--------- Forwarded message ---------- From: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Date: Fri, 1 Feb 2002 08:41:56 -0600 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: [EMAIL PROTECTED] To: [EMAIL PROTECTED] Date: Tue, 19 May 1998 Subject: TH7DX >From: [EMAIL PROTECTED] (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. ________________________________________________________________ GET INTERNET ACCESS FROM JUNO! Juno offers FREE or PREMIUM Internet access for less! Join Juno today! For your FREE software, visit: http://dl.www.juno.com/get/web/. ------------------------------------------------------- Subscribe/unsubscribe, feedback, FAQ, problems, etc DX-NEWS http://njdxa.org/dx-news DX-CHAT: http://njdxa.org/dx-chat To post a message, DX NEWS items only, [EMAIL PROTECTED] Archives http://www.mail-archive.com/dx-news%40pro-usa.net -------------------------------------------------------