Control Channel Signal Strength

[DaveC56]

I would like someone to explain control channel signal strength and other tower freqs output.
I was trying to listen to Walker County SO the other night from the Canyon Ridge tower. This is a stand alone tower, that is not part of simulcast or multi-cast. The output freqs were very weak, choppy and often cutting out altogether. However, when I checked the control signal strength it was in the 90% range with only a little fluctuation.

I would have thought that the control channel and the other output freqs would all have the same power output. Why would one be strong and the others weak?

Thanks for any input on this question.

 

[b7spectra]

Is it digital or analog? Also, what type radio are you using? I used to have a Pro96 and the reception of digital was to pitts.

 

[davidgcet]

channels can vary a little in power, one system i maintain has 150W transmitters but power out of the combiner varies from 40W to 65W. another with 150W transmitters the power only varies station to station from 60-70W. the difference is combiner type and bandpass settings which can cause more or less insertion loss. but overall there should be see enough difference to notice, it takes roughly 1/2 power to see a channel as less.

maybe the problem was the units themselves were scratchy, possibly a problem with the tower top amp or RX antenna.

 

[DaveC56]

I am using a Radio Shack Pro-197.

In terms of quality, I am pleased with this scanner on VHF, UHF. My job takes me to Kentucky where the State Police use UHF P25 no trunking - no talk groups. It does great on those. It decodes the digital system very well.

But, here in North Georgia the Tenn Valley 800 Mhz Trunking p-25 system it just plain stinks. Since I don't have another digital scanner to place beside it, I can't say if it is the scanner or something else.

But, in the future I might like to purchase a Bearcat digital scanner and see how they compare.

DC

 

[N8IAA]

I am using a Radio Shack Pro-197.

In terms of quality, I am pleased with this scanner on VHF, UHF. My job takes me to Kentucky where the State Police use UHF P25 no trunking - no talk groups. It does great on those. It decodes the digital system very well.

But, here in North Georgia the Tenn Valley 800 Mhz Trunking p-25 system it just plain stinks. Since I don't have another digital scanner to place beside it, I can't say if it is the scanner or something else.

But, in the future I might like to purchase a Bearcat digital scanner and see how they compare.

DC

Some questions for you DC: What antenna are you using with the scanner? Do you have the multisite set to OFF? Is the squelch open (all the way to the left)? These all have an effect on how the scanner receives. Let us know
Larry

 

[rmiller818]

I don't recall having much problem listening to that system when I was in Ringgold last summer on my Pro-106. Which site(s) did you program into your scanner and which are you listening to?

 

[N8IAA]

I don't recall having much problem listening to that system when I was in Ringgold last summer on my Pro-106. Which site(s) did you program into your scanner and which are you listening to?

Check the original post, second sentence
Larry

 

[rmiller818]

Check the original post, second sentence
Larry

Whoops, glazed over that.

I won't claim to know all the answers to this system but I am curious as to why there is that site when Walker and Dade are part of the "NW Georgia Simulcast" "site" Have you tried listening to the NW Georgia Simulcast site? I recall monitoring that and the Chattanooga simulcast pretty well.

Monitoring the Cobb system I am showing constantly 95%+ on the decode yet the audio will occasionally come and go. While that tells us how well the scanner is decoding the control channel, it is not the best indicator of performance. I guess (not positive on this) that it is easier for the scanner to decode a control channel (just data info) instead of voice (kinda a different part of the scanner).

Maybe someone with more knowledge can explain how this system is setup.

 

[MTS2000des]

Control channel raw RSSI is misleading, especially on simulcast trunking systems. Even on a system radio, it is possible to have a strong control channel with a low BER, but voices come through garbled and drop out. I experience this nightly where I work, we are users on the Cobb DTRS and many places throughout the building our radios can affiliate just fine but voice channels sounds like crap.

Most trunking scanners cannot handle CQPSK worth a flip, and they sound poor even though raw RSSI on the voice channels and control channels is high. It's all about BER with digital.

In the iDEN world we refer to this in a different number, SQE for Signal Quality Estimator, and the subscriber radio calculates the overall SQE based on RSSI and BER of the forward control channel. It's more of a "real world" number than raw RSSI.

 

[DaveC56]

Thanks MTS2000DES. Your explanation fits in perfectly with what I am experiencing.

I did some further testing this weekend. Drove a few miles up the road to the tower and parked a few hundred feet away. Output freqs were 5 bars (max) but audio at times was a bit like the orginal Star Trek computer or an early music recording that has a tin sound to it. Seems that scanner technology has not kept pace with the commercial radios. Any idea if an improvement in the scanner technology is close?

I got my first scanner in 1975 and couldn't help but thinking how on a strong VHF freq you could hear the emotions in the voice. I don't hear that very well on the 800 Mhz trunking.

Also to the poster about Dade County being part of the NW GA simulcast. This isn't true. Only Catoosa and Walker (possibly Whitfield) use the Ringgold and Taylor's Ridge simulcast towers. Dade uses the Canyon Ridge (800 Mhz) and Trenton (700 mhz) towers. When working the North end of the county they use the Point Park (Chattanooga Simulcast) tower.

I know I am not a young man anymore but from the scanner listener point of view the move to 800 Mhz trunking has not been positive for me. I will take the old VHF days anytime. At least I could hear them.

Thanks

 

[ButchGone]

From my experience reception depends on what tower/site your are listening to. Dade, Walker and Catoosa counties all come through the Chattanooga simulcast site. Most comes through the NW Georgia simulcast site too. Depending on what kind of scanner you are using, there are settings that can help improve reception.
BG..