Batboard

I'm about to perform a wideband to narrowband and DES to AES migration, all on a conventional system with several hundred handheld/mobile units (XTL-5000, XTS-5000). I did a top to bottom review of our codeplug, something I always do before a mass-reprogramming. It occured to me that I'd never asked the question. Under conventional personalities, the ASTRO tab, digital modulation type, C4FM or CQPSK, what's the difference in practical application? Is there any benefit to receive sensitivity, decreased receive errors, more efficient operation with more complex ciphers (256 bit AES vs 64 bit DES), etc. between the two modulator types? Keep in mind, the system is conventional only. Have a good one!

C4FM is for single transmit site systems, CQPSK is for LSM simulcast [SZ6/7], Wide pulse is for Motorola simulcast [SZ3/4].

xmo wrote:C4FM is for single transmit site systems, CQPSK is for LSM simulcast [SZ6/7], Wide pulse is for Motorola simulcast [SZ3/4].

Careful there - there is a big difference between LSM and true APCO-25 CQPSK. CQPSK reduces the occupied bandwidth to 6.25kHz, while LSM retains the 12.5kHz bandwidth of a normal C4FM single. The difference is that the LSM signal will reach the correct symbol deviation sooner, and stay there longer, which is why it handles multipath better: the two transmitters can have a longer time-of-flight difference between them and still not be interfering with each other at symbol time. In CQPSK, the signal hits the correct deviation only briefly before moving on. I could generate the the different waveforms and get eye diagrams and constellation plots to show the difference Monday if you are interested.

The post did not ask about "true APCO-25 CQPSK"

The post asked the meaning of the programming choices available in the CPS for specific current production Motorola transceiver models - XTS5000 and XTL5000.

I believe the answer I provided is correct in that context. The Astro25 CPS help has this to say on the subject:

C4FM: Compatible 4-Level Frequency Modulation for non-simulcast operation.
CQPSK: Compatible Quadrature Phase Shift Keying for narrowband simulcast operation. Available When: The radio model is equipped for CAI (Common Air Interface) Digital Operation.
WIDE: Wideband simulcast operation. Available When: When the Tx Deviation field is not set to “2.5 kHz”.

The factory default is C4FM.

I'm just trying to head off confusion between the various modulation schemes - so that if somebody searches for CQPSK and finds your statement, the fact that there are different forms of QPSK that are compatible with C4FM is noted right below.

I didn't say you were wrong - I just noted that you need to be careful when using those terms to differentiate between LSM and true APCO-25 CQPSK.

XMO- msg rx'd. I'm on the same page as far as the appropriate situation for use of one of the three particular modulation schemes. Since Motorola's CPS help files have GREATLY improved from what I can tell over the past several revisions, I did catch the descriptions you included in your post.

WOWBAGGER- I've noticed some seriously granular information in other posts I've read from you and I love it man. Relative to the question at hand or not, it's always fun to read. It reminds me that no matter how much I know, there's always somebody out there that knows a helluva lot more so thanks! I'd actually like to see those diagrams if you wouldn't mind. We may soon transition to a single site trunking system using GTRs so the more I can cram in, the better for me when developing the comm plan.

What I'm actually asking here is more big picture, as opposed to detailed schematic. With over 15,000 professionals and very talented amateurs, there's a lot of experience here. I'm wondering if anybody has firsthand knowledge of transitioning their system from C4FM to CQPSK and noticing a difference, positive or negative, in performance. Keeping in mind of course that I'm running a conventional, single transmit site so my situation wouldn't be a common place for that to happen.

Thanks again, you two, for all the info so far.

"I'm just trying to head off confusion ..."
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A never ending battle when dealing with a certain radio company.

These are the same guys that keep saying "9600 baud" when they really mean "9600 bps"

One presumes that the CPS choice in these radios optimizes the demodulation for the format in use on that channel but since they really mean LSM they should have just said "LSM".

Trying to head off confusion in the world of P25 would seem to be a 'tilting at windmills' sort of undertaking.

"I'm about to perform a wideband to narrowband and DES to AES migration"
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You might clarify that. For example, if you are currently using +/-5KHz wideband FM on 25 KHz channels and converting to digital.

A digital only Astro25 conventional non-simulcast system using the XTS/XTL radios is intrinsically narrowband [12.5 KHz channel spacing].

You would only choose the "CQPSK" selection of you were using Motorola's LSM simulcast, otherwise you would use the C4FM selection.

I don't believe there are any 'true P25' CQPSK / 6.25 KHz channel spacing products on the market at this time.

HAHA I guess 9600 "bits per second" required too much effort (and many syllables) while 4800 baud just sounded too slow.


Actually, I'm already all digital. BUT, all channels (listed in "zone channel assignments") are set for +/-5KHz wideband FM on 25 KHz channels. For example, are you saying that if the modulation type is C4FM, then the radios are broadcasting at +/- 2.5 kHz and only using 12.5 kHz bandwidth regardless of the settings in zone channel assignments? That would definately be news to me....

