RF interference issue again (esp. for E Drucker and Jim Weir and other RF wizards)

Aaron Coolidge wrote in message ...
Cool, I thought that you might have kill-filtered me for some reason, because
no one other than me seemed to be getting my messages!

No, not at all, though I'm reading news through groups.google.com
which is flaky on propegation

BTW someone said they emailed me. I didn't receive it. This
email address no longer works. If anyone wants to email me
try hoeltzli at swbell dot net. Though this discussion seems
on-topic and of possible general interest so I'd just as soon keep it
on the net.

On further reflection, this may be a red herring. Digital TV is in the
220+ MHz region.

Can this kind of intereference be caused by subtracting frequencies?

Channel 2 is 54 to 60 MHz, the 2nd harmonics of are 108 to 120 MHz.

That's too low for the frequencies where we're getting interference
(124.2 is clean, 126.5 is trash)

This leads me to suspect one of the *NAV* radios. Can you physically
remove them from your plane, one at a time, and leave them in your car?

Not a problem. Can this really be caused by a radio which is *powered
off*? Because I did try switching the navs to different frequencies
and also turning them off, along with all the electrical power in the
plane.

Since I changed jobs I don't have my trusty HP 8591E spectrum analyzer
anymore, if I did I'd consider a trip to St Louis!

Oh, bummer! That would have been nice.

: If this is a possibility, how do we safely remove the
: marker beacon antenna for testing purposes? Do we need

If you've got the bent metal rod kind

Pretty sure it's a blade, though I admit the MB antenna is "out of
sight out of mind" to me.

If you wish to electrically remove the antenna from the plane while leaving
it physically in place

I'm perfectly happy to take it off and slap some 50 mph duct tape over
the resulting hole, providing it's not going to hurt the MB receiver
to be attached to dangling coax.

If I were doing this, I'd probably
terminate the RF input to the radio, as well.

IIRC this would be a PITA -- the coax goes to the antenna with a
standard BNC connector, but is soldered on to the radio tray.

Please keep us (me) informed, we're trying to help the best we can!

I appreciate this. It's a vexing problem and one which apparently
lies outside our radio guy's experience

Thanks,
Sydney

: This leads me to suspect one of the *NAV* radios. Can you physically
: remove them from your plane, one at a time, and leave them in your car?

: Not a problem. Can this really be caused by a radio which is *powered
: off*? Because I did try switching the navs to different frequencies
: and also turning them off, along with all the electrical power in the
: plane.

Yes, it can be caused by a radio switched off. With those ACK elt units that
cause problems, they are off when their problems occur!

: I'm perfectly happy to take it off and slap some 50 mph duct tape over
: the resulting hole, providing it's not going to hurt the MB receiver
: to be attached to dangling coax.

It won't.

: If I were doing this, I'd probably
: terminate the RF input to the radio, as well.

: IIRC this would be a PITA -- the coax goes to the antenna with a
: standard BNC connector, but is soldered on to the radio tray.
:

It would be OK to terminate the coax where the antenna was connected.
As someone else pointed out, you can short out the antenna at its
BNC connector to electrically remove it from the plane. You could
probably make a BNC shorting plug from parts found at Radio Shack.

--
Aaron Coolidge (N9376J)