Astro modulation type

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ElPolloDiablo
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Astro modulation type

Post by ElPolloDiablo »

C4FM
CQPSK
WIDE

What's the difference? Which should I use?

Also, I'm used to programming my Kenwoods. Nice and simple. You can pick wide or narrow bandwidth. Looking at the Astro programming, there's options for deviation and channel spacing. I'm assuming 2.5 kHz deviation/12.5 kHz spacing is narrow and 5.0/25.0 is wide. What's the 4.0/20.0 for?

Any other hints, tips or tricks for making my pair of VHF AS1/R's as sexy as possible would be super (other than making them AS3's, that's something for me to do later, when I have a real job and some disposable income).
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motorola_otaku
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Post by motorola_otaku »

CQPSK is for simulcast trunking systems and I forget what WIDE is for. Use C4FM.

The only place I'm aware of where 20kHz spacing is used domestically is in the 800 band. Maybe it's present in VHF/UHF radios for overseas systems?

For public safety monitoring, you'll want to crank the spacing back to 12.5. For hammy use, leave it at 25.
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10-95
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Post by 10-95 »

Just did a google search for the heck of it and found this ...

http://www.apcointl.org/frequency/proje ... ation.html

I have not read through it, but maybe some answers you want are in there somewhere.
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Wowbagger
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Re: Astro modulation type

Post by Wowbagger »

ElPolloDiablo wrote:C4FM
CQPSK
WIDE

What's the difference? Which should I use?
Short answer: whatever the system you are on uses.

Longer answer:

C4FM is the APCO-25 standard specified modulation. It occupies a 12.5 kHz channel, and has no AM component (it is pure FM), and so does not require a linear amplifier.

CQPSK is one of the standards called out for APCO-25 phase 2. It occupies a 6.25 kHz channel spacing, but achieves this by using both AM and FM (technically it uses phase shift keying, but I'm trying to keep this simple). As such, it requires the amplifiers to be linear, rather than class C.

Linear Simulcast Modulation is a form of CQPSK in which the signal parameters have been modified to make it more resistant to multipath interference and more amenable to multicasting (technically, they have increased the time the signal is at the correct symbol deviation, "opening the eye" of the signal when viewed in the time domain.) These modifications increase the occupied signal bandwidth to 12.5 kHz, and require a linear amplifier as they also have an AM component.

Widepulse is a different modification of the signal parameters to allow for multipath resistance. It has no AM component, and so can use class C RF amplifiers, but as a result it occupies 25 kHz bandwidth.

In almost all these cases, the only difference it makes is to the base radio (repeater), not to the mobile radio - the mobile almost ALWAYS sends C4FM.

So, unless you are setting up a BR, you should use C4FM.

HTH.
These opinions are mine, not Aeroflex's - if you want service info, manual, or other official support please contact Aeroflex directly.
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