[ARC5] Altitude Adjustments

[Michael Hanz]

There was another altitude adjustment that doesn't get much notice, and 
that was with the interphone systems used in multi-place aircraft that 
were not pressurized, which was basically all of them for WWII except 
the B-29.  The reason wasn't due to HV arcing, but to compensate for the 
decreased density of the transmission medium (air) between the 
reproducer (phone diaphragm) and the ear drum. Beginning with the 
AN/AIC-2, there was a four position local amplifier switch, (as well as 
an optional remote switch), to raise the volume level of the amplifier 
for every 10,000 feet in altitude.  Beginning with the AN/AIC-2A, this 
increase was handled by a pressure switch that didn't need the radio 
operator to worry about it.

  - Mike  KC4TOS



On 7/16/2017 11:33 AM, Robert Eleazer wrote:
> I had always assumed that the automatic altitude power adjustment used 
> on transmitters like the ARC-3 was designed to reduce range of 
> transmissions both for OPSEC and interference reasons.  The idea that 
> the purpose was to reduce arcing makes sense.
> The standard Hi-Pot test required something like 550 V insulation 
> resistance.  This was a problem for some integrated circuits, so we 
> sometimes used an alternate instrumentation specification that 
> required a test to at least twice the operating voltage and I think 
> not less than 125 V.  The IC's could handle that.
> The ARC-27 addressed arcing problems by sealing the radio in an 
> airtight case and running cooling air through a layer of the outer 
> case with a blower.
>
> Wayne
> WB5WSV


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