Richard Clark wrote:

On Sun, 10 Apr 2005 18:17:42 -0500, Tom Ring
wrote:

Hi Tom,

The number of variables in the description of your (Mark's) method is
rather considerable, so I will remark by the parts you offer:


The range has a source yagi for each band, that yagi has a low power AM
modulated signal on it (as I remeber, might be wrong on this).


So far, fine.


The other end has a reference yagi off to the side from the test position.


Commendable.


A yagi with "known gain" is run against the reference yagi, and the
relative signal strength is measured.


I might slyly point out how do you know the gain? It visits the age
old logical knot offered:
In a town of clean shaven men,
there is a barber who shaves everybody who does not shave himself;
who shaves the barber?



As I state later, the absolute gain number is suspect. And I quoted
"known gain". That's a clue to it really being a variable to a certain
extent.

And, as you well know, having been in the business since day minus one,
it is possible to build standard gain antennas for UHF and microwave
that will pretty much dead on every time. They are available in many
texts you already probably own.

OK, the method is good and robust, but your sudden departure from
expected results are on the scale of 5 to 6 times the range of your
typical error.

snip

I would offer that if the elements oxidized, so did the connectors (or
connections). Simple, repeated connector matings (like swapping in
and out for the range test) were sufficient to break bad contacts and
make the difference which was attributed to scrubbing the elements.
In the normal course of my calibration of various items with
connectors, I always inspected and cleaned them first. N connectors
have erosion problems that will give rise to variations outside of
0.1dB - comes from those threads. The "standard gain" antenna should
be suffering from this erosion by now, but you don't report it.


The corrosion was on an antenna that had not been in the barn, it had
been used for 4 years in an EME array, and was fairly well corroded. We
tested it to see how it would compare to the protected identical
prototypes, and then we cleaned it for a second test run. And the
connectors are always N connectors. 'nuff said.

The standard gain antennas are also not left out in the rain, and do not
live in a city.

This raises suspicions for me - you have too much fulfillment of
expectations which is truly extraordinary. I have made thousands of
calibrations of isolators, pads, couplers, meters and so on that have
shown a gaussian distribution of results for premium equipment. Your
range experience shows very little variation - much too little when we
are talking about being within 0.1dB.


I can't address that; maybe he has been lucky, extraordinarily careful,
or there aren't enough points graphed yet.



73's
Richard Clark, KB7QHC

Thanks for getting me to call him and review how it was done. I spent
an hour and 3 quarters getting up to date. And he is about to get 500
watts at the feed point on 2304 going. That is a fairly impressive
amount of juice homebrewed on that band. Only 4 transsitors to do it.
Ain't technology wonderful? And he has a 32 foot homebrew dish.

tom
K0TAR

On Sun, 10 Apr 2005 20:27:55 -0500, Tom Ring
wrote:

HP ratio meter, 1kHz tone on AM. He thinks the HP is a model 340, but
would have to go out in the garage to look.

Hi Tom,

Not one of their numbers against the characteristics. However, I am
familiar with what you describe as the characteristics.

It is a tuned AC voltmeter, commonly used for SWR measurement in
slotted lines connected to a the detector where the source is
modulated at 1KHz. The meter is tuned to 1KHz and has a very high
gain and selectivity. This allows it to employ a variable gain, by
10dB switch steps (and a variable knob to set zero, or the reference).
The scale is read in combination with the attenuator (gain) switch and
thus the scale offers considerable resolution, easily 0.1dB and
better. It is probably an HP-415.

I've calibrated these too (Boonton, I think, also built them, but as
Boonton was acquired by HP, it isn't a remarkable difference).

73's
Richard Clark, KB7QHC

Richard Clark wrote:

On Sun, 10 Apr 2005 20:27:55 -0500, Tom Ring
wrote:


HP ratio meter, 1kHz tone on AM. He thinks the HP is a model 340, but
would have to go out in the garage to look.


Hi Tom,

Not one of their numbers against the characteristics. However, I am
familiar with what you describe as the characteristics.

It is a tuned AC voltmeter, commonly used for SWR measurement in
slotted lines connected to a the detector where the source is
modulated at 1KHz. The meter is tuned to 1KHz and has a very high
gain and selectivity. This allows it to employ a variable gain, by
10dB switch steps (and a variable knob to set zero, or the reference).
The scale is read in combination with the attenuator (gain) switch and
thus the scale offers considerable resolution, easily 0.1dB and
better. It is probably an HP-415.

So for relative gain it's possible, in your opinion, to measure +- .1dB
with this, if properly used?

tom
K0TAR

On Sun, 10 Apr 2005 21:42:21 -0500, Tom Ring
wrote:

So for relative gain it's possible, in your opinion, to measure +- .1dB
with this, if properly used?

