[222mhz] RFI on 222mhz

[Dr. Gerald N. Johnson]

On 11/28/2013 9:44 AM, Paul wrote:
> I've finally stumbled on a problem that has me stumped. I am using an Icom
> IC-706MkII as the 28.0mc if into an Elecraft XV-222, into a TE systems
> 2210G, feeding a M2 222-10EZ at 45 foot thru  82 feet of LMR-400. The
> problem is RF interference heard thru the IC-706 when transmitting using the
> TE 2210G. The audio level of the interference remains the same regardless of
> the position of the audio control including fully down/clockwise.

Are you using an external amplified speaker? Is the interference the 
same with headphones?

What does the interference sound like? is it like copying SSB on an AM 
receiver? What does the interference sound like if you transmit AM?

  The
> siginificant thing is that the level of the interference varies with the
> direction of the antenna. The tower/antenna is offset from the shack by
> about 25 feet horizontal distance and 55 feet vertical distance (shack in
> basement). The interference is strongest when the antenna is pointed
> directly at the location of the station. As the antenna is rotated left or
> right of a direct bearing to the shack, the interference begins to reduce
> until at about 20 degrees left or right, it is nearly gone, and by 30
> degrees left or right it has completely disappeared. Transmitting barefoot
> with the XV-222 only (23 watts), there is no interference regardless of
> antenna bearing. Reducing the drive to 1 watt from the XV-222 into the
> TE-2210G still provides about 80 watts out and the interference level
> remains about the same. I have changed power supplies, I have changed power
> and RF interconnect cables between all the gear including varying cable
> lengths and run positions.

Have you tried running the PA on a separate power supply from the IF 
rig? I hope you aren't driving the PA with all 23 watts when it needs 
only 4 to 10 for rated power output. Splatter can be broad band, wider 
than a ham band.

Ground wires longer than a couple inches are ineffective at 222, where 
about 13 inches is a quarter wave and effective for RF an open circuit.

If it sounds like diode detection of SSB (would be clear audio if AM) 
its likely RF getting into some apparatus in the shack that has a 
speaker and it might not be the IF tranceiver, it might be the stereo or 
TV speaker wire picking it up. It might be that the RF is coming in to 
the shack on the outside of the coax just because the coax gets coupled 
to the antenna more effectively when the antenna is pointing at the 
shack. That might be from the loop around the rotor moving closer to the 
antenna in that one direction. If its RF on the outside of the coax a 
ferrite bead may be of benefit. If its detection on a speaker wire a 
ferrite bead or toroid may be a help.

Another test with the common supply is to run the PA into a dummy load.

With the antenna directivity effect it seems like the antenna has a 
strong sidelobe down and its radiated pick up by something like an audio 
amplifier detecting the RF.

  I have also changed the if transceiver to use my
> TS-690S. The problem remained, this time being heard on the TS-690S. The
> interference is only heard on the radio being used as the if. Everything is
> well grounded. The coax cable run is offest from the bearing to the shack,
> the interference is not strongest when the antenna is in a direct bearing
> line over the coax run, but is strongest with the bearing directly pointed
> at the shack.
>
>
>
> I am certainly open to any suggestions and ideas on how to troubleshoot this
> problem.
>
>
>
> 73, Paul W2EC

73, Jerry, K0CQ