Wondering if someone could recommend some suggestions:

I have a situation in my basement where I am using an MX-980 with an MRF-350 in a closet. The TV is in the main area and I have it connected via HDMI to my Denon receiver. I wanted to add my PC to the mix and all I had in the wall was a CAT-6 (Non shielded wire). I used two Zuum HDMI baluns and the signal works perfectly - however the HDMI is sending a signal back to my rack which is interfering with the control system - some sort of interference. When I unplug the HDMI wire to the PC the red light on the RFX antenna goes off and the system works again. I plug it back in, the red light is pinned and the control system is crippled.

Anyone have any ideas short of using a shielded CAT6? The walls are already in place and impossible to wire another run without damage. All I need to do is disrupt this interference which is going back to the rack via the HDMI cable connected to the computer. Any ideas would be appreciated.

Are you sure you have all HDMI CEC off?

I don't think CEC would affect the RF interference he is experiencing.  I'm also not certain he's picking up interference over the cable run, but more likely the RFX is picking up interference from something nearby in the HDMI chain to the PC.

My recommendation would be to try and relocate the RFX antenna.  Sometimes moving it just a few inches can be all you need.  Is the RFX antenna located near one of the HDMI baluns or PC?

Also make sure that you don't still have the MRF-350 on the default RF ID channel "0". Channel "0" is termed the "interference sniffing" position and you should always run the unit set to another channel.

Another installers trick is to remove the RFX antenna by unscrewing the small screw and see if this gets rids of the interference.  If it does get rid of the interference, you might find that you still have enough range with the remote (30-60ft) to just leave it off.

The problem is that the interference is not wireless. It is being conducted by the HDMI wire back to the rack and ultimately to the RF unit. I can shut down the PC and literally watch the pinned red light on the RFX antenna go off. Also, if I unplug the HDMI wire from the PC the interference clears up instantly. The antenna is located high in the equpment closet so its not even near anything like a balun or component and the system works perfectly when the PC is not on. Does anyone know if I could anything between the PC and the HDMI wire to reduce the problematic signal that is being sent back to the rack?

have you tried another source to the balun instead of the PC? it sounds like it may be the PC not the balun.

The interference is wireless. After all HDMI does not directly connect to any of the URC system. I would try moving the antenna first, and if that still doesn't do the trick, try moving the antenna cable. Even the emitters cabling introduce interference into the system, although this doesn't happen very often.

I don't think you can say which end of the chain causes the interference. It could be that there's some RF that travels along the HDMI cable to the rack. It could be that when you plug the HDMI cable in at the rack, some circuit in the rack that generates RF interference becomes active.

When you state where the interference comes from, you have to have proof of it and knowledge of just what it is. I see blanket statements with nothing to back them up, which is to say you don't know what's causing it, because if you did you'd know what to do!

Also, it's better to say the interference is RF, which is mostly what was said, rather than use the term "wireless." That term strongly implies WiFi or some other purposeful RF communication scheme, which does not seem to be in play here.

For now, move the antenna.

When interference is present all the emitters are lit up and pinned. There are two red lights on the base unit (one for power and the other is a steady red which is not good). The system does not respond to any commands.

I moved the antenna and it's not even making any of the lights blink or issue any kind of feedback that the situation is getting better.

As soon as I unplug the cable OR shut down the PC it clears up instantly. When the PC is booting up it does not happen until it reaches a point where a video signal is present, then it stays stuck. I think its coming from the PC as well.

Where is the actual base station unit in relation to the PC? I have had to move it on occasion also. PCs will throw off all kinds of stray RF. Sometimes turning the wireless off will help, if your installation allows.

If you touch and hold the antenna while sending commands, does that clear it up?
If so, you can get a wire with alligator clips on each end and clip one to the antenna and the other end to something to ground it.

Also, try and make sure none of the IR emitter wires are near the anything with power or the PC.

Try fitting one of those wrap-around ferrite cores that come with some TV power cords on each end of your HDMI cable. Should at least eliminate the (slight) possibility that the HDMI cable shield is acting as some sort of hf receiving antenna.

Gotta get the RFX250 antenna module away from that rack.

I've had this issue with the wire running to the RFX250 running too close to my PC power cord/power conditioner. Moving the antenna didn't help, but eventually moving the base station a bit so the signal wire did not run near the PC power supply or AC wires did. 

try disabling the computer's wifi card if you have one there.... just in case the 2.4 is traveling over the shield of the hdmi... i dont know... try it