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RE: [TowerTalk] New antenna system

To: "'4x1ad'" <>,"'TowerTalk'" <>
Subject: RE: [TowerTalk] New antenna system
From: "Joe Subich, K4IK" <>
Date: Mon, 8 Nov 2004 16:11:46 -0500
List-post: <>

> But what about F/B or F/S ratio?  Aren't they of any importance? 

Of course they are.  If you spend a little time working with the 
modeling programs (or reading the ARRL Antenna Book), you will find 
peak F/R is relatively narrow on most yagi designs and most fixed 
tuned antennas fail to achieve real pattern performance over even 
half of a given band.  Often the F/R of an antenna set up for CW 
will fall to less than 10 dB on phone.  For example, a three element, 
16 foot boom 20 meter yagi might show F/R > 20 dB below 14.100 but 
at 14.200 it's down to 11 dB and only 7 dB at 14.300.  Similarly, 
SWR is greater than 2:1 shortly above 14.100.  

> Personally, I can't take too seriously the manufacturer claim 
> that "a long boom is not needed to achieve near optimum gain 
> and front to back ratios on 20 - 10 meters since the SteppIR 
> can control the element lengths" !!!!

The adjustable element lengths allow the SteppIR antennas to achieve 
a very nice balance between the gain available for a given boom 
length, F/R and SWR.  Quite simply, modeling will show that, within 
limits Gain and F/R are nearly constant flat as one changes the element 
spacing (e.g., the position of the driven element in a three element 
yagi with a fixed boomlength) as long as the element tuning is 
adjusted to compensate.  

With the SteppIR antennas, the boom length has been compromised 
slightly in favor of higher gain on the low end of the range to 
the detriment of best possible F/R on 10 meters.  That is a trade
that many are willing to make.  


   ... Joe, K4IK 


See:  for "Self Supporting Towers", "Wireless Weather 
Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any questions 
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