Richard Clark wrote:

On Sat, 09 Apr 2005 21:12:47 -0500, Tom Ring
wrote:

A 432 MHz antenna scrubbed with a
ScotchBrite showed a .6 dB gain increase.
So B as in B, S as in S, as we say here in Minnesota.


Hi Tom,

You could measure to the accuracy of better than 0.2dB between two
separate tests? And at UHF too? Care to share how?

73's
Richard Clark, KB7QHC

Well, you'd have to ask Mark Thorsen, WB0TEM, what equipment was used,
but the range is checked several times against the reference antenna
during each band we run, and is generally within .1 dB between checks.
Except that one day in KS. Boy was it hot.

I wouldn't bet absolute values are on the mark, but an antenna measured
against itself was reproducable. So I do believe the antenna improved
due to having the oxide scrubbed off.

tom
K0TAR

Cecil Moore wrote:
Jay in the Mojave wrote:

... a much higher frequency

than the 31 Mc ...
^^
Showing our age, are we Jay? :-)

You know I didn't even notice that when I read it. :-)
...lew... ( ex W3SLX circa. 1950 )

On Sun, 10 Apr 2005 09:23:19 -0500, Tom Ring
wrote:

I wouldn't bet absolute values are on the mark, but an antenna measured
against itself was reproducable.

Hi Tom,

But the point of accuracy, even reproducible accuracy, requires a very
absolute source to compare against. Sometimes that absolute is quite
simple to achieve, but now you have upped the ante to 0.1dB. This
implies a measurement accuracy of at least three times better; which,
in turn, means you have access to a standard that can discern 0.8%.

To say you test the antenna "against itself" does not really say much
when it comes to power and gain. That is no benchmark. The
presumption here is that you have an external source of power that is
constant. This then raises the same question. Over a span of time,
what guarantees this degree of accuracy? By what method is it
confirmed? That source's "absolute" power level needn't be an issue,
but there is no way to escape casting that "absolute" requirement into
another standard to confirm the fact of its stability.

73's
Richard Clark, KB7QHC

Based on some of the other responses you received it may not be worth
it but there is another type of coating for aluminum called alodyne
which protects the same way as anodizing but is electrically
conductive.

jtm

Jim Miller wrote:
there is another type of coating for aluminum called alodyne
which protects the same way as anodizing but is electrically
conductive.


Alodine (R) coatings are not conductive. You can specify a "type 3"
coating that is thin enough that fasteners will usually punch through
the coating layer.

See MIL-C-5541 chromate conversion coatings.

Kevin Gallimore

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Another corrosion-inhibiting coating for aluminum is iridite. There are
conductive and non-conductive versions, something I learned the hard way
long ago.

Roy Lewallen, W7EL

axolotl wrote:
Jim Miller wrote:
there is another type of coating for aluminum called alodyne

which protects the same way as anodizing but is electrically
conductive.



Alodine (R) coatings are not conductive. You can specify a "type 3"
coating that is thin enough that fasteners will usually punch through
the coating layer.

See MIL-C-5541 chromate conversion coatings.

Kevin Gallimore

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On Sun, 10 Apr 2005 14:30:04 -0700, Roy Lewallen
wrote:

Another corrosion-inhibiting coating for aluminum is iridite. There are
conductive and non-conductive versions, something I learned the hard way
long ago.

Tell me about it [g].

I was the engineer responsible for transferring the design of the then
new Phoenix Missile IMPATT diode transmitter from the development lab
to the production floor.

The transmitter had three stages: a single diode driven by a
phase-locked Gunn oscillator fed a three diode cavity that drove a 16
diode cavity.

The development hardware used aluminum cavities that were comprised of
two pieces, with third copper piece that mounted the sixteen diodes.
So there was one aluminum-to-aluminum and one aluminum-to-copper
interface in each sandwich. Since this was a product for the U.S.
military, "passivation" was required for all aluminum parts.