Hi Tom,

Quite easily.

73's
Richard Clark, KB7QHC

Richard Clark wrote:

On Sun, 10 Apr 2005 21:42:21 -0500, Tom Ring
wrote:


So for relative gain it's possible, in your opinion, to measure +- .1dB
with this, if properly used?


Hi Tom,

Quite easily.

73's
Richard Clark, KB7QHC

So he's using decent equipment. Whether it's used correctly is another
matter. I'm betting he did a good job, given the results I've seen, and
what I know of him.

But you are correct to be be skeptical on the results.

tom
K0TAR

Dan Richardson wrote:

Jay,

We just replace them more frequently than dry desert dwellers. After
about five years (sometime sooner) they are about shot.

My two-meter omni is incased in a fiberglass radome and my wire
antennas are made with insulated wire with ends sealed.

How close to the ocean are you? It sounds like you are right in the spray!


- Mike KB3EIA -

On Sun, 10 Apr 2005 21:54:26 -0500, Tom Ring
wrote:

So he's using decent equipment. Whether it's used correctly is another
matter. I'm betting he did a good job, given the results I've seen, and
what I know of him.

Hi Tom,

As I've offered, the test protocol is very precise, and the
instrumentation (as far as has been discussed or inferred) is up to
the resolution. However, many mistake what accuracy, precision, and
resolution mean.

Resolution is the number of digits in your reading. It usually
implies that you can read more digits than you report. So, to say you
have measured a voltage to be 1.5V means that you have an instrument
that can read in hundredths of volts.

Precision is the repetition of readings. High precision means your
measurements all can be reported as 1.5V because they vary no more
than 4 hundredths of a volt in readings around the reported value (or
by more fancy regression techniques).

Accuracy is how far from actual your report is. It is enough to say
that resolution and precision are not accuracy, but that they are
necessary components of accuracy.

Insofar as the range goes, it remains to be seen if it has been
calibrated in its own right. The test is not necessarily found in
absolutes, but rather in its response to perturbations. In other
words, inject a known variable and measure its ability to support a
report that faithfully records the value of that variable as evidence
of its robustness. You have to perturb the system with small changes
as well as large changes to see if it is linear in its response. This
is not easy and makes great demands upon not only the instrumentation,
but the ingenuity of the tester. Then you repeat the tests from a
different angle to see if it is symmetric. Then you test for
background contributions - noise (actually this is probably best done
first as it sets the boundaries of your low end and defines part of
the dynamic range).

You do all the above, and then some, pool the results and describe
your limits of error. Test results that are reported without knowing
the limits of error are not very informative. Hence, when I hear that
readings are repeatable to 0.1dB for UHF and I hear nothing of the
range of error (I must presume that it is no greater than 0.033dB);
then I am more than skeptical because 1% accuracy in power
determination is the extreme of very tightly controlled laboratory
conditions.

That there are repeated measurements in the field to this level of
precision is suspect because there is very little instrumentation AND
combinations of many pieces of gear that come close. It takes only
two pieces of 1% gear to create a situation that is at best 1.4%
accurate and you are already crossing the 0.1dB threshold. For those
trying to balance the ledger, a 1% accurate determination requires a
method that is at least 3 times more accurate. The usual aggregation
of error arrives through RSS (root sum square); some may like to gild
their prospects and compute RMS (root mean square) and if they are
lucky, this is not far off. Given enough results, luck washes out to
sea and RSS dominates. Given enough results that conform to RMS, then
you find you have qualified your methods and instrumentation to
superlative standards.

73's
Richard Clark, KB7QHC

On Sun, 10 Apr 2005 23:58:12 -0400, Mike Coslo
wrote:


How close to the ocean are you? It sounds like you are right in the spray!


About a half mile. I live in the northern California "Mendocino"
coast. We have a lot of rain too and that combination is a killer for
aluminum exposed to the elements.

Danny

Richard Clark wrote:

On Sun, 10 Apr 2005 21:42:21 -0500, Tom Ring
wrote:


So for relative gain it's possible, in your opinion, to measure +- .1dB
with this, if properly used?


Hi Tom,

Quite easily.

73's
Richard Clark, KB7QHC

HP416A.

tom
K0TAR

On Mon, 11 Apr 2005 09:48:17 -0500, Tom Ring
wrote:

HP416A.

Hi Tom,

By description and application, probably, but I need a picture or
manual to be able to confirm. I've calibrated and used so much
different gear that the numbers blur.

73's
Richard Clark, KB7QHC