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john6483

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hello all, so i live within 2000ft of my local pd repeater and i'm getting alot of bleed over, is there a choke i can build to help stop this.. current set up is: scantenna st-2 to a PA-18 amp up 35 ft with a total run of 80ft RG6 cable into a 8 way splitter and then to 6 scanners, i have a fm radio band trap installed and 8 ferrites clamped onto feed line at this time... If i rotate the antenna it gets better and worse depends on position,
 

jonwienke

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Ferrite beads on feedline will do nothing to reduce interference. You need to know the exact frequency and get a filter specific to that frequency. It's unlikely you could DIY something that wouldn't take out the rest of the band with the PD freq.
 

Ubbe

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Are there several frequencies and what are the nearest frequencies you do not want to miss? Maybe a filter cannot be made narrow enough. Your best bet might be to turn the antenna to get the minimum signal from that tower and then add some sort of screening to the antenna to decrease signal further from only that tower.

/Ubbe
 

jonwienke

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sense i have installed them it has cut down on noise.
Placebo effect, most likely.

The only thing ferrite beads can do is cut down on common-mode currents in the feedline. They cannot filter out RF "noise".
 

jonwienke

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Then something is wrong with your antenna install and you have common-mode currents in your coax.
 

john6483

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I'm asking about the bleed over.. the ferrites are not an issue .. end of story...
 

dlwtrunked

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hello all, so i live within 2000ft of my local pd repeater and i'm getting alot of bleed over, is there a choke i can build to help stop this.. current set up is: scantenna st-2 to a PA-18 amp up 35 ft with a total run of 80ft RG6 cable into a 8 way splitter and then to 6 scanners, i have a fm radio band trap installed and 8 ferrites clamped onto feed line at this time... If i rotate the antenna it gets better and worse depends on position,
I assume the "fm radio band trap is for the FM broadcast band. Depending on the FK filter and closeness of the nearest FM broadcast band station, a single filter may not be enough. If the bleed over is from the PD and on VHF, that is a problem. You can get filters made for any frequency from PAR, but their width *may* weaken other stations that you wish to hear within a MHz or so.

The PA-18 is likely not a good idea at your location unless you spend a lot of time testing filters and get used to compromises.
 

jonwienke

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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.
 

john6483

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i went with the PA-18 from what i read on here and a friend has one on his set up.. i was thinking on splitting the scanners with another vhf filter due to i only use them on am mode for milair... I only have two scanner for pol/ems/ vhf. the rest are for milair
 

prcguy

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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.
 

john6483

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thank you prcguy, just for the fun of it i took a 4ft piece of coax (rg6) and did 2 full turns with the ferrites placed at 12 and 6 position, it has reduced it to the point now it not stopping on alot of the channels i have programmed. i have tried to turn the antenna slightly and i loose the refueling tracks near me, so i guess some of it i have to deal with.. thank god for the ATT button..lol
 

jonwienke

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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.
A better approach would be to move the coax away from the noise source(s) so that you aren't getting the common-mode currents in the feedline in the first place, rather than band-aiding the installation with the ferrites.
 
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