On Fri, 30 Mar 2007 09:59:04 -0400, Buck
wrote:

On Fri, 30 Mar 2007 12:37:53 GMT, Cecil Moore
wrote:

Buck wrote:
Ok, I have seen that. It isn't that the antenna isn't tuned, it is
tuned with the twin-lead instead of a conventional tuner.

It has a tuned feeder instead of a conventional tuner.

I am curious to know, have you measured the power both at the antenna
and the radio to see what loss there might be? I wouldn't expect very
much, personally.

On a G5RV, it is taught that the twin-feedline is also part of the
antenna itself, is that true in your model as well?

thanks
Buck


Please refer to my new thread. Thanks

--
73 for now
Buck, N4PGW
www.lumpuckeroo.com

After reading your webpage more closely......

On Fri, 30 Mar 2007 10:42:26 -0400, Buck
wrote:


http://www.w5dxp.com/notuner.htm

I see you use 450 ohm ladder line (or window-line as some call it.) I
am wondering if the concept will also work with other impedance
feedline such as 600, 300 or 75 ohm twin-line or even possibly with
coax. ****

Does the feedline act as part of the antenna? I am sure it will, at
least up to the 'no-tuner' if it acts like a G5RV, but do you know if
the feedline radiates?

That answer would be 'no'. I see that the purpose of the feedline
length is to get the maximum current at the center point of the
dipole.




I see a couple of the frequencies are above 1.5:1, which I am not
comfortable going over with solid state rigs. Do you think that could
be fine-tuned with the addition of a 1/2 foot section or maybe with
that and a 1/4 foot section?

Based on the fact that the antenna is being fed maximum current at the
center, I would guess that this should work.





Buck
N4PGW

--
73 for now
Buck, N4PGW
www.lumpuckeroo.com

Buck wrote:
I see you use 450 ohm ladder line (or window-line as some call it.) I
am wondering if the concept will also work with other impedance
feedline such as 600, 300 or 75 ohm twin-line or even possibly with
coax. ****

Might as well go into some detail here. The feedpoint impedances
encountered in a 130 foot dipole may range from ~50 ohms to
~5000 ohms. In order to limit the maximum SWR the feedline Z0
should be ~SQRT(50)(5000) = ~500 ohms. Thus the choice of 450
ohm line. Given that the feedpoint impedances may range from
~50 to ~5000 ohms, here are the maximum SWRs that may be
expected for the different Z0s. Since the antenna system
is fed at a current maximum point, I have included the
impedance at the current maximum point which needs to be
between 25 ohms and 100 ohms in order to avoid foldback.

Z0 SWRmax Imax Impedance
600 12:1 50 ohms
450 11:1 41 ohms
300 17:1 18 ohms
75 67:1 1 ohm
50 100:1 0.5 ohms

It should be readily apparent why coax is a no-no for this
antenna system. Even 300 ohm twinlead will result in a
50 ohm SWR of 50/18 = 2.8:1, high enough to cause foldback.

I am interested in making one, but I only have 300 ohm.

Let's take 40m as an example. The dipole is one wavelength
and will have a 300 ohm SWR of 16:1 on 7.2 MHz according
to EZNEC. 300/16 = 18.75 ohms at the current maximum
point resulting in a 50 ohm SWR of 2.7:1 enough to cause
foldback without an antenna tuner. Such is life.

I do use 300 ohm line on my 20m rotatable dipole and it
does work 20m-10m but there are probably 10m frequencies
where the 50 SWR is too high.

Does the feedline act as part of the antenna? I am sure it will, at
least up to the 'no-tuner' if it acts like a G5RV, but do you know if
the feedline radiates?

I monitor the current balance in my feedlines. They are
so well balanced that there is no hint of common-mode
current on the coax side of my current/choke/balun.
Balanced currents radiate a negligible amount.

Have you measured the power at both sides of the 'no-tuner' to see
what loss there might be? I doubt there would be much considering
that you are using window-line.

