[arm-allstar] hum on my allstar nodes

[Doug Crompton]

I can almost say with certainty that this is caused by EMI from the FOB
and/or PI getting into the microphone. The mic has a 5V regulator and when
you run it on 5V (vs the usual 8V on a Kenwood radio) the regulator does
not regulate and instead passes all the 5V bus garbage to the high gain mic
amp. This is very hard to get rid of with filtering. What has been done by
some is use a 5V to 8V boost supply (they are very small) to boost the 5V
back up to 8V for the mic. Then the regulator in the mic will function and
it will eliminate the noise. I have heard them and they are very clean.
This is also why we did not use Kenwood or Alinco mics on the the
Technobygeorge radioless nodes but rather the Yaesu mics.

*73 Doug, WA3DSP*
*http://wa3dsp.org <http://wa3dsp.org>*

On Sun, Apr 26, 2020 at 6:02 PM "Michael Fleetwood via ARM-allstar" <
arm-allstar at hamvoip.org> wrote:

> I am having a problem with a background hash others hear when I
> transmit using a radioless node with a Pi3A+ an Alinco EMS57 mic,
> modified sound fob and audio amp. Received audio is perfect, but when
> I listen to myself on the parrot the noise sounds a bit like an FM
> signal that is not fully quieting. I have tried optimising grounding
> and using different power supplies including a 12v battery and 7805
> regulator, but the problem persists.
>
> Mike
> VK2AMF
>
>
> At 05:23 AM 27/04/2020, you wrote:
> >The "RF" hum is caused by some odd phasing relationship and/or RF overload
> >at the site. When you think of it you rarely transmit RF that close to the
> >destination most of the time. We have found that distance and selecting
> >locations that are best are about the only thing you can do in this case.
> >It usually only happens when you are very close to the node. If this is
> >your problem the only thing you can do is change locations of equipment or
> >antennas and distance from your node.
> >
> >*73 Doug, WA3DSP*
> >*http://wa3dsp.org <http://wa3dsp.org>*
> >
> >On Sun, Apr 26, 2020 at 11:57 AM "Chris Smart via ARM-allstar" <
> >arm-allstar at hamvoip.org> wrote:
> >
> > > Thanks Doug.
> > >
> > >
> > > What is typically the source of this hum? Wall-wart type power
> supplies?
> > >
> > > 73
> > >
> > >
> > > Chris
> > >
> > >
> > >
> > > On 4/26/2020 10:46 AM, "Doug Crompton via ARM-allstar" wrote:
> > > > Hum on local RF nodes is a common problem when transmitting TO your
> node.
> > > > It is usually because you are too close to your node. If the hum
> stops
> > > when
> > > > you move to another location, sometimes just a foot or two one way
> or the
> > > > other then that is probably the problem. It happens more often when
> using
> > > > antennas that are mounted on the node itself. One way to get rid of
> it is
> > > > to use those small mag mount antennas that have 10-15 feet of coax
> and
> > > get
> > > > it away from your operating position or use an outdoor antenna. Other
> > > than
> > > > that there is no filtering or other way to eliminate it. If the hum
> is
> > > > constant at any location even walking hundreds of feet away then it
> is
> > > not
> > > > this phenomenon.
> > > >
> > > > *73 Doug, WA3DSP*
> > > > *http://wa3dsp.org <http://wa3dsp.org>*
> > > >
> > > >
> > > >
> > > > On Sun, Apr 26, 2020 at 4:08 AM "Jed Barton via ARM-allstar" <
> > > > arm-allstar at hamvoip.org> wrote:
> > > >
> > > >> Hey guys,
> > > >>
> > > >> So i'm sure i'm not the only 1 with this problem. I've got all my
> > > >> allstar pies plugged in.  They each have their own power supply.
> It's
> > > >> the typical wall wart.  They all produce a nice little hum that's
> just
> > > >> annoying.
> > > >> I'm sure a lot of you guys have delt with this.  You hear it on the
> > > >> node transmitter such as the Shari.  Any ideas for getting rid of
> it,
> > > >> or reducing it?
> > > >>
> > > >> Cheers,
> > > >>
> > > >> Jed
> > > >> _______________________________________________
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> > > >>
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> > > >>
> > > > _______________________________________________
> > > >
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> > > >
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> > > _______________________________________________
> > >
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> > >
> >_______________________________________________
> >
> >ARM-allstar mailing list
> >ARM-allstar at hamvoip.org
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> >
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>
> Mike Fleetwood
> Canberra Australia and Sidcup UK.
>
> Worldwide email address is:     mfleetwood at gmail.com
>
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