[R-390] CU-872 Multicoupler

[Flowertime01 at wmconnect.com]

Ward K8FD,

Would you like to part with the CU872 antenna coupler?
Do you know if Fair Radio has any more?

The 6922 are industrial grade E88CC  6DJ8

 1 in and 8 out, 70 ohms. Wonder what system it was used in and if anyone has
experience using it. Plan on using it with my R-390 and R-390A, etc.

If you were ASA educated as a 33B20 Radio repair man you learned to service 
these items. 

If you was an ASA educated 05H you had 1, 2 or maybe 3 of these between your 
antennas of choice and your receivers. 05H likely had 2 receivers and each 
receiver was on a different antenna. The place was called a field station. The 
antennas were called an antenna farm. 15 guys, 30 receivers, 15 mills were in a 
room called a bay.

In the corner of the bay was two racks filled with CU872 The racks had patch 
panels. The OP could pick a coupler output and patch it over to one of his two 
receivers. The guy may swap the patch 3 or four times in a 8 hour shift. Some 
guys had skeds that never needed to have an antenna swap.

Some where else was a room where all the antenna leads come into the 
building. Each antenna feed one CU872. The 8 outputs went down the cable ways to 8 
different bays. into a CU872 in the rack in the corner. If more than 8 guys (very 
likely) wanted to use the same antenna in the bay then one CU872 output would 
be patched into a second CU872. That way 15 outputs would go to one of two 
receivers at the 15 operator positions. There were 7 positions down the side of 
the room that had the two CU872 racks. There were 8 positions down the other 
side of the room.

No one wanted to set the 15 position across from the coupler racks. The 
coupler racks had blowers and made it cold across from the rack. The racks were 
also next to the bay doors and you cough all the noise from the hall. At the 
other end of the room was a supervisor position on one side of the room with 2 
more receivers. Across from the supervisor was the traffic analysis desk. 
Supervisors handed out sked. (your freq, antenna and time) while the analysis tried 
to make some sense out of who you were copying. Lots of 05 ops copied cut 
numbers. You hear ditty EISH5 and type 12345. you hear TMO 4 dah and 0 and you 
typed 67890.

Some ops had RTTY machines and some ops had AN/THN11 tape recorders.

So CU872 antenna couplers will work at least across the R390 spectrum.
They will work up to 50 real easy. Good tubes will get you above that. I 
never had receivers that went that there that I could patch into a CU872 to see 
how high it went. We had OPS that did this, but I was not allowed to just play 
with it to see what was what.

On the bottom end the CU872 has a filter in the bottom pan that cuts every 
thing under 2 MHz off. It got the AM broad cast band out of the noise mix. The 
filter has BNC input and output. you can use a barrel connector and by pass the 
filter and use the CU872 all the way down to at least the bottom of the AM 
band.

The CU872 is two sets of four amps. you can get inside and uncable one side 
of the amp and populate only half of the tubes. This will drive 4 outputs.

The CU872 was considered zero gain. One output had the same level as the 
input. As the output was fanned from 1 to 8 the gain was 8.

If you have several receivers a CU872  is nice to have as you can put 8 
receivers on one antenna. The Army, Navy, Marines and Air force all used the CU872 
antenna coupler in receiving sites. If you were a far end and all your antenna 
pointed to north America you likely had CU872s for the receivers. Then the 
transmitters had separate antenna. You likely looked at the propagation charts, 
clock on the wall and patched the RTTY tape to the correct transmitter.

You can get into the transformer outputs. By bringing the transformer output 
out without grounding one side (as is done with the N connectors) you can put 
the phase correct and drive the R390 balanced input from two coupler outputs 
and get a gain that way. Not something that one could do with military 
equipment in service. But owning one of your own opens lots of applications for you.

The circuits inside are very redundant. This will help you if you have had a 
tube go bad and have crispy things to repair. Finding 20 new tubes can be a 
bite in the pocket book.

I took care of these critters at several stations between 68 and 75. If you 
checked the tubes every 6 months you were OK. The front panel meter is a real 
nice 50 UA movement. I have two meters that I still use in home built volt 
meters.

Roger KC6TRU