[TowerTalk] Log periodic antennas and front end overload?

[w2lu]

Hi Mat -

I have a fairly large LP which I designed and built about 10 years ago and 
still use.  It covers 7-55 MHz with a 15 elements on a 46 foot boom up 100 
feet. When I first started using it I had TS- 440. It was a pretty good 
radio but for some reason they didn't run the receive path thru the antenna 
tuner. The result was that everything from 7-55 MHz was presented to the rx 
frontend resulting in gross overloading and all sorts of bad stuff. It was 
particularly noticeable on 20m in the evening when there were lots extremely 
big shortwave broadcast station beaming our way. Going to any kind of 
reasonant antenna made a huge difference. I then moved to an IC-756 and now 
a 756 PRO 2. They run the rx thru the antenna tuner and the problerm has 
gone away.

Although it might be said that LP's are equally mediocer on all bands. I 
find it's preformance to be quite acceptable and having just one boom and 
one feedline to deal with is sure nice. I also think it's a real  plus to be 
able to have all bands at the top of the tower, therefore lowest take off 
angle and don't have to worrty about interaction between stacked yagis.

Bottom line -  I think LP's are worth considering provided you have some 
sort of tuned circuit ahead of the rx front end.

73's,

Gene / W2LU


----- Original Message ----- 
From: "Mat Eshpeter" <kk1c at live.com>
To: <towertalk at contesting.com>
Sent: Sunday, October 25, 2009 7:55 PM
Subject: [TowerTalk] Log periodic antennas and front end overload?


>
> I have searched the Towertalk archives and read that log periodic antennas 
> can have the undesirable side effect of capturing too much RF; their 
> broadbanded capability results in all signals in the antenna's "passband" 
> being presented to the receiver. Strong out-of-band signals such as SW 
> broadcast signals, strong contest stations, etc. could lead to undesirable 
> performance at the receiver -- it is this issue that I am trying to 
> quantify.
>
> I am looking for solid factual experience from folks who have directly 
> witnessed how log periodic antennas can affect the front end of today's HF 
> transceivers. My ridge-top QTH will have a clear shot to the horizon in 
> almost all directions and I am trying to figure out if a log periodic will 
> work for me. The other option would be a multiband antenna like the Force 
> 12 5BA or similar.
>
> thanks in advance,
> Mat
> KK1C
>
>
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