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C4FM or CQPSK

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SlipNutz15

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I have a question in reference to the programming of the radios in my county. I've been reading that if the channel is a single repeater site the channel should be programmed with the C4FM for field units. The radio company that programmed all our radios across the county made all of the digital channels CQPSK. I'm assuming this is incorrect if I've read properly? CQPSK is only for the tower sites to transmit of they're on a simulcast setup, correct?

Our Dispatch channel is analog simulcast and is PL 250.3. We then have 3 individual digital regional repeater sites for fireground ops.

My questions is this: field user mobiles and portables should transmit C4FM, not CQPSK, correct?

Another questions is would there be a performance/quality difference if the field users were C4FM or is them transmitting CQPSK not going to make a difference?

My county: Juniata County, Pennsylvania (PA) Scanner Frequencies and Radio Frequency Reference
 
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MTS2000des

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CQPSK is used in P25 simulcast configurations. Looking at the license, it appears that there are multiple transmit sites on some of the channels.

Since you appear to be programming radios for your agency, I STRONGLY recommend contacting the system engineers to confirm what type of buildout your network is comprised of.

Using the wrong type will result in seriously degraded performance of subscriber units, which could lead to someone getting hurt or worse. Also, it is a good idea to take the train the trainer class for whatever model(s) of subscriber radios you will be programming.

Programming of public safety subscriber radios is not something to take casually. These type of questions would be answered by an instructor in such a class.
 

SlipNutz15

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I have reprogrammed over half the county's radios because the company that did them programmed them incorrectly as far as options (scan lists, identifiers, etc). I did not touch the C4FM/CQPSK option as they originally came from the shop as CQPSK.

There is NO simulcast P25 in the county. There are 3 tower sites in the county and, as stated originally, the only simulcast channel is analog dispatch for pager/siren activation. The operation channels are regional, single tower P25 repeaters, each covering the southern, middle and northern parts of the county.

There are two FCC licenses. One is for the dispatch frequency (453.4125).

The other license, http://wireless2.fcc.gov/UlsApp/UlsSearch/licenseFreqSum.jsp?licKey=3286848, is a trunked license that is used for conventional frequency acquisition. There is no TRS in the county. Yes, I know it shows the same frequencies one each tower site but the county did not opt to do simulcasting of all Ops channels due to budget issues.

Nonetheless, field user radios should still be programmed as C4FM, correct?





As far as train the trainer class, I teach a radio operation class for companies who wish to take it. But as far as knowledge of the shop that originally programmed the radios, I don't trust them. They screwed up programming 300 pagers for the whole county and yet they still received the radio bid and I found out a field install tech was the one that was elected to program the radios and he admitted outright to me that he did not know all the options for the radios.
 
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MTS2000des

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I have reprogrammed over half the county's radios because the company that did them programmed them incorrectly as far as options (scan lists, identifiers, etc). I did not touch the C4FM/CQPSK option as they originally came from the shop as CQPSK.

You really should reach out to who implemented the system but if you are sure there is no simulcast controller online, than most likely the correct modulation would be C4FM. But again, not knowing who setup YOUR system, I can't tell just from looking at licenses on RR.

Nonetheless, field user radios should still be programmed as C4FM, correct?

This is typically the case in non-simulcast single site operation. But see my comment above about speaking to the engineers who implemented the system. Without doing a site visit and reading whatever repeater/base radio (Quantar/Quantro, GTR8000) it's hard to say for SURE. And I am sure you'll agree you want to be SURE.

As far as train the trainer class, I teach a radio operation class for companies who wish to take it.

I too have been involved in the business for several years. The agency I just accepted a position with is sending me to train the trainer. I wasn't implying that you didn't know what you were doing, just saying it's a good idea to have the manufacturer led course under your belt. We're never too old to learn right?

But as far as knowledge of the shop that originally programmed the radios, I don't trust them. They screwed up programming 300 pagers for the whole county and yet they still received the radio bid and I found out a field install tech was the one that was elected to program the radios and he admitted outright to me that he did not know all the options for the radios.

That's a scary situation but not all uncommon. A recent P25 phase 2 network rollout in my area resulted in all subscriber radio ID's being screwed up in Provisioning Manager. The users all had to key up for a couple of weeks and play "who's on first" while the correct aliases were added in PM by the radio shop who hosed up the job. It happens.

That's why we as comm techs need to be on our game and catch stuff like that. It's what justifies us getting the paycheck.

Good luck with your project.
 

dcr_inc

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Easiest way, besides asking the original installer/system engineer, is to listen to a scanner.. If it decodes 100% its a safe bet to say its C4FM.. If it has a hard time decoding the calls, its a good bet its a CQPSK system..
 

exkalibur

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Without doing a site visit and reading whatever repeater/base radio (Quantar/Quantro, GTR8000) it's hard to say for SURE. And I am sure you'll agree you want to be SURE.

Surely I hope you're not serious. There are many ways to know for SURE if it is C4FM or CQPSK without doing a site visit. The OTA waveforms look totally different as one uses FM and the other is PSK. 10 seconds with something like Audacity would tell you that.
 

SlipNutz15

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I know for a fact every portable and mobile is set to CQPSK but there is no simulcast digital ops channels. The scanner decodes it ok but I was just wondering if it was actually set up correctly.
 

slicerwizard

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Just listen to the repeater outputs. You shouldn't have any problem differentiating C4FM vs CQPSK. That *is* all you're trying to determine, isn't it? Or am I missing something?
 

MTS2000des

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Surely I hope you're not serious.

I am serious. We aren't talking about someone programming a scanner. We are talking about someone who is programming public safety subscriber radios on a public safety radio system.

