[R-390] Going to own a R390A soon.

[Roger Ruszkowski]

Larry,

Welcome.
 
The cable you referenced would be the elegant deep in you wallet way.
 
There is a C connector beside the balanced input connector.

Here are some of the following ways to get this done.

One is via the cable you posted.

Two is to just ground one of the two pins in the balanced connector and plug your antenna wire into the other pin. In twenty five feet or less of wire this is what that cable does.

Three is to just ground one of the two pins in the balanced connector and plug your antenna wire into the other pin but insert a .01 uf cap in the antenna lead for static DC voltage isolation.

Four use the C connector with coax. This is unbalanced and skips the first set of tuning filters in the front end. OK and used by the signal corp that way.

Five use the C connector on the back. Move P206 to J105, short the input pin to J107 to ground. It is some times easier to find a C to other coax adapter or C to coax connector than some twin ax coax and connector.

Six use a length of IBM computer network cable and IBM twin ax connector ground one inner conductor to the shield and feed the other conductor with or with out an isolation cap. Patch a length of what ever cable and connector you want to the twin ax  with some shrink tubing to make up the inline splice.

Seven Bring the twin ax away from your receiver into a small metal box (Faraday shield). Connect the shield of the twin ax to your small box. use a toroid core wind a unbalanced to balanced transformer. In the small metal box put the two twin ax conductors to one side of the transformer and the antenna to the other side of the transformer. As the real input impedance for the receiver in in the range of 200 to 300 ohms a better match can be achieved between the antenna and the receiver. Depending on the selection of the core you can band pass filter the antenna input. You mite use a core material that drops out above 10 megs and thus get good AM and low short wave and 160 80 40 meter operation. You may try a high pass materiel that starts around 5 - 10 megs and filter out the low ends AM band signals. You can use air core coils in the box and do all kinds of circuits in the box. I grounded my twin ax in the connector (normal assembly) And used a rubber weather electrical connector into my match box. I did not ground the twin ax shield in or to the match box. I keep the two conductors balanced and also ungrounded. The box was / is grounded outside away from the receiver where the antenna feed line comes to the earth. Not grounding the twin ax shield in or to the match box helped me filter out some local San Diego neighborhood noise.

Eight there is a right angle twin ax to C adapter that was / is used by the military. One pin of the twin ax is grounded in the adapter and the other pin is the center conductor of the C connector.

Nine wire a length of coax into a twin ax connector with the center conductor to one pin and the shield to the other pin. Ground or not ground the shield and pin to the twin ax shell and thus the receiver chassis. Include or not a bushing to reduce the twin ax shell locking nut hole down to fit the coax you use. This looks to be the solution as used in the cable sited in your post.

This Is not an exhaustive list of options.

You can have a 100 foot of twin ax with connectors on both ends for $30.00 from the E bay place. a connector for the old IBM fat cable for 9.00. Buy a 100 for of cable. cut 6 = 8 feet off one end to use in the shop to the signal generator and such. String the other 90 feet out to the yard and hang your self the longest highest dipole you can manage and wire the balanced coax to the center. Make sure you have the breakin wired and switched on before you hit any transmit switches.

Do go find the http://www.r-390a.net/  web site and read read read. There are also other good R390 sites.

Do down load the Y2K manual and read it. The fellows worked hard to produce that manual and it is so much more readable the original TM's
TM 11 5820 - 358 - 35 for the R390A has several sections missing. It was assumed you had a copy of TM 11 5820 - 357 - 34 on hand for the R390 and could use paragraphs from that manual to service the R390/A Thus the Y2K having the good stuff in current English is a better reference source. 

Roger Ruszkowski AI4NI