[ARC5] Drift in ARC-5s - and other matters.

[Mike Morrow]

>> These units were designed for aircraft to aircraft and aircraft to
>> ground operation using VOICE. Not CW.
>
>Sorry. That is wrong. They were used very heavily on CW. The 
>main use of voice with them was in fighter aircraft before the AAF 
>switched to VHF.

There's not much evidence that WWII command sets were ever often used
for Morse CW or MCW.  The WWII military aircraft radio operators that
I've talked to, or read about, seem to consistently indicate that while
the *LIASON* MF/HF sets (SCR-187/287, AN/ARC-8) were usually used for CW,
the MF/HF *COMMAND* sets were essentially always voice mode.  The Morse
key was completely eliminated from the design of ALL of the USN's AN/ARC-5
pilot's transmitter control boxes (C-29/ARC-5, C-30/ARC-5, or C-30A/ARC-5).
The most commonly used AN/ARC-5 transmitter control box (C-30A/ARC-5)
normally has the TONE-CW-VOICE control set to VOICE and obscured with a
screwed-down cover.  The most commonly used AN/ARC-5 receiver control
boxes (C-27/ARC-5, C-38/ARC-5, C-125/ARC-5) do not even have the
capability to switch on the BFO of the associated receiver.

>> They were also only intended fro short range communication.
>
>Again, not necessarily so.

It was true far more often than not.

>> I seem to remember these units having provision for MCW operation.
>
>No. None for transmitting.

The modulators ALL have a 1000-cps TONE (MCW) oscillator, and the
transmitter control boxes for all command sets allow choosing TONE (MCW).
This mode is discussed in the ARA/ATA, SCR-274-N, and AN/ARC-5 manuals.  

>> And in the early days it was transmit or receive. Not QSK. When these
>> units were in the transmit mode the oscillator was keyed continuously.
>
>No. Not for CW. Only for voice. The keying relays (selector relays) 
>keyed BOTH the oscillator and finals. If one adjusted the contact 
>spacing, one could easily achieve a differential keying mode: i.e., 
>the oscillator would start first, followed by the final, then the final 
>would be un-keyed first, followed by the oscillator.
>
>I am not sure about this, but I believe the antenna relay was ALSO 
>keyed, which would, all thiings being equal (which they certainly 
>were not) result in QSK keying...slowly.

The only two relays (K53-power, K54-antenna) in the command set transmitters
are NEVER keyed.  They are strictly TRANSMITTER SELECT relays that energize,
and remained energized, as long as that transmitter is selected by the
transmitter control box.

*ALL* high voltages going to a transmitter (including oscillator HV) are
keyed by closure of the PTT button or the Morse key.  PTT button or Morse key
closure energizes HV relay K52 in the modulator, which then supplies all HV
going to the transmitter.

The main difference in transmitter control for the three operating modes is
that in VOICE mode, the transmitter dynamotor runs only when the PTT button
(or key) is closed, while in TONE and CW the dynamotor runs continuously.
The oscillator never runs continously (i.e., while receiving) in any mode.

Only hams improperly used the K53/K54 SELECT relays as keying relays, and
then were surprised when results often turned out poorly.

Mike / KK5F