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.

Hayden

 

Date: Wed, 17 May 2017 04:11:51 -0500
From: Chuck Henderson <rpt2@chuck.midlandsnetworking.com>
To: Users of Asterisk app_rpt <app_rpt-users@lists.allstarlink.org>
Subject: Re: [App_rpt-users] RTCM/Voter pulse noise
Message-ID:
        <CADEYVwi5LNafXXuzaZ-zS3FgQt5578TH-jz5YGJdvPMrR-FA7w@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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