No I haven't measured the losses. I have trusted Owen's
transmission line calculator for that data.

I see a couple of the frequencies are above 1.5:1, which I am not
comfortable going over with solid state rigs. Do you think that could
be fine-tuned with the addition of a 1/2 foot section or maybe with
that and a 1/4 foot section?

The disadvantage of this method is that it lacks one dimension
of tuning necessary to achieve 50 ohms. Unless you do one more
impedance transformation, no amount of fine-tuning the ladder-
line length will get any closer.

Would it be safe to assume that I can create a mono-band dipole, maybe
even multi-band - if I am lucky, by fixing the length of the dipole
and the feedline such that the increment gives me the imax at the
balun for the desired frequency(s)?

One such example is at: http://www.w5dxp.com/HEDZ.htm
This antenna works on 75m and 40m with a fixed length of ladder-
line.

Finally, you have a 1:1 choke at the feeder. I see that the better
quality coax, the more toroids are needed. Would there be a problem
with using a foot of RG-58 with the fewer toroids and then connect
that to the high-quality line?

Just use RG-58 entirely unless you are running high power.

Does the 'no-tuner' feedline need to be spread out. I see from the
photo that your 16 foot section is one large loop, I figure it must be
close to a four-foot diameter loop.

I have my 16 foot loop coiled in a 4 turn spiral around a piece
of fiberglas fishing pole.

Is there a similar system that would work with a vertical?

Verticals are not usually fed with ladder-line so probably
more trouble than it is worth.
--
73, Cecil, w5dxp.com

Yes, and it should hurt , because we are using
English and text to show something that
s/b shown in pictures .

Im E.E. , KC7CC, and more..

i can simply show you with pictures.
It will be instantly clear .

---BTW------
Im doin ARM computers , I will give a free
Op System . It will NOT use English nor
ASCII . No arbitrary definitions ...
No C++ , No Linux , No M$ , no
more "Free Lunch" .....

We use Coax for its isolation from nearby
absorbers .. parallel line is much lower loss
but absorbs into other objects close .
We do not use caps , but stubs .
But they are tuned ( freq dependent ) .
The fast way to follow this , is to draw
a picture , then edit it as you go .
English will only get you a college degree
and a free lunch ( Liberals ) .


__________________________________


Now my head *really* hurts! This is a VERY confusing subject, to
say the least. (And I also thought antenna tuners actually had a
*loss* due to their limited Q...I think I'm going to change careers
now and just become a pet groomer; or perhaps simply give up
completely and work at Radio Shack).

-Bill

Bob Myers wrote:
"Cecil Moore" wrote in message
... while at the same time this overall trend results in
a very localized DECREASE in entropy (increase in order;
in this case, the evolution of complex systems on Earth).

How about considering the localized W5DXP system? :-)
--
73, Cecil http://www.w5dxp.com

"Dave Oldridge" wrote in message
9...
If the lossless transmission line (obviously no such animal exists) were
tuned with a lossless tuner, then VSWR would not matter at all.

Dave, I'm pretty sure I know what you mean here, but it should
be noted that this isn't entirely true. The line would have to have a
couple
of other characteristics besides being simply "lossless" for VSWR
not to matter at all.

The problem, of course, is that a VSWR of other than 1:1 implies
(by definition!) that the voltages and currents along the length of
the line are not constant; there are cyclic variations in each, with
maxima and minima located at half-wavelength intervals (that's
the whole "standing wave" thing in the first place, right?).
Particularly in high-power situations, it is possible for the maxima
to exceed the ratings of the source or of the line itself.

Bob M. (KC0EW)

"Cecil Moore" wrote in message
. net...
bw wrote:
Entropy increases

Seems to me that evolution violates that principle.

