Topband: 2 wire beverage

[Tom Rauch]

Hi Mauri,

I respectfully disagree with this:

> Leaving one wire open and grounding the other you typically achieve 12 dB
> F/B that's finally not bad

The F/B ratio will vary greatly with antenna length, and never be 
much more than transmission loss through the antenna for 
common mode current. 

Grounding one wire and floating the other does not produce the 
desired "push-pull" reflection from the far end, it simply creates a 
mismatch.

> be instead designed to work decently on 3 octaves. Amidon best materials
> for your purposes are 73 75 and 77 althought material 73 is not available
> in a toroidal form.

Amidon is a retailer, they do not manufacture cores nor do they 
stock all types. Virtually all cores are available in all types of 
materials, but you may have to check with other sources.

Most ferrite cores in the USA actually come from Fair-Rite Corp in 
Wallkill NY at (914) 895-2055.

73 Material has the impedance peak at about 2 MHz, while higher 
ui cores (initial ui is a dc value, not the actual ui at the operating 
frequency) have peaks lower in frequency.

That means a higher ui core than 73 can actually require MORE 
turns for satisfactory impedance, not less as might be expected. 
Many people only consider the dc permeability when selecting 
cores.

Binocular cores have higher impedance for a given length of winding 
through the core, and give better overall performance. I have a large 
stock of 73 mix binocular cores available is anyone gets "stuck" 
and can't find a core.

73, Tom W8JI
w8ji@contesting.com



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