[ARC5] ARC5/SCR-274N question - L-52 - Correction

[Mike Hanz]

Hi Mike!

On 3/14/2013 12:28 AM, Mike Morrow wrote:
> KC4TOS wrote of the T-15 L-52:
>> Actually, it is an outer ceramic coil and an inner phenolic
>> coil...similar to the TN-6 antenna tuner coil approach.
> Mike, that description must apply **only** to L-52 (ARC-9271) for the
> T-15/ARC-5.

Yes, it does.

> Even the T-16 L-52 is conventionally wound on ceramic.
> I don't have a T-15 to look at.  Is the inner coil in series with
> the roller coil inductance, such that the inner inductance is always
> in the antenna circuit even when the roller is at zero?

Correct.  It looks like they simply used an ARC-7992 coil with 60 turns 
and stuck this smaller 1.5"D coil inside the 2"OD ceramic form.  The 
output of the link coil T-54B feeds the roller as in all the sets.  The 
right hand end of the outer coil (looking from the rear of the 
transmitter) then feeds across internally to the left end of the smaller 
coil that is suspended within the ceramic one. The right end of that 
smaller coil then feeds the pickoff for the antenna relay.  So, you 
always have a small amount of inductance in the series circuit, 
regardless of roller position.  Given the frequency range and aircraft 
antenna limitations, that was probably not a problem.  Sadly, my 4342A 
appears to be suffering from oxidized contact disease, so I couldn't get 
a reliable reading of the inductance of each section.  I'll have to pull 
out the Deoxit when I get a chance.

> It makes a little sense, I guess, but it's still surprising.
>
> The AN/ARC-5 maintenance manual says that only a fraction of one watt
> will reach the antenna when using the TN-6 and a short fixed antenna,
> but it also says that the TN-6 allows use of short antennas from 1.0
> to 2.1 MHz.  So even a TN-6 won't help a T-15 and a short antenna.

Probably not, but I never say never. :-)

> One wonders why the T-15 to T-17 exist.  If they were to support actual
> aircraft command communications, they were most likely on small aircraft
> without trailing wire antennas, and radiating that fraction of a watt.
> Larger aircraft could fire up the AN/ART-13 with O-16, and use the
> trailing wire.  The documented intended use of these three "special purpose"
> transmitters remain one of the more interesting mysteries.

On the web page I provided in response to John Rose's query about the 
insides of a TN-6, I mentioned the only story that made sense to me, and 
that was actually corroborated by someone (now a SK) who flew in the 
float plane scouts that battleships and large cruisers used to carry.  
Like you, I have never seen any documentation.

            73,
  - Mike  KC4TOS