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Date: Mon, 29 Jan 2007 23:41:18 -0500
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From: "Paul Lipps" <elippse@sbcglobal.net>
Subject: LEDs-Xmit
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First off, planes don't have GROUND, unless you carried some aboard on =
your shoes. GROUND is what you stand on before climbing into your plane. =
Every circuit requires two conductors, source and return. If your =
problem is with a 10 segment LED, the device that I am familiar with is =
driven from an IC which lights the digits based on an analog input =
voltage. This IC also has a control for brightness. If rf energy from =
transmitting gets into that circuit, it can effect the digits or the =
brighness. One way this energy gets into a lot of our circuitry is on =
the OUTSIDE of the coax; this is known as an antenna current. Anytime =
your coax goes away from the antenna element such that the coax is =
illuminated stronger from one half of the antenna that from the other, =
you have antenna currents flowing on the outside of the coax. Those =
currents will walk right up into your instrument panel where they will =
get into many susceptible circuits. That's the price we pay for having a =
non-metallic airplane that allows the radiation to enter the plane. One =
of the things these antenna currents cause is squealing feedback  into =
the mike circuit at certain Comm frequencies, usually in the higher =
portion in the 130s. What to do? Most often, putting a clamp-on ferrite =
at the antenna end of the coax and one near the rx will stop it. You can =
get them at Radio Shack, where they charge you a bundle, or order them =
from Jameco, www.jameco.com, PN 218173, 0.2" ID, $0.99,  217841, 0.34" =
ID, $1.45, or 318705, 0.45" ID, $1.19. They call them EMI Suppression =
Cores. 'Don't believe it? Ask Larry Kruchten, who just put some on his =
Thorp T-18 to get rid of squeal. The other good thing to do, if you've =
put a lot of money in your stack, is to throw out any RG 58 or even the =
RG 400, and replace it with Andrew FSJ1-50 coax; there's no better on =
the market. You'll tx  an rx much farther, with lots less nulls in your =
pattern, because of its low loss and solid outer conductor with =
essentially NO leakage! Same weight and bend radius as the leaky braided =
coax. But hey! why spend lots of bucks on good coax, when there's such =
cheap s**t available! $15k on the Garmin '03s but $10 on RG58.
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<DIV><FONT face=3DArial>First off, planes don't have GROUND, unless you =
carried=20
some aboard on your shoes. GROUND is what you stand on before climbing =
into your=20
plane. Every circuit requires two conductors, source and return. If your =
problem=20
is with a 10 segment LED, the device that I am familiar with&nbsp;is =
driven from=20
an IC which lights the digits&nbsp;based on an analog input voltage. =
This IC=20
also has&nbsp;a control for brightness. If rf energy from transmitting =
gets into=20
that circuit, it can effect the digits or the brighness. One way this =
energy=20
gets into a lot of our circuitry is on the OUTSIDE of the coax; this is =
known as=20
an antenna current. Anytime your coax goes away from the antenna element =
such=20
that the coax is illuminated stronger from one half of the antenna that =
from the=20
other, you have antenna currents flowing on the outside of the coax. =
Those=20
currents will walk right up into your instrument panel where they will =
get into=20
many susceptible circuits. That's the price we pay for having a =
non-metallic=20
airplane that allows the radiation to enter the plane. One of the things =
these=20
antenna currents cause is squealing feedback&nbsp; into the mike circuit =
at=20
certain Comm frequencies, usually in the higher portion in the 130s. =
What to do?=20
Most often, putting a clamp-on ferrite at the antenna end of the coax =
and one=20
near the rx will stop it. You can get them at Radio Shack, where they =
charge you=20
a bundle, or order them from Jameco, <A=20
href=3D"http://www.jameco.com">www.jameco.com</A>, PN 218173, 0.2" ID,=20
$0.99,&nbsp; 217841, 0.34" ID, $1.45, or 318705, 0.45" ID, $1.19. They =
call them=20
EMI Suppression Cores. 'Don't believe it? Ask Larry Kruchten, who just =
put some=20
on his Thorp T-18 to get rid of squeal.&nbsp;The other good thing to do, =
if=20
you've put a lot of money in your stack, is to throw out any RG 58 or =
even the=20
RG 400, and replace it with Andrew FSJ1-50 coax; there's&nbsp;no better =
on the=20
market. You'll tx&nbsp; an rx much farther, with lots less nulls in your =

pattern, because of its low loss and solid outer conductor with =
essentially NO=20
leakage! Same weight and bend radius as the leaky&nbsp;braided coax. But =
hey!=20
why spend lots of bucks on good coax, when there's such cheap s**t =
available!=20
$15k on the Garmin '03s but $10 on RG58.</FONT></DIV></BODY></HTML>

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