Topband: Loop Antenna Questions

[w2pm at aol.com]

The so called (poorly) "magnetic loop"  only works when it IS small -  
.1 wavelength maximum but that is not the optimal size..  According to 
several texts that should be .037 wavel. which is the 5 ft diameter 
loop.

But I think there remains confusion over the term LOOP.   The magnetic 
loop is a tiny antenna used primarily to null out strong, highly 
localized single-point noise. Secondarily, you get a general receiving 
antenna with very poor characterics starting with very low sensitivity 
and no directivity vertically  - so it won't discriminate between high 
angle atmospheric noise and low angle DX despite nulling out local crud 
noise if you can.   It always work well for local work, but is truly an 
antenna of last resort for DX. I've worked VK with it from noisy NNJ 
but the conditions were exceptional at those times.  However, without 
that magnetic loop those days I could not work VK.  None the less it is 
a VERY POOR receiveing antenna for DX.

The terminated loops (diamonds, flag, pennant, K9AY) and entirely 
different.  They are also larger (although there is a mini diamond Flag 
of 5 ft dimensions).  The nulling they provide are not nearly as useful 
for nulling out local noise crud - like a bad insulator on a power 
pole, light dimmer, etc.BUT that null is broader and much more 
particular to a certain arrival angle. That null is used to increase 
the S/N ratio but the directional characteristics of the cardiod 
pattern and the overall pattern has fairly low angle sensitivity. This 
is a good DX antenna but is much larger than a magnetic loop.  That 
said you can build a half size Flag (7 by 15 ft) or even a mini diamond 
config flag of 5 ft per side and still get the same cardiod pattern of 
the full sized models (15 by 30) but with much lower sensitivity.   
When these antennas get smaller and their outputs become much lower the 
chances of feedline pickup and pattern distorion come into play and 
that can ruin everything but those conditions can be avoided.  ON4UN's 
book remains the "Bible" and lots of other on line resources out there 
with this stuff -- including the w8ji.com site.

73

Pete W2PM

-----Original Message-----
From: Rick Karlquist <richard at karlquist.com>
To: RICHARD SOLOMON <w1ksz at q.com>
Cc: TopBand List <topband at contesting.com>
Sent: Fri, Jan 1, 2010 10:46 pm
Subject: Re: Topband: Loop Antenna Questions


I found that a 40 foot perimeter square loop, roughly
equivalent to your 12 foot diameter round loop had
an inferior null to a loop half as big.  It did of cource
produce about 10 dB more signal (and noise, same SNR).

Rick N6RK

RICHARD SOLOMON wrote:
>
> I have an NZ4O(KN4LF) Loop Antenna for receiving now. I was wondering
> what folks thought about using a "bigger" Loop ??
> By that I mean around 12' diameter instead of the 8' diameter I have 
now.
>
> Would I gain anything by doing this ?
>
> Tnx es HNY, Dick, W1KSZ
>
> _______________________________________________
> "160-meters is a band for men, not for sissies!" - SM5EDX
>
>


_______________________________________________
"160-meters is a band for men, not for sissies!" - SM5EDX