Possible tweak for Multipath problems with P25

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brucebuck1010

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This could have been posted in many different categories, hope I chose the better one!

Longtime (40+ years) scanner here. I recently got back into the hobby after not being able to get my local Dayton, OH police on my older Trunktracker. I researched a bit and found my area is now on a P25 (Ohio MARCS-IP). I bought a BCD996P2 and was shocked to find the transmissions garbled and unlistenable. I tried lots of things, including bare wire, and TV rabbit ears, etc. Did more research and found out because of my location, I am probably picking up several multicast towers at once, causing multipath interference.

Well, today, by accident, I found that if my RadioShack rubber ducky was bent, the reception got better! So I tied a shoelace to the top of it, and bent it around and tied the other end on to the mounting knob on the side. You can vary the "bentness" by rotating the knob. It's not 100% better, but I'd say probably 75% better. Here is a picture:

http://oldbuckeye.com/bent_rubber_ducky_sm.jpg
 

DJ11DLN

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With LSM, "less is often more." There's a thread on here somewhere referring to people using straightened paper clips as antennas and having much improved reception on LSM systems. Glad you got it working but I can't think that keeping the RS duck bent is going to be good for it over the long term.
 

brucebuck1010

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Yes, I tried various lengths of paper clips and wires. A tried set of TV rabbit ears (with the VHF ants made small and the UHF element bent down), and it had an adjustment knob that seemed to work not too bad. I tried all of those in combination of setting the set's attenuator - but the latter did not work well. The bent rubber ducky seemed to work the best!
 

RFI-EMI-GUY

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This could have been posted in many different categories, hope I chose the better one!

Longtime (40+ years) scanner here. I recently got back into the hobby after not being able to get my local Dayton, OH police on my older Trunktracker. I researched a bit and found my area is now on a P25 (Ohio MARCS-IP). I bought a BCD996P2 and was shocked to find the transmissions garbled and unlistenable. I tried lots of things, including bare wire, and TV rabbit ears, etc. Did more research and found out because of my location, I am probably picking up several multicast towers at once, causing multipath interference.

Well, today, by accident, I found that if my RadioShack rubber ducky was bent, the reception got better! So I tied a shoelace to the top of it, and bent it around and tied the other end on to the mounting knob on the side. You can vary the "bentness" by rotating the knob. It's not 100% better, but I'd say probably 75% better. Here is a picture:

http://oldbuckeye.com/bent_rubber_ducky_sm.jpg
This post caught my eye for the novelty! But its f'n hot today so i can't brain today.

A shelf top steerable FM stereo antenna from the 70's . An idea that could be scaled to 700/800 MHz vertical polarity: The original was for urbanites to tune out nasty multipath from NYC broadcasters.

BIC Beam Box | Audiokarma Home Audio Stereo Discussion Forums


Here is an idea(patent link below) that is probably practical with manual phase shifting. Leave out the ADC and brains and use an adjustable phase shifter. Essentially, you would be tuning to align the direct and reflected waves in phase so that a stronger more conherent signal arrives. Try this at home, use a mobile scanner tuning to the distorted P25 system and drive your vehicle toward a metal garage door until the signal clears up. It might work at your garage door, the neighbors across the street etc until you get the direct and reflected rays to coincide.

I have seen this same idea using two antennas to notch out an interfere,

Patent US20100317309 - Antenna System And Method For Mitigating Multi-Path Effect - Google Patenti
 

a29zuk

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I have had decent results laying my 396T down so the antenna is horizontal.
The 325P2 works fine in the standing position as long as my P25 threshold is set to manual 7.

Jim
 
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