Okay, anybody want to chime in on this one? XMO brought up a point that definately has me asking for clarification. I'd love to hear the final verdict on all digital, P25 radios being "intrinsically narrowband", regardless of the deviation and channel spacing settings in zone channel assignments. AND, am I to understand that the CQPSK option in the CPS is Motorola LSM (12.5 kHz and not 6.25 kHz), NOT APCO25 phase II CQPSK? Damn I'm a rookie!!! I'd love to hear the disposition on this one.

Your Astro25 CPS package came with contact information for Motorola's CPS help team. Ask them. Let us know what they say.

I believe that you will find that the CPS setting should actually be called "Digital Demodulator"

Ignoring 'wide-pulse' as not relevant to your situation, it comes down to two questions:

1.)What effect does the choice of C4FM vs. CQPSK have on the operation of the radio.
2.) What effect does channel spacing / deviation choice have on the operation of the radio in digital mode.

I think you will find that the answers are:

1.) The C4FM vs. CQPSK choice optimizes the radio's demodulator for either standard P25CAI or LSM. In either case your radio will always transmit Phase 1 P25 CAI [12.5 KHz emission mask compliant]

2.) The channel spacing and deviation settings associated with them affect analog operation. In digital mode the radio will always transmit Phase 1 P25 CAI. This setting changes the receiver's IF bandwidth to match the requirements of the corresponding analog FM signal in order to support mixed-mode operation.

All of this is very confusing but here is what the TIA says:

"A Project 25 CQPSK-c receiver is compatible with C4FM, CQPSK 6.25 KHz channel bandwidth modulation (none known to be deployed) as well as 12.5 KHz WCQPSK and 12.5 KHz LSM. The inbound, uplink direction uses C4FM modulation."

XMO,
From what I can tell, you're spot on brother. I didn't contact Motorola, I'm several hours ahead of the states and the rest of the real world so I did some experimenting in the shop. Turns out, no matter the settings in zone channel assignments, the deviation was uniform for each digital modulation type.

My test radio on average:

C4FM = 2.25kHz
CQPSK = 2.25kHz
WIDE = 3.05kHz

Zone channel assignment settings did in fact adjust deviation from 2.5kHz to 5kHz when the channel was changed to analog. There was no effect at all when choosing mixed-mode or ASTRO, transmit properties remained the same.

Thank you very much for throwing that at me, otherwise I probably would've never taken the time to check it out. I made an assumption that I think a lot of people make, a lot of people in my circles anyway. That's what I get for learning everything I know about Motorola on the job, huh? I remember the days when I actually had to troubleshoot C2 systems down to a bad transistor, repair it, and put it back in service. Now, you've gotta call dell tech support to fix your radios.

Thanks again for taking the time, I very much appreciate it! I ended up getting a lot more information than I started out looking for.

I beleive your 2.25 kHz deviation level is a bit low. The APCO P25 P1 spec calls for a peak deviation of 4.0 kHz for CAI, or an RMS value of 2.83 kHz (e.g., Root Mean Squared value: 0.707 x Peak = 0.707 x 4.0 kHz = 2.83 kHz). GD uses the RMS value (2.83 kHz) as the nominal bogie for setting deviation via their R2670. (Note: Keep in mind that since this is digital, the peak value of 4.0 kHz is the same as the constant (or steady state) value of 4.0 kHz).

Hope this helps!

ASTROMODAT wrote:I beleive your 2.25 kHz deviation level is a bit low. The APCO P25 P1 spec calls for a peak deviation of 4.0 kHz for CAI, or an RMS value of 2.83 kHz (e.g., Root Mean Squared value: 0.707 x Peak = 0.707 x 4.0 kHz = 2.83 kHz). GD uses the RMS value (2.83 kHz) as the nominal bogie for setting deviation via their R2670. (Note: Keep in mind that since this is digital, the peak value of 4.0 kHz is the same as the constant (or steady state) value of 4.0 kHz).

Hope this helps!

Agreed! I thought the same thing myself, but my testing wasn't scientific at all. I tested over the air on encrypted channels without loading the encryption into the service monitor. At the time my intent was to verify that the rate of deviation was determined by the digital modulation type, not the additional settings in the radio. Knowing that now, I feel pretty stupid not having known it in the first place. I'm responsible for such a wide scope of systems and equipment types that I'm forced to be a Jack of all but a Master of few. Looking at it now, it's the kind of rookie move that's actually embarrassing but it's not the first time I've done something stupid! I'm in Europe for the weekend, but when I get back to the desert I'll break out some radios and put them through some more clinical trials and post the results in this thread. That way somebody who comes behind us here doesn't get confused because of what I posted above. Thank you much for the info, especially for breaking out the numbers. It definitely is a help!