Topband: Re:Receiving Loops

[W9UCW at aol.com]

In a message dated 12/29/2003 11:01:01 AM Central Standard Time, 
topband-request at contesting.com writes:
in high local noise, would it be advantageous to put a small receiving loop 
on top of a tower? In my simple mind this would at least remove the antenna 
some 15 m away from the sources. Is that worth the effort?
Hi Thomas,
Putting your small receiving loop atop your tower might make things worse. 
The best example I remember of that was demonstrated by W1BB, Stew Perry. In the 
1970's, Stew asked me to build a receiving antenna for him. He had serious 
noise problems at his "tower" location on the cliff above the Atlantic shore 
which was located in downtown Winthrop, MA. I built a multi-turn shielded loop 
using 1" aluminum encased hardline and shipped it to him. 

Stew called later to say that it didn't help and in fact was noisier than his 
big two element inverted "V" array atop the water tower, 250' above the 
ocean. Upon questioning I found that he had hoisted the loop to the top of the 100' 
tower. It seemed to me that the 100' of vertical coax was doing a fine job of 
noise pickup, negating the benefits of the loop. Besides that, it was in the 
center of the dipole array. It took some talking, but I convinced Stew to try 
the loop on the wall of the little control hut at the base of the tower, where 
his station was crowded into a corner. He then realized the loop's signal to 
noise characteristics. The 3' diameter loop performed like a champ in that 
position, about 4' above ground. He used the loop to good advantage until he had 
to abandon the "tower" location, years later.
If it were me, Thomas, I would keep the loop close to ground with a short 
feedline, but as others have mentioned, perhaps be able to turn it  to null the 
major noise source. An actual rotator might be a waste as the loop will likely 
have little directivity to DX stations.
Best DX, Barry, W9UCW