Rocket Radio testing

[Terry Perdue]

I hope I can get away with another off-topic note on this, since it's
apparently of interest to several on the list.

I got my signal generator operational again, and made a simple test of
sensitivity. With 1kHz, 100% modulation, I could just detect a 10mV RMS
signal. (If it was a broadcast station, I wouldn't be able to understand
anything at this level.) Since it doesn't have provision for a ground, this
measurement was with the antenna clip connected to the generator output, and
the earphone cord acting as somewhat of a counterpoise. I removed the diode
and measured its forward drop at approx. 0.3V, so it is Germanium. Still, I
replaced it with a 1N34A that measured 0.28, and the sensitivity *seemed* to
improve. I can just make out 3mV. I have some surface mount 'zero-bias'
diodes at work, and will try one of those next.

Tuning range is 500 kHz to 1300 kHz with the 200pF cap supplied, so it
doesn't quite cover the top end of the band. I think you could lover this
value slightly and gain more on the high end than you'd lose on the low end.

Someone suggested that the cyrstal earphone supplied might not be as
sensitive as the original ones. It looks very similar, except that it is red
to match the radio. I found three of the original flesh-colored ones in my
junk box - one brand new - and tried each of them. I was surprised to find
that the one included with the radio is much more sensitive!

With the radio connected to the frame of a hanging lamp (cord weaves through
a metal chain), I can receive four or five stations with adequate
selectivity and barely adequate sensitivity - during the daytime. As someone
said, there isn't much to this radio, so I guess that's about as good as
it's going to get. If I do see a big improvement with the new diode, I'll
let you know.

Terry

Sponsored by the City of Tempe 

Listserver Submissions:  heath at listserv.tempe.gov
Listserver Subscription: listserv at listserv.tempe.gov - "subscribe heath 'name' 'call'"
Listserver Unsubscribe: listserv at listserv.tempe.gov - -"signoff heath"