We know the ferrite wiil have no effect on the bleedover from the PD repeater, but it certainly can reduce interference traveling up the coax via common mode currents. I had this problem and didn't know it until I installed very effective ferrite loaded common mode chokes on one of my feedlines.
Turns out this coax ran right past my computer, monitor, router and several switching power supply wall warts before running through the wall and to the antenna. Interference from some of these devices was being picked up by the coax shield and it traveled up to the antenna where is was then picked up by the antenna and sent back down to the radio. Placing the first ferrite chokes gave me a significant reduction in my noise floor and eliminated a number of pesky birdies. A second choke made a very slight improvement but nothing like the one up near the antenna.
Most snap on ferrite beads are #43 material and good for the VHF/UHF spectrum but you need at least 3 in a row to make any noticeable difference. Or wrap a few turns of coax through the bead and doubling the amount of turns will give you 4X the inductance.
For the OPs problem, moving a directional antenna away from the PD repeater can give a little relief and if they are the only thing within that frequency range you might want to hear, you could get a notch filter for their specific frequency. Notch filters will have a negative effect for a couple of MHz above and below the design frequency and hopefully there is nothing else nearby that needs to be received.
prcguy
Wrong. They are a symptom of another problem that may be related to the interference issue you are complaining about. If your antenna is setup and grounded correctly, you shouldn't need a bunch of ferrites on your feedline to block noise. It is likely that whatever is causing the noise is making the interference issue worse than it would be otherwise, and the ferrites are a band-aid that is only solving part of the problem.
