Zaon MRX causing radio interference 2

On Jul 22, 2:32*pm, Eric Greenwell wrote:
Itsaplane wrote:

* As such, they don't have any real solutions for running with external

power. * He did suggest either a) trying more ferrite cores on the
Zaon power lead (!), b) trying a ferrite core on the negative (?) side
of the radio's power lead, or for the sure fix c) running the Zaon off
its internal battery or a *separate* external battery other than the
one driving the radio.

1) Does the static problem go away when you use it's internal battery?
If it doesn't, your problem isn't the power lead and could be a radio
wiring problem, or maybe an MRX defect.

2) Have you tried another MRX to see if it has the same problem? Try to
borrow the newest one you can find, as the older ones did not have as
much "rf emission control".

3) Run a new power lead to the MRX directly from the battery terminals,
using shielded, twisted pair cable. Connect the shield to the negative
(-) terminal on the battery, along with the negative lead. Don't connect
the shield to anything at the MRX end. I believe this cable from Radio
Shack will work:

$9.89

50-Ft. Audio Cable - RadioShack.com
* * * * * * * * 50-Ft. Audio Cable
Model: CL2 UL Approved *| *Catalog #: 278-513

Do the simplest - but still safe - installation to test the idea. You
can do permanent installation it works, including fusing the lead at the
battery.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly

* "Transponders in Sailplanes"http://tinyurl.com/y739x4
* * * Sections on Mode S, TPAS, ADS-B, Flarm, more

* "A Guide to Self-launching Sailplane Operation" atwww.motorglider.org


I too have the Radio/Mrx intermittent squelch problem, as do 3 or more
of my club members; all of us are using an external battery source,
not all of us have a transponder, so I don’t think the transponder is
the problem. In my particular case, I'm using a separate/ dedicated
battery with shielded cable to power the MRX & Transponder.

A few observations:
1) The separate battery for my Mrx is not fully isolated as Eric
suggested above, but it is fully shielded up to the Positive and
ground busses at the panel, and the Mrx unit has been serviced and
upgraded recently.
2) The squelch problem does not occur when the internal battery is
used on the Mrx.
3) I’ve noticed, for example, I can be on 123.3 when the squelch
interference occurs however if I quickly switch to 123.5 or any other
frequency no open squelch is detected. I can then go back on the
original 123.3 freq. and the squelch problem is still occurring. This
odd Mrx squelch interference behavior has also occurred on other
frequencies, a complete mystery to me.

Perhaps a full isolation of the Mrx external power system will be my
next step as I’ve nearly run out of ideas. We seem to have a deep pool
of smart minds here; perhaps someone will be able to take up the
challenge of this annoying mystery that Zaon has so far failed to do.

21

Rick:

There is nothing surprising about what you describe. That is how
harmonic interference is likely to play out. Let's say for instance
that the MRX has a 9.5 Mhz microprocessor clock; the 13th harmonic of
that would be 123.50 Mhz. But microprocessor oscillators don't need
to be perfectly precise. If yours happens to be low by 0.2% then
yours falls on 123.30 and someone else will find interference on
another nearby frequency or not at all if the 13th harmonic happens to
land right between radio channels or on a frequency that pilot B never
tunes in. I have an MRX with sloppy external power connections and
have never had interference; so maybe I am the pilot B case. Of
course, I don't really know what clock freqencies are actually used in
the MRX and I don't know which harmonic is the nasty in this case --
my numbers are just for illustration.

Bob:

The business of pushing on the connector is most likely that your
fingers are capacitively coupling into the spurious radio propogation
path between the MRX and radio. The propogation path is shunted or in
some manner altered enough to make a big difference in the
interference that you are hearing. I'll bet that if you just squeezed
the connector without pushing you would find the same effect.

Steve Koerner
(retired EE)