[ARC5] My "ARC-5" Impressions (long)

[Fuqua, Bill L]

Maybe there was some logic behind the  wide band width of the receivers' IFs.
73
Bill wa4lav
________________________________________
From: arc5-bounces at mailman.qth.net [arc5-bounces at mailman.qth.net] On Behalf Of Mike Morrow [kk5f at earthlink.net]
Sent: Friday, October 14, 2011 12:24 AM
To: arc5
Subject: Re: [ARC5] My "ARC-5" Impressions (long)

> Why would a pilot want to net his receiver to his own transmitter?
> That would probably set each plane's receiver significantly different
> from every other plane in the flight.

Interesting.  That statement implies that the various transmitters are on
"significantly different" frequencies!  That is NOT at all probable, not
the least reason being that the transmitters were lock-tuned pre-flight
and have no coffee-grinder remote control box dial to which the pilot has
access to screw things up.  Unfortunately, receivers were not so protected
until the era of the lock-tuned stabilized R-25, -26, -27/ARC-5 receivers
that were used only by the US Navy in late WWII.

Even if all the receivers were set *exactly* on correct frequency, having
the various transmitters on "significantly different" frequencies would
never have worked for a command net.

The transmitters were likely the best frequency standards available for
the command set while in flight, certainly much better than the receiver and
its miserable poorly-graduated 2-inch diameter remote control box dial (with
tuning spline backlash) that the pilot (not radioman) had to use to adjust
receiver frequency.  And that receiver setting could NOT even be locked in
place to prevent inadvertent adjustment!

> Surely the procedure would have been for each pilot in a flight to net
> his receiver to the transmitter of the control tower, or more likely the
> transmitter of the flight leader, using his BFO. Then everyone is at
> least *listening* on the same frequency.

I doubt there was ever any BFO-assisted command set netting done by pilots.
The command set was operated by pilots, not radio operators.  Late WWII US
Navy AN/ARC-5 receiver control boxes for the transmitters and receivers
lacked or blocked even the capability of aligning for anything but VOICE
operation, but those by then had usually eliminated the capability of any
remote communications receiver tuning by the pilot.  Tuning was allowed only
in the instance where a R-23*/ARC-5 beacon band receiver was installed.

Certainly there would *often* be pre-flight radio checks.  Let's say it
was perfect.  But then...

What happens if the coffee-grinder controls get mechanically disturbed
inadvertently or intentionally WHILE IN FLIGHT???

  -- OR --

What happens if the non-stabilized receiver drifts due to gross temperature
change WHILE IN FLIGHT???

There are well-documented complaints from pilots about the coffee-grinder HF
command set receivers.  Some communication failures were caused by pilots
with best intentions tuning the affected receivers to "better" tune the net
frequency, who then only got even further away from it.  There was NO netting
feature available to correct in flight such easily -created problems with
command sets that were otherwise operating perfectly per their design.

Thus, there are several obvious and very sound reasons it would have been
advantageous for the pilot to be able to net his ARA or SCR-274-N non-stabilzed
and non-lock-tuned receivers to the associated transmitters.  All it would have
required was a remote switch to drop out the receiver rack sidetone switching
relays that energize on key-down conditions.  And...one wouldn't want to do
it when radio silence was required.

Mike / KK5F
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