If you want to risk it by listening over the air or using some $15 dongle and free software downloaded from the Internet to make such a decision, that's your liability.

The OP indicated some strange configuration of subscriber equipment was performed. I personally would want to do a PROFESSIONAL analysis of the system. But hey, what do I know. I only do it for a living.

I know for a fact every portable and mobile is set to CQPSK but there is no simulcast digital ops channels.

All the more reason to see how the FNE is configured. C4FM is the default modulation type in Astro 25 CPS for both mobile and portables. Why someone would have changed this to CQPSK is worth looking into.

Again, if you want to be SURE do a site visit if you can't get ahold of someone who wrote the existing templates. Find out what is on the other end. But hey, that's just me I guess. I would want to know what the system is I am taking care of from top to bottom.
 

SlipNutz15

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MTS2000- the problem I have going in to asking anyone why it was changed is because I'm sure no one knows. Which scares me. Like I found out personally, a field install tech was the poor soul who was put in charge of programming the radios and he did not appear he had much programming experience.
 

KevinC

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What you will lose by having a C4FM system set to CQPSK is about 1 dB of sensitivity on the downlink side. The subscriber always transmits C4FM, whether the system is C4FM or CQPSK. Setting it this way saves from having to reprogram all the subscribers if you ever go CQPSK....assuming you can afford to lose 1 dB right now. :wink:
 

slicerwizard

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If you want to risk it by listening over the air or using some $15 dongle and free software downloaded from the Internet to make such a decision, that's your liability.
Exactly what risk are you envisioning? What will a site visit tell you that listening won't? Or that looking at a waveform won't? Is there some ambiguity in these screencaps?
 

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MTS2000des

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Exactly what risk are you envisioning?

The risk of not knowing what specific parameters your network is set at, what equipment is actually in place, but I am sure sitting behind a desk with your roomful of scanners you are omnipotent when it comes to how we setup, optimize and maintain our systems and we are all just wasting our time with our expensive test gear when we could just whip out our laptops and freeware and go "see they're doing it all wrong. I've got this." Well not in my world it doesn't work that way.

Or that looking at a waveform won't? Is there some ambiguity in these screencaps?

Look, your point it well taken, if we were just talking about programming a SCANNER or hobby radio for casual listening, I've got no issue with that.

But anyone who's role is to maintain a public safety radio system should be intimately familiar with the network upon which they are configuring subscriber radios.

I am sorry you have an issue with that. I say anything less is just being lazy. It's what I get paid to do. Maybe it isn't that way everywhere. But I would want to be SURE and KNOW beyond what some toy radio stuff would tell me.

How would you explain that if by some small slim chance something went wrong and some lawyer down the road starts digging and finds out one went to a hobbyist forum asking such questions? I would want to be able to say with absolute certainty I used the correct test gear to industry standards, documented my site visits showing I had complete configuration data, and wrote my templates based upon the engineering specifications.

But hey, it isn't my system and the O/P is free to do as he/she pleases. I gave what I believe is the complete and correct method. If one wants to cut corners and use hobby toys and make guesses, so be it.
 

MTS2000des

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assuming you can afford to lose 1 dB right now. :wink:

That may be 1db one can't afford to lose. I know of an agency near me that narrowbanded on VHF and is already fighting a losing battle. Another db would be a big deal to them.

they are already looking at replacing their radio system or joining a neighboring county DTRS as a result.

I understand not wanting to do another touch of the fleet but if you end up going LSM in the future chances are other changes like adding channels or trunking would be in the future and would require it anyway.
 

slicerwizard

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I am sure sitting behind a desk with your roomful of scanners you are omnipotent when it comes to how we setup, optimize and maintain our systems and we are all just wasting our time with our expensive test gear when we could just whip out our laptops and freeware and go "see they're doing it all wrong.
Yes, too bad I haven't worked on analog/digital/TDMA conventional/trunked/networked radio systems or programmed thousands of two way radios or fixed microwave links in the middle of the night or written custom software to nab cloners or any of the other hundreds of tasks that the LMR landscape throws at you. Oh wait, I did all of that and much more for a living. Nice strawman though.
 

MTS2000des

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Yes, too bad I haven't worked on analog/digital/TDMA conventional/trunked/networked radio systems or programmed thousands of two way radios or fixed microwave links in the middle of the night or written custom software to nab cloners or any of the other hundreds of tasks that the LMR landscape throws at you. Oh wait, I did all of that and much more for a living. Nice strawman though.

Yawn...put it back in your pants

(I am sure you did all this using hobbyist tools like DSD+ and your $15 dongle...I mean, who needs an R8000 or 2975, GenWatch? Why buy that when Unitrunker can do all that and more:roll:)

We agree to disagree.
 

SlipNutz15

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Stop with the penis measuring contest. I just want to know what the biggest difference is for C4FM and CQPSK that they would make a non-simulcast, non-TRS system set up as CQPSK instead of C4FM. I did read where someone said subscriber units ALWAYS transmit in C4FM. Is this true? If so what is the option selector for? Decoding?
 

APX7500X2

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Stop with the penis measuring contest. I just want to know what the biggest difference is for C4FM and CQPSK that they would make a non-simulcast, non-TRS system set up as CQPSK instead of C4FM. I did read where someone said subscriber units ALWAYS transmit in C4FM. Is this true? If so what is the option selector for? Decoding?

The biggest question you should be asking yourself is...Why am I on Radio Reference asking this question.

This is a scanner hobby site, not a site to ask real questions about Public Safety radio systems

If you don't know why or how the system was/is set up you should not be touching the radios at all, yes even if the company messed up a scan list.
 
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