Re: B&W Folded Dipole over an Armory

Posted by k6dgw on Aug 13, 2017; 10:15pm
URL: http://elecraft.85.s1.nabble.com/Is-it-my-KX3-antenna-or-is-it-lousy-band-condx-tp7633243p7633368.html

Not sure where he got the "chief use" from, all the T2FD's I've ever
seen [and can remember] were transmit/receive, usually using KWM-2A's.  
But, yes, the amount of power dissipated in the termination depends on
the frequency vs the overall length. We used them in the 60's in SE Asia
and our maint depot guys would adjust the length so that the lowest loss
areas were around our assigned frequencies which were generally in the
2.5 to 10 MHz range, usually two of them [day/night], sometimes a third.

Same situation with the large V-beams and Rhombics in commercial
servicewhich accounts for the land area occupied by a commercial MF/HF
TX site: One V-beam does not fit all frequencies.

TheT2FD's sure beat a fan dipole since, once on the ground, we had way
more important things to do than adjust antennas. [:-)

73,

Fred ("Skip") K6DGW
Sparks NV USA
Washoe County DM09dn

On 8/13/2017 2:41 PM, Roger D Johnson wrote:

> Cebik, W4RNL, modeled two versions of the T2FT. One 165ft long and the
> other 100ft.
> Here is what he said about these antennas:
>
> Terminator Resistor Losses
> Although transmitting uses have been made of the T2FD, its chief use
> appears to be as a short wave reception antenna. In this application,
> the excess available receiver gain can largely make up for losses
> incurred in the terminating resistor.
>
> The losses in the terminating resistor are considerable, ranging from
> nearly half power to amounts in excess of 90% of the available RF
> power. The pattern of losses is not a simple smooth curve, but varies
> throughout the operating range of the antenna. The following graph
> plots the losses in terms of dB. For reference, a 3 dB power loss
> represents half the power being dissipated in the resistor. Higher
> values indicate more of the power being dissipated rather than being
> radiated (or transferred to the receiver).
>
> 73, Roger

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