[Milsurplus] Conjecture motor start-up - ARC-5 vs 274N modulation

[Mike Hanz]

Unserviceable but Repairable wrote:

>So comes the question about why Navy used high level plate modulation
>in their MD-7.
>

The manual gives some clues:  "Due to the use of plate plus screen-grid 
modulation in AN/ARC-5 equipment, the transmitters may be tuned for 
maximum output in the VOICE position of the control unit."  [As opposed 
to the usual CW tuning procedure.]  "This results in a slightly higher 
power output than in the corresponding transmitters of Model ATA 
equipment.  Modulation distortion resulting from improper tuning of the 
antenna circuit has been considerably reduced in AN/ARC-5 compared with 
Model ATA equipment." 

So, it would appear that improper tuning in the heat of combat was at 
least one driver.  I suspect that the Navy may have asked for two 
options in the original contract, for evaluation - status quo and plate 
modulation.  The difference in cost would have been relatively minor for 
the improvement in intelligibility under certain conditions.  By 1943 
Bell Labs had engaged in a great deal of research into improving 
intelligibility of radio and interphone equipment, so this output may 
have factored into the mix as well.  Also, don't forget that 
occasionally these transmitters had to be used to fill in for the 
liaison transmitter, so a little extra oomph was probably not a bad thing.

73,

Mike