[Elecraft] Elecraft Digest, Vol 160, Issue 18 - More on the TTFD

[Joel Hallas]

I agree with most of the statements about the TTFD, or B&W FD, if you
prefer. While not as efficient as some, it meets a number of particular
needs, especially that it has a similar directional pattern over a 5:1
frequency range -- especially useful for point-to-point links using multiple
HF frequencies, either manually or by ALE. 

I did an assessment of this antenna and wrote a QST article on it that I
recommend for those interested. The one point I disagree with is the
statement that the terminating resistor dissipates half the power. The power
dissipated is a function of frequency and, while it is not far from 3 dB at
the high end of the frequency range, it absorbs much more at the low end --
about 90%! Not only is that 10 dB less signal on transmit, but the resistor
power rating needs to be 90% of the transmit output, if high duty-cycle
modes are used. Note that it is not as big a problem on receive, since the
receive S/N on the lower bands is sufficiently atmospheric noise limited,
that the receive S/N is not greatly impacted, even though the s-meter will
read lower by 10 dB. 

My article is available to ARRL members on the QST print archive on the ARRL
website. 

Sep 2010 - QST (Pg. 51)
A Close Look at the Terminated Folded Dipole Antenna

Regards, Joel Hallas, W1ZR
Westport, CT