[App_rpt-users] Paging

Jim Duuuude telesistant at hotmail.com
Wed Oct 29 12:19:22 EDT 2014


Currently, POCSAG operation is *really* only supported with a URI (or hand-made USB
device) with chan_usbradio (I dont believe I support it in chan_simpleusb yet, but it
certainly COULD be...). The mechanism is also supported in chan_voter, but none of the
current hardwares support its use.

If all of that "works" for you (logistically) you then need a transmitter that is capable of
REAL DIRECT FM. Any of the common transmitters, commercial or amateur, even with a direct
modulation input, have some sort of AC coupling of the modulation input. This will not work with
POCSAG paging.

POCSAG, because of the fact that it is direct FSK, not AFSK, needs a transmitter with direct DC
coupling of its modulation input. In other words, the modulation input must be capable of something
like this:

Say, for example, a change of 500mv of modulation voltage changes the transmitter's frequency
3 KHz. So, your modulation voltage is normally 2 volts. At that 2 volt input, your transmitter
outputs a 440.000 MHz. You raise the modulation voltage to 2.5 volts. Your transmitter then
shifts to 440.003 MHz. You keep the modulation voltage at 2.5 volts for 10 minutes, During that
ENTIRE 10 minute period, the transmitter stays at 440.003 MHz. 

Any normal, capacitive-coupled input modulator is just NOT capable of doing that (for hopefully
painfully-obvious reasons).

Commercial paging transmitters have a DIGITAL voltage (like just a 0V/+5V) input to select one
of the two frequencies (+/- from "center" carrier freqency for FSK). That is how they deal with the
true FSK nature of paging.

Do you have something that will accomplish this?

Jim


Subject: Re: [App_rpt-users] Paging
From: hammin75 at gmail.com
Date: Wed, 29 Oct 2014 06:05:05 -0500
CC: app_rpt-users at ohnosec.org
To: telesistant at hotmail.com

Yep. 

Sent from my iPhone
On Oct 28, 2014, at 11:55 PM, Jim Duuuude <telesistant at hotmail.com> wrote:




Are you referring to POCSAG pagers?

> From: hammin75 at gmail.com
> Date: Tue, 28 Oct 2014 19:02:07 -0500
> To: app_rpt-users at ohnosec.org
> Subject: [App_rpt-users] Paging
> 
> Was thinking about the fuction of getting some  alpha pagers tuned up.  Can u page from the software if so who has done it and how well does it work. Etc
> 
> Thanks
> 
> Sent from my iPhone
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