On Sat, 13 Dec 2003 00:06:16 GMT, Roger Halstead
wrote:

|
|Every HF antenna here will go 1:1 "some where" ...

Not so.

"Wes Stewart" wrote in message
...
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 have a dipole that is 1:1 at both it's main length design frequency and
the single fan dipole design frequency underneath it. Each began life 10%
longer than design (formulas), one actually had to have a few inches added -
and that was soldered when the line was still brand new. The other required
shortening in 2" increments. Over a period of two months, the antenna still
has "1:1" on those two design frequencies. Checked with reliable equipment
besides the MFJ 962D tuner, which now rests on "Bypass" except for higher
frequency diversions. This was designed and built for two frequencies only,
and performs flawlessly in that respect.

So yes, achieving 1:1 SWR is not only possible, but nothing less was
acceptable in the specific need I had for that antenna.

Jack
Virginia Beach

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?

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 Thu, 18 Dec 2003 07:29:39 +0000, 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.

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.


I was going to say something similar. a 1:1 SWR means that the Load
matches the Transmission line. It says nothing about the condition of the
antenna. Most antennas have a matching system or "Tunner" built into
them, like a Gama Match for example, to transform their Impedance back to
the standard 50ohm coaxial transmission line.

Ron

When the so-called SWR meter is located immediately at the output the
transmitter, or inside it, as it usually is -

THE METER TELLS YOU NOTHING ABOUT THE SWR ON THE TRANSMISSION LINE TO THE
ANTENNA.

It only indicates WHETHER or NOT the load on the transmitter has a
particular value, usually a nominal 50 ohms. And nothing more.

In all other respects, SWR meters and the corresponding reflected power
meters, are a hoax, a scam, a swindle. It's time they were, or at the very
least their name, consigned to oblivion.


Call out the riot police!
----
Reg, G4FGQ