Odd reception issue on different scanners/antennas

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unwinr

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Oct 31, 2012
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I have been in this hobby on and off for nearly 50 years, starting with a tuneable RS or Lafayette low band receiver (no squelch!) and moving to crystals and now computer programming with SD cards. I have been reading the different forums for years and have solved many issues through reading the suggestions of the contributors. I have an odd problem involving one EDACS frequency and different antennas and different scanners that I haven't seen in the forums. I have a discone, 1/4 wave 800 mhz (homemade) (both attic mounted) and one RS 800 mhz rubber ducky. I can freely interchange the antennas through the BNC connection. When I use the RS rubber duck or the 1/4 wave on the Uniden 996P2 I can easily receive (4-5 bars) on 854.0125. When I connect the discone I get no reception at all on the 996P2. However when I connect the same 3 antennas to a GRECOM PSR-800 (Whistler WS1080 upgrade), PRO-97, PRO-63 and others I receive 4-5 bars (even on the discone antenna). So the antenna functions and the 996P2 functions but just not in the discone/996P2 combination.

Any thoughts?
 

unwinr

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Oct 31, 2012
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All the other scanners receive the 854.0125 on all three antennas. It is just the 996P2 that won't receive it on the discone only. It receives loud and clear on the 1/4 wave and even the back of set rubber duck.
 

Mike_G_D

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As the discone is a wideband antenna while the others you listed are tuned for the 800 MHz band I am gussing that the discone is picking up some out-of-band signal that is strong enough that it gets through the 996's internal mixing scheme and interferes with the desired 800MHz signal. The Uniden's have a feature called "IFX" or IF Exchange. Try toggling that and see if the scanner still won't receive the desired signal when connected to the discone. It basically swaps the IF mixing from high side to low side or vice-versa so as to attempt to mitigate some types of internal mixing problems like images. All scanners have some form of mixing issues but because different brands may use a different schema they will react differently to various interferers. What bother's brand X might not bother brand Y. Try the scanner on the discone and use the IFX feature and see if that makes any difference. It might or might not but it is worth a try. There are many ways that strong signals can mix inside a typical scanner radio and produce undesired results; the relatively well known "image" product is just one example but not the only one.

If you want to delve into this Google "superheterodyne receiver design interference issues" and "IF image interference" or something along those lines and have fun!

-Mike
 

unwinr

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Oct 31, 2012
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Thank you tvengr and Mike_G_D for your help. I checked the center pin on the antenna and receiver ends and both were snug. I was totally ignorant of the IFX feature. After some reading of the 996P2 manual I found how to access this feature and toggled it. That did the trick! I am now receiving the 854.0125 control channel loud and clear. I am planning this evening's reading on superheterodyne interference issues to learn more about this subject. Thank you both once again.
 
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