On Wed, 17 Dec 2003 07:58:25 -0700, Wes Stewart
wrote:

On Wed, 17 Dec 2003 06:44:06 GMT, Roger Halstead
wrote:

|On Fri, 12 Dec 2003 22:32:07 -0700, Wes Stewart
|wrote:
|
|On Sat, 13 Dec 2003 00:06:16 GMT, Roger Halstead
wrote:
|
||
||Every HF antenna here will go 1:1 "some where" ...
|
|Not so.
|
|I'd like to know how you can say that?

I can say it because it's true.
|
|Have you measured all my antennas?

I think an important word has been missed. :-))


No, but I've measured some of mine. Why just yesterday, I was out
measuring my vertical that started out as a Cushcraft AV-80. I'm
looking to use it on 40 meters. At resonance, at about 5.43 MHz, the
base impedance was 38.5 +j0. That's a 1.3:1 SWR.

What do your antennas have to do with mine?


And BTW that's a datum taken using a method described in HP
Application Note 77-3, "Measurement of Complex Impedance 1-1000 MHz."

I understand that.

You mistakenly believe that because an antenna *has a resonance* at
some frequency, its SWR is *1:1*. Not so, as shown above.

I don't think I used the word resonance any where in my post although
at the end I did refer to the antennas being cut according to formula
and the 1:1 point not being where the formula said it should.


I have shown at least *one* example where you are wrong when you say
*every antenna*.

Ummm...no you haven't.

Nor did I say every antenna. I said "Every HF antenna here",
paraphrased, "Every HF antenna at this location does show a 1:1 some
where in the band for which it's used".

I am speaking solely about the HF antennas at this location and was
careful to point that out. All have been checked with a Bird 43 watt
meter and each one has a point where it shows no reflected power.
Their heights and angles are such that they are non reactive at those
points, or at least as near as I can tell on a Palomar bridge and are
so close to 50 ohms I can't measure the difference.

So as the question was asked and the thread titled. "Is it possible to
have a 1:1 SWR", the answer is yes. If I can do it, so can someone
else. I didn't give any probabilities, but the odds are relatively
slim that any one throwing up a wire is going to be lucky and find it
1:1 with J=0. However if some one reads 1:1 on their bridge it
doesn't mean the bridge is necessarily bad.
I should also point out that the wire antennas here are relatively
high at an 45 degrees to horizontal. Probably not a typical
installation.


| You are welcome to come over and
|check them out.

No thanks. The weather here is much nicer for doing antenna work.

Hey, it's nicer than when I put up the tribander. I think the chill
factor was 4 degrees that day.

Current conditions:
Temperature 29 °F / -2 °C
Windchill 17 °F / -8 °C
Humidity 69%
Dew Point 20 °F / -7 °C
Wind WNW at 17 mph / 27.4 km/h
Wind Gust -
Pressure 29.70 in / 1005 hPa (Steady)
Conditions Overcast
Visibility 10 miles / 16 kilometers
Clouds
(Above Ground Level) (FEW) : 2700 ft / 824 m
Overcast (OVC) : 6500 ft / 1983 m

It's a veritable heat wave. :-)) Although we did have nearly two
inches of snow today.



| Every one "according to my meter which is a Bird"
|reaches 1:1 some where in the desired band. It may not be exactly the
|frequency the formula predicted, but it'll be relatively close.

They are cut to formula plus a tad. Shortening equal amounts did not
put the 1:1 point at the same frequency on each of the 75 meter
antennas. However both do reach 1:1 with j=0 or as near as I can
measure. The Palomar bridge isn't exactly a precision instrument.

OTOH the AV-640 Hy-Gain multi band vertical reaches 1:1 (50 ohms and
J=0) at some point on every band 40 through 6. However I'm convinced
it's a perfectly matched dummy load on 20.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com
Return address modified due to dumb virus checkers
|
|Roger Halstead (K8RI & ARRL life member)
|(N833R, S# CD-2 Worlds oldest Debonair?)
|www.rogerhalstead.com
|Return address modified due to dumb virus checkers
|

On Wed, 17 Dec 2003 09:18:30 -0600, Cecil Moore
wrote:

Roger Halstead wrote:
Wes Stewart wrote:

On Sat, 13 Dec 2003 00:06:16 GMT, Roger Halstead
|Every HF antenna here will go 1:1 "some where" ...

