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Re: [TowerTalk] HF LOG-PERIODIC ANTENNAS Comments Please

To: <>
Subject: Re: [TowerTalk] HF LOG-PERIODIC ANTENNAS Comments Please
From: "Larry Phipps" <>
Reply-to: Larry Phipps <>
Date: Wed, 23 Jun 2004 15:17:06 -0400
List-post: <>
I used a 3 element model in EZNEC... I'm pretty sure there's a model of stacked 
3 el SteppIRs on my website at in the downloads 
section. You can delete the wires for the second beam. I assumed 100' of RG-8, 
and used TLW to calculate loss. I added out-of-band feedpoint mismatch loss and 
antenna response as well.

My assumptions about distortion numbers were made with regard to a preamp stage 
only with a NF of 10dB and IP3 of 10dB. I did not include any preselector 
attenuation, which in some rigs might be substantial. It might be that there 
would be enough attenuation in the preselector that the difference between a 
yagi and LPDA would be inconsequential, with distortion products being below 
the noise floor in both cases. My main concern would actually be the blocking 
dynamic range spec of the rig, and nearby big signals. The use of LPDAs in a 
multi-multi environment, for instance, might require a more judicial use of 
traps, bandpass filters or external pre-selectors to block out strong local 
interference to reduce de-sensitization.

Larry N8LP 

----- Original Message ----- 
From: Jim Lux 
To: Larry Phipps ; 
Sent: Wednesday, June 23, 2004 10:29 AM
Subject: Re: [TowerTalk] HF LOG-PERIODIC ANTENNAS Comments Please

Could you publish the model you used, including the length and type of
feedline you assumed?  I'm assuming that you're talking about out-of -band
mismatch loss?

----- Original Message -----
From: "Larry Phipps" <>
To: <>
Sent: Wednesday, June 23, 2004 12:28 AM
Subject: Re: [TowerTalk] HF LOG-PERIODIC ANTENNAS Comments Please

I just ran a quick sweep of a 3el SteppIR model and the loss in the feedline
alone due to mismatch is about 4dB at 1 mHz out and 10dB at 5 mHz out. Add
to that the pattern loss and you're well over 10dB total out-of-band loss
compared to a LPDA. That might not seem like much, but 10dB lower
interfering signal is roughly 20dB lower distortion products. It all adds

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