KRC2 /K3

[HP]

I have a KRC2 that is presently using the AUX Bus input to  drive an Array Solutions remote antenna switch .  At 100 watts , it is usable but at 1500 watts is unusable. This evening I even unplugged the 12vdc supply and it still drove the K3 nuts - froze it once and several times it would show KPA500 (dunno where that comes from , I don't have one ).ONly thing that kills it is to unhook the AUX Bus line. I am not real wild about it changing antennas randomly -- even with two SWR triggers in use.

I won't bore you with the ferrite cores etc I have tried and or still have in place.and other details -  - my questions are  ----

Anybody have any experience with how much RF filtering I could insert in the 1 foot K3/KRC2 aux bus cable ?

OR -   is it worth changing to the RS232 bus and using the BCD data from  the K3 ?  Looking at the KRC2 schematic , it looks like the microprocessor is still in the act with the RS232 inputs going thru it . But I have filtered  RS232 data lines with   Ferroxcube VK400 2 1/2 turn hi mu ferrite chokes and 0.001's at least on PTT and KEY  lines with no problems.

I am tempted to sell the KRC2 and build my own BCD  RS232  to serial  converter, just thought the KRC2 would be a quicker solution. Its overkill for what I need  to do.

Hank K7HP

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[AD6XY]

Hello Hank

I sympathize with these difficult issues - the KRC2 is out of date and its about time it was replaced but at least it has always been reliable. I have one and it has never suffered from RF getting into it. Sorry if the below is stating what is already obvious to you.

This may be a symptom of an RF in the shack problem. The 1ft line should not be a problem and as long as it is screened additional filtering should not help. Using RS232 may cure the symptoms but not the cause and your own BCD interface likewise.

If it is an RF getting into the system problem,  how might that be happening? A good way to check if it really is RF in the shack is to ask yourself if you have issues with lots of noise on the bands from the shack computer. As antennas are reciprocal, if you have significant coupling of RF back you will also have coupling of noise in.

Obviously with 1500W the antennas will have to be a long way away from the operating position (for safety if nothing else) so we can probably rule out this being due to direct radiation from the antenna.  I assume you have remote antennas and the array solution switch somewhere remote with a long feeder back to the shack. Maybe at the base of a tower.

Could RF be getting back on the control lines from the remote switch? Are the control lines screened? Are they running close to the feeder. Putting ferrite on the switch control lines may help. Ditto the feeder. Burying the feeder helps a lot but isn't always practical.

One of the worst configurations for this problem is a feeder on a catenary because it will pick up like an antenna, especially if you have an effective RF choke at the antenna end. If you have that arrangement, ferrites are the answer - plus a good short connection to your RF ground where the cable enters the house.

The other possibility is you are using several feeders via the switch with an ATU in the shack. That's a problem because you will potentially have a bad match on the feeder in use, almost certainly a bad match on the feeders not in use which will result in the pickup from all the feeders merging at the switch. So, if the remote switch is actually in the shack I would investigate if you can improve the grounding and maybe move it somewhere else - like right next to the ground stake.

Mike

[Jim Brown-10]

On 9/5/2013 1:09 PM, Pfizenmayer wrote:
> OR -   is it worth changing to the RS232 bus and using the BCD data from  the K3 ?  Looking at the KRC2 schematic , it looks like the microprocessor is still in the act with the RS232 inputs going thru it . But I have filtered  RS232 data lines with   Ferroxcube VK400 2 1/2 turn hi mu ferrite chokes and 0.001's at least on PTT and KEY  lines with no problems.

I inherited a pair of KRC2s from N6RNO as part of the bandpass filter
kit for our CQP multi-op setup. As built, they are FULL of Pin One
Problems, and they are completely unshielded (thanks to paint between
the chassis and things that are intended to contact it, and paint
between sections of the enclosure that should make contact but do not).
It took me an hour or two on each unit to clean up the mess.

Most "RF in the shack" is the result of Pin One Problems.  If your
antennas are close to your shack, they will put RF in your shack, but
our equipment SHOULD be designed to reject it. Pin One Problems are an
open door into equipment for hum, buzz, and RFI.

Lots of detailed stuff about Pin One Problems on my website.
http://k9yc.com/RFI-Ham.pdf and http://k9yc.com/publish.htm

One very useful piece of information is that all that is required to get
band data from a K3 to a KRC2 is a single run of coax to connect the AUX
BUS.  Pin One Problems can be avoided by connecting the coax shield at
both ends to the SHELL of the DB-connectors. BUT -- in the KRC2, the
shells of the DB-connectors are insulated from the chassis, so that's
one of the messes that you must clean up.

Both the K3 and KRC2 are designed to be "universal" in their AUX
interfaces, so they provide BCD data on other pins in the DB15 for use
with other radios and other interface equipment.

Another idea Hank -- if you're using an RS232 interface, see my notes
about using CAT5 cable to build your own RS232 cable. Twisted pair
provides strong rejection of hum, buzz, and  RFI.  Use one pair for each
signalling circuit, with the solid color going to the high side pins (2,
3, 4, 7) and the striped conductors twisted together and connected to
the DB9 shell.

73, Jim K9YC
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