Topband: First attempt at beverage antenna, not working as expected

[donovanf at starpower.net]

Mark,

While "The Benchmark Beverage" makes interesting reading, it conflicts significantly with years of practical Topband experience. The credibility of "The Benchmark Beverage" suffers badly because its based entirely on an undisclosed computer model not benchmarked to the measured performance of actual Beverage antennas.

Those of us who have installed Beverages much longer than 1000 feet have had consistently disappointing results.  The sweet spot for good Topband Beverage performance seems to be 500 to 900 feet, with 700 to 850 feet being close to optimum.  This inconsistency between model and practical results may be caused by several effects not adequately modelled for a very long Beverage, for example:

 1. decorrelation of the arriving wavefront along the length of a long Beverage.

 2. signal attenuation along the length of a long Beverage.  Signals received at the far end of a Beverage contribute significantly less to the received signal than signals received closer to the matching transformer,

 3. phase interference between the incoming wavefront and signals propagating more slowly (by the velocity factor) along the length of a long Beverage (the article says this is accounted for, but doesn't reveal the details)

Another significant conflict between "The Benchmark Beverage" and practical experience is that Beverage antennas are not very sensitive to small changes in length (changes of about 100 feet or less).  This insensitivity to relatively small length variations is probably related to the three factors above, especially the attenuation of signals received at the far end of the Beverage.

I definitely don't recommend that any of rush out to add or remove 50 feet or less to our Beverages!

73
Frank
W3LPL



---- Original message ----
>Date: Mon, 17 Jan 2011 03:58:14 -0800 (PST)
>From: Mike Waters W0BTU <mrscience65704 at yahoo.com>  
>Subject: Re: Topband: First attempt at beverage antenna, not working as expected  
>To: Mark Lunday <mlunday at nc.rr.com>, topband at contesting.com
>
> Mark,
>
>I went back and studied Greg Ordy's page at 
>http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/Beverage.htm
> at length. From his chart and animated GIF, it appears that merely adding 
>another 25 or 50 feet onto your 250' Beverage might do wonders for it on 160. 
>(Having said that, if you have the room then by all means extend it a lot 
>farther than that).
>
>I went back and studied the page  in detail. Pretty interesting reading. 
>Regardless of the minor grounding error, this guy spent a lot of time modeling 
>Beverages  of various lengths, presents his findings in interesting and  
>easy-to-understand graphs and text, and it is very informative. You have  to 
>admire that. I don't know about the practicality of using the very  long lengths 
>he mentions (watch the GIF animations there), but that's another matter. See 
>what you  think. :-)
>
>Let us know how the Epsom Salts works for you both on 160 and 80.
>
> 73,
>Mike Waters
>www.w0btu.com
>
>
>
>      
>_______________________________________________
>UR RST IS ... ... ..9 QSB QSB - hw? BK