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

Snowbird wrote:

> Mark Mallory <[EMAIL PROTECTED]> wrote in message news:<[EMAIL PROTECTED]>...
> > Isn't troubleshooting fun?  ;^)
>
> Just Ducky (pun intended).  
>
> So what do you suggest to distinguish?
>
> My ideas are:
> 1) return to antenna farm w/ handheld and try to stay long enough
>    to get a station ID, also confirm lat long coordinates
>    if interference received:

> 2) fly w/out handheld in the plane
>    if interference received:
> 3) remove #2 nav com and ELT from plane
>    fly again
>    if no interference:
> 4) put one back


Sounds like a good plan.

I would try disconnecting *all* the antennas on the plane except for the *good* 
com's (and the transponder's, which you need under the clsB and which IMO is 
unlikely to be the problem.)  Note the results on the good com, then hook them 
back up one by one...


> I'm also thinking it might be worth a call to the TV station,
> to see if they have someone who cares because maybe they have
> better equipment and could check this out.  (or maybe I can get
> the FAA guy to call...)


Yes, I mentioned this in my first post... get in contact with their Engineering 
Department and explain the problem.  They'd be *more* than interested, they're 
technically qualified guys, and they have the necesssary equipment.

As a ham radio guy and former Broadcast Engineer myself (1970s), I know I'd be 
chomping at the bit  to track it down!


> > 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?
>
> No problem, but it would be easier (as well as owner-allowed maintenance)
> to just remove the radio -- if that would suffice?  Or are you thinking
> it's the antenna/cable?


Unless the problem is a corroded connector or such, probably not.  I like the 
idea of disconnecting the BNC at the antenna because it eliminates as much as 
posible.




> IF it's the radio -- unfortunately it's a TKM.  Are there bench
> checks our local avionics guy should be able to run to see if it's
> up to spec, before we ship it out to them?


Possibly... if they're clever and have the equipment, they might be able to rig 
up two signal generators with a 3db hybrid combiner to simulate the two suspect 
interfering signals.

Another idea that doesn't require any test equipment is as follows:  go flying 
and check the frequency 119.5 (also 119.475 & 119.525) on all your radios, and 
see if you receive distorted TV audio.  This is the second harmonic of ch. 2's 
aural carrier, and if something on the plane is generating second-order intermod 
(at 127.0), the same mechanism should generate the second harmonic as well. 
(Think of this as the sound carrier mixing with *itself*)  It's likely that ch.2 
has gone to pains to ensure their radiated 2nd harmonic is quite clean... so you 
DON'T hear it, it *might* mean that the problem is outside the airplane (or the 
interference is caused by some different mechanism.)

If you drive back to the farm, you can check these frequencies with your 
handheld as well.


> Thanks!
> Sydney


Good luck!  Keep us posted...