[Premium-Rx] Wellbrook excellence !

[Al Klase]

Carcia, Francis A HS wrote:

>I was thinking or a similar problem with open wire feeders to a wire
>antenna. It is a pain to readjust a tuner so wanted to make a broadband
>interface to the radio....
>
My suggestion is to use a 9:1 balun, assuming you want a 50 ohm output.  
Assuming the antenna's a doublet it will look like about 50 ohms around 
resonance ranging to a couple of thousand in a narrow band near anti 
resonance.  450 ohms splits the difference nicely and the VSWR at any 
particular frequency in never really bad.  (Maybe better than 5:1)  It 
helps to have the antenna broad-banded a bit, e.g. a double doublet (one 
half the size of the other)  This concept was worked out during the 
1930's at the height of the short-wave craze. My WAS-50 that I marketed 
in the early '90's was a reverse engineered version of the General 
Electric V-doublet. See: Riders manuals Volume 6, first page is on line 
here: http://www.nostalgiaair.org/Resources/273/M0008273.htm  The Vee 
section serves the same purpose as the second set of element in the 
double doublet.  The trick is making the feed network treat the whole 
thing as a T-antenna below the cutoff frequency of the dipole, so it 
will also work at MF and LF.

>........A loop is a low
>voltage device so I bet a FET or a pair of source follower FETs at each
>end driving a BB transformer....... 
>
The problem with a non-resonate loop is that it's a current device, and 
you need to sense the current circulating in the loop.  If , for 
instance, you stick the 50-ohm input to an amp in the loop, you'll never 
get a low enough noise figure to recover the piddling current flowing in 
50 ohms.  I'm betting the Wellbrock potted box is some sort of current 
to voltage converter with very low input impedance.

Regards,
Al

-- 
Al Klase - N3FRQ
Flemington, NJ
http://www.skywaves.ar88.net/