Topband: Receive loop observations

[donovanf at starpower.net]

Hi Jim, 


A properly constructed loop antenna absolutely requires a preamp. 
If signals are so strong that you don't require a preamp then its 
likely that the signals you're hearing are not actually coming from 
the very inefficient loop but from other sources such common mode 
from your coax feed line if its not very well isolated from the loop. 


If your loop is operating correctly it will be omni-directional for 
skywave signals and it will have an extremely deep null for an 
unwanted signal propagated to your antenna from one local 
vertically polarized interference source. A well constructed loop 
should have a null depth of 60-80 dB and a null beamwidth of just 
a few degrees. A very rigid mechanical mount is required to 
keep the deep null pointed directly at your interference source. 


A properly constructed loop should be transformer matched 
to keep the loop balanced and both the coaxial cable and power 
cable must be exceptionally well isolated from the loop. 


A low noise figure high gain preamp is essential. 


73 
Frank 
W3LPL 









----- Original Message -----

From: "James Rodenkirch" <Rodenkirch_LLC at msn.com> 
To: "Top Band Contesting" <topband at contesting.com> 
Sent: Friday, April 1, 2016 7:04:25 PM 
Subject: Topband: Receive loop observations 

I have installed a receive loop ( http://www.qsl.net/kc2tx/ ) and finished measuring and observing... 


Measurements: 


VSWR --- 1.7 @ 1.830 

ZO ----- 77 at 1.830 


Observation: 


Following ON4UN's comments regarding needing a preamp or not, measured S1 to 2 noise level with antenna connected during mid-day, S0 with dummy load connected. 


During evening hours, notice some improvement - S2 drop in noise level when switching from xmt antenna (inverted U) to the loop - but not hearing much in the way of receive signals (e.g., hear a fairly strong signal from the west coast on the xmt antenna, nothing on the loop and I have it oriented east/west). 


I'm uncertain if a low noise amp will help my cause (thoughts??) 


I do not have a common mode choke installed, yet...will one make that much difference? 


The loop is located about 60' away from the Inverted U and radials. 


Comments/suggestions appreciated. 



Thank you, in advance, for constructive, relative to what I have now, replies....non-"constructive" means I can't erect a BOG, Beveridge or Waller Flag so don't ask why I didn't go that route. 


71.5/72 de Jim Rodenkirch K9JWV 
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