lot of dangerous voltage on
the speaker field wire (90 to 250
I found out the hard way while
checking out the innards (a lot larger
and more component-laden than the
De Wald 618) of a cabinet radio for a
coworker who was finishing the
I didn't measure the voltage with
a regular meter, but my "skin meter"
said REALLY HIGH and biting.
Tim Brown N&V Q&A
Good point, Tim. I had one of
these old speakers and know exactly
what you mean. Also, a good way to
learn XL = 2piFL is if you disconnect
the speaker while energized (my skin
meter registered that, as well)
Radio and Rockets
I found Bryan Bergeron’s editorial
on amateur radio interesting. I agree
with him on the points he made.
I would like to take the time to
call attention to an increasing use of
amateur radio: model rocketry.
It has been done in the past, but
I’d like to call specific attention to the
efforts of Bdale Garbee and Keith
Packard in producing Arduino-based
open source flight computers for
model rockets. I have no financial
connection to the Altus Metrum
company but have had the privilege
of attending launches where Altus
Metrum products were in use, and
sometimes Bdale and Keith were
there developing stuff.
GPS coordinates of the rocket’s
location and throughout the flight are
relayed to ground via telemetry using
one of the ham bands. This link —
altusmetrum.org —should take you to
more information that could/should
be part of a future application/article
of amateur radio.
The flight computer is powerful
enough to have a role in balloon-sats
I hope to see a future article on
amateur radio applications in
READER FEEDBACK Continued from page 7
August 2015 33