ARC unit Identification

[John10b]

I wonder if any forum member can identify this unit please. It was shown on another site trying to see what it was used for. Mods if this is not permitted please delete with my apologies, thank you.
John

[turretslug]

Looks very much like some sort of control box, or possibly ground test set for a radio compass?- the frequency ranges are the sort that a radio compass is useful over, not to mention the controls labelled loop and the compass dial itself. The meter at top left is a vibrating reed frequency meter, maybe this confirms 400Hz (or whatever) from aircraft supply or ground converter for running PSU/motorised components of the system?

[Radio1950]

Made by Aircraft Radio Corp of USA.

As per John's reply, it is an aircraft ADF Radio Compass Unit (using NDB or BC stations), or a ADF Test Set.
The vibrating reed (centered on 100Hz) meter suggests the latter, as there is no need for this on an ADF/NDB receiver?

I am not an historical expert, but I seem to remember ...
Older Auto Loop Antennas sometimes used commutation (switching) of two loops at 100 Hz to generate a simulated "Needle points to selected bearing".

This 100Hz commutation as the reason that we always kept hum on ground NDB carriers (and mod) to be as low as possible, and always less than 5%.

Otherwise it had the potential to interfere in the aircraft ADF sense.

.

[Radio Wrangler]

The tuning scale, bandswitch and BFO switch says it contains a receiver. The frequency meter says it is a test box. The frequency ranges include the NDB band plus other stations that might prove useful for getting a fix.

I think it's a tester specifically for ADF antenna systems.

David

[turretslug]

Originally Posted by Radio1950

Made by Aircraft Radio Corp of USA.

As per John's reply, it is an aircraft ADF Radio Compass Unit (using NDB or BC stations), or a ADF Test Set.
The vibrating reed (centered on 100Hz) meter suggests the latter, as there is no need for this on an ADF/NDB receiver?

I am not an historical expert, but I seem to remember ...
Older Auto Loop Antennas sometimes used commutation (switching) of two loops at 100 Hz to generate a simulated "Needle points to selected bearing".

This 100Hz commutation as the reason that we always kept hum on ground NDB carriers (and mod) to be as low as possible, and always less than 5%.

Otherwise it had the potential to interfere in the aircraft ADF sense.

Having angled the screen here appropriately, I can now make out the "100 CPS" centre and "105" right-hand markings on the meter, so the commutation check makes sense. The meter switch at RHS lower also suggests a ground check device, in the air there wouldn't really be time, inclination or purpose in investigation beyond "Log it as U/S".

Possibly the small round window beneath the frequency meter is a carrier level indicator?

Interesting observation about keeping hum out of NDB carriers.

[John10b]

Thank you all for your replies, I have passed this information on.
John

[WB6NVH-GEOFF]

That is an ARC BTK-21 ADF test set system circa 1960. It is for bench testing units of the ARC Type 21 and 21A ADF equipment. It measures loop compensation, among other things, and when mated with a Type 21 receiver, loop and power supply will make a complete ADF installation. Runs off either 14 or 28 Volts. I guess no one here ever worked in an avionics shop 50 years ago?

[Radio1950]

Hmmm!
50 yrs ago, I was working on ANAV Ground eqpts, ILS, and RSR.
On the other side of the airport.

Thanks for ID'ing the equipment.
Just shows the breadth of experience on this forum.

There is something to be said for type plates on the front of equipment.

http://www.bunkerofdoom.com/lit/ARC_1960_cat.pdf

[Radio Wrangler]

Approaching 50 years ago, I was working on the avions not the avionics Now it's the avionics turn.

These sorts of testers came and come in two families:

'Bench Testers' are comprehensive testers designed to test equipment to full manufacturer's or certification specs.

'Ramp Testers' are portable cut-down versions which get taken to the plane and used to do more limited checks of the equipment in situ. (The ramp is the name of the place the plane is parked for maintenance) Ramp testers assume that the equipment being tested either has already been fully bench tested and it's just the installation job which is being checked, or that if something incorrect is spotted on a ramp test, the offending unit will be quickly pulled out of the plane and sent to meet a bench tester.

Some of these bench testers are staggeringly expensive.

David

[M0FYA Andy]

Coming from the aircraft manufacturer's side (I spent my career at BAC/BAe/BAE Systems Warton on aircraft such as Tornado and Typhoon), our term for such test units was always STTE, for Special to Type Test Equipment. This distinguished it from standard lab equipment such as oscilloscopes or test meters.

Andy