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