[R-390] Antenna...folded dipole...

Mon, 15 Dec 2003 21:54:16 -0800

A couple of things to think about:

(1) If the terminating resistor must be large (10-200 watts), then the
resistor must be called upon to dissipate a significant amount of power.
The power source is RF energy generated by a transmitter.  That power is
dissipated as heat and is not radiated as a radio wave.

(2) The antenna will provide a match over a wide range of frequencies.  This
is the major advantage of the antenna.  Nothing is said how efficent the
antenna is over that same range of frequencies.  The antenna may indeed be
more efficent off resonance, when compared to a mistuned dipole.   Still, it
can be very inefficent, especially when compared to a resonant antenna at
the operating frequency.

(3) The military (and govenment) uses this design when establishing local
communication paths with oversized transmitters.  The antenna will work well
in this application, where operators are not expected to know how to work
with technical equipment, particularly transmitters and antenna tuners.

73 de Bill, AB6MT
[email protected]

----- Original Message -----
From: Marshall M. Dues
To: Kenneth G. Gordon
Cc: Dave Faria ; [email protected]
Sent: Monday, December 15, 2003 6:45 PM
Subject: Re: [R-390] Antenna...folded dipole...

There is an antenna called a Terminated, Tilted, Folded Dipole (T2FD) that
has a
terminating resistor.  You can do a Google search on T2FD antennas and come
up
with a number of sites on this antenna.

For example, see the following web site:

T2FD design -- antenna special on hard-core-dx.com

<http://www.hard-core-dx.com/nordicdx/antenna/wire/t2design.html>

Marshall Dues,  WB5MYO

Kenneth G. Gordon wrote:
> On 15 Dec 2003 at 10:56, Dave Faria wrote:
>
>
>>GM list.  I want to build a Folded Dipole antenna for my station.  I
>>can wind the balun but, cannot find a suitable terminating resistor.
>>Can anyone point me to a source for a non-inductive 400ohm or 800ohm
>>resistor 300 watt??  I can build a combination of resistors to meet
>>the resistance and wattage if necessary.
>
>
> No folded dipole I have ever seen in antenna books or other
> literature, or that I have built, ever needed a terminating
> resistor. If you plan to use this antenna with an R-390, my
> understanding is that the R-390's input impedance is already
> 300 ohms, balanced, and a properly built folded-dipole exhibits
> 300 ohms impedance, balanced, at the resonant frequency.
>
> Of course, the folded dipole is resonant only around one
> frequency or band, so you would have to have several
> depending on what bands you intend to listen to.
>
> Terminating resistors are only needed for antennas such as
> rhombics, Beverages (sp?),  and the like, not for a folded-dipole.
>
> Ken Gordon W7EKB
> _______________________________________________
>

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