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

[Bob Macklin]

The HF transmitters had a MCW tone generator in the modulator. The TX
control box had a CW and MCW position. The transmitter was keyed with either
the PTT button on the stick or the KEY on the control box. That key is not
like using a J-38 key.

The bombers and cargo aircraft that carried a radio operator did not use the
Command Sets for CW. They used the ART-13/BC-348 or the set that preceded
them for CW.

The fighters had very short antennas and no trailing wire antennas. I have
never seen a trailing wire antenna for a Command Set.

I do have the Command Set  Tech Manuals.

Yes the BC-453 had a narrow IF. But it was strictly a navigation receiver.
All the HF Command Set receivers had broad IFs. They did not require a pilot
with a heavy glove on his hand to try and do fine tuning while also flying
the airplane.
----- Original Message ----- 
From: "Kenneth G. Gordon" <kgordon2006 at verizon.net>
To: "Bob Macklin" <macklinbob at msn.com>; <ARC5 at mailman.qth.net>
Sent: Monday, December 08, 2008 2:47 PM
Subject: Re: [ARC5] Drift in ARC-5s - and other matters.


> On 8 Dec 2008 at 13:10, Bob Macklin wrote:
>
> > I have  not looked at an ARC-5/SCR-274 rig in over 40 years but I do
> > remember some about them.
>
> You might want refresh your memory by reading the manual here:
>
> <http://www.mines.uidaho.edu/~glowbugs/PDF%20files/ARC5/ARC
> -5-man.PDF>
>
> > 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.
>
> > They were also only intended fro
> > short range communication.
>
> Again, not necessarily so.
>
> > I seem to remember these units having provision for MCW operation.
>
> No. None for transmitting.
>
> > Also remember that these units had receivers with pretty broad IFs.
>
> True to a certain extent, but that depended on WHICH receiver: the
> LF versions, covering 190 to 550 Khz were VERY narrow. In fact,
> at their narrowest, too narrow for voice. Ever heard of the "Q-5er"?
>
> The IF frequencies depended on the band. As I remember it they
> went like this:
>
> 190-550 Khz, IF was 85 Khz.
> (Max BW at 60 db down was 4.5 Khz, min BW was 1.1 Khz at the
> 3db point)
> 550 - 1500, IF was 239 Khz (Max 8 Khz, min 2.1 Khz
> 1.5 to 3.0 Mhz, IF was 705 Khz (Max 8 Khz, min 3.2 Khz)
> 3.0 to 6.0 Mhz, IF was 1415 Khz, (Max 26 Khz, min 7.3 Khz)
> 6.0 - 9.1 Mhz, IF was 2830 Khz. (Max 56 Khz, min 13 Khz)
>
> The reason for the wider IF at the higher frequencies was to enable
> reliable communications with OTHER rigs which were far less
> stable.
>
> Also, ARC chose the IF frequencies to follow the usual convention
> at the time of 5% of the lowest RF frequency in order to minimize
> images.
>
> > 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.
>
> > What hams did with them after WWII is another story.
>
> Boy! You sure have THAT right! :-)
>
> As far as I and many others are concerned, they essentially ruined
> most of them, especially the BC band versions.
>
> I, myself, was guilty of that. I totally ruined, among others, one that
> covered 160 meters. Those are very rare now.
>
> Ken Gordon W7EKB
>