Observations
 

Owen Duffy wrote in
:

....
This is a property of any directional wattmeter of this type when the
sensor is calibrated for an impedance that is real (ie non reactive),
irrespective of the load or the type of coax that might be attached to
either side of the instrument.

I should have posted a link to an explantion of why this is so. The article
at http://www.vk1od.net/VSWR/VSWRMeter.htm contains an explanation.

Owen

Observations
 

**Pop!**

Thanks- It's really about minima and maxima being more intense in the
complex vector addition of the reflections.

I see a lot of the same math for light. Polarization was interesting.

Observations
 

Obviously,
the stress of the weight would distort the line from factory specs and
shoot 'em to hell ... not to mention power handling capacity would be
reduced ...

Haw! doesn't help to put a speed bump only 10' down the line. But if there
is 30 db of loss in the first 10 ft. who cares.

Observations
 

Jim Kelley wrote:
Cecil Moore wrote:
I suspect that all necessary reflections take place
at the impedance discontinuity and the characteristic impedance
is established immediately.

Cecil - you might like this. What I got out of Feynman's QED was
that the probability for a reflection to take place would be
highest at the discontinuity.

Even better. It is known to take a few radii to clearly
establish the characteristic impedance. The effect apparently
can be measured and there exists an equation for it. I just
had a flashback that it might be in Chipman.
--
73, Cecil http://www.w5dxp.com
"According to the general theory of relativity,
space without ether is unthinkable." Albert Einstein

Observations
 

Cecil Moore wrote:

The effect apparently
can be measured and there exists an equation for it.

Otherwise, how would they be able to make it?

73, ac6xg

Observations
 

On Sep 28, 2:38*pm, "Frank" wrote:
According to:http://ham.srsab.se/ww/temp/test_MFJ269.pdf
ARRL lab measures the range of the MFJ 269 is 6 to 400
ohms. Not sure what the difference is between this and
the MFJ 259.

Frank
The anti resonant points are well within the MFJ 259 specifications
stated above.

The results you are measuring are certainly within the range of the
MFJ 259. *As an example: a 493 ft dipole, 50 ft above an average
ground shows anti-resonance, at 1.9 MHz, and is 15,000 ohms.

Frank

Frank, that is twice that you have mentioned dipoleas a comparison.
May I remind you again that for equilibrium purposes the radiator
must be a wavelength or multiple there of, assuming ofcourse we are
considering a single radiator
To talk of a "dipole" when considering my design is totally
unreasonable.
Regards
Art

Observations
 

On Sep 28, 4:47*pm, "JB" wrote:
Actually, I will go out on a limb over this point.

I have always found that a mis-matched, or "out of specs", antenna will
continue to "ring the ether" a bit more efficiently than it will "pluck
a signal from the ether."

Concur.
RX level can be even more noticeable on high Q antennas off-resonance as you
would expect.

Now add the line loss. *Also, reflections don't seem to matter much with CW
and SSB but can have an effect on some digital modes and certainly
television.

With solid state PAs, not all are created equal, and shutback often errs on
the side of keeping warranty costs down. *Stability is in the reach of most
modern ones now. *The current can be dealt with if you can get the heat out
of the junction to a point. *But the voltage rise is the killer.

Also be aware that any transmission line will be significant in your
measurements at the rig end.

The MFJ can see anti-resonance if it doesn't get confused on other oddities
such as coax length or connector humps, reflections. *It can get pretty
dicey when you sweep because all these things jump out at you when the load
is out of resonance and or mismatches anywhere on the line. Not to mention
the harmonics in the unit when you are looking at high impedances.

Correct, that is why you measure in it's final environment and at
the source to the antenna.
Again JB let me state I am not a newby with respect to antennas and
are very much
aware of the circumstances that you point to which is why I measure
at the antenna feed point.......
....Same goes for any tuner arrangement I use which is also at the top
of the tower as well as a camera when needed
Art

Observations
 

The results you are measuring are certainly within the range of the
MFJ 259. As an example: a 493 ft dipole, 50 ft above an average
ground shows anti-resonance, at 1.9 MHz, and is 15,000 ohms.

Frank

Frank, that is twice that you have mentioned dipoleas a comparison.
May I remind you again that for equilibrium purposes the radiator
must be a wavelength or multiple there of, assuming ofcourse we are
considering a single radiator
To talk of a "dipole" when considering my design is totally
unreasonable.
Regards
Art

But that is the typical input impedance of a one wavelength long
antenna (15,000 ohms).

Frank

Observations
 

On Oct 5, 11:29*am, "Frank" wrote:
The results you are measuring are certainly within the range of the
MFJ 259. As an example: a 493 ft dipole, 50 ft above an average
ground shows anti-resonance, at 1.9 MHz, and is 15,000 ohms.

Frank
Frank, that is twice that you have mentioned dipoleas a comparison.
May I remind you again that for equilibrium purposes the radiator
must be a wavelength or multiple there of, assuming ofcourse we are
considering a single radiator
To talk of a "dipole" when considering my design is totally
unreasonable.
Regards
Art

But that is the typical input impedance of a one wavelength long
antenna (15,000 ohms).

Frank

Yes Frank but you have to remember mine is a new design. The antenna
is now on the ground
and has a resistive impedance of three figures. I anticipate that when
I put it on my 30 foot tower the impedance will drop
on top band by 50% where I will add a transformer to drop it to 50
ohms. Now on the other bands it may well not need a transformer
so I can play around on 20 M for the winter until I can achieve a good
match or place a tuner at the tower top.
As I have stated many times a radiator does not have to be straight so
figures found with a dipole are just not applicable in my case.
In fact a anti resonant impedance can be driven below 50 ohms if one
wanted to so prior findings are just not applicable.
In a month or so you will be able to put my antenna on your computor
program and check for yourself I promise you.
Regards
Art

Observations
 

J.B. wrote:
"As soon as the load gets reactive, the phase between the voltage and
current are different and the length of the coax and its velocity factor
now contribute unless it is really short compared with wavelength."

The Bird wattmeter won`t affect tuning and loading of an antenna if it
is made part of a half-wavelength of line inserted for the measurement.
This may be important at VHF and higher frequencies. The inserted line
and its meter need to be specially tailored to make up a half
wavelength, if it is to be inserted in nonflat lines. For several
different frequencies, several line measurement assemblies are required.

Best regards, Richard Harrison, KB5WZI