[ARC5] ATD Transmitter Longwave Tuning Unit Repair

[David Stinson]

Mike KK5F wrote:

>CRR-47207 TUs should have PA PLATE SWITCH position 4 (360-450 kHz) wired to a higher inductance >tap than than the tap for position 3 (295-360 kHz).  That's what the CRR-47207 schematic shows, >and that is how my #317 is wired...

Agreed.  I think it must be a factory
wiring error.  Not the first one I've
found.  Had a beautiful RBC receiver
which had been depot-refurbed and,
it appeared- never re-issued because
one of the bandswitch units had been
re-installed with the switch wafers
180 degrees out.  Could never have
worked, so probably became a "shelf
queen" the depot was going to "get
around to" and never did.  We're not
the only ones who do that.
Also had a ZM-11 bridge with no
cap leakage test voltage.  That
had a factory wiring error which
meant it never worked.  There have
been a couple of others, but don't
remember them at the moment.

>I like how you've put a semi-exotic unit on the 630m band and I like your report on its signal >quality.  What antenna did you use and how many RF amps are typically indicated?

Always had a "thing" for Longwave.
My 630M antenna is a Marconi "T",
variometer-tuned,
about 40 feet high with the four wire
capacitive top-load about 40 feet across.
It is directly above my barn's tin roof.
All the tin is tied together and grounded,
forming a "counterpoise" for the Marconi.
Practically a "mobile whip" on 630M, but
I've worked 32 states, 4 provenances
and ZF5 so far without
much trouble, emitting under 5W of EIRP.
Takes about 75W from the modified Icom735
to get there.  My milliwatts EIRP WSPR
signal is copied all over North America
and the Caribbean when I run it.
I need to cut a couple of
trees to both reduce near-field losses and
make room for a larger top load.

I don't remember now how much antenna current
the ATD was making- need to get it on the
bench and find out why no Audio and discover
that burning smell.  Unfortunately, there
are some priority projects ahead of it,
so probably won't address that until spring.

>The fact that the ATD was not supplied with the 200-540 kHz tuning unit but was supplied >standard instead with the CRR-47208 540-1500 kHz tuning unit seems to indicate that someone >told Bendix to make operation in that band of higher importance than operation on 200-540 kHz >and the important naval and maritims frequency of 500 kHz.  Perhaps that had the same >motivation which the T-15, T-16, T-17/ARC-5 and the O-16/ART-13 had.

Unless one of us who cares hits the lottery
and spends 6 months digging in the archives
in Washingtoilet, we're never going to know
for certain why these BCB transmitter
capabilities existed.

What do you think of the informed speculation
that "tertiary powers," such as Coasta Rica
and Afganistan, without the money to outfit
their aircraft and maritime fleets with
"modern" equipment, would likely have been
following the 1920s radio accords with obsolete
gear, which would have spotted many ship
and aircraft freqs from 500-2000 KC.
If one were patrolling the Canal Zone with
a U.S. Navy flight and came-upon some
tramp steamers from Panama, the only way to
talk to them might be 500-2000 KC.
  
I have a problem with the "homing beacon"
theory when it comes to the T-15 to T-17 ARC-5.
I do know a little something about electrically
short antennas at longwave.

If one is in a B-24 with an SCR-287 or ARC-8,
a long trailing wire-antenna and high power
would be able to do the "homing" mission.
But the MF ARC-5s not only lacked the power
output of the larger sets- the TN-6 tuner
clearly is designed designed to make small
antennas radiate at least something on MF.
The few milliwatts of EIRP provided by an
ARC-5 MF set would work just fine to talk
to a ship or aircraft or tower 3000 feet away
on a known/established frequency,
but it would be hopeless at providing a usable
"homing beacon" to a flight 100-150 or more
miles away.  We had plenty of big patrol
bombers properly equipped for that mission.

Command Sets were designed for tactical comms,
and I think the most likely reason for the
ARC-5 MF sets was exactly that.  No U.S.
tactical forces were using 500-2000 KC
for comms, but I'd lay money the
three patrol planes and two patrol boats
in Upper Gababootoo or
ItchyScratchy, Iran were.

I would be interested in other views.

Got to get to work!
GL ES 73 DE Dave AB5S


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