On Tue, 21 Nov 2006 22:10:19 -0800, Richard Clark wrote:

By turns, you've painted yourself into a corner when we add up this
wish list. Worse yet is the complaint you anticipate with:
If I can't keep the efficiency above 50 percent across the range, then it
probably isn't going to be worth doing.

When you lead with your chin with:
It cannot use any sort of antenna tuner
this simply breaks the camel's back. Also, come to terms with there
is also no such thing as a miracle BalUn.

Good morning, Richard.

I was hoping to mitigate all of that by restricting the frequency range.
I'm not asking for 1.8-30 or even 4-30, but 4-9.

Can a T2FD antenna not be made 50 percent efficient across that restricted
frequency range?

The 50 percent efficiency floor is somewhat arbitrary but is driven by the
fact that some of the users of this antenna are going to be using power
levels as low as 5 watts. That's hard enough to do with a cut NVIS
dipole, without throwing an inefficient antenna into the mix.

The inability to use a tuner is driven by the fact that eventually, these
antennas are going to need to be usable with ALE radios. I don't know
very much about ALE (yet) but I have a hard time imagining an autotuner
that is consistently fast enough to use with ALE. Also, the users of these
antennas are, like me, going to be paying for them out of their pockets.
Few if any of the potential users that I know of today can afford to buy
an autotuner. I know I can't.

If it can't be done, then it can't be done. I'm realistic enough to
accept that and move on to something else, or drop the idea. It just
seems to me that within the limited frequency range, something like that
should be possible with the right choice of design parameters.

On Wed, 22 Nov 2006 07:10:55 -0500, "C. J. Clegg"
wrote:

I was hoping to mitigate all of that by restricting the frequency range.
I'm not asking for 1.8-30 or even 4-30, but 4-9.

Hi OM,

That has been evident from the beginning. Still and all:
The 50 percent efficiency floor is somewhat arbitrary
Exactly. It is just such arbitrariness along with competing,
conflicting restrictions that leads to self-defined failure tacitly
accepted with:
If it can't be done, then it can't be done.
However, it has been done, and without the unnecessary complications
of forcing ANY design to span an octave without a tuner. Hoping that
a resistor will solve this is dope-slapped with the expectation of
efficiency.

some of the users of this antenna are going to be using power
levels as low as 5 watts
So what is all this angst about efficiency? Pour 100W into any hank
of wire and you will achieve at least that. Or do you mean that the
design you are looking for will be used as a model for others? If
that is the case, more the pity that the requirement of having a $25
tuner is an unreasonable expectation of Amateur radio operators. I
cannot imagine they will spend less on those resistors....

73's
Richard Clark, KB7QHC

On Wed, 22 Nov 2006 12:37:20 -0800, Richard Clark wrote:

So what is all this angst about efficiency? Pour 100W into any hank
of wire and you will achieve at least that. Or do you mean that the
design you are looking for will be used as a model for others?

Good afternoon, Richard.

Actually, what I mean is that some, including me, will be using 5-watt
radios (Yaesu FT-817). If the option of pouring 100W into any hank of
wire was available to all, the issue wouldn't be critical. It's not,
so it is. :-)

more the pity that the requirement of having a $25
tuner is an unreasonable expectation

Remember the ALE requirement. I am only just now becoming convinced that
some autotuners might work for ALE. I'm quite certain manual tuners won't.

In article ,
C. J. Clegg wrote:

Actually, what I mean is that some, including me, will be using 5-watt
radios (Yaesu FT-817). If the option of pouring 100W into any hank of
wire was available to all, the issue wouldn't be critical. It's not,
so it is. :-)

There's another approach to the antenna that you might want to
consider, _if_ the ALE ranges are limited to a few (say, no more than
four or five) and aren't too wide (say, no more than perhaps 5% of the
center frequency).

If your usage pattern fits this model, then you could construct a
multi-wire "fan" dipole array... simply a set of individual wire
half-wavelength dipoles, each cut for the center frequency of a given
ALE range, spread apart physically, and fed from a single coax at a
single feedpoint. They can be spread vertically (e.g. hang the
longest one as a flat-top from a convenient set of trees, suspend the
next-shortest beneath it on 6" spreaders, hang the next-shortest on
another set of spreaders, etc.) or horizontally (run one north/south,
another east/west, etc.).

There will be some amount of coupling/loading between them, so you'll
need to trim them for lowest SWR once they're installed, and you may
find the SWR bandwidth less than you'd get from individual dipoles.
Coupling/loading is greater for the vertically-stacked case, and less
for a star-like horizontal pattern (which takes more space and more
trees or etc., of course).

The nice thing about this approach, if it's suitable for your needs,
is that the losses are quite low. The wire which is resonant on the
band in question loads up and radiates, and the other wires (which
will typically have high, reactive impedances) accept very little
current. No lossy termination resistor is needed.

