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Author Topic: Looking for a good receiving antenna  (Read 3100 times)
K3VAT
Member

Posts: 709




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« Reply #15 on: December 12, 2012, 12:30:14 PM »

I wouldn't use the ZL9HR dxpedition as a guide to how well your antenna is receiving.
Just about everybody on eham had difficulty receiving them.  Whenever their signal
broke out of the noise it was quite readable.  I am using a hex beam at 25 feet and
have been able to work all but a couple of this years'  dxpeditions with little problem
WHEN the noise allowed.  So don't expect too much from small antennas, as the
guys with fantastic signals and can hear a flea bat it's eyes usually have fantastic
arrays at hundred or more feet.
Good Luck
Allen KA5N

I second this observation.  This is a sample size = 1 and can't be inferred to be the norm.  Additionally, solar flux fell fairly dramatically from the beginning of their operation to the last day, so their signals on 10, 12, and even 15 were much weaker toward the end of their operation.  How did you do with some of the recent DXPeditions in the Caribbean or Africa? 

Finally, what is your noise floor?  If it is high, say ~-110db then you might want to investigate the possibility of excessive HF noise pollution in your vicinity.  Even strong signals can be buried by high noise and make operation frustrating.  There are lots of good posts in this Forum and on the Elmers Forum for ascertaining if you're victim of noise pollution - just do a simple search.

GL, 73, Rich, K3VAT
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LA9XSA
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Posts: 376




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« Reply #16 on: December 12, 2012, 06:29:42 PM »

Am I correct that the nulls on these costly small loops (Pixel, Wellbrook)  just work on pinpoint groundwave crud like powerline noise or a bad switching power supply in a neigbors house. I don't think they're even effective in reducing static from distant storms. 
As you know distant noise comes with all polarities and from a wider direction than local sources; just from looking at antenna patterns it seems to me that a beam or a phased array would be better than a sharp nulled loop in case you have a storm to the east and a desired station to the west. The front-to-back ratio would be more important than the sharpness of the null. Correct?
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W0BTU
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Posts: 1665


WWW

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« Reply #17 on: December 12, 2012, 08:07:49 PM »

Am I correct that the nulls on these costly small loops (Pixel, Wellbrook)  just work on pinpoint groundwave crud like powerline noise or a bad switching power supply in a neigbors house. I don't think they're even effective in reducing static from distant storms. 
As you know distant noise comes with all polarities and from a wider direction than local sources; just from looking at antenna patterns it seems to me that a beam or a phased array would be better than a sharp nulled loop in case you have a storm to the east and a desired station to the west. The front-to-back ratio would be more important than the sharpness of the null. Correct?

I agree. I modeled some small low loops, and the null is very sharp only at very low angles. There's a 3D EZNEC plot showing this at http://www.w0btu.com/magnetic_loops.html . See figure 2 there, which shows the deepest null at about 5 degrees and lesser nulls as the elevation increases.

This is not to say that a small loop is worthless. But a beam, phased array, or Beverage would be far superior.
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