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General Scanning Discussion For general questions not specific to a model of scanner or general discussion of use of a scanner. Location specific posts should be directed to the regional forums listed below.

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Old 06-08-2014, 12:23 PM
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Question Simulcast Fire Paging Monitoring

Are the simulcast issues I keep reading about as big an issue on fire paging in VHF High or is this more of a trunking/P25 thing ?

Most of my listening interest is fire paging and response. Before I go spending on my next scanner really would like feed back on what /if any issues folks are hearing out there.

I know I had to turn the CTCSS off on some of my furthest dispatch channels in VHF NFM to hear anything. Any and all feed back welcome.
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Old 06-08-2014, 1:15 PM
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Simulcast shouldn't have anything effect on tones opening up a receiver (be it a pager or FTO capable scanner) as long as you have one of the frequencies that the tones go out over programmed (of course with the receiver able to receive the band that you want to use).

P25 is another story, as there is no receiver capable of doing tones on a digital system as of yet. There may be in the future; just have to wait and see if any manufacturer will be able to deliver on this.

Trunking (conventional - NOT digital) is going to have variables, such as if the tones are always broadcast on a static channel.

Hope this helps!
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Old 06-08-2014, 3:21 PM
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Thanks ... was mostly referring to the scanner being able to get good audio on a VHF simulcast system. I have heard this is an issue mostly in Wisconsin were I spend time mid summer.

But your post helped reaffirm somethings. (hats off)
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Old 06-08-2014, 5:13 PM
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Quote:
Originally Posted by 1268 View Post
Thanks ... was mostly referring to the scanner being able to get good audio on a VHF simulcast system. I have heard this is an issue mostly in Wisconsin were I spend time mid summer.

But your post helped reaffirm somethings. (hats off)
The simulcast issue you have heard about is only on trunked systems that have multiple transmitters sending the exact same voice signals simultaneously. No connection with your FD paging.
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Old 06-08-2014, 9:14 PM
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I beg to differ, and I base that differing on 40+ years in the two-way radio and paging business. Looking in the RR database, there are numerous simulcast analog emergency services paging systems in place in this country, and all of them suffer from the same malady: multiple transmitters on the same paging frequency transmitting the same intelligence simultaneously.

I live in a county with a metro fire system that has UHF analog simulcast paging. It is not multicast on different frequencies from multiple sites, it is simulcast on the same UHF frequency from multiple sites, and even with the transmitter synchronization equipment in place and operating, it still creates a problem because of multipath issues.

You may be able to synchronize the transmitters to near perfection frequency-wise and modulation-wise, but with multiple sites transmitting on the same frequency, there is absolutely no way to fully compensate for multipath distortion and audio cancellation in any given location. The greater the number of transmitter sites involved and the closer the sites are located to each other, the greater the multipath audio distortion and audio cancellation problems.

Scanner receivers and pager receivers ain't all created equal, and most don't deal with multipath as well as some higher end mobile and portable radios will, but the bottom line is that regardless of your receiver's ability to deal with multipath, you will never be at a point that is equidistant from each of the sites where you could theoretically have synchronized signal arrival times. The reality is that since you cannot be at a perfect location, and if your receiver is able to copy more than one site at a given location with good signal levels, the audio is still going to be distorted for no other reason than the difference in arrival times of the signals at the antenna.

It ain't a perfect world out there.

Last edited by CCHLLM; 06-08-2014 at 10:09 PM..
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Old 06-09-2014, 7:37 AM
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I agree with "CCHLLM" and add my 40+ years in the two-way radio business. If your system uses simulcast paging (no matter what the frequency band) you will experience problems. It is just the nature of the beast. As was said some radio receivers are better than others but most will have problems at one time or another.
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Old 06-09-2014, 3:52 PM
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Thank you .... I am hearing some of the distortion locally and understand that it's a bigger issue elsewhere. I will take all my gear with me next month and report back.
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Old 06-09-2014, 6:10 PM
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The MultiPath Distortion on the new P25 systems is terrible - and it is in no way equal to a simulcast issue on VHF or UHF Single site systems .... 2 Seperate issues .... spend 5 minutes trying to decode it and you will understand what people are discussing .... Its not a matter of Distortion ..... its a matter of decoding the audio about 20% of the time in some places. It is usually cured with a YAGI antenna pointed in the proper direction.

Multipath System Decoding - Digital P25 Problem

Simulcast Problems - not the Same
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Old 06-09-2014, 6:30 PM
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OK............ I believe you need to read the posts a bit more carefully. The above discussion is about MULTISITE analog simulcast paging on ONE frequency, not one site analog paging or multisite paging on different frequencies.

And for the record, audio in the current modes of public safety radio is still a form of FM or phase modulated audio, and multipath issues show their ugly heads whether the audio is digital format or analog format. If it wasn't an audio format, you wouldn't be able to hear the "motorboat" sounds of the digital format on your analog radio. Basically what separates the two formats is how the audio is processed in the receiver to produce the desired intelligence interface.

Analog format receivers process the entire extracted audio envelope, circuit and atmospheric noises and all. Digital formats only process the extracted audio for what the firmware/software says are digitally significant components. Block, distort, or interrupt too many of the desired components and no audio is produced, or if the unknown component or components most nearly resemble a digital component on the acceptable list, an R2D2 audio response is what may be heard. Multipath audio distortion and cancellation suppression from receiver front end overloading are the prime causes of the inability to decode/process digital audio formats where there is sufficient on-frequency signal level to otherwise process the desired signals.

Last edited by CCHLLM; 06-09-2014 at 7:42 PM..
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