Not so.

I'd like to know how you can say that?
Have you measured all my antennas?

Basic problem was the lack of a defined boundary for
"here". I figured it meant, "here in the US".

Here as in http://www.rogerhalstead.com/ham_files/tower.htm which is
about 5 miles west of down town Midland MI. IE, my own installation.
:-))

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair?)
www.rogerhalstead.com
Return address modified due to dumb virus checkers

an antenna has an impedence at the frequency it is being used at, and an
impedence at its resonant frequency. If either of these impedences happen to be
50 ohms and the coax being used is 50 ohms, and the transciever is working at
50 ohms, then the swr is 1:1, and the swr is on the transmission line, not on
the antenna.

The antenna does not have to have an impedence of 50 ohms at either the
frequency being used at or at its resonant frequency, and these two freqeuncies
could be the same, and the transmission line does not have to be at 50 ohms,
and for that matter neither does the transciever. If any one of these is
mismatched, then the swr is not 1:1.
An impedence transformer at the antenna-transmission line junction will
transform a mismatch so there is no reflection on the transmission line, amd if
this impedence is the same as that of the transmitter, then the swr is 1:1, if
the impedence is not the same, then the swr is not 1:1 unless it is also
transformed at the transmitter, and again the swr would be 1:1 on the
transmission line, which is where the swr is, it is not on the antenna.

William F. Hagen wrote:
an antenna has an impedence at the frequency it is being used at, and an
impedence at its resonant frequency. If either of these impedences happen to be
50 ohms and the coax being used is 50 ohms, and the transciever is working at
50 ohms, then the swr is 1:1, and the swr is on the transmission line, not on
the antenna.

One source of confusion is, on systems with both coax and ladder-line,
the SWR on the coax Vs the SWR on the ladder-line. A 12:1 SWR on 600
ohm ladder-line can result in a 50 ohm SWR of 1:1 without a tuner.
The ladder-line can be used as an impedance transformer.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

William F. Hagen wrote:
an antenna has an impedence at the frequency it is being used at, and an
impedence at its resonant frequency. If either of these impedences happen to be
50 ohms and the coax being used is 50 ohms, and the transciever is working at
50 ohms, then the swr is 1:1, and the swr is on the transmission line, not on
the antenna.

One source of confusion is, on systems with both coax and ladder-line,
the SWR on the coax Vs the SWR on the ladder-line. A 12:1 SWR on 600
ohm ladder-line can result in a 50 ohm SWR of 1:1 without a tuner.
The ladder-line can be used as an impedance transformer.

That lily really didn't need the gold paint job, Cecil.

But thanks for providing a source of confusion. How could we have a
good argument without one. :-)

73, Jim AC6XG

Jim Kelley wrote:

Cecil Moore wrote:


William F. Hagen wrote:


an antenna has an impedence at the frequency it is being used at, and an
impedance at its resonant frequency. If either of these impedences happen to be
50 ohms and the coax being used is 50 ohms, and the transceiver is working at
50 ohms, then the swr is 1:1, and the swr is on the transmission line, not on
the antenna.





One source of confusion is, on systems with both coax and ladder-line,
the SWR on the coax Vs the SWR on the ladder-line. A 12:1 SWR on 600
ohm ladder-line can result in a 50 ohm SWR of 1:1 without a tuner.
The ladder-line can be used as an impedance transformer.



That lily really didn't need the gold paint job, Cecil.

But thanks for providing a source of confusion. How could we have a
good argument without one. :-)

73, Jim AC6XG


For additional confusion, *IF* your transmission line (coax or ladder
line) is low loss,
and if your rig can load into it, SWR doesn't much matter. Reflected
power will
"bounce" off the rig and go back to the antenna. Our rigs actually
present a very
low impedance to the antenna and transmission line. This is by design;
we want all
of the RF we manufactured to go to the antenna and none wasted as heat
in the
rig. Our rigs don't really look like the Thevinian equivalent (voltage
source with
internal resistor of 50 ohms) feeding a 50 ohm load. For a fixed
voltage and fixed
internal resistance, using a 50 ohm load gets you max power *into the load*,
ignoring the wasted power in the source resistance. Your electric power
company doesn't do that, efficiency would suck. They want all the energy
used to be in paying customer's loads. They do that by keeping their source
impedance very low. Actually, our rigs have a source impedance
of only a few ohms, and are designed to pump power into a 50 ohm load.
There is a delay involved with the reflected power getting to the
antenna, but
for the narrow bandwidth signals we transmit (SSB voice or code) this is not
significant. It will matter for amateur television up on UHF, though.

