Picket fencing on a still radio (800MHz)

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ki4lqu

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I have 2 Radio Shack scanners (Pro 94 and Pro 97) When I lived on the west end of town, I was able to trunk my local public safety system with no trouble using the default duckie that came with the scanner.

I've recently experienced a serious picket fencing effect ever since moving to the west side of town, fluttering noise on the local 800MHz trunked system. Some channels on the system are clear as a bell, and others go to town fluttering and spitting. I've tried yagis, amplified antennas and even specialized 800MHz whips., all to no avail.

There are places in the room where it will reduce on some frequencies, but it is always ever present on at least one channel. When I configure one channel for clarity, some of the others start fluttering again. The fluttering is bad with a decent 800MHz whip while out in the neighborhood, so I know it's nothing locally here interfering. Both of my RS scanners do this.

I've had several suggestions, including intermod filters. I'm sad to say that FM, VHF and UHF pager notch filters do nothing to reduce this flutter interference. I have yet to find cellular or Nextel filters.

I'm in a position at the moment where I can't get the antenna out on a mast, so I can't try increasing height.

I am wondering if this is an issue with the RS front end for 800MHz. Would another model/brand of radio remedy this? I'm not very familiar with the front end selectivity for 800MHz, however I do know that a radio on the system would not experience the same interference as these scanners, both listening to the same frequency.
 

N8IAA

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I'm guessing that there is more multipathing where you are located now. Buildings, trees, other towers. I don't believe that a higher antenna will make the difference. You haven't said which scanner has the problem, or, if both do. Have you tried using the attenuator feature? Tightening the squelch? Just so you know, the 94 is a Uniden scanner, and the 97 a GRE. Two different scanners made in different years.
 
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bigbud42010

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Springfield, Ohio
I Have The Same Problem With The Montgomery County Ohio TRS I Live With in The Radius But i Still Have The Fluttering Sound Seems Like It Is A Cellular Wave Cause They Haven't Rebanded yet.
 

tcomm_specialist

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The first question is how close to the nearest tower are you? Especially compared to where you were.

Secondly, I would recommend getting the RS 800MHz rubber duck. (If you only scan 800) It is one antenna that RS got right. We did testing on it and other 800MHz only antennas and it was the clear winner.

Third, have you tried moving around your home? I have "dead spots" in my house and this is common with 800MHz even if you have a radio from the system. When we went 800 back in 1995 the rule was move 2 feet and try again.
 

ki4lqu

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Knoxville, TN
@N8IAA: It does sound like multipathing, somehow it's getting random reflections out of phase and cancelling itself out. Both scanners are getting this interference, and at different spots of the neighborhood. The ATTenuation setting seems no different, with the exception of slightly more hashed reception in some spots. It doesn't affect the drop-outs.

@bigbud42010: It has been suggested that strong Nextel and/or cellular is causing intermod and ACI. This system is supposed to have already re-banded.

@tcomm_specialist: The nearest simulcating tower is roughly 5 miles from me on Sharpe's Ridge. During the steady phases of reception it's S9, but something is randomly blocking or directing an out of phase reflection and knocing it down to S3-S0. It sounds like 'dead spots' you'd hear while travelling down the road. The drop-outs are just as random, although the scanner and antenna system is completely still.

I usually operate/montir at 70cm and below, so I am rather unfamiliar with 800MHz propagation. I know a guy who works for the police and patrols this area, and he states his car radio very rarely has dead spots in this area. The police cruisers use specially designed/enclosed 1/4 wave antennas.
 

ki4lqu

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@tcomm_specialist I almost forgot: Yes I do have that little 800MHz duckie from RS. It is a great antenna! I am able to receive many conventional transmissions and another trunking system (both from the same area -- Sharpe's Ridge -- as the PS Trunked system. They have no flutter or drop outs.

Also, you are right, moving the antenna around the room clears some channels up, but the others go haywire. It's hard to find a 'sweet spot' where all of them go quiet. A couple of inches and one will quiten down, another channel on the same system will be severely plagued. I'm guessing they're using different antennas on the same tower for groups of channels.

Some of the OTHER conventional frequencies and another trunked system that are at the same site (perhaps same tower) and same TX power have great coverage here with next to no dead spots at all.
 

tcomm_specialist

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If you can get other transmissions from the same location and on the same band (800MHz) then it is probably not your scanner. Is there a pattern to the times that this TRS drops out? 5 miles is not that far, but there may be something locally generating interference or there may be something in the TRS itself that is fluctuating from time to time. There may be a problem with their transmitter. A mobile set up will hear better than a portable set up. How does the officer's HT work in your area? That would be a better comparison.
 
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