[Milsurplus] Re:ARC 65 and ARC 21 control heads, a rare exception

[Mike Morrow]

I wrote:

> The AN/ARC-21 replacement, and that unit's auxiliary receiver,
> the AN/ARR-36, and the USB upgrade AN/ARC-65, were essentially *not*
> usable in any sort of "scan-the-band" mode since one has to encode the
> desired frequency by setting pins on an encoder drum, then select that
> channel, just to make any change in frequency.  There are no manual
> frequency selection dials. 

BOEING377 wrote:

>Not exactly true. The test set for the ARC 21 ARC 65 had a control box that 
>had decade freq selector knobs so you could dial up any freq, no code books
>needed no pin settings either as in the 20 channel ARC 21  ARC 65 control
>head.  The full freq selector control head in the test set was made for acft panel
>mounting, same dimensions as normal control heads, but seems to have rarely
>been used in aircraft.

That's interesting info.  I was writing of the normally installed airborne unit (C-451/ARC-21).  I wonder what the nomenclature of the test set control box was, and if the test set control supported the slave remote controls (C-455/ARC-21) that were usually employed.

I always thought that it was a mistake that a second C-451 was used to control the auxiliary receiver used with the AN/ARC-21 (the R-224/ARR-36), which made it practically impossible to "tune around" with the ARR-36.  If they had used the type of control box that you described, then that would have made the ARR-36 more useful, IMO.  I think the Navy got it right with their auxiliary receiver for their AN/ARC-38, the R-648/ARR-41.  It has direct digital frequency readout and continuous tuning a la the R-390/URR. 

> As an interesting ARC 65 sidelight, Hughes Aircraft conducted worldwide
> HF RTTY tests for the USAF in the 60s using a C-131 (Convair 340) and
> both an ARC 65 and an ARC 58 onboard. The ARC 65 consistently
> outperformed the ARC 58 in every test, thought to be because of a superior 
> receiver.

The AN/ARC-65 is sort of awkward and heavy overall, compared to the AN/ARC-58.  The RT-400/ARC-65 drum just by itself weighs 140 lbm.  Add the racks, separate power unit, emergency keyer units, and antenna coupler, and I recall that you were looking at close to 300 lbm total.  The AN/ARC-58 was significantly lighter, and having the receiver/exciter in one 50 lbm box and the amplifier in another certainly make it easier to remove and install units in the aircraft.  The AN/ARC-58 has higher rated PEP output than the AN/ARC-65, and required no separate external power units.  The performance difference must have been in the receivers, as you state.  But the AN/ARC-58 must have been a good enough system overall, since the USMC adapted the design as the AN/TRC-75.

I'm fascinated most by the RT-128A/ARC-21, but I'll never own one just due to the great weight of the RT unit.

There's been some discussion over the past few years about NTIA requirements for HF sets used on those US government HF networks (CAP, SHARES, etc.) that have committed to those specs.  The critical specs seem to be for spurious output and frequency stability.  According to the tech manuals for the AN/ARC-65, AN/ARC-58, and the USB AN/ARC-38A, these old sets still meet or exceed what the NTIA requires today.  Pretty impressive for half-century old designs!

73,
Mike / KK5F