[App_rpt-users] RADIO THIN CLIENT MODULE and "Simulcast Transmit System"

[Peter Elke]

Hi Shaun,

 

At the moment we are limited to transmitters that use 14.4Mhz as their
oscillator base (MCX. Syntors, MSF500s, MaxTrax) since the Motorola UHSO
only creates that frequency from the 10mhz Trimble GPS.  

 

If we select a different transmitter model (that is not 14.4 based) a
clock generator like Mark's Programmable Clock Generator Module will be
needed.  We were lucky in that I had a bunch of UHSO units for a 900Mhz
project that we could borrow for the thin client 440 project.

 

Pete/WI6H

 

From: app_rpt-users-bounces at ohnosec.org
[mailto:app_rpt-users-bounces at ohnosec.org] On Behalf Of Jim Duuuude
Sent: Thursday, December 22, 2011 4:25 AM
To: shaun at pmbnet.co.za; app_rpt mailing list; zs5bg at harc.org.za;
zs5z at harc.org.za
Subject: Re: [App_rpt-users] RADIO THIN CLIENT MODULE and "Simulcast
Transmit System"

 

Yes. That's how simulcast systems work.

When you base your syncronization on a GPSDO (GPS Disciplined
Oscillator)
such as the Trimble Thunderbolt (which has accuracy typically of 10-20
parts
per TRILLION, which means that if you were transmitting at 1GHz, you
would
be no more then 0.010 to 0.020 Hz off) *and* the audio is in sync with
that timing
source *and* the deviation is set consistently accurately between all
transmitters,
then, yes, its quite possible.

Obviously, you need to use transmitters appropriately suited for this
type of application,
which either by initial design or by modification, allow injection of an
external (to the
transmitter) reference frequency. Some transmitters are designed with
this in mind.
Others can be trivially modified to allow this.

For example, the Trimble Thunderbolt has its precise frequency output at
10 MHz.
Some transmitters will operate directly from the frequency reference.
Others need
some other frequency. If this is the case, a clock generator (locked to
the Thunderbolt's
10 Mhz output) that produces the appropriate frequency is needed.

Some radio manufacturers, such as the one that Pete Elke (WI6H) was
referring to
make devices specifically suited for this purpose (he was using the
clock generator
within a high stability oscillator unit from an old Motorola paging
transmitter).

Another option would be to use the PCGM (Programmable Clock Generator
Module) that
Mark at Micro-Node (K7IZA) is coming out with soon. It takes the 10 MHz
input from the
Trimble Thunderbolt, and generates pretty much whatever reference
frequency you
"tell it to" (from 6-200 MHz), and also, acts as a power supply for the
Trimble Thunderbolt.

The reason I keep making specific reference to the Trimble Thunderbolt
is because they are
readily available on the surplus market (rather inexpensively), and are
EXTEREMELY well-suited
for this application (probably the best selection given all of the
parameters involved here).

JIM WB6NIL

> Date: Thu, 22 Dec 2011 12:41:11 +0200
> From: shaun at pmbnet.co.za
> To: app_rpt-users at ohnosec.org; zs5bg at harc.org.za; zs5z at harc.org.za
> Subject: [App_rpt-users] RADIO THIN CLIENT MODULE and "Simulcast
Transmit System"
> 
> Before I break open my kid's piggy-bank for a couple of "ALLSTAR RTCM 
> (RADIO THIN CLIENT MODULE)'s " http://micro-node.com/thin-m1.html
> I need an important question answered. .............please?
> 
> If both rptr's are in the same coverage area, and transmit at the same

> time on the same freq, BUT perfectly in sync using the GPS sync 
> option...................... will the end user (client/club member)
hear 
> a perfect signal? (even if he/she where in range of both
transmitters?)
> One would think you would hear a heterodyne of some sort with both 
> signals reaching and mixing into the users transceiver.
> 
> We all know that if 2 hams try use their local repeater at the same
time 
> (doubling) then the end result is Yucky, unless the one users tx
signal 
> is much stronger than the other user.
> 
> Is this RTCM system so accurate, that the user hears a perfectly
synced 
> and clear signal?
> 
> Shaun
> zr5s
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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