800 Mobile Reception - Peculiar Situation

[doctordave]

Folks,

I installed one of Larry's (BNC antenna) 2-2067, 5db gain antennas for 800 and have noticed tremendous performance on mobile 800 reception....basically added another 8-10 miles of reception over a standard multi-band antenna. Odd thing is, in my locality, there are areas in which I barely get any reception (often lose the lock on 800 trunking control channel)- despite seeing 4+ bars on my 796's signal strength meter...when I take the antenna off (leaving no antenna), the bars drop down to 0-1....BUT audible quality dramatically improves! Both ways, I have manually monitored trunking freqs out of trunking mode and confirm the same audio quality/signal strength findings.

Does/could this represent signal overload??? I would think that if signal overload were the problem, I would still copy clear audbile signals when monitoring the individual freqs out of trunking mode. Anyone have thoughts on what might be going on? I appreciate DX reception w/ my system - but obviously need good local reception.

Thanks to any who respond.

Dave

 

[N_Jay]

Folks,

I installed one of Larry's (BNC antenna) 2-2067, 5db gain antennas for 800 and have noticed tremendous performance on mobile 800 reception....basically added another 8-10 miles of reception over a standard multi-band antenna. Odd thing is, in my locality, there are areas in which I barely get any reception (often lose the lock on 800 trunking control channel)- despite seeing 4+ bars on my 796's signal strength meter...when I take the antenna off (leaving no antenna), the bars drop down to 0-1....BUT audible quality dramatically improves! Both ways, I have manually monitored trunking freqs out of trunking mode and confirm the same audio quality/signal strength findings.

Does/could this represent signal overload??? I would think that if signal overload were the problem, I would still copy clear audbile signals when monitoring the individual freqs out of trunking mode. Anyone have thoughts on what might be going on? I appreciate DX reception w/ my system - but obviously need good local reception.

Thanks to any who respond.

Dave

Sounds like it could be local Cellular or Nextel interference.
Or a strong carrier elsewhere in 800 MHz.

 

[greenthumb]

Yep - NJay's got it right - you're being overloaded by something in the area. I've seen this numerous times and it always turns out that having a not-so-great performing antenna (less gain) actually works better on 800 MHz.

Pull that rubber duck back out :lol:

 

[Landman]

I have had the same problem when monitoring the Louisiana State system while on the road. The way I got around it was to use two scanners. One scanner was connected to a high gain mobile while the other simply had a unity gain stubby. The high gain pulled in signals when I was far from a tower site in rural areas and the stubby pulled in signals from the system when I was in an area with cell sites. About 80% of the time, both scanners received the same transmissions. If one of the above situations applied, however, either one scanner or the other received the transmissions.

 

[CCHLLM]

You're leaving out another possibility which, unfortunately, is quite common but not talked about by the sales people and engineers in simulcast systems. This is a bit oversimplified, but when two or more synchronized simulcast transmitters are transmitting, there is said to be little to no "cancellation" effect within the designed coverage area, BUT when there is multi-path taking place, the receiving antenna is in effect "seeing" two separate signals on the same frequency. This results in distorted audio on analog systems and a higher than normal but acceptable Bit Error Rate on digital if the degradation is not too serious, but when the "timing" of arrival puts at least one of the signals sufficiently out of phase of the first, and the second signal's strength is sufficient, the analog receiver audio goes silent and the so does the digital because the holes in the bit stream are too large to compensate for. The receiver is still seeing the signals, but the intelligence on one signal is being cancelled out by the out-of-phase intelligence of the second signal. This has been a real problem in earlier simulcast alpha paging systems. There are supposed to be devices and system factors designed into the commercial systems that "eliminate" this effect in the "professional" radios, but it ain't necessarily so.

 

[doctordave]

Thanks for all the responses. I've done some tests while driving around - and have noted a dramatic decrease in performance when using the high-gain 800MHZ 2-2067 antenna within 1/2 mile or so of cellular and/or paging transmitter sites.....obviously this pertains to quite a few chunks of my locality............reception is markedly better in the same areas when using a considerably less resonant antenna. Suppose I'm going to be forced to return to the low-gain antenna when in the suburban/metro areas and only use the high-gainer when quite rural.

Appreciate the input.

Dave

 

[loumaag]

doctordave
You may find this FAQ and answer on the Icom America site to the point, even though it deals with a Ham radio:

(Reference http://www.icomamerica.com/support/faq/amateurfaqs.asp#handheld )

Q: My Icom IC-W32A or IC-T7A handheld radio receives just fine with the supplied "rubber duck" antenna. But, the receive seems to go down when I connect my handheld to an external high-gain antenna (yagi, etc.) Why?

A: These particular Icom radios have been optimized for best performance while used with the supplied portable antennas. External high gain antenna will overload HTs front end resulting in poor reception.

 

[doctordave]

Lou,

Thanks for the posting!

Dave

 

[ECPD279]

... Suppose I'm going to be forced to return to the low-gain antenna when in the suburban/metro areas and only use the high-gainer when quite rural.

Dave

Or you could try turning attenuation on when in populated ares. It's easier than changing antennas.

 

[okla-lawman]

I have teh same problem with my preamp. When I am out in the country I crank the amp up. If I forget to turn it off in the city reception goes to hell..turn the amp down it comes back up.

 

[doctordave]

The idea of a pre-amp is interesting. Have you noticed much of a boost on low-band and 800 when using that device? What particular brand do you recommend?

Thanks.

Dave

 

[okla-lawman]

The one i have is off a diamond anteena. The antenna had problems and
never really got to try it much on other than 800 mhz. You could tell a difference. One think to remember though is anything times zero is zero
in other words if you dont have a descent signal to begin with it cant amplify it. Unlike scanners most police/ham radios have a preamplifier built into them. That is why I think they are a good addition. GRE and
grove sale them and you can usually find a few on ebay. As this post kind of brought out make sure it has an adjustable gain on it. I am going
to work on my patrol cars radios today and will try to get the amp hooked back in and will let you know.