[Antennas] RE: B&W Ant. Quest.

[NA4FM (Buck)]

What you have there is a Tilted Terminated 2-wire Folded Dipole (TT2FD).
Below are the specifications for the original Patented antenna I
received from a local ham who is currently testing and working with the
TT2FD made by B&W.  The numbers can be reduced easily enough, but I am
copying them as-is so you do the math.

For those who don't know, the TT2FD is a center-fed, folded dipole with
a terminating resistor between each side of the top wire directly above,
but not connected to the feed-point of the lower wire.  

>From end to terminator or feed point:  (50,000/lowest frequency in
KHz)*3.28 = length in feet.

Spacing between wires: (3000/lowest frequency in KHz)*3.28 = separation
in Feet.

Slope angle should be from 30 - 40 deg. 

Terminating Resistor Wattage = 35% of Xmit Power.

Terminating Resistor Resistance is as follows (I have no formula): 
Xmission		Terminating
Line 			Resistor
Impedance		Resistance

300			390
450			500
50			60

NOTE:  The originator of the design says that the lower the feed line
impedance, the harder it is to match the terminating resistor.  300 and
450 ohm feed line seemed to match most easily.

The test results thus far are that TT2FD is operating, at best, equal to
a dipole, but not as well as a slanted dipole in the same angle.
However, it is a perfect match across all ham bands!  That means
something.  

I have decided to build one and store it in my emergency comms pack.  In
an emergency, I can put it up and have a perfect match with any radio.
In an emergency, I am not as interested in gain vs. loss as the getting
up an running quickly is most important and even a poor antenna can be
heard.  (evidenced in the Hurricane Hugo disaster comms)

I am figuring that a line over a tree and a stake in the ground and I
could have a working antenna for all bands up in 5 minutes or less
without needing an antenna tuner.  

I don't know just how much loss there is in the antenna, but I don't
believe it can be more than a 75 meter Hustler whip on a mobile.  I did
well with that, and in one instance, I had to get on 75, I rolled a
spool of wire out about 65 feet with the shield connected to a ground
rod and the center conductor to the wire.  I got a 1.3:1 match and
checked into the GASSB net on time.  It wasn't a great signal, but I was
heard.  My thinking is that a poor antenna is better than none at all. 

BTW, the antenna used as a folded dipole (horizontal) is terrible.

Since you are only receiving, I recommend a long wire Zep type antenna.
Run the wire as high and long as possible, drop a single wire down to
the entrance of your room.  Use a piece of coax to bring the wire inside
(just use the center conductor only long enough to get through the
window or other entrance.)  Then connect to the radio. If you want
improved reception from that, get a tuner and tune the antenna.  You can
make one from plans you see can find on the internet for less than
$10.00 or buy a small kit.  You don't have to worry about power since
you aren't transmitting.


Hope this helps,
Buck
NA4FM

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> -----Original Message-----
> From: Orrin Bentz [mailto:minmar at 2z.net] 
> Sent: Monday, June 28, 2004 7:18 PM
> To: antennas at mailman.qth.net
> Subject: [Antennas] RE: B&W Ant. Quest.
> 
> 
> Hello
> 
> There is an antenna made by Barker Williamson a model BWD-90. 
> This is a folded dipole with spacers and a Balun at the feed 
> point for coax.
>>>> SNIP<<<<
> 
> This antenna is to be used for receive only. www.bwantennas.com
> 
> Thank You
> 
> Orrin Bentz
> 
> 
> - - - 
> 
> Your moderator for this list is:
> Larry Wilson KE1HZ antennas-owner at mailman.qth.net 
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