[R-390] Interesting AN/SRA-50 antenna multicoupler on the E place

[John KA1XC]

Item # 1336334840
No connection to seller, just a FYI for the list so no flames!  :^)

It's a BIG AN/SRA-50 receiver multicoupler which was reportedly used with
390s and may still be in use. It's been up several times without  meeting
the reserve, but the pics are definitely worth a look.

A friend of mine picked up a couple of the tuning units two Hosstrader, NH
hamfests ago and I got to poke around inside them and take a look.
Construction was classic high quality military, and the components look like
they are sized for transmitting rather than receiving.

Referencing the top  picture, you can see two shielded RF compartments each
with an LC tank circuit. What is not readily apparent (but what I saw up
close) is that the tank circuits are actually inductively coupled to each
other through a small rectangular cut-out in the wall that separates the two
compartments. Cool!  One knob and gear train tunes the whole compartment.

Mounted on the top side of the wall (in the pic), right between the coils,
and on top of the cut-out is a piece of fiberglass board which was partially
covered with copper. It was mounted on a sliding mechanism that allowed it
to moved up or down, thus changing it's position over the slot opening. My
guess is that it served as an adjustable Faraday shield between the two
tanks, or possibly as a means of adjusting the coupling between the two
circuits. However, the copper section did not seem to be connected to ground
which I thought was strange.

73,
John