Topband: [Fwd: Re: Twin Lead Marconi Antenna]]

[Herb Schoenbohm]

-------- Original Message --------
Subject: 	Re: Topband: Twin Lead Marconi Antenna]
Date: 	Wed, 17 Jun 2009 07:15:00 -0400
From: 	Herb Schoenbohm <herbs at surfvi.com>
Reply-To: 	herbs at surfvi.com
To: 	TopBand List <topband at contesting.com>



  
>> Herb wrote: I do recall however that the theory that the ground losses were 
   reduced by a 4 to 1 base impedance multiplication factor has been disputed.
>>     
>
> Ross Wrote:  Citation? That's still the working theory in Low Band DXing.
>
> Herb Replied:

> Not any longer...about 15 years ago a series of antenna test range 
> experiements were conducted on a antenna range by King and Rankin (not 
> sure of the spelling) who wrote a paper with there results presented 
> at a NAB conference or published in the IEEE proceedings. I had a copy 
> but can't find it at the moment. The experiments with FSM's on ground 
> wave signals from a 60 degree tower with a skirt feed at, if I 
> remember coreectly at 1580 Khz, demonstrated that that there was no 
> signal increase when the skirt was connected directly to the tower 
> base and the strap to ground (it was a base insolated tower for the 
> purpose of these tests) was removed and the antenna fed as a normal 
> series fed vertical. The was a notice however of increase bandwidth 
> due to the cage with both the cage feed (tower grounded) and cage feed 
> (tower base ungrounded and connected to the cage at the bottom and top.

There also is a significant benefit to increase B/W with shortened 
towers where in AM applications the B/W is so narrow that the sidebands 
of the signal trigger the VSWR protection circuit resulting in power 
cutback of some of todays solid state transmitters such as the Nautel 
ND-5.  Additionally there is a noticeable reduction of air quality with 
the narrow B/W antennas that the cage feed can mitigate.  But as far as 
increase radiation efficiency it appears to have been a self sustaining 
urban legend which Tom, W8JI and Joe, W4TV have recognized some time ago.

Herb, KV4FZ