Yes, most folks look at the terminating resistor and immediately think of a dummy load.
What most fail to realize is the total amount of loss of tuners and coax. The rule is that matching impedances causes the most power transfer to occur. There was an excellent article in QST showing the different antenna/tuner configurations and the amount of loss. Most of the time much greater than loss in this system. Thanks for taking the time to read up on it. All antennas are a compromise. 73! Bill Crowell Pearland, TX From: BVARC <[email protected]> on behalf of Jonathan Guthrie via BVARC <[email protected]> Reply-To: BRAZOS VALLEY AMATEUR RADIO CLUB <[email protected]> Date: Tuesday, August 25, 2015 at 1:30 PM To: BRAZOS VALLEY AMATEUR RADIO CLUB <[email protected]> Cc: Jonathan Guthrie <[email protected]> Subject: Re: [BVARC] TTFD Antennas - N4HPG I would be concerned that the terminating resistor would be consuming most of the power on the lower frequencies. The article talks about the small amount change in SWR over a 5:1 frequency range, but SWR by itself tells you nothing about an antenna's performance, and the article says that the power lost to the terminator is an open question. On 8/25/2015 10:50 AM, Bill Crowell via BVARC wrote: > > Howdy All, > > > > > I was listening to the net last night and John, K5IZO, was encouraging folks > to get on 75m. Yay! > > > > > I¹ve been working on a project for a number of months. Some of you know that I > use a TTFD antenna. TTFD or T2FD. It stands for Tilted Terminated Folded > Dipole. This antenna is not widely known because it¹s not featured in any ARRL > publications at least since 1949. There are some good reference sources such > as the RSGB wire antenna book. There are also some detractors that don¹t > understand the theory of operation. > > > > > Here¹s a link to the original article: > > > > > http://www.scribd.com/doc/42625655/An-Experimental-All-Band-Nondirectional-Tra > nsmitting-Antenna-T2FD > > > > > You¹ll notice that the antenna is a 600-ohm design. It is a balanced antenna. > > > > > Perhaps Rick Hiller and I should give a presentation on it. > > > > > I¹ve been using the B&W version for a number of years, but want to run higher > power. That means a better matching transformer for 50:600 ohms and also a > more robust terminating resistor. The antenna works well from 75 to 10m with > 1.5:1 SWR or better on all bands. This is because it¹s a traveling wave > antenna. Mismatch is soaked up by the terminating resistor. No tuner is > needed. The antenna works from the lowest frequency up. That means a 80m > antenna works on all bands from 80-10m. A shorter antenna works from 40-10m. > B&W says 6m, but I¹ve not tested my high-power balun for 6m yet. I never > promise what I haven¹t tested. > > > > > I¹m hoping to bring a completed unit of the high-power design to the club > meeting on 9/10 so y¹all can look at it. I should probably fire up N4HPG.com > website and post some pictures. > > > > > If you can have only 1 antenna, this is the one to have. I like to hunt DX and > change bands without having to tune. Get as long an antenna as possible! > > > > > > > > > > > The folks at B&W now want $825 for their version. That¹s insane! But they sell > mostly to military and governments. > > > > > I¹m making one antenna for myself that will be all my build. I¹m also making a > heavy-duty one for N5XZ. Being gainfully unemployed and having a workshop, I¹m > testing the waters to see if others might want one. > > > > > When we put up an antenna, the neighbors usually notice. I¹m making my version > with 14awg white MTW wire and clear, acrylic spacers for the antenna and the > ladder line. The balun box mounts on the wall and transforms the 50 ohm > unbalanced to 600 ohm balanced. It¹s a 6x6x4 box because there are 4 toroids. > > > > > Based upon present materials, I believe I can produce the standard antenna > 1kW for normal operation for $349. I¹m still working on the N5XZ 1.5kW RTTY > Contesting version that will be a bit more. > > > > > If you want to build your own, feel free to steal my design! > > > > > For those who would like a built and tested unit, let me know. I¹m trying to > decide if I should get into the antenna business. > > > > > 73! > > > > > N4HPG > > > > > > Bill Crowell > > Pearland, TX > > > > > _______________________________________________ > BVARC mailing list > [email protected]http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org > -- Jonathan Guthrie KA8KPN _______________________________________________ BVARC mailing list [email protected] http://mail.bvarc.org/mailman/listinfo/bvarc_bvarc.org
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