Steve's recent post which included the gains of the TH7DX made me curious.
I found the original project book on the TH7, dated May 21, 1981. My gain
measurements on the TH7, dated Sep 4, 1981 show the following gains:
14.000 MHz 5.0 dBd
14.175 MHz 5.0 dBd
14.350 MHz 5.2 dBd
21.000 MHz 5.8 dBd
21.200 MHz 6.1 dBd
21.450 MHz 5.7 dBd
28.000 MHz 3.8 dBd
28.800 MHz 5.5 dBd
29.700 MHz 7.0 dBd
These measurements were taken on our rotating pole as seen on the cover of
QST Feb 1985. A transmitter at the south end of our property (aprox 2500
feet distance) generated the signal. The receiver was the same as used for
radiation patterns. The meter was calibrated against a calibrated step
attenuator. The TH7 was replaced with a resonant dipole for each of the
three bands, and a monitor antenna was also used to ensure a stable signal
during and between the tests. The measurement uncertainty in these
measurements is likely on the order of 0.5 - 1.0 dB, but the numbers shown
above are my original measurements on the first prototype. Better accuracy
(on the order of 0.5 dB) could be obtained by using a directive gain
reference such as an NBS yagi, and by constructing an ideal HF range free
of reflections.
As was pointed out earlier, an amplifier can produce more "gain" than any
single antenna. However, the antenna also helps with the received signal,
both in gain and discrimination (F/B, F/S and takeoff angle).
73 Roger WB0DGF
Telex Communications, Inc.
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