In a message to Wayne Sarosi  Bruce LeGrande wrote:
 MC> I have a different approach to direction finding (found in another old
 MC> QST.) It involves shielding your ht, and
 MC> using the "Body Effect". The ht is
 WS> Hmmm. Interesting. Is the duck inside the downspout such that it
 WS> shields the antenna except for the opening at the top? That
 BL> Would the HT necessarily have to be inside the gutter, or could
 BL> one build a shield just around the 'duck' and have the bottom
 BL> closed with a slip on end that has a BNC bulkhead connector
 BL> through it to connect the antenna to ? 
 BL> Then what if you used one of those telescoping quarter waves with
 BL> the BNC (instead of the 'duck') to adjust the ammount of antenna
 BL> presented to the signal.  It would seem like this would make the
 BL> unit a bit more stable, and sturdy,
 BL> although slightly more costly to build.
Hard to tell. I'm waiting on a reply so I can get more info. Basically
it looks like you shield the antenna pattern save the top end of the
'donut' thus it provide direction if pointed at the suspect signal.
The use of the telescoping antenna is that the less extended the less
it picks up. Kind of like your commercial FM portable. The theory behind
using an omni antenna for direction finding is to home in on the 
strongest signal by trial and error. Numb the antenna by shortening it
and do the same again until the point comes where you remove the 
antenna  at close range. The point of this is the signal and the 
receiver. The only tool you have is the antenna which you can control.
Kind of a hearing aid and volume control.
 BL> And what if copperclad was used instead of alum'.  Seems like, in
 BL> essence, we're talking about the same theory as that of a
 BL> waveguide, although much scaled down ?
I have done tests with different materials such as aluminum, stainless
steel and copper and found no difference in dipoles at VHF and UHF
frequencies. Waveguide theory at VHF is out the door concerning
material and a size like this.
Shielded rooms use Steel. Some screen rooms use copper screening.
Just a thought.
-WS
  
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