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Date: Sat, 01 Oct 2011 12:42:56 +0100
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Subject: Re: LF: Ferrite RX antennas
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My favourite "scam" has to be a "faboulous product" offered to us by a
wholesale supplier just about the time CB was legalised in the UK.
This was "guaranteed" to improve the performance of "any" mobile
antenna. The product? "SWAR GREASE". The instructions were that by
coating the conductive surfaces (whip) with the "specially formulated
radiofrequency-active grease" skin effect would be enhanced. "Twig
performance might improve by as much as 2 pounds". The product was
widely promoted in CB magazines and I sometimes wish now that we had
decided to stock it because we had numerous requests. A jar of the stuff
sold at approximately 25% of an average "twig"!

73


On Sat, 2011-10-01 at 10:47 +0100, James Moritz wrote:
> Dear Mal, LF Group,
> 
> G3KEV wrote:
> > NEW
> > 500 series  HI-Q COILS
> > Q over 400, mobile antenna individual coils, one for each band 160 - 10
> > metres
> > ( These coils are air wound and sealed in a transparent gas tube.
> > DAVIS ELECTRONICS,  BURBANK, CALIFORNIA
> 
> 
> A Q of over 400 for a large coil is not unusual or suprising.
> 
> Re the "helium coils" I guess you mean something like the advert in the 
> attachment, which came from the web site of  K0BG 
> (http://www.k0bg.com/history.html). In such a coil, most of the losses are 
> due to RF conductor resistance, perhaps significant Q reduction is also 
> caused by dielectric losses in the solid insulating components, eddy current 
> losses in conducting parts, etc. The losses in the air around the coil would 
> be minute in comparison. So filling the casing with helium would make no 
> detectable difference - whether the helium would stay there for any length 
> of time, or if they actually bothered to put it in initially, is debatable. 
> So the helium bit is just a marketing ploy.
> 
> There are a lot of similar scams around, where something expensive is 
> justified by claims of exotic-sounding materials and techniques, and results 
> that are in some way remarkable. The hi-fi world seems especially prone to 
> this - the Tara Labs website is always good for a laugh, see 
> http://taralabs.com/shop?page=shop.product_details&flypage=flypage.tpl&product_id=118&category_id=17 
> if you want to buy a 1m long audio cable for nearly 16,000 dollars!
> 
> Coming back to loop receiving antennas, the Q of the winding is only one 
> factor; the "effective area" is another factor which determines the amount 
> of signal power available. This depends mostly on the actual area of the 
> coil in the case of an air-cored loop, and on the length, geometry and 
> permeability of a ferrite rod, as was discussed some weeks ago on this 
> reflector. You can certainly make an air-cored loop with a similar Q to a 
> ferrite rod, but it will be more bulky and less portable than an equivalent 
> ferrite rod that achieves adequate noise performance, which was the original 
> reason for discussing ferrite rod antennas.
> 
> Cheers, Jim Moritz
> 73 de M0BMU 

-- 
73 es gd dx de pat g4gvw
 qth nr felixstowe uk
(east coast, county of suffolk)