You can get a lower SWR reading than what your antenna is doing if you have
lossy feedline. The lossy feedline is absorbing some of the reflected
power.
So don't be suprised at the worse SWR if you upgrade your coax. As long as
you can load up into it, it's not a real problem.

=============================================

"What did Santa say at the house of ill repute?"
"Ho ho ho!"

============================================
Keep Santa in Xmas

Standing wave ratios on ordinary 1/2-wave dipoles can soar as high as
10-to-1.


With all the fuss made about excessive SWR everywhere else, why is it the
guru's never mention it, let alone show anxiety about it? What are they
trying to cover up?

Reg Edwards wrote:

Standing wave ratios on ordinary 1/2-wave dipoles can soar as high as
10-to-1.


With all the fuss made about excessive SWR everywhere else, why is it the
guru's never mention it, let alone show anxiety about it? What are they
trying to cover up?




It's a communist plot! ;-) Actually, if your feedline is low loss,
and is
able to handle the higher voltages you'd get with high SWRs, and you're
using a narrowband mode like voice SSB, and your rig can tune load
into it, high SWR is not a problem.

BTW, if you're using coax to feed a dipole, be sure to make a coil of
the coax feedline of several turns at the antenna feedpoint. The object
of this is to keep RF currents from traveling down the *OUTSIDE*
of the coax shield. Otherwise your antenna's radiation pattern will
be goofed up, and also the SWR will get even worse. This also
keeps stray RF out of the shack.

On Wed, 24 Dec 2003 06:11:10 GMT, Robert Casey
wrote:

Our rigs actually
present a very
low impedance to the antenna and transmission line. This is by design;
we want all
of the RF we manufactured to go to the antenna and none wasted as heat
in the
rig. Our rigs don't really look like the Thevinian equivalent (voltage
source with
internal resistor of 50 ohms) feeding a 50 ohm load.

Hi Robert,

Actually none of this is true. It is the glib explanation that is
bandied about commonly in this forum, but it contains its own internal
inconsistency of logic.

This illogic is present in the single statement:
Reflected power will
"bounce" off the rig and go back to the antenna.
The presumption is that the point of bouncing back, the transistion
point of the so-called low Z transmitter to the high Z line, performs
this action. It contains to howlers:
1. if it were true, no one would ever need a tuner whose sole purpose
is to do exactly that (the bouncing back);
2. if it were true, the original power coming from the transmitter
would see the same reflection and bounce right back in to turn to heat
(which is a fairly true representation of the problem of SWR).

As for the reality of the situation, answer me this:
1. How much power does your rig transmit?
2. How much power does your rig draw?
Correct me if the operation of dividing the first by the second does
not reveal an efficiency of roughly 40% and a power loss to heat of
roughly greater than that transmitted. Your rig has a massive heat
sink with a fan, n'est pas?

Too many of the pundits want to force a literal carbon composition
resistor into the mix so that they can point to its absence proving
Thevenin's Theorem does not apply. The same pundits ignore the fact
that Thevenin did not specify a resistor, he specified an impedance to
satisfy his theorem. It was Edison's pervsion of logic in trying to
persuade the investors that AC distribution was for the birds when it
came time to match loads. He inserted the false claim of resistance
forcing inefficiency. This perversion has been with us ever since and
qualifies such believers only as possible investors in the Edison DC
Power distribution company (which folded immediately due to
inefficiency in the market place).

73's
Richard Clark, KB7QHC

On Wed, 24 Dec 2003 08:09:55 +0000 (UTC), "Reg Edwards"
wrote:

Standing wave ratios on ordinary 1/2-wave dipoles can soar as high as
10-to-1.


With all the fuss made about excessive SWR everywhere else, why is it the
guru's never mention it, let alone show anxiety about it? What are they
trying to cover up?


Ah Punchinello,

You have had your crown returned to you by those same gurus who have
abandoned the field, and who quixotically made just those
protestations you now so miss.

We will leave it in your capable hands to argue both sides of the coin
on this one, in your fulsome, best oratorio.

73's and the best of the season to ye,
Richard Clark, KB7QHC