I won't go into the considerable amount of detective work that it took
to decide that despite being "conductive" Alodine and its ilk are not
suitable coatings for rf components.

Gold is your friend, if of course, it's thicker than a few skin
depths, which is another long story. [g]


Roy Lewallen, W7EL

axolotl wrote:
Jim Miller wrote:
there is another type of coating for aluminum called alodyne

which protects the same way as anodizing but is electrically
conductive.



Alodine (R) coatings are not conductive. You can specify a "type 3"
coating that is thin enough that fasteners will usually punch through
the coating layer.

See MIL-C-5541 chromate conversion coatings.

Kevin Gallimore

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Amen! If gold did not exist, it would need to be invented just for EE
purposes. 73 Mac N8TT

--
J. Mc Laughlin; Michigan U.S.A.
Home:
"Wes Stewart" wrote in message
...
snip


I won't go into the considerable amount of detective work that it took
to decide that despite being "conductive" Alodine and its ilk are not
suitable coatings for rf components.

Gold is your friend, if of course, it's thicker than a few skin
depths, which is another long story. [g]

"J. Mc Laughlin" wrote in message
...
Amen! If gold did not exist, it would need to be invented just for EE
purposes. 73 Mac N8TT

I've often entertained thoughts about the utility of gold in my other
hobby. I reload ammunition and cast lead bullets. Anything over 1200 to
1500 fps leads to leading from friction and gas cutting. Gold shares with
lead a high mass and malleability. Its higher melting point should allow
considerably higher velocities. Unfortunately I've not found suffient
quantities at economically feasible acquiral rates. Once Oklahoma gets its
lottery running and I win I'll get myself 4 or 5 pounds and find out if my
theory about gold bullets proves out. Another complication stems from the
high melting point which may prove damaging to my bullet molds. If that
should occur, I'll have to get someone to extrude me some gold rod and
lathe cut my gold bullets. Hmm, with gold rods, can gold ground plane
antennas for 2 and 6 meters be far behind? So many fun homebrew projects,
so little time, sigh.

Harold
KD5SAK

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?

That gives us a known gain point
on the meter. A yagi is then placed in the test position and the
relative gain or loss is recorded. The "known gain" yagi can be put
back into the test position at intervals to check the calibration.

This method is called using a "transfer standard." As I offered, that
requires an absolute knowledge somewhere, and you have identified it
in this "known gain" yagi. However, the gain is actually immaterial
until you begin making claims of absolute gain. That is, most of this
correspondence is satisfied with relative gain comparisons as you
point out:

Obviously the absolute values may be suspect, but relative measurements
work well.

Quite true, however, you having once acknowledged suspicions you then
plunge back into the murky pool of absolutes:

The results also agree very well with YO predictions, with a
yagi in the 18.4 dBd predicted range being low by .3 as measured, which
is roughly what he expected to happen. Most more normal gain, 14 to 15
dBd for 432, were within .1 of predicted. Bands tested on this range
were 144, 220, and 432.

Well, here we run counter to my experience with real life components.
They varied by several times your 0.1dB, and this was often times for
the same item tested repeatedly (I never measured any item less than
five times and never five times repeatedly, in a row).

Multiple prototype 2M and 70cm EME antennas that my partner and I built,
stored safe from corrosion, tested the same +- .1dB with a several year
gap between the tests.

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.

If this is to be attributed to oxidation on the elements, that still
seems suspect. The oxidation is not lossy, and certainly is not
sufficiently thick enough to shift the resonance. Oxidation is one of
the charms of aluminum, it is self sealing.

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.

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.

What equipment he uses for the ratio measurement, and precisely how it
is done, I don't know. I will attempt to contact him and find out if I
can get this damn sinus infection under control in the next few days.

Well I hope you shake the infection off. Further details are unlikely
to resolve this corrosion as it is too much a matter of "you had to
have been there" kind of thing.

73's
Richard Clark, KB7QHC