[Milsurplus] re bc442 cap

[Mike Morrow]

> The cap was used to tune antennas that were too long or too short.

The various manuals describe using the antenna relay vacuum capacitor for only *one* specific case, when the 7.0 to 9.1 mc transmitter is installed and the antenna is too long to be properly tuned by the output circuitry of that transmitter.  The capacitor would be inserted in series with the antenna by connecting the lead from the 7.0 to 9.1 mc transmitter to one end of the antenna relay capacitor, and connecting the other end of the capacitor to the nearby transmitter terminal on the antenna relay.  The other transmitter(s) would connect directly to the transmitter terminal of the antenna relay, and would thus be unaffected by the capacitor.

Has anyone seen any military installation of the antenna relay where the capacitor was used in some other manner?  If it were connected to shunt the antenna, then there is no way for the connection to be made without affecting *all* transmitters in the rack.

It would appear that the need for the capacitor was so infrequent that, as Robert wrote, the BC-442-AM units were configured to delete the capacitor and its connecting post hardware.

With respect to the vacuum capacitor on the antenna relay, all ATA, all AN/ARC-5, and nearly all SCR-274-N units have that capacitor.  But a small number of of SCR-274-N units do not, so that if you have a BC-442-AM (without the capacitor) you have a minor rarity.

With respect to the LOCAL-REMOTE antenna current meter switch on the antenna relay, all ATA, all AN/ARC-5, and early SCR-274-N units had that switch.  But the vast majority of SCR-274-N units did not, so that if you have a BC-442-A with the switch you have a minor rarity.

I have photos of a one-transmitter, two-receiver AN/ARC-5 installation in a post-WWII USN basic training aircraft.  It shows an R-23 (.19 to .55 mc), R-26 (3.0 to 6.0 mc), and T-19 (3.0 to 4.0 mc), with MD-7 modulator and and two C-125 receiver control panels.  Thus it could, for example, listen to the tower on 278 kc, transmit to the tower on 3105 kc, and communicate with other aircraft on 3105 kc.  As expected, in a single transmitter installation that was configured for voice only, no transmitter control box was required (just the PTT switch on the RS-38 microphone).  The biggest surprise in the photos was the antenna relay, which was very clearly a late version unpainted BC-442-A without meter switch.  I guess sometimes they had to install what was available, and the antenna relay is the *only* transmitter component other than the dynamotor that is electrically interchangable between the SCR-274-N and the AN/ARC-5.

Mike / KK5F