amplification and p25

Forum for the promotion and understanding of digital voice on the amateur bands.

Moderator: Global Moderator Team

Posts: 31
Joined: Wed Jul 12, 2006 3:48 pm

amplification and p25

Postby m33kr0b » Tue Sep 22, 2009 10:31 pm

Can I use a normal amp with a p25 portable or do I need a special amp for digital modulation? I am looking at this for my EFJ 5100


Posts: 116
Joined: Thu Jul 20, 2006 8:03 pm

Re: amplification and p25

Postby MattSR » Wed Sep 23, 2009 9:23 am

I've used a TPL PA6 on 70cm on P25. Worked really well, but I never checked the output of the amp on a service monitor or anything.

User avatar
professor of rectalingus
Posts: 4395
Joined: Thu Mar 30, 2006 1:54 am
Location: Chief of the CAREPOLICE

Re: amplification and p25

Postby escomm » Thu Oct 15, 2009 2:53 am

i would love to know how an amp could affect the signal since it's all fm from the time it leaves the radio til it makes it to the antenna

maybe wowbagger can shine some expertise on this matter
I'd hit it so hard you'd have to be to King of England to pull me out

Posts: 2697
Joined: Mon Aug 02, 2004 1:45 pm
Location: 10-20

Re: amplification and p25

Postby KC8RYW » Thu Oct 15, 2009 4:08 am

As far as I know...

As long as you are using C4FM modulation, it shouldn't be an issue. Class C works.

Now, if you're driving an amplifier into compression, than you might have some issues. Wowbagger, speaketh!

Posts: 116
Joined: Thu Jul 20, 2006 8:03 pm

Re: amplification and p25

Postby MattSR » Thu Oct 15, 2009 4:24 am

User avatar
Posts: 1025
Joined: Tue May 23, 2006 10:14 am
Location: Wichita, KS

Re: amplification and p25

Postby Wowbagger » Thu Oct 15, 2009 7:21 am

C4FM is FM - a class C amp won't do anything to it, because the signal is constant amplitude.

Now, if you were to be using the CQPSK modulation scheme and you used a class C amp, you'd basically end up turning the signal into C4FM - you'd widen the spectrum back out to 12.5kHz rather than 6.25kHz.

That's one of the reasons you see the manufactures going to some form of TDMA rather than FDMA CQPSK, which wouldn't require any protocol changes (thus you'd still have simplex talk-around) - making the radio do TDMA is pretty much purely software (other than buying an AMBE chip from DVSI rather than an IMBE chip, which is no big deal these days), while making the radio do CQPSK means making the radio have a class AB RF amp rather than a class C (or doing lots of trickery to make a class C amp act linearly).
These opinions are mine, not Aeroflex's - if you want service info, manual, or other official support please contact Aeroflex directly.

Posts: 95
Joined: Tue Dec 01, 2009 11:50 am

Re: amplification and p25

Postby kb8vul » Sat Jan 09, 2010 11:02 pm

You will need to be aware of type acceptance though if you are using this outside ham bands.
With ham of course there is no type acceptance but commercial is a different story.

I only mention this because you were looking at something that Universal Radio sold.
Nothing against Universal but they don't sell commercial gear, and NO ONE in there knows anything about commercial gear.
Great guys, I know most all of them. But they ain't a commercial shop.

Return to “Astro DStar and other digital voice formats”

Who is online

Users browsing this forum: No registered users and 3 guests