[Towertalk] Fw: TH7DX Gain Measurements / Improvements

[n4kg@juno.com]

I have received several requests for the revised
10M dimensions to improve performance in the
CW / SSB portion of 10M on the TH7 so I decided
to simply post them on TowerTalk (in addition to
DX-News where the original question originated).

Tom  N4KG

--------- Forwarded message ----------
From: N4KG@juno.com
To: TOWERTALK@CONTESTING.COM
Date: Fri, 1 Feb 2002 
Subject: Fw: TH7DX  Gain Measurements / Improvements

HyGain's desire to make the TH7 cover the *entire* 10M band
resulted in a 3.2 dB gain slope from 28.0 to 29.7; NOT a good
plan for most users (DXers and contesters).  Roger Cox has
posted a better set of dimensions for DXers as shown below.

Tom  N4KG

--------- Forwarded message ----------
From: Roger.Cox@telex.com
To: n4kg@juno.com
Date: Tue, 19 May 1998 
Subject: TH7DX

>From: n4kg@juno.com (T A RUSSELL)

>Roger

>Do you have measurements for the TH7 which will optimize 10M gain
>between 28.0 and 29.0 MHz?

>I believe the vast majority of TH7 users would prefer to have better
gain
>in the bottom 1 MHz of ten meters and to let the high end performance
>slide.

Tom,

>From looking at my original design notes on the TH7DX, it looks like the
following changes should help performance on the lower part of 10 meters:

Change R2-3 from 38.5 to 39.5 inches
Change RDE-2 to 33 inches (DX setting)
Change FDE-2 to 42 inches (DX setting)
Change D2 from 43.5 to 44.5 inches
Change D3-2 from 27.5 to 28.5 inches
Change D3-3 from 74.5 to 74 inches (to compensate for the 10m change)

All of these changes have NOT been tested together, however most have
been
tried individually.
Lengthening just the reflector shows no change.
Lengthening D2 by 1" lowers the resonance approx 100-150 KHz.
Lengthening D3-2 by 2" (to 29.5") made patterns worse above 28.5 MHz, no
change below.
The DX setting of the DE's changes the resonance only (by 250 KHz).

73 Roger WB0DGF

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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