Not at all; "entropy increases" is with respect to the total
entropy of a closed system. But in the case of "evolution,"
the only closed system which makes any sense to consider
is the entire solar system, or at the very least the Sun-Earth
system. It is entirely pemissible for an overall increase in entropy
to occur (i.e., the Sun slowly loses energy to the rest of the
universe) while at the same time this overall trend results in
a very localized DECREASE in entropy (increase in order;
in this case, the evolution of complex systems on Earth).

Bob M.

--
73, Cecil http://www.w5dxp.com

Bill ...

I would bet that most of the "confustion" comes from the conditions people
put on their answers to the question.

Some postulate a "tuner" between generator and load.

Some postulate a specific internal impedance of the generator.

Some postulate a specific length of feeder line (either lossless or
resistive, which is another parameter in and of itself).

Some postulate lots of other stuff, almost all of which is valid in the
context of their answer.

What exactly do we mean when we say that we have a "100 watt transmitter"?
What we are actually saying is that the transmitter will cause a resistor of
a specific value to dissipate 100 watts of energy when tied to the
transmitter output port and the transmitter keyed. Let's not muddy the
waters up by asking if we are talking about peak power, PE power, average
power, or whatnot. Let's just assume an unmodulated carrier putting out a
constant power into the resistor that gets just as hot as when 100 dc watts
(E*I) is pumped into it from a battery.

What value resistor? Whatever the designer/engineer/manufacturer specifies.
32 ohms? Sure. 50 ohms? No problem. 300 ohms? Certainly. Any competent
engineer can give you a specified power into a specified resistive load.

The crux of the question becomes, "What happens if my transmitter is
specified into a 50 ohm resistor and I put a 100 ohm resistor as the load?
How much "loss" do I get (or another way of asking that same question is how
much power is dissipated in the 100 ohm resistor)?"

The answer is that it is impossible to tell without making the measurement.
That may seem like a "wiggle" answer, but the truth of it is that the output
stage design of the transmitter will dictate how it handles a "VSWR load".
In some output stages, the output voltage will increase to the point of
nearly driving 100 watts into the 2:1 VSWR resistor. Some will shut
themselves down with a protection circuit. Some will go into parasitic
oscillation. Some will fry the output devices.

Now increase the magnitude (and probably the sign also) of the problem to
toss in a complex impedance instead of a resistive load and the confusion
factor goes up rapidly. What DOES that output stage do when the load has an
inductive component? Or a capacitive component? And both a resistive
component and an imaginary component that varies with frequency?

The simple answer to your question outside the "laboratory environment"
where everything is nicely matched and the internal impedances are set "just
so" is that there IS NO SINGLE RIGHT ANSWER to this simple question.

And that is most probably the cause of your confusion.

Jim



"billcalley" wrote in message
oups.com...


But here again, I'm probably not seeing the
entire picture here. What am I missing??

Confused!

-Bill

"Bob Myers" wrote in news:MmdPh.1809
:


"Dave Oldridge" wrote in message
9...
If the lossless transmission line (obviously no such animal exists)
were
tuned with a lossless tuner, then VSWR would not matter at all.

Dave, I'm pretty sure I know what you mean here, but it should
be noted that this isn't entirely true. The line would have to have a
couple
of other characteristics besides being simply "lossless" for VSWR
not to matter at all.

Not if there's a lossless tuner.

The problem, of course, is that a VSWR of other than 1:1 implies
(by definition!) that the voltages and currents along the length of
the line are not constant; there are cyclic variations in each, with
maxima and minima located at half-wavelength intervals (that's
the whole "standing wave" thing in the first place, right?).
Particularly in high-power situations, it is possible for the maxima
to exceed the ratings of the source or of the line itself.

In which case it's not truly "lossless" (and after breakdown becomes VERY
lossy).



--
Dave Oldridge+
ICQ 1800667

Cecil Moore wrote:
bw wrote:

Entropy increases


Seems to me that evolution violates that principle.


Duh, life always violates it locally, but makes the sum total of entropy
higer than it would have been. You aren't the idiot you appear, I hope.

tom
K0TAR