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Antenna report EFHW vs Random wire


eladner65
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Well, this is interesting, and not what I expected.  I built the 49:1 unun and put up a 20m EFHW as a sloper[sp?].  I got the SWR nice on 10, 15, 20 and 40 with a little cheap scanner I have.

For reference, my Random wire on my 9:1 unun has a noise floor on 20m of about S3.  The EFHW with the same feed had a noise floor of S8!  My attic 20m dipole is normally S4-S5 on the same band (tested at the same time).  Both antennas have the nulls in roughly the same direction (N-S).

I did some more testing.  I listened on WSPR on 20m on both the random wire and the EFHW.  The EFHW couldn't bring in any station further than 2000km.  My random wire on the other hand was reliably bringing Australia at 14000km.

SO.  Random wire stays up, EFHW goes back on the bench.  I think the attic dipole might become a fan dipole on 6 and maybe 10.

73,

Ed L. ke0tsd.


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Jeff Karpinski
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That's very weird as a 20M EFHW should not work at all on 40 or 15M. 2nd harmonic of 20 would cover the lower end of 10M so that makes sense. I've also found EFHW antennas need a 1/4 wavelength counterpoise (or equivalent length of feed coax running on the ground).

What's the length of your random wire? Does it have a counterpoise?


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eladner65
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Jeff,

I might have been unclear, the EFHW worked on 10, 15, 20 and 40.  The noise floor was the killer.

My random wire is approx 58 feet with a counterpoise of about 20 feet.  I have an ugly balun at the feed point to kill any RF coming into the shack.  My random wire behaves very nicely.

73,

Ed L.


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Jeff Karpinski
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No, I understood. Remember, antennas don't know the difference between noise and signal. The fact that you're hearing more "stuff" on the EFHW could actually imply it's more sensitive.

I was simply pointing out that a 20M EFHW should not have anything remotely like a nice SWR on 40 or 15. When I run a 20M wire on my 49:1 ununs (one commercial QRP, one home-made for high power), the SWR is over 30:1 on 40 and 15M. I do get a nice dip on the low end of 10M.

58' is in the goldilocks zone for "random" wire antennas. Good pick. I quit using 9:1 random wires for portable as I found the counterpoise length was very sensitive and different deployments would give me wildly different SWRs. I found EFHW to be less picky about counterpoise length and terrain, plus I don't need a tuner.


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Jed Baer
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That's very weird as a 20M EFHW should not work at all on 40 or 15M.

Ed mentioned, elsewhere, the "ARRL EFHW Kit", which is a 40/20/15/10, from HF Kits. I don't know whether it's the 100W or 250W model - ARRL is doing site maintenance right now, but you can look at the HF Kits site for both of them. There's a big writeup on QRZ about it too.

It's difficult to speculate about noise floor. That EFHW, at 67 feet or so, has more capture area than the random wire, but by itself that wouldn't seem to be enough difference. Things such as the orientation of the wires could account for it.

Alan - W2AEW has a couple videos up about this kit, but no full-bore test yet.


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eladner65
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I've attached the panadapter output (video) of my 20m attic dipole compared to the 10-40 EFHW.  The 20m dipole has about the same noise floor that the random wire antenna has.

Down side is that I couldn't have both EFHW and Random wire up at the same time as the mount in the exact same position.

What really caught my attention was the constant static crashes on the EFHW, which were not apparent on any other antenna.  All other settings were identical.

I'm open to ideas.

73

Ed L.

 


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eladner65
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@kd0ymg ,

Yes, that is the kit that I picked up.  I got the 250W 10/15/20/40 kit.


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Jeff Karpinski
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Posted by: @eladner65

I built the 49:1 unun and put up a 20m EFHW

Posted by: @kd0ymg

Ed mentioned, elsewhere, the "ARRL EFHW Kit", which is a 40/20/15/10, from HF Kits.

Different kettle of fish entirely! A 65' EFHW is resonant on 40M. The 2nd harmonic would cover 20M, 3rd 15M, and 4th, 10M. That makes perfect sense.


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eladner65
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@webmaster 

Yah, I thought I had been unclear.  The wire is 20m, not the wavelength.

Sorry,


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