Observations
 

On Sep 28, 1:55*pm, "Frank" wrote:
Oops, sorry for the double posting. *Anti resonance for a free
space dipole is typically in the range of 7000 ohms. *The
MFJ 259 is only accurate over a limited range of 5 - 500 ohms
so any measurements of anti-resonance is highly questionable.

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

Observations
 

Art Unwin wrote:

...
You think so?
Art

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."

I have simply grown to accept this from actual hands-on experience ...
your mileage may vary ... and, of course, a poor antenna will continue
to be poor even when perfectly matched and within original design specs.

Regards,
JS

Observations
 

On Sep 28, 2:05*pm, John Smith wrote:
Art Unwin wrote:
...
You think so?
Art

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."

I have simply grown to accept this from actual hands-on experience ...
your mileage may vary ... and, of course, a poor antenna will continue
to be poor even when perfectly matched and within original design specs.

Regards,
JS

John, do you really think you can calibrate an S meter by ear if the S
levels were scrambled ?

Observations
 

Art Unwin wrote:

...
John, do you really think you can calibrate an S meter by ear if the S
levels were scrambled ?

Absolutely not ... you simply asking that question forces me evaluate
your sanity ...

However, when I ran rigs with NO s-meter, my ear served well enough ...

Regards,
JS

Observations
 

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

Observations
 

On Sun, 28 Sep 2008 11:48:18 -0700, John Smith
wrote:

Cut power to 25% and the other guy will see (if his s-meter is accurate)
a drop to half the reading ... at 80% power, little difference, other
than if you were just above noise floor in the first place ... however,
"tweaking" an antenna to perfect match/design criteria has always proved
to we worth the effort ... and especially to my ears--but my s-meter
also ...

I think you mean guess-meter:
http://www.seed-solutions.com/gregordy/Amateur%20Radio/Experimentation/SMeterBlues.htm
S-meters are notoriously inaccurate.

We have an Icom PCR-1000 remote receiver setup on a local mountain top
run by HRD (Ham Radio Deluxe) software. It's quite handy for tuning
and adjusting antennas and generating a polar plot for HF yagi's and
quad's. There are substantial site errors in doing it this way, but
it's still better than a field stength meter, or the traditional
"how's my signal" report.

I designed the 150w PEP power amplifier section for the Intech M3600
HF marine radio. Using VMOS xsistors, I was able to demonstrate
unconditional stability, at rated power, with any non-resonant load up
to about 8:1 VSWR. Above that the current went up a bit too high for
the 12 ohm load, and Vce climbed for the 400 ohm load. I might have
done better but didn't want to destroy the test radio. The radio was
specified to operate up to a 2:1 VSWR at full power and would reduce
power when the threshold reflected power was detected. Although I
demonstrated that it was possible to operate quite nicely up to 8:1
VSWR, without power reduction, nobody wanted to add that to the data
sheet for fear that someone would actually use it that way.

My guess(tm) is that most modern HF radios can also safely operate
into high VSWR loads, but suspect that manufacturers are also hesitant
to guarantee such operation. Most manufacturers don't even specify a
maximum VSWR and simply reduce power if excessive reverse power
(usually 2:1 at full power) is detected.

Disclaimer: If you trash your radio trying this without monitoring
the Pout, PA temperature, PA xsistor voltage/current, and checking for
oscillations on a spectrum analyzer, don't blame me.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Observations
 

John Smith wrote:
However, when I ran rigs with NO s-meter, my ear served well enough ...

Indeed, the 1-9 Signal Strength system was in operation
before S-meters were in standard use, dating back to the
very early 20th century. The "x dB over S9" came later.

Even when I got my first ham license in the early 50's,
the RF gain control used for CW rendered the S-meter
reading invalid.
--
73, Cecil http://www.w5dxp.com
"According to the general theory of relativity,
space without ether is unthinkable." Albert Einstein

Observations
 

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.

Observations
 

Frank wrote:
Oops, sorry for the double posting. Anti resonance for a free
space dipole is typically in the range of 7000 ohms. The
MFJ 259 is only accurate over a limited range of 5 - 500 ohms
so any measurements of anti-resonance is highly questionable.

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 269 has the 440mhz band.

Dave WD9BDZ

Observations
 

"Jeff Liebermann" wrote in message
...


My guess(tm) is that most modern HF radios can also safely operate
into high VSWR loads, but suspect that manufacturers are also hesitant
to guarantee such operation. Most manufacturers don't even specify a
maximum VSWR and simply reduce power if excessive reverse power
(usually 2:1 at full power) is detected.

That sounds right..

I have two HF radios, (Kenwood TS-120, TS-870) and I often observe the
forward power climbing as I manually tune and reduce the reflected power.
At first glance, this would seem to indicate the rig had previously
throttled back its output in response to the consequences of a mismatch.

I never intentionally tune at anything more than a few watts, so perhaps the
protection circuits operate at less than full power, too. The autotuner in
the TS-870 uses about 10 watts.