I've been using a three-wire fan dipole (5" vertical spacing) cut for
40/20/10 for several years, with very satisfactory results.

This approach won't give you continuous coverage of your 4:9 range...
unfortunately I can't suggest any which would, which don't require an
agile tuner/transmatch and which don't introduce high losses in some
portions of the band.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

On Wed, 22 Nov 2006 15:56:45 -0500, "C. J. Clegg"
wrote:

more the pity that the requirement of having a $25
tuner is an unreasonable expectation

Remember the ALE requirement. I am only just now becoming convinced that
some autotuners might work for ALE.

I seriously doubt that. What you are describing is a sacrifice in
Link Quality for the sake of not using something like a fan dipole
which would immediately satisfy every requirement and fulfill mission.
How this is justified with
multiple-legged dipole with legs cut
for different frequencies (well, I probably could, but it would be
impractical).
forces a new meaning to the word impractical. Perhaps you would care
to elaborate how the simplicity of two extra wires has been trumped.

73's
Richard Clark, KB7QHC

On Wed, 22 Nov 2006 15:15:35 -0800, Richard Clark wrote:

Perhaps you would care
to elaborate how the simplicity of two extra wires has been trumped.

I'll try, though from the tone of your message it sounds like your mind is
made up. :-)

We will be operating on many different frequencies across the range of 4
to 9. I don't even know (yet) how many different frequencies will be in
use (they won't tell me).

So I can envision many pairs of dipole elements, each cut for a certain
frequency in the range, and laid out like the spokes of a wheel.

I have plenty of land here but I don't have ready supports for that kind
of an array.

That's what I mean by "impractical".

I've learned a lot from you guys the last few days, though, and maybe
something like that isn't so impractical ... I'll have to experiment.
Perhaps an array of inverted vees on a single feedline...

On Wed, 22 Nov 2006 18:59:31 -0500, "C. J. Clegg"
wrote:

On Wed, 22 Nov 2006 15:15:35 -0800, Richard Clark wrote:

Perhaps you would care
to elaborate how the simplicity of two extra wires has been trumped.

I'll try, though from the tone of your message it sounds like your mind is
made up. :-)

My mind is made up? I've repeatedly wondered why you have approached
this with a defeatist attitude.

We will be operating on many different frequencies across the range of 4
to 9.

Again, this has been apparent from the beginning.

I don't even know (yet) how many different frequencies will be in
use (they won't tell me).

That doesn't matter all that much, except to anticipate failure.

So I can envision many pairs of dipole elements, each cut for a certain
frequency in the range, and laid out like the spokes of a wheel.

If you re-read my posting, I've done nothing more complex than to add
TWO more wires. ALE may easily jump between 200 frequencies, but
there is absolutely nothing about that which demands a resonant
frequency for each of them.

I have plenty of land here but I don't have ready supports for that kind
of an array.

That's what I mean by "impractical".

Then the solution is not impractical by any definition, you are simply
over embroidering the problem with a slavish interpretation of
necessity. One pair of wires cut to a low end, one pair of wires to a
high end, both pairs fed at the same point. It may take as many as
four pairs (I doubt it), but to abstract this wildly to 200 goes
beyond the pale when a skeleton biconical could easily accomplish this
with flat response (over a much larger bandwidth) with only 16 pairs
of equal sized wires.

This cage monopole:
http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm
is flat over 5 Ham bands.

This discone:
http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm
operates flat over more than two octaves of bandwidth. With scaling,
I can count at least 55 discrete frequencies that would fall into the
2:1 mismatch region - and this say nothing of those frequencies
between them, nor of their end points which could be made to span 4 to
9 MHz.

Yes, a lot of wire, but use less wire for a rougher approximation. If
you are looking at an arbitrary 50% efficiency, a 5:1 circle
encompasses a lot more points for less wire.

73's
Richard Clark, KB7QHC

On Wed, 22 Nov 2006 22:35:39 -0800, Richard Clark wrote:

This cage monopole:
http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm
is flat over 5 Ham bands.

This discone:
http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm
operates flat over more than two octaves of bandwidth.

Thanks. I have said earlier that I considered a discone (I also
considered a cage monopole but didn't mention it here) but those are
vertically polarized antennas and I'm pretty sure they're not good for
NVIS. Am I wrong?

I am also considering an array of inverted vees cut for selected
frequencies within the range, Something like that is likely to be much
better for NVIS.

Sorry if I seemed to fit all those names you called me... you say I'm
defeatist, one or two others here say I'm too optimistic. Can't please
everybody I guess. For the most part I do very much appreciate all the
help everyone has offered here, in a thread that has grown way beyond
anything I envisioned when I started it ... you guys are great. :-)