[Premium-Rx] Broad Bandwidth HF RX Antenna

[Carcia, Frank A. HS]

Al,
What if 2 dipoles were connected to an open wire line say 450 ohms to the
shack,
with a bb transformer in the shack. This way the antenna could also be used
for transmitting also. I wonder if you still get the same effect? The BB
transformer would just be replaced with an antenna tuner when you want to
transmit. I will have the same problem on my beach lot.   fc  

-----Original Message-----
From: Al Klase [mailto:skywaves at webex.net]
Sent: Monday, January 26, 2004 12:25 PM
To: Mark Donaldson
Cc: premium-rx at ml.skirrow.org
Subject: Re: [Premium-Rx] Broad Bandwidth HF RX Antenna


Mark Donaldson wrote:
> I am looking for ideas on a wide bandwidth HF RX antenna for use with my
premium receivers.

Hi Mark,

This is a subjuct near and dear to my heart, so I'll try not 
to go on and on.  I designed and marketed such an antenna 
about 15 years ago known as the Skywaves WAS-50.

The problem was actually solved pretty effectively during 
the short-wave craze on the 1930's.  The approach was to use 
the available span for a broadband doublet, and use this 
structure as a T-antenna against ground below it's cut-off 
frequency.

Quasi-aperiodic doublets:  Two example were the Double 
Doublet and the General Electrical V-Doublet.

The double doublet is two dipoles sharing a common balanced 
feed line, say 50 and 100 feet.  The resonate points of one 
set of elements correspond with the anti-resonate (high 
VSWR) points of the other.  A good average approximation of 
the feed point impedance is in the 300-450 ohm neighborhood. 
  (For effective reception, one only needs to come close!)

The GE V-Doublet takes a slightly different approach: 
Imagine two 20 ft sections of wire with a 10-ft insulated 
section (rope) between them.  The inner ends of the elements 
are connected to 10-foot sections extending down to the feed 
point, forming a Vee.  The WAS-50 used 300-ohm twin lead for 
the feed line.

I've been using a 100-ft version of this antenna, with the 
same 10-foot vee, for years.  It's connected to a 
multicoupler and feeds the entire house via TV coax.

A 50-foot doublet will roll-off pretty steeply below about 
5MHz and a 100-foot span will get you down to about 2.5MHz.

Either of these can be connected to the receiver with a 
balun.  Below the cut-off frequency either antenna can be 
used as a T against ground by connecting the two sides of 
the balance line together.

The WAS-50 and later WAS-100's have a frequency slective 
feed network the automatically accomlishes this mode change. 
  thus they can be effective from LF through HF if you have 
a decent ground.  Performance above the cutoff frequency is 
pretty well independent of ground.

I'm keeping the feed network propriety incase I decide to go 
back into production, but a simple balun is good for HF.
See: http://www.webex.net/~skywaves/ANTENNA/antsys.htm

Regards,
Al





-- 
Al Klase - N3FRQ
skywaves at webex.net
Flemington, NJ 08822
Web Page:  http://www.webex.net/~skywaves/home.htm


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