REFLECTOR: Nav/Comm Coax in FB Wings

[Jim Agnew]

OK here is a proven method that is inexpensive and easy.  Get a cheap 12 volt SPDT relay.  connect + 12 volts to the common relay point, connect the NC point to one side of the coil and the other side of the coil to  the battery minus.  The relay is now a buzzer and if you take a lead from the + side to the coax center conductor  and a lead from the minus side to the shield you can then run a cheap AM radio over the wing or wing-let and you will hear a lot of static as the radio approaches the antenna.
 
You can also use an old fashion mechanical buzzer or door bell as long as they use points to control the coil.
 
Nothing but an old fashion spark gap transmitter.  PS - it will cause noise on almost any receiver nearby so keep your testing short.
 
Have fun.
 
Jim
 
James F. Agnew
Jim_Agnew_2 at Yahoo.Com
Tampa, FL
Velocity 173 Elite Aircraft Completed & Flying 



----- Original Message ----
From: Dave Black <dvblack at comcast.net>
To: Velocity Aircraft Owners and Builders list <reflector at tvbf.org>
Sent: Monday, August 28, 2006 3:43:43 PM
Subject: Re: REFLECTOR: Nav/Comm Coax in FB Wings


bdtopp at comcast.net wrote:

>    I am having difficulty determining which of the coax cables exiting 
> the wing roots is the Comm cable and which is the Nav cable.

I remember a few years back when I asked Alan Shaw this question, he 
suggested I pull on the cables. Since the Comm cable is longer, it would 
stretch more.

That test proved inconclusive for me, but I was able to determine which 
was which through the use of an antenna analyzer. Connect it to one 
cable or the other, then run your hand along the wing or winglet. When 
your hand passes the associated antenna antenna, you'll see an increase 
in SWR on the analyzer. The NAV antenna is in the wing, while the Comm 
is in the winglet.

If you don't have access to an antenna analyzer or SWR meter, just 
connect the antennas one way or the other. No harm will be done if you 
get it wrong. But you'll get better reception one way than the other.


dave black
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