3467Re: [BCD396XT] Re: 155.25 freqy interference
- Dec 31, 2009I think I would try two facilities on the XT to see if it improves the situation . One being to switch in Front end Attenuation (assuming you can tolerate the drop in Fundamental signal level) and other being to switch XT to alternative IF. These two tests could give some further clue to nature of interference problem.
----- Original Message -----
From: Rich Carlson
Sent: Thursday, December 31, 2009 10:06 AM
Subject: Re: [BCD396XT] Re: 155.25 freqy interference
The 1/4th mHz. interference is common with cable TV, there are
numerous other sources of interference all over the place. Mixing two
signals together to result in interference on a third frequency is
called Intermod, it is possible that two or more cable TV leaks or
other types of noise on different freqs could result in intermod on
Another issue is image rejection. While newer scanners are much better
at image rejection than older models, they usually are not better than
the actual radios used on the systems. The radios are built for a
specific band segment while the scanners have to cover a wide variety
of freqs, therefore system radios usually are much tighter with
respect to image rejection.
On Thu, Dec 31, 2009 at 8:43 AM, shelleysh1@... <shelleysh1@...> wrote:
> Rich, I haven't heard it in the 1/4 th MHz, but I have major interference here in St. Louis, mobile, at the intersection of I-64 and I-270. The problem here is, I'm almost sure, due to the fact that that our MO Dept. of Transportation has an active facility as well as two large hospitals all residing on either side of the interchange - one of the hospitals being a level one trauma center. When going through the interchange one of the frequencies for the Muni covering this area will always lock up in a "high whine" (typical birdie type signal). But the frequencies involved are 158.790 173.8 PL, 154.650 156.7 PL and 154.115 no PL. Once a mile or so past the interchange, then the muni returns to normal. Since I regularly monitor them I know that this doesn't happen on their equipment, in fact I'm hearing them right now, on all their frequencies. So why would I experience this interference (on both of my 396XTs) and they wouldn't? I've also tried using the radios with the handheld antenna instead of the Larson installed on the car - same results.
> --- In BCD396XT@yahoogroups.com, Rich Carlson <rich.n9jig@...> wrote:
>> If you get interference and it goes away or weaken when you remove the
>> scanner antenna, then it is likely from outside sources. It seems to
>> be a common situation for frequencies at the 1/4 th MHz. (151.250,
>> 155.250 etc.) to originate from cable TV installations, often a poorly
>> grounded amp or connection.
>> My agency also uses 155.250 and when I hear noise on it I try to
>> locate the specific area and call Comcast, they usually get it fixed
>> pretty quickly.
>> If you are getting it in your home, then try to find where the drop
>> come into the house for cable TV and disconnect it, then see if the
>> interference goes away, if so then the issue is likely inside.
>> On Wed, Dec 30, 2009 at 2:45 PM, dataman60435 <dataman60435@...> wrote:
>> > I agree, nothing stops the hetrodyne whine in with the 155.25 (Bolingbrook PD)here in my area not the PL or IF shift...I wish they would change freqys...I have been told it has something to do with the Comcast Cable??....
Rich Carlson, N9JIG
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