Astro digital mod schemes

[bradlington]

Could someone give me the rundown on where and when does one use the different modulation scemes .
I have three :C4FM , CPQSK and WIDE .

If there is any technical aspects relating to the trunked or simplex / conventional use of these platforms ,I would appreciate your input.
Thanks in advance.

[n1pfc]

C4FM -> used for subscriber units (read portable / mobile) and for stand alone repeaters / trunking sites (read non-simulcast)
-Can actually use class C FM only amplifiers and works just fine if you need to.

CQPSK -> used for simulcast and is supposed to be used for P25 phase 2 (6.25 TDM). Typically just used on infrastructure (i.e. repeater tx)
-Needs a class A or class AB amplifier as has AM products in addition to the regular 4 offset shifts of C4FM


Haven't played with WIDE, so I'm not going to comment on it.

Kurt

[bradlington]

Thanks for that -I did read up on it a bit and it is still grey at the moment.

What do the normal systems operate in ? assume C4FM and those that want to operate in a "narrow allocation "operate CQPSK .

This is interesting to see as the question of "add on" CAI interfaces as I understand it .

This would mean that the migration would have to be total repeater swap out .

Also I assume that the system operators can use PA's in their site especially for combining purposes would now have to get more expensive means of PA equipment that would be compatible ??

We in the gsm use TDMA and I had an interesting talk to an Engineer that had discussed this very topic of PA's etc and this DR odf Eng commented that the FDMA is still more efficient at the end of the day.

[Twisted_Pear]

Haven't played with WIDE, so I'm not going to comment on it.

IIRC, it's for Simulcast sites operating in wideband mode. 800MHz Simulcast sites use it, for exmaple.

[bradlington]

Thanks for that -is there any other parameter that one has to change on the radio setup to allow for simulcast.

The strange thing is it gives you a choice of one of the three so it does not tell one what mod scheme it is -bit in the dark on this one.

Thanks
Brad

[n1pfc]

Thanks for that -is there any other parameter that one has to change on the radio setup to allow for simulcast.

The strange thing is it gives you a choice of one of the three so it does not tell one what mod scheme it is -bit in the dark on this one.

Thanks
Brad

Everything I've pretty much played with has been setting the subscriber side to C4FM. That's what I have all of my equipment set to and it all works fine. Of course I'm on UHF not running simulcast with this.

Kurt

[akardam]

Interesting... when I first got into Astro radios, I was told to run Astro channels on CQPSK, not C4FM. Do I understand correctly that on simplex channels and standalone repeated channels (e.g. a single Quantar not part of a trunked or simulcast system) that it makes balls odd difference which one you use?

Do I also understand correctly that CQPSK, since it's involved with P25 Phase II, is backwards compatable with C4FM, e.g. if your subscriber unit is programmed as CQPSK and you're dealing with a simplex unit programmed as C4FM or a repeater, it will just work?

[bradlington]

Hi

About the mod schemes I found this link to have the best basic explination of the differences - may warrent to experiment with the filter options in the S/W .

http://www.signalharbor.com/ttt/03nov/index.html
Brad