tim2542(at)sbcglobal.net
Guest
|
 Posted: Thu Dec 20, 2012 9:56 am Post subject: RF interference on GRT fuel pressure with PTT |
 |
|
Hi Bob
This post from several weeks ago but Id like to revisit it please, I plan to try to fix this problem soon.
Again the problem is fuel pressure indication spike on transmit from either comm at the higher end of the band.
The engine monitor connector is a DB-25. My plan is to install the capacitor listed between the fuel pressure "Aux" input and ground pins inside the connector if possible using short-as-possible lead length, then a split toroid on the wire bundle coming into the DB-25connector.
Thanks for any clarification, Tim
| Quote: | --> AeroElectric-List message posted by: Tim Andres <tim2542(at)sbcglobal.net (tim2542(at)sbcglobal.net)>
If it makes you feel better I have the same problem. On mine it only occurs when on the upper end of the band, like center frequencies above 130 MHz, and happens when I key either the 430W or Icom A210 on those upper frequencies.
I spoke to Carlos at GRT about this and he suggested the split ferrite that you have tried. I have not attempted to fix it yet and was about to ask the group what specs I need when I buy it.
I wonder if a small capacitor could be used to drain off the RF since the torrid didn't work. It could be installed inside the D-sub between the fuel sensor pin and ground. Can anyone here tell if this might work and if so what cap to use?
|
The value of such capacitors is not so critical
as their construction. A few days ago I published
a capacitors-in-the-connector fix that I crafted
on a Hawker 800 a few years back. See http://tinyurl.com/dxeuj6b
and scroll down to bottom for pictures.
Those capacitor were monolythic ceramics, 0.1 uF
at 50 volts. But probably any value between 0.01
and 0.47 would have worked. What we're interested
in is tiny size so that they can make short lead
connection to the pin and low inductance characteristics
for which the monolythic construction is noted.
Radio Shack used to stock a 0.1 uf cerami (about
1.5 times size of a paper match head). Here's an
exemplar part
http://tinyurl.com/bsk27pw
Ferrites are a whole other ball game. They tend
to improve on an RFI problem with a combination
of two characteristics. (1) they add a lumped
inductance into the wire or wires that are coupling
the energy into the victim (or out of the antagonist).
(2) Ferrites designed for RFI mitigation are TERRIBLE
transformer cores. I.e. they're designed to be
very lossy at the frequencies of interest. By lossy,
we mean that energy coupled into the core is converted
to heat.
BOTH effects are enhanced by the capacitor that
lowers the parallel impedance against which the
series impedance of the ferrite can work. The BEST
ferrite in the world does nothing if the downstream
path to the victim is a high impedance at the
frequency of interest.
This is why the odds are so long that ferrites
alone will fix a problem. The problem would not
have existed had the victim's i/o leads been
designed for that environment in the first place.
So the best moves call for capacitors first with
ferrites stacked on top.
Bob . . .
[quote][b]
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
