[ARC5] TEL A - TEL B

[Mike Morrow]

BACKGROUND
The receiver racks for all related systems RAT through AN/ARC-5 are wired identically, and contain two separate audio bus headers...bus A and bus B and associated bus phone jacks.  The switch at the front of a receiver bay aligns the AF output of that receiver in to bus A, or to bus B, or to no bus.

In pre-AN/ARC-5 systems, there is also a control box switch for each receiver that performs the same function as the switch on the rack.  For that reason, the rack's audio bus select switches were seldom used.  The rack switch normally has a collar installed that maintains the switch in the middle "no connection" position.  The control box audio bus switch is used instead.  The communication receivers were normally aligned to bus A and the beacon band navigation receiver was normally aligned to bus B.  This allowed one pilot to hear ONLY the navigation receiver in his headset plugged into the range filter that was plugged into any phone jack marked B.  The other pilot would hear ONLY the communications receivers in his headset plugged into any phone jack marked A.

The AN/ARC-5 system eliminated the audio bus select switches on receiver control boxes.  The communications receivers (including the R-28 VHF receiver) were all normally connected to audio bus A using the rack switches.  The navigation receiver (usually the R-4/ARR-2 VHF receiver) was normally connected to audio bus B using the rack switch.  (The AN/ARC-5 system receiver racks are the only ones with an anchor point for the lock-wire used to keep the audio select switches in their correct positions.)  The usual receiver control box was the C-38/ARC-5, which controlled the audio bus A level of ALL communications receivers with one potentiometer marked VOLUME.  The audio output of the R-4/ARR-2 homing receiver was varied by the SENSITIVITY control, which adjusted the gain of the R-4 homing receiver on bus B.  These audio outputs were tied together and then fed to the aircraft interphone or to headphone jacks in J-16 or J-22/ARC-5 audio connection boxes.

SUMMARY
Before the AN/ARC-5 system, the receiver rack audio bus select switches were normally kept in the center no-connection position.  The audio bus select switches at the receiver control box were used to align communications receiver audio to bus A phone jacks and navigation receiver audio to bus B phone jacks.

The AN/ARC-5 system has audio bus select switches ONLY on the receiver rack.  There are none on receiver control boxes.  Rack audio bus select switches align communications receiver audio to bus A and R-4 homing receiver audio to bus B.  Bus A audio is passed through the C-38 VOLUME control and then combined with R-4 homing receiver audio from bus B to make just one system audio output header.  The C-38 VOLUME control adjusts communications receiver audio output into the common audio header.  The C-38 SENSITIVITY control adjusts R-4 homing receiver output into the common audio header.

MISCELLANEOUS
The single receiver rack used with AN/ARC-5 is MT-7/ARR-2.  It has no rack audio bus select switch, and instead uses a jumpering plug MX-2/ARR-2 in the rack control connector to put R-4/ARR-2 receiver audio on bus B.  The later MT-7A/ARR-2 rack restores the audio bus select switch on the rack, just like the AN/ARC-5 two- and three receiver racks.

That's about it for command set receiver audio bus selection and routing.

Mike / KK5F

-----Original Message-----
From: AKLDGUY
Sent: Oct 10, 2018 3:51 PM
To: ARC-5 List 
Subject: [ARC5] TEL A - TEL B

A friend has an AN/ARC-5 two receiver rack in which he mounts two receivers. He wants to know what the toggle switches at the front of each half do. They operate to left and right and are labelled TEL A and TEL B with arrows pointing to left and right headphone jacks. I'm not familiar with the racks and can't help him. Anyone able to shed light?

Neil ZL1ANM