Question RE:LASO heard on 500MHz bandplan

[rananthony04]

A while back when I still had my Bearcat installed in my truck with an 800MHz glass mount antenna, I could hear LA Sheriffs in the 505.000 thru about 508.000 frequency range, sometimes really clear, so clear in fact I thought they had moved over to the 500MHz band plan( I heard more than one Sheriff dispatch and L-Tac frequency) when I put in the pro-2096, I no longer was able to monitor LASO in the 500mhz , same with the pro-96.

Today while at Rose Hills, I went to the highest point I was allowed, which is considerably high (you could see downtown LA and way beyond on a clear day of course). I was barely able to hear LASO in the 500MHz. Why was I able to hear LASO (in the 500MHz bandplan) through my Bearcat clear as day, yet barely be able to hear them on the pro-96/2096 while atop the highest point at Rose Hills? Furthermore, why was I able to hear them on the 500MHz bandplan in the first place? Anyone?

 

[code6]

intermod

I have experianced that the Uniden scanners are more prone to intermod problems
than the RS scanners are.Sometimes one agency will bleed over another one clear
as a bell even though it is on a totally differant freq. Maybe this is what your encountering?

 

[RobertW1]

Image Harmonics.

 

[nhp9943]

21.600 meg for Bearcats. Take that and subtract it from the 500 meg and you will find that it gives you the correct 480 freq. Way back in the old days that is how you could monitor beyond the standard range of your scanner.

 

[rananthony04]

Boy, I guess there is much more to scanners than I thought, thank you for your input guys.

-Robert

ps, what is Image Harmonics?

 

[nhp9943]

In telecommunication, the harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. For a sine wave, it is an integer multiple of the frequency of the wave. For example, if the frequency is f, the harmonics have frequency 2f, 3f, 4f, etc.

 

[RobertW1]

In telecommunication, the harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. For a sine wave, it is an integer multiple of the frequency of the wave. For example, if the frequency is f, the harmonics have frequency 2f, 3f, 4f, etc.

In simple terms the scanner is producing an image or a reflection of a different frequency. It is most common in scanners that use dual conversion. Triple conversion circuits reduce or eliminate them entirely. The "false" frequencies will always be the same spacing away from the true frequency: 21.4 MHz, 21.6 MHz or 21.7 MHz. The image may be higher or lower than the true frequency.

As noted by nhp9943 above, it can be 21.x MHz above or 2 x 21.x (43.x MHz) or 3 x 21.x (64.x MHz) above, etc. Back in the day, it was just as easy to monitor cell phones even though the band was blocked by scanning the "image" area of the band for the transmissions. With strong signals the strength didn't degrade too much as you listened in on the "image" frequency.

 

[rananthony04]

Is it still possible to listen in on "image" freqs.....like cell phones, as mentioned above?

 

[RobertW1]

Is it still possible to listen in on "image" freqs.....like cell phones, as mentioned above?

Yes, especially on some of the older scanners that use "dual conversion". Cell phone towers transmit in the 869 - 893 range. While this area of the band is blocked on today's scanners, the image will appear up in the scanners "unblocked" 900 MHz range. But remember this is for analog cell phones. Many cell phones are now digital.

Here is more info:

http://www.snapshield.com/www_problems/Inter/All_you.htm

 

[rananthony04]

Interesting read, Thanks for the info RobertW1.