[Milsurplus] BC348Q Usage

[Mike Morrow]

Mark wrote:

>First,  when operational frequencies were given out,  was there any
>particular granularity as to the frequency itself ?   Today, one can
>specify 7.03128 with no problem,  but with the granularity of the
>BC-348Q, one would be kept to 25 Khz, 50 Khz, etc.

In the WWII era of HF radio, a channel might rarely be specified at 0.5 kc precision if crystal control was used.  For example, some of the frequencies for the SCR-536 (BC-611 handie-talkie) and AN/ARC-9 (Bendix RTA-1B ten channel HF set) were specified to that precision.  But normally, 5 or 10 kc precision was more likely.  (This is NOT adjacent channel spacing!)  

>Second,  since there is no on-board calibrator, I assume all
>frequencies would be approximate,  and that to keep the radio
>relatively calibrated would be a depot level function, or perhaps a
>reference signal came from an ART-13?

There was an on-board (the aircraft) calibration frequency indicator (CFI) called the SCR-211 (BC-221 frequency meter).  This external calibration source was a definite requirement in the pre-AN/ARC-8 days of the SCR-287 HF liason set in order to precisely adjust the BC-375 transmitter to desired frequency.  There was a monitor/normal switch that, when key-down, disabled transmitter sidetone and kept HV supplied to the BC-348.  This allowed the BC-348 receiver to be quickly netted to the transmitter.  Or the reverse process could be used.  It doesn't really matter how accurate the BC-348 dial calibration is.

With the arrival of the USN's ATC or T-47/ART-13, the CFI became much less important.  There is a good crystal controlled calibration unit in the transmitter itself.  Once calibrated at the nearest calibration point (located every 200 kc), the VFO circuits are such that frequency calibration book data are identical for *all* units of the ATC or T-47.

The USN's ATC and T-47 calibration book specifies frequencies at 5 kc intervals from 2 to 8 mc, and at 10 kc intervals from 8 to 18.1 mc.  The USAAF's improved T-47A has a vernier scale above the VFO dial that allows for adjustments as small as 0.1 of a minor dial division.  Thus the calibration book for the T-47A/ART-13 is at 1 kc intervals throughout the whole range of operation.

So, a WWII USAAF radio operator could easily and accurately set his T-47A to a frequency at 1 kc intervals, or even smaller intervals by interpolating calibration book data (also identical between all units).  The T-47A/ART-13 was part of the AN/ARC-8, whose receiver was the BC-348.  The AN/ARC-8 also has a monitor/normal switch which allows the receiver to be quickly adjusted to the transmitter.  There is no real need for a BC-221 frequency meter at all.

BTW, your BC-348 was also known as the AN/ARR-11, though none were marked that way.

>Finally, was the 348Q use primarily as an air to ground radio, or air to air?

Primary function was air-to-ground long range liason communications.  In the ETO, the VHF SCR-522 provided most of the air-to-air and even much air-to-ground command radio communications.  To a much lesser extent, the HF command radio SCR-274-N did also.

>Really enjoyed using the BC-348Q. ... An ART-13 is on the shelf,
>and I'm looking forward to getting that working soon.

Pair it up with a T-47A, and you'll have most of an AN/ARC-8 system.  Get a O-17/ART-13A LF/MF oscillator and CU-32/ART-13A LF/MF tank coil and maybe you'll even be ready for some of the experimentation proposed on the old 420 to 520 kc maritime Morse band.  IMHO, this is the finest LF/MF/HF airborne radio of WWII, one that was still serving on active duty on some older USAF aircraft even in the early 1970s.

Mike / KK5F