Today's Message Index:
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1. 10:06 AM - Hand-Held NAV-COM (Lynn Cole)
2. 02:24 PM - Re: turn coordinator causing noise in headset (D L Josephson)
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Subject: | Hand-Held NAV-COM |
I have an old hand-held NAV-COM marketed by Satellite Technology
Services, Inc. of St. Louis, MO. It works well on 720 channels of COM
and 200 channels of NAV, but the center pin of the external power-supply
jack is broken. It has a removable battery pack that takes 6 AA
batteries. The instruction manual talks about a 7.2-volt NiCad battery
pack, but it works well using 6 alkaline batteries (9 volts). However,
it uses up the batteries quite rapidly, and I would like to find a way
of attaching an external power supply.
I checked the web and found 3 references to the company, a BBB report, a
lawsuit, and a patent assignment. Apparently they don't have a web
site. I don't know whether they still support the radio.
My options seem to be:
1. Replace the power-supply jack. It seems to be a special jack that
is soldered into the main board. I have not been able to find the
correct jack from any of the usual electronics suppliers.
2. Remove the jack, solder a pigtail to the board, and connect the
pigtail to a new jack that would dangle from the case.
3. Modify the battery pack, possibly by making a pair of dummy
batteries that would connect to an external power jack. This is
attractive because the instruction manual says to disconnect the battery
pack (to avoid damaging it) when the external power supply is used.
Whichever option I choose I will need two power supplies, one to connect
to connect to the cigarette-lighter in the airplane, and the other to
connect to the 120-V AC power. Any suggestions for these?
-----
Lynn Cole
LynnCole@foxvalley.net
Message 2
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Subject: | Re: turn coordinator causing noise in headset |
> If this antagonist is propagating through the power leads, then an L/C
> filter having inductance facing the T/C is called for. The interesting
> detail is a notion that the noise spectrum covers VHF frequencies and
> gets into the victim via the antenna. This suggests that relatively
> small values of L/C would be effective.
It's an interesting puzzle, but I think the antenna part is a wrong tree
up which to bark. He hears it while transmitting too, and it's in his
headset as soon as he turns on the intercom -- not necessarily on top of
a received signal. My hunch it that it's common impedance coupling and
that the antenna cable is getting a path to ground even for his
"isolated" rubber duck antenna. One of these ground paths or power paths
is shared with the current spikes from the t/c.
Batteries are an effective filter impedance but only in the early part
of their lifecycle. As they age, and long before they stop being
effective batteries, the internal impedance rises. The landing light
doesn't do that.
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