[ARC5] Bendix Model 3801

[Jack Antonio]

On 12/13/2012 12:08 PM, Mike Morrow wrote:

> Jack Antonio has doubtless done more recently to put one on the air than
> anyone else I know.  So, Jack...?

Well, since you asked....

Yes, I have put one of these on the air. My
dynamotor/modulator/IF unit is a bit ugly,
electrically but not mechanically complete.

No real surprises in getting it going, just
the usual things you'd run into when working
on older gear, here are a few observations.

1.  Dynamotor.  This unit uses one dynamotor for
both transmit and receive. In receive the dynamotor
is allowed to only run at half speed due to a dropping
resistor in the 28V supply line. This resistor is
shorted out in transmit.

2. The usual transmitter output circuit for rigs
of this era seems to be a 2 coil arrangement, one
for the PA tank, with some sort of variable coupling
to a series loading coil.  In the Bendix transmitters
I've seen(which isn't all of them), they only use one
coil, and this transmitter fits that bill. I'm pretty
sure the TA-12 and RTA-1B use a similar output circuit
as well.

3.  The receiver works fairly well, but has a fast tuning
rate. The set has CW capability, but tuning CW on a nice
stable work bench takes a *very* light touch, using it
in a bouncy, vibrating aircraft would seem to be somewhat
frustrating. But I would venture a guess that these sets
were used in AM most of the time.

4. It uses an odd little crystal holder, which holds three
crystals in an octal based unit. An FT-243 will work if
plugged in exactly one way, and the channel selector set to
channel 3.

5. Most of these units I know about have a Navy origin, but
I know of one other RF head, and the unit now up on the
auction site, which have Signal Corps inspection stamps.
Like Mike, I know of no documented "in-service usage" of these
sets, and would surely like to find out more about them.

6. The Navy sets seem to have serial numbers in the 1100 range,
the Army ones seem to have serial numbers in the higher 3 digit
ranges.

7. One manual I have refers to this set as an "Altair" communications
system, but whether this refers to the Lockheed Altair aircraft or is
a Bendix marketing name is unknown.

If anyone has any specific questions, I'll be glad to try an
answer them.

Jack Antonio WA7DIA/4