Pete,
Please explain WHY you would think a 24 ft boom TH7 would have
a higher F/B than a 14 ft A3? It is a well known fact that 2L
parasitic Yagi's have relatively LOW F/B (<15 dB, often <10 dB).
If you look at the 3L Yagi designs (Chapter 2 in the W2PV Yagi
Design Book), you will note that F/B peaks when the boom length
is around 0.25 WL which comes to 18 ft on 20M, 12 ft on 15M,
and 9 ft on 10M. The SHORT BOOM 3L tribanders MAY have
higher F/B than their Big Brothers, depending on how they are tuned
and indeed have higher potential F/B than some longer boom 3L
Yagi's.
Tom N4KG
On Mon, 02 Dec 2002 Pete Smith <n4zr@contesting.com> writes:
> At 08:51 PM 12/1/02 -0500, KI9A@aol.com wrote:
> >In a message dated 12/1/02 5:40:58 PM Central Standard Time,
> K7LXC@aol.com
> >writes:
> >
> >
> > > You need a copy of the N0AX and K7LXC Tribander Comparison
> Report
> > > available from <A
> > HREF="http://www.championradio.com/";>www.championradio.com
> > > </A>
> >
> >Nice....a list that acts as a sales pitch instead of real info.....
> >
>
> I think this is kind of a bum rap, considering that Steve spends a
> lot of
> his time (and some of his money) keeping this list up and running.
> It's a
> tremendous resource, and I don't think he's overdone the
> "commercials" in
> proportion to the amount of list traffic. Stick around and see if
> you
> don't agree.
>
> On the report itself, I complained a little about the methodology
> when it
> came out, but the authors are quite up front about the limitations
> of their
> method. I think I would be inclined to trust it in relative terms
> (one
> tested antenna vs another).
>
> Those old Cushcraft gain numbers are definitely not to be believed.
> A few
> years ago, I modeled the C-3 versus a TH7DXX in NEC-2, using an
> idealized
> TH-7 model (no traps) and a C-3 model derived from the actual
> hardware. The C-3's forward gain was within .5 to 1.5 dB of the
> TH-7,
> depending on band. As Dick says, the C-3's F/B is considerably less
> than
> the TH-7's (with its additional elements and 24-foot boom). I would
> not
> expect it to be much less than an A-3, though.
>
> 73, Pete N4ZR
> Sometimes a tower is just a tower
>
>
>
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