[TowerTalk] CobWebb antennas - success stories?

[Jim Lux]

At 11:45 PM 9/22/2004 +0100, John Tait wrote:



>>Anyone have any success stories regarding the CobWebb antenna?
>>
>>http://www.g3tpw.ukgateway.net/
>>
>>
>>I'd like to get one but it's about $500 to get one here after the exchange
>>rate and shipping.  Just wondering if anyone had tried one of these before
>>and had any opinions to share...  or if there's a better list to move the
>>thread to i'd be happy to take it there.
>>
>>73 Jason N1SU
>
>  It's a clever and effective antenna for people with little room, and 
> with TVI problems.
>  Basically it's a nest of FOLDED dipoles with a choke balun at the 
> feedpoint. Ordinary dipoles in such a configuration would have a low feed 
> impedance, and narrow bandwidth,
>Using folded dipoles gets over both problems..


I don't think they're folded, just wrapped. A folded dipole doesn't change 
the bandwidth, just transforms the impedance (which would be nice in this 
case, since it would transform the 10-12 ohms of the dipole in a square up 
to 40-50 ohms..).  You'd still have the efficiency and bandwidth problems 
though.  Can't get around that physical size Chu-Harrington thing.

Sure a lot easier to tune up in design, too, since all the ends that need 
trimming are all in the same place.

An autotuner and this beast might be a good combo.  Then the narrow band 
nature wouldn't be as big a deal. X varies from about -20j to +30j (on top 
of a 11-12 ohm R) over 14.0-14.5 MHz.. 3.5:1 VSWR range 14.050 - 14.350