[App_rpt-users] 12.5 kHz repeaters support

Doug Bade kd8b at thebades.net
Thu Mar 11 08:54:51 EST 2010


I do understand, however because it has a commercial flat audio point does
not mean it has the appropriate noise component for the software to detect .
The manufacturer does not necessarily allow much white noise content on a
flat audio line... as flat audio by definition is not discriminator as a
discriminator is not flat unless the received signal is flat and normally it
is pre-emphasized... 

So to be flat it is processed.. and white noise may be stripped.

The white noise we are talking about is in the audio band above 3khz.. up to
maybe 6-7 khz.. you might sweep your receiver there for flat audio and watch
that with a scope.. flat in band audio does not mean flat to 6khz... 

If the chosen radios do not have sufficient white noise the only real option
is to add COR or CAS detection... as I do not think it is a wideband
narrowband issue you are seeing.. 

The way to test that is see if the same radios align suitably in wideband
mode assuming they can be programmed to test... If the URI cannot find an
answer there.. it is most likely just a bad spot to pick noise from...

What I will also add is the level output is different on many radios (
especially in 12k5) and in my case I had to play with external padding as
well as the 20db gain/pad switch to get levels into a range the rx tuning
software and hardware could deal with... The internal resistors of the URI
are designed for a certain working range and load.. 

In most wideband and narrowband installs where I use the URI ( 6
installations I am involved in) , I had to go to the capacitive-ly coupled
input as DC component on the rx line had adverse effects on the URI's
ability to function and calibrate.


Doug
KD8B



-----Original Message-----
From: Ralph A. Schmid, dk5ras [mailto:ralph at radio-link.net] 
Sent: Thursday, March 11, 2010 8:22 AM
To: Doug Bade; 'Jann Traschewski'; 'app_rpt mailing list'
Subject: RE: [App_rpt-users] 12.5 kHz repeaters support

Hi,

> mhz band is mostly 12k5 equipment these days... It did work.. However.. in
> general The audio pickup point in the discriminator chain has more to do
> with getting enough white noise I think.. I had to play around some in the
> 900 gear but found points suitable for either distro..

Please note that this is a commercial grade radio, no searching for a
discriminator tap, but using the flat out that is provided by the
manufacturer. Those radios should remain exchangable without modifying them,
so this is not really an option :-) I will definetely not start soldering
thin wires into my repeater radios, as I rely on direct replacement with a
brand new radio in case of failure.

> Doug
> KD8B

With best regards

Ralph.




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