Anodized Alumium for Antenna Elements

Richard Clark wrote:


Ok. I'll give the details I remember, but be advised I didn't implement Mark's system, I just assisted in using it.
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). The other end has a reference yagi off to the side from the test position. A yagi with "known gain" is run against the reference yagi, and the relative signal strength is measured. 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. Obviously the absolute values may be suspect, but relative measurements work well. 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.
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.
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.
tom K0TAR
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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.
tom K0TAR
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wrote:

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
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Richard Clark wrote:

So for relative gain it's possible, in your opinion, to measure +- .1dB with this, if properly used?
tom K0TAR
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wrote:

Hi Tom,
Quite easily.
73's Richard Clark, KB7QHC
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Richard Clark 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.
But you are correct to be be skeptical on the results.
tom K0TAR
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wrote:

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
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Richard Clark wrote:

HP416A.
tom K0TAR
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wrote:

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
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wrote:

http://www.qsl.net/n7ws/HP416.pdf
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wrote:

GAD!
I had forgotten that white elephant. Thanx Wes.
Tom,
It is pretty much in the same class of expanded range, 1KHz tuned AC Voltmeters. As long as you reference and return to a Cardinal point on the scale, accuracy you describe can be supported.
In fact, this class of instrumentation is probably the best leverage to building a very good RF lab. You can spend more, you could even find equipment that does most of the grunt work for you, but it is still a long shot that you will obtain more accuracy.
Accuracy is steadfastly bound to method and this style of instrumentation reveals an example of method thought out and polished with the best of engineering thought.
73's Richard Clark, KB7QHC
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Richard Clark wrote: ...

Errrk?? From Boonton's web site:
"In July 2000 we became a member of a larger family as we were acquired by Wireless Telecom Group, Inc. (doing business as Noise Com). Being a wholly owned subsidiary of Wireless Telecom Group, Inc. has enabled us to further our product development and customer service initiatives."
See http://www.boonton.com/2002/about-history.html
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They left out part of their history.
H-P *did* acquire Boonton at one time. I have both a black crackle Boonton 250 RX meter and an H-P gray HP 250 RX meter out in my storage building.
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wrote:

Another rec.crafts.metalworking crosspost kibbitz: Double check that - they could have been owned for a while, but it's far more likely H-P ordered some made by Boonton in gray cases with the H-P name on them. Far cheaper than H-P duplicating them from scratch, and doing a total redesign so they don't infringe on any patents.
Happens all the time - for one example, Sears doesn't build power or hand tools themselves, but they have the OEM suppliers put their name on tons of them. Sometimes they're customer specific designs, others are only 'badge engineered' from an existing design and change the plastic feedstock color in the case molding machine.
In the past I've saved an average 20% by going to the OEM (like Skil-Bosch) for parts when you can identify them, rather than the Sears Parts Center.
--<< Bruce >>--
--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
  Click to see the full signature.
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Both half wrong. Back in the dark ages there were two Boontons. BRC, Boonton Radio Co., and Boonton Electronics who dropped the Electronics when HP absorbed BRC. Both were in the electronic instrumentation business. Used to drive purchasing agents berserk.
-- Crazy George The attglobal.net address is a SPAM trap. Please change that part to: att<dot>biz properly formatted.
wrote:

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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:

So far, fine.

Commendable.
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?

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:

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

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).

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.

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

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:

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wrote:

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]

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