Re: Going on an Antenna Hunt (was: RF interference issue again (esp. for E Drucker and Jim Weir and other RF wizards)

Snowbird wrote:

> *TV Channel 2 antenna was the big winner.  Where the other
>  big antennae just produced noise, I could sit near the
>  base of the Channel 2 antenna and listen to a program about
>  college football.  Further out, came through in snatches.  Right 
>  there by the antenna, came through 3x5 on 126.5 and 5x5 on 127.0
> *Didn't have time to fly and conduct the obvious experiment of
>  leaving Mr Handheld on the ground

> *Now here's where it gets wierd: according to the TV schedule,
>  channel 4 and Channel 5 were broadcasting college football.
>  Channel 2 was showing a movie.  Didn't have time to stay and
>  listen until we got a station identification.  From what I 
>  heard, sounded like Channel 5.


This makes sense! ...a possible intermod scenario (see my other post) is the 
ch.4 aural carrier (71.75) mixing with the ch.2 visual carrier (55.25) resulting 
in a product at 127.0 MHz.  If the mixing were occuring in ch.2's visual xmtr, 
IT would be the source of the 127.0 signal (even though the audio you hear is 
coming from ch.4's xmtr, some distance away.)


> > ->If I drive to the antenna farm and get the interference,
> > ->does it prove the problem is outside my plane, or just that
> > ->the handheld is also more susceptible to it?


It could mean:

The antenna farm is clean; the handheld and your plane *both* have a problem.

or,

The antenna farm has a problem; the handheld *may* be clean and your plane *may* 
be clean.

Since you don't have enough information to distinguish between the above cases, 
you can't rule your plane IN or OUT.  On the other hand, if you HADN'T gotten 
the interference on the ground with the handheld, you could probably rule the 
plane IN (but still not conclusively if the problem is intermittent.)

Isn't troubleshooting fun?  ;^)

> But just to confirm: what I'm hearing is that frequencies can
> mix and be reradiated by a turned-off radio, *but they need an
> antenna* to get anywhere?  ie, if the ELT is in the plane but
> disconnected from the antenna, it's not likely the source of
> the problem...likewise, if the portable nav/com is disconnected
> from its antenna?
>
> Have we likely absolved my plane at this point?


You mentioned the problem was considerably worse on *one* com than the other... 
if the problem IS in the plane, that's my guess as to the source (see my other 
post).  Can you disconnect the antenna from *that* com, and fly with just the 
other one?