[App_rpt-users] RTCM/Voter pulse noise

Hayden Honeywood haydenph91 at gmail.com
Wed May 17 21:09:43 EDT 2017

Thanks Chuck,
I'll have a play around. I have tested with two separate boards on separate
systems with different cables and it does the same.

Maybe I'll try some ferrite beads on the audio cables.

I built the boards with all the specified components from digikey except
the following which were not available anymore -

*IC14* - 74HC4053N
*C25* - 0.015uF
*C78, C79* - 1uF
*C75, C80* - 4.7uF
*E1-E11* - Ferrites
*IC5 *- 74HC139N

The ferrites have an impedance of about 65 ohms at 100MHz as compared to
the ones specified in the original listing which are 50 ohms at 100MHz.
This is probably the most likely reason this noise is breaking through.


> Date: Wed, 17 May 2017 04:11:51 -0500
> From: Chuck Henderson <rpt2 at chuck.midlandsnetworking.com>
> To: Users of Asterisk app_rpt <app_rpt-users at lists.allstarlink.org>
> Subject: Re: [App_rpt-users] RTCM/Voter pulse noise
> Message-ID:
>         <CADEYVwi5LNafXXuzaZ-zS3FgQt5578TH-jz5YGJdvPMrR-
> FA7w at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
> I don't have any noise like that with voter boards or RTCMs.  My first
> thought is that you may have a ground issue, or may not have your
> audio wires shielded from your power/logic wires that are running in
> the same cable.  Have you tried other boards or RTCMs with the same
> cables?  Did you use the exact components to build the boards or did
> you substitute any components, such as the regulators or capacitors?
> I always use 2 separate cables into the common connector, one cable
> carries shielded audio and audio ground and the other carries power,
> logic levels (cor, ptt, etc) and power/logic ground.  If you have this
> issue with both the boards and the RTCMs then IMHO, it must be a cable
> issue.  (or a nut loose behind the control panel, just kidding :-)
>  Chuck
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