[MRCA] [MRCG] R&S FK859 Coupler

Sun Nov 14 12:02:58 EST 2021

I do have some documentation, but limited to schematics and parts layouts. Unfortunately, no theory of operation. This will be hard to troubleshoot if there aren't any obviously burned components (fingers crossed for burned components!). I do have a bunch of spare modules, but, of course, not this one. 

73 Eugene W2HX
Subscribe to my Youtube Channel: https://www.youtube.com/c/w2hx-channel/videos

-----Original Message-----
From: mrcg-bounces at mailman.qth.net <mrcg-bounces at mailman.qth.net> On Behalf Of FRANCESCO LEDDA via MRCG
Sent: Saturday, November 13, 2021 6:50 PM
To: 'West Coast Military Radio Collectors Group' <mrcg at mailman.qth.net>; mrca at mailman.qth.net; army-radios at groups.io; HarrisRadio at groups.io
Subject: Re: [MRCG] R&S FK859 Coupler

That looks nice, from a mechanical point of view.  Do you have documentation?

Best, Francesco K5URG

-----Original Message-----
From: mrcg-bounces at mailman.qth.net <mrcg-bounces at mailman.qth.net> On Behalf Of W2HX
Sent: Saturday, November 13, 2021 1:43 PM
To: mrca at mailman.qth.net; West Coast Military Radio Collectors Group <mrcg at mailman.qth.net>; army-radios at groups.io; HarrisRadio at groups.io
Subject: [MRCG] R&S FK859 Coupler

Hi friends. I thought some of you might enjoy seeing some really beautifully built antenna equipment by Rohde & Schwarz.

This is a fascinating antenna coupler. There were two variations of this.
One for use with a vertical or long wire (FK859).
https://w2hx.com/x/RohdeSchwarz/FK859/Pix/0525181435.jpg

And another variant where the HV top was replaced with a dipole adapter where this whole thing (weighs over 200 lbs) would be mounted aloft. The dipole adapter held four horizontal radiators to make the dipole.  That variant is called the HX002. https://w2hx.com/x/RohdeSchwarz/HX002/aloft.jpg
(stock photo!)

I have a bit of a hybrid approach where I have the 859 base and the dipole attachment at the top, which gets the HV wire over to my vertical.
https://w2hx.com/x/RohdeSchwarz/FK859/With%20HX002/1103201618a.jpg

I've been using this in my shack for a few years and I really love this coupler. It is spec'd for 1.15KW CCS but in ICAS SSB service I would say 2KW (maybe even 5KW) would not be a problem.  What I like about it is that it accepts 50W-300W for tune power. this makes it really convenient for tuning 100-150W transmitters where you can simply key up at full power and have the unit tune. Past couplers I had forced me to lower output to certain levels (not too low, not too high) which was always a little involved to get it just right. Although I chose to run about a dozen lines from it into the shack, this R&S coupler can be set in "auto" mode and needs only 28VDC and nothing else.

So this has worked really well for me for a while now. Recently I acquired a 1KW Harris transmitter and while I was learning how to use it, I must have accidentally dumped about 1.5KW into the coupler before it was tuned up and I believe I have fried the directional coupler. If I don't get this fixed before the winter weather really sets in, I'll be QRT all winter. So today was a warm and sunny day and I decided to take it apart to pull out the directional coupler and see what was what.  This thing is quite heavy and thoroughly installed outside so I thought I would take it apart, bring back the directional coupler to the workbench.

Most of the control circuits are mounted on removable modules accessible through this front door which tilts down.
https://w2hx.com/x/RohdeSchwarz/FK859/Pix/0525181508.jpg

But as my luck would have it, there is one module that requires the whole top to be taken off to access it. Big job. And here are some pictures. The build quality is really spectacular.
First step was to remove the dipole adapter to reduce the weight of the shell.
https://w2hx.com/x/RohdeSchwarz/FK859/Pix/Top%20Removed%20for%20Repair/20211
113_123707.jpg

And the internals.
https://w2hx.com/x/RohdeSchwarz/FK859/Pix/Top%20Removed%20for%20Repair/20211
113_132351.jpg

There are 32 motors around the base, 8 on each side. Each motor actuates a push rod that forms a switch to switch L and C components in and out until it finds match. Everything is silver or gold plated. Tuning is pretty fast on this and it remembers the Ls and Cs for each frequency so subsequent tuning is very fast 70 ms - 500 ms when a solution is stored in memory.

And finally the directional coupler was accessible.
https://w2hx.com/x/RohdeSchwarz/FK859/Pix/Top%20Removed%20for%20Repair/20211
113_132402.jpg
https://w2hx.com/x/RohdeSchwarz/FK859/Pix/Top%20Removed%20for%20Repair/20211
113_132540.jpg
https://w2hx.com/x/RohdeSchwarz/FK859/Pix/Top%20Removed%20for%20Repair/20211
113_132452.jpg

But just as I was strategizing about its removal. I heard thunder and realized some weather was moving in rapidly that I hadn't noticed! So a mad scramble ensued to get everything back together to a reasonable degree and pack up the tools and get in the house!
https://w2hx.com/x/RohdeSchwarz/FK859/Pix/Top%20Removed%20for%20Repair/Scree
nshot_20211113-133352_MyRadar.jpg

Well that is my story for Saturday. Hope it was of some interest.

73 Eugene W2HX
Subscribe to my Youtube Channel:
https://www.youtube.com/c/w2hx-channel/videos

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