[Milsurplus] 24 Volt BC-312's & KC-97L

[Mike Morrow]

Jim wrote:

>The lower frequency IF of the BC-312 would make it more frequency
>selective then the BC-348 for starters.  I was surprised at how well the
>BC-342 that I have up and running, performs receiving SSB.

The would have been no need for a BC-312, or even a BC-348.  The R-348/ARR-36 HF auxilary receiver was specifically designed for use along side the AN/ARC-21 and AN/ARC-65 systems.  It tunes exactly the same frequency range and increments as the AN/ARC-21/65.  The R-348 (not BC-348!) is quite an elaborate all subminiature vacuum tube design whose control box is identical to the AN/ARC-21's control box.

>I agree it is a strange installation.

It is a completely implausible installation, IMHO.  

>other receivers, like the Navy ARR-41 may have been more appropriate
>but not available?

No need...the USAF had the AN/ARR-36.

The Navy's equivalent to the RCA AN/ARC-21 was the Collins AN/ARC-38.  And just as most AM AN/ARC-21 units were modified to become the USB capable AN/ARC-65, the AM AN/ARC-38 was modified (by RCA!) to become the USB capable AN/ARC-38A.  Also, just as the AN/ARC-21/65 had the dedicated HF auxiliary receiver AN/ARR-36, the AN/ARC-38/38A had the dedicated HF auxiliary receiver AN/ARR-41.

Some sidetracking follows:

Though some sources state that the AN/ARC-38 is a military version of the 618S, that is incorrect.  The 618S is crystal controlled, while the RT-311/ARC-38 is tunable in .5 to 1 kc steps (depending on frequency) using a stabilized master oscillator assembly.  IMHO, the AN/ARC-38 and its coupler CU-351/AR is a superior design to the AN/ARC-21 and its several antenna couplers.  It has the same rated 100 watts AM output, a slightly broader frequency range (2 to 25 mc vs. 2 to 24 mc), and is much much lighter and less bulky.  It lacks only pressurization.

There is a code book stored in the AN/ARC-38 main control box with the frequency vs. manual dial setting vs. channel memory drum settings that are required to set frequency.  You can't directly dial in the digits of the desired frequency.  I'm sure that this was due to limitations of technology at the time that the AN/ARC-38 was developed, and not some "security" measure as I heard some speculate.  With the AN/ARC-38, one can still tune around a bit by altering the manual dial settings, but it's unnatural.  The AN/ARR-41 really helps for tuning around.  The AN/ARC-21/65 and AN/ARR-36, by comparison, are set on frequency by positioning pins on a channel memory drum according to the numerical value of the desired frequency, then selecting that channel.  The main control box has no manual dials for setting frequency (though a special control box that is part of a test set does).  Though one doesn't need a code book, this method allows no real capability for tuning around.

The AN/ARR-41 covers exactly the same modes and frequencies as the AN/ARC-38, plus the LF/MF beacon band.  The information I have seems to indicate that while many USAF AN/ARC-21/65 installations did not include the AN/ARR-36, almost all the USN AN/ARC-38 installations included the AN/ARR-41.  Anyone re-creating an AN/ARC-38 should also include the AN/ARR-41 as a de facto part of the set (along with the CU-351/AR coupler).

The greatest misinformation is the claim that the USN's AN/ARR-41 was used as a replacement for the USAF's BC-348.  There is absolutely no evidence of that being true anywhere except in ham shacks!  (The last active service USAF aircraft that I saw (in 1970) that still had the old AN/ARC-8 aboard still had the BC-348.)

73,
Mike / KK5F