Zaon MRX causing radio interference 2

Hi, Tim,

Thanks for your thoughts. While at the glider port yesterday I talked
with club member who’s a EE, and he seconds your suspicion that Zaon
is using a switcher. From their specs, it’s pretty inefficient (as
well as being noisy)! Your idea of replacing the batteries with an
efficient, RF quiet, 12VDC to 3VDC supply might be a good way to go
(although I don’t have the resources to do it).

I did a quick experiment and found that the RF noise is indeed coming
from the power lead, and it's polarized. The noise is less when the
VHF antenna is vertical when the power lead is in the horizontal
plane.

I found the original thread on this subject. In it, Henryk Birecki
posted a Zaon noise filter, made up of 4 Miller & Bourns FB20010-3B-RC
coils and 1 ceramic 0.47 uF capacitor. See
http://groups.google.com/group/rec.a...eafbb2ca4182c?

I found a 0.1 uF cap and some torroidal coils, Radio Shack 273-0108,
and built something similar to Henryk’s filter. It worked much better
than the 0.01uF ceramic and 0.1uF metal film caps I reported on
befo

Test 1 Test 2 Test 3 Test 4
Int Bat Ext 12V Ext w/ caps Ext w/ coils
123.300 5 18 14 11
123.075 5 24 21 12
122.800 5 24 16 10

Hopefully this week Zaon’s technical people will come back from
Oshkosh, and they'll have ideas to tackle this problem at the source.

-John

On Jul 30, 10:43 pm, "Tim Ward" wrote:
Not an EE, but it might be interesting to see how a the length of the llne
to the battery affects things. I have a suspicion that the radiating
element is the power lead, rather than the antenna. They could be using a
switching regulator for external power (not unreasonable if you want a wide
input range and decent efficiency).

See if, with the Zaon antenna and power cord at right angles, rotating the
receiver antenna from parallel to the Zaon antenna to parallel to the
power cord makes the problem worse.
Sometimes it's useful to find how to make things worse, and that gives you a
clue as to how to make things better.

A different approach might be to supply your own regulator as a "battery
eliminator" that goes in place of the battery, supplying a filtered nominal
battery voltage.

But if a little is good, a lot may be better. Try paralleling a 10 uF cap
with what you have.
Keep increasing the capacitance until it doesn't help or gets worse.
Some linear regulators will oscillate with too little capacitance on the
input, but I would think Zaon would catch that.

Also, is the power cord through the ferrite as many times as it will fit?
The inductance is non-linear, it's proportional to the number of turns
squared. So managing another turn or two through the toroid may help.

Gosh, it's easy to come up with work I don't have to do myself.

Tim Ward