Silver Platiing Solutions (Cyanide free)

They keep that for ICE systems and wiring up HIFI

Ahem, skin depth may not change, but a diameter increase of 1% means circumferential change of 3.14%m, therefore an area change of 3.14%

Neil

That's a bit suspicious. Perhaps the calculator only does an approximation? I know nothing about designing filters but that seems counter-intuitive. I may have a book somewhere.

Dave

Circumference = pi x D

pi is constant so circumference is proportional to D

Russell

I doubt there will be much of a material difference in performance by using silver plating. Agreed that the resistivity of silver is slightly better than copper. However, to make use of the increase the plating thickness will need to be higher than quoted in the original post. While AC currents tend to flow on the outer surface of a conductor they do not all flow within the skin depth. Only around 63% of the current flows in the skin depth. However, most of the current (>98%) does flow in a band 4 times the skin depth. So ideally the silver plating would need to be around 8µm thick.

I'll be interested to know how the performance of the filter will be assessed. In my experience measuring small percentage changes at RF is pretty tricky, even with a bench full of HP test gear.

The diameter of the tubes will certainly have an effect on the tuning of the filter. A long time ago I made some ground probing radar antennas, and we had to change the resonator length slightly as they were designed using imperial rod, but I could only get metric diameters.

Andrew

Agreed. Unfortunately I cleared out my text books when I retired and moved to France so have to rely on memory.

Russell (former RF engineer)

Just having a look in one of my ARRL publications, and they suggest that there is a plating powder that is applied with a damp cloth, it's called COOL-AMP, made by a company of that name,8603 S>W> 17th Ave., Portland, Oregon. Unfortunately it is only sold in 1lb jars, and that will cover 6000 sq inches. This method is considered an alternative to the normal electrolytic method with cyanide. After plating the ARRL recommend that you spray with lacquer to protect the surface(doesn't effect soldering).  At UHF it's probably worth while going the silver plating way.

Ian S C

Edited By Ian S C on 28/03/2017 12:47:09

You can buy the same powder on ebay; silvering powder

I've used it successfully on clock faces but I am dubious that the thickness will be adequate to make any significant difference.

Russell.

Did a bit of swotting and found that Q can be calculated from:

Q = f0 / (f1 - f2)

where: f0 is the centre frequency, and f1 and f2 are the frequencies either side of f0 where the response falls to 0.71 of maximum.

I guess the online calculator crunches an expected response curve and then suggests a likely Q from that. As such perhaps it's unlikely to account for small differences in Q caused by less significant factors.

I haven't found anything (yet) in my amateur library on either Intradigital Filters or any evidence supporting silver plating. (Though it's frequently recommended.)

A new mystery. My 1938 Admiralty Wireless Telegraphy Handbook says that antenna wire performance is damaged by funnel smoke and that they should be cleaned regularly. Insulators yes, but cleaning the wires themselves?

Dave

DOH!

However, my intuitive feeling that skin cross sectional area increases more than diameter is correct.

Imagine a 10mm rod with a 5mm skin - the skin occupies the whole cross section of the rod.

Increase rod diameter to 20mm, rod area is now four times as great, and the skin reaches all but a 10mm diameter in the middle so its cross-sectional area has tripled.

BUT my mistake was to extrapolate this effect to thinner skins and larger diameters.

For a thin skin in relation to the diameter the effect is much smaller. A 150% increase in the diameter of a 10mm rod with a 0.1mm skin increases the skin cross section by 152%.

Rather than being a method of predicting Q that is a method of measuring Q but it only applies to a single tuned circuit not coupled resonators.

To calculate the performance of a coupled resonator filter you need to know the Q of each resonator (usually assumed to all be the same) and plug the numbers into the mathematics of the circuit design.

The main determinant of the Q of the resonators is the effective series resistance at the working frequency hence the need to know the resistivity of the material and the skin depth.

Russell.

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Or perhaps the mistake was to assume that the thick layer you described would qualify as a skin.

MichaelG.

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I am way out of my depth here [please forgive the inevitable pun] but

... I think this 'calculator' may be of interest:

**LINK**

http://chemandy.com/calculators/skin-effect-calculator.htm

While working on a VHF equipment we had lots of problems due to humidity, solved it by making a tray with 2 x 100 watt bulbs under the stack of trays that made up the equipment.

Obviously the moisture affected the Rf in some way making it unusable?

Clive

That seems to tie up fairly well with the results from my Excel spreadsheet that I wrote some 30 years ago

Russell

Yes, apart from corrosion, a high level of water in the air is likely to change its permittivity and thus any capacitance effects.

Russell

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That's encouraging, Russell

MichaelG.

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[quote]

From Transmission Lines and Networks by Walter C. Johnson, McGraw-Hill 1963 p58.

Dave, I think the reference to funnel smoke may be because of the corrosive action of wet sulphurous coal soot on the copper wire, Bunker oil also has a high sulphurer content.

Ian S C