After missing out on a line coupler on ebay, then having another one that I had arranged a trade for sold to someone else, I decided that I would try to build one. I have a mostly complete schematic from the Radio Systems manual and a closeup picture that I got from somewhere on the net.
Three important pieces of information are missing from the schematic. First, the schematic shows the rotary switches as boxes. The switches for the taps on the toroids are straight forward. Not so with the switches for the mica caps (using four caps in combination to produce ten values). Second, there is no informaton about the number of windings on the toroids, or the type/size of ferrite used. Third, the schematic labels the meter as "microamps". The manual says "milliamps". After I build the circuit, I can easily determine which it is.
I haven't figured out what the switching arrangement is on the caps, as they are shown on the schematic (and backed up by the picture). However, I have figured out a way to accomplish the same thing with a different wiring scheme.
Looking at the picture that I found, I think I have also figured out the toroids. I counted the turns as shown on the picture. I believe that I have the correct numbers, as the primary/secondary ratios come out as whole integers that have a logical progression. For the size of the ferrite cores, I estimated that from the size relative to other components in the picture. As to the type of ferrite, I picked some common types that could be used at these frequencies and ran some calculations for impedance, based on the number of windings that I counted. To be on the safe side, I ordered two different ferrite types.
The manual states that the coupler matches 15 values of impedance, ranging from 1-50 Ohms. If I am understanding the circuit, I calculate the range as 1.47-25 Ohms. It is possible that I am missing something.
I just received most of the parts from Mouser and Amidon. I am still awaiting the ceramic rotary switches (NOS Russian surplus). I have some perf board and a suitable metal box to house things in. It won't be layed out like the original, but should do the job just fine.
Hopefully, the switches will arrive soon. The big question is, did I pick the correct size and type of ferrites? I think that even if I got close, things should work well enough to get a reasonable match. Keeping my fingers crossed.