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STC Coupling unit Ae

Posts: 377
Joined: Sat Jun 15, 2013 10:59 am
Location: Near Glasgow

STC Coupling unit Ae

Post by niall » Sat Jun 07, 2014 4:33 pm

Picked this up at the Livingston mini rally for a pound.

Some sort of remote aerial tuner. First thoughts were the connectors are very Larkspur, but it's painted black. Some research on line suggests it is aircraft equipment. I suspect from the size it's VHF and quite low power, but the aerial connections are for open wire, not coax. Inside there is a powered rotary switch which switches some capacitors and a small coil.

Manufacturer is STC. Front panel markings:

(STC badge)
WT 2lbs 2ozs

I have looked in the usual places like VMARS but no hits on the model no. or NSN.

Anyone have any info or a circuit?

Posts: 11
Joined: Thu Jun 07, 2012 9:59 pm
Location: Camberley Surrey

Re: STC Coupling unit Ae

Post by Beamcurrent » Sat Jun 07, 2014 9:38 pm


It is probably from the STC "STR xx" series of aircraft radios.

I have some bits of the STR18 series awaiting restoration, when I can find the time! My ATU looks like this:- 24-LRU-52b Not quite the same number as you quote, Have you a picture?

Anyway a real bargain at a pound!

Posts: 377
Joined: Sat Jun 15, 2013 10:59 am
Location: Near Glasgow

Re: STC Coupling unit Ae

Post by niall » Sun Jun 08, 2014 12:02 pm

Hi Brian,

Not much to see, it's a plain black box about 165mm x 80mm x 75mm deep with a mounting flange.
One end has an RF socket, old 75 ohm type with screwed retaining ring, Plessey type 104 2 way socket for 28VDC, type 104 12 way for control. Other end has an earth terminal and insulated aerial terminal.

I have traced out the circuit. There are two switch wafers on the Ledex shaft apart from the Ledex control wafer.

Switch positions are:
1 Straight through
2 series cap, shunt coil top connection
3 series cap, shunt coil top
4 straight through.
5 series cap, shunt coil tap
6 series cap, shunt coil tap.

From the component sizes, I'm thinking this is probably a matching unit for airband VHF.

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