[Top] [All Lists]

[TowerTalk] What about hams with small lots???

To: <>
Subject: [TowerTalk] What about hams with small lots???
From: (Tom Rauch)
Date: Sun, 2 Sep 2001 13:50:52 -0400
> The problem with the GAP antennas is on the LOWEST 
> band of operation where a capacitive reactance is transformed
> through a length of small coaxial cable inside the tubing to
> present a SERIES INDUCTANCE at the feedpoint, only on 
> the LOWEST band of operation.

A length of coaxial cable, used to generate a reactance, is about 
the worse thing possible anyone could ever use.

Not only is the conductor length long and generally thin, it does not 
even have uniform current distribution. If you translate the 
impedance to a reactance in series with a resistance (that the 
antenna current flows through), the ESR (equivalent series 
resistance) it is dozens of times worse than a good inductor!

The second problem is they have just as much current trying to 
flow into the radial system as any other vertical the exact same 
high and current distribution. Moving the feedpoint around does NOt 
change that.

Ground losses are terrible with that system.       

> I know of a couple of users of the 160 / 80 / 40 / 20 M GAP  
> vertical who do reasonably well on 40 and 80 meters and 
> surprisingly better than one would expect on 160M.  It is 
> NOT a great antenna on 160, but any antenna is better than 
> NO antenna.

I've always found antennas to work exactly like one would expect. 
Even an antenna 15dB down will allow contacts, so almost 
anything will "work".  

So that is true enough Tom. Any antenna is better than no antenna 
at all! 

I've worked a half-dozen VK's and even Europeans on 160 SSB 
mobile. I can even beat some home stations on 160 meters while 
mobile. My antenna is less than 1% efficient on that band. It 
doesn't work any better than I expect. With a big full size antenna, 
I'm well over S-9 even 12,000 miles away if conditions are good. 
With my mobile antenna, under the same conditions on 160, I'm 
~25dB  weaker. So I might even get an S-9 if I time it right.

73, Tom W8JI 

List Sponsored by AN Wireless:  AN Wireless handles Rohn tower systems,
Trylon Titan towers, coax, hardline and more. Also check out our self
supporting towers up to 96 feet for under $1500!!

FAQ on WWW:     
Administrative requests:

<Prev in Thread] Current Thread [Next in Thread>