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Thread: Quantar P25 Waveforms?

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    Default Quantar P25 Waveforms?

    With some Quantars I noticed that the transmitted waveform in P25 (displayed on a scope) looks different.
    I was used to the kind of mix of several sinus waveforms, now it looks like a mix of subcarrier waveforms?
    It also sounds different in FM but decoding with P25 gear still works.
    Any hints?


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    Where are you measuring - on a wideband demod at the transmitter output or are you looking at the low or high band modualtion input to the transmitter?
    It is a fine thing to be honest, but it is also very important to be right

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    Measured the demodulated Quantar signal on a service monitor with a build-in scope.
    Big difference between the 2 waveforms, wondered if Moto did change their P25 waveforms somewhen?

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    Two possibilities 1) there are two modulations supported an Astro 'wide pulse' and standard. You should only use the standard, 12.5 kHz setting. Or 2) the station is not aligned properly, if this is the case it will negatively affect your range.
    It is a fine thing to be honest, but it is also very important to be right

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    O.K. Range has not been affected so far and station has been aligned properly by myself.
    What is the principle difference between "standard" and "wide pulse"? Do their respective waveforms look different?

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    170 Hz. Actually the wide pulse aka Astro simulcast, was a wider deviation +/- 3 kHz rather than the standard 2.83 kHz. Apart from better tolerance to simulcast distortion it worked better for off frequency stations and was noticeably better when used in high speed platforms such as jets. It's history now.
    It is a fine thing to be honest, but it is also very important to be right

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    Means that apart from the slightly higher deviation the waveform should basically look the same?
    My concern is that the newly observed waveform looks noticeble different, or maybe it is due to a defective Quantar?
    The system otherwise still works fine. I discovered this by coincidence during system maintenance.

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    It will only look the same if you run the same test traffic, you're looking with the V.54 BER test on I assume?
    It is a fine thing to be honest, but it is also very important to be right

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    Thats right! I will have a closer look at this by configuring 2 spare Quantars accordingly and play around with the settings.
    Just never noticed this before.

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    With everything the same (including exciter firmware which is not able to be flash updated) they should look identical.
    It is a fine thing to be honest, but it is also very important to be right

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    There are 3 or 4 possible choices, CPQSK, C4FM, WIDE, and PII TDMA. Each is a different modulation technique to encode essentially the same data in several different ways. The receivers auto-switch so you really can't tell unless you look at it with a scope (as you are) or check the TX modulation type.

    Also Astro Spectra has an excellent point about data, if you think about it, even a very simple encoding system like NRZ will produce widely different waveforms based on the sequence of data it is encoding...

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    Just as an aside, I thought this was only available on the GTR8000s and not on the Quantar...?

    Quote Originally Posted by Alpha View Post
    ...PII TDMA. Each is a differ...

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    Yes, correct, I was talking about P25 in general, but you are correct in that Q-Boxes can only do the Phase I stuff, the first 3.

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    I am still trying to figure out the "benefits" of standard C4FM versus wide mode (linear simulcast mode).
    Seems that the audio quality of LSM is slightly better than C4FM, so our system users say.
    We run our Quantars in "wide" mode (Pulse filter setting in CPS).

    Interestingly the uplink to the repeater (Quantar) is always C4FM but the downlink is CQPSK / LSM
    (with XTS-5000 radios programmed for "wide" mode in the CPS ASTRO settings).

    Don't know how this makes sense? Any idea which mode is best to use?