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Earl Cox
 

A couple of times my unit locked up but most of the times, keying the mike multiple times released the transmit lockup. I haven't worked on ti yet but I intend to put a small cap and RF block of some kind just inside of the mike socket.

Earl Cox? KB5UEW?
Reply or E-mail me at:? kb5uew@...


On Monday, July 12, 2021, 07:55:42 AM MDT, Stephen KO4CVU <goinfishin1952@...> wrote:


My uBITX v6 has recently locked up in the TX mode while I was using it with JS8Call running on my laptop. When yours locked up, was the TX indication visible on the LCD? Mine wasn¡¯t. I realized that the unit was locked up when I noticed that an external power meter was showing what is usually the full power output when I ¡°tune up¡± in the CW mode. I disconnected the lines to the microphone and speaker jacks but the unit was still locked up. I turned the power off and then back on and it was still locked up. I plugged in a microphone and hit the PTT button and that unlocked it! Thanks in advance for sharing. Stephen, KO4CVU

 

A minor clarification:
At 60mhz, skin depth is 8.4um.
At 60hz, skin depth is 8.4mm.
So according to that calculator, skin depth is inversely proportional to the square of the frequency.
Exactly.

Jerry, KE7ER


On Mon, Jul 12, 2021 at 12:16 AM, Gordon Gibby wrote:

Skin effect is curious, here's a calculator.??
For copper, it shows that the skin effect at 10mhz is 20 micrometers, so at that depth the current density
is only 37% of what it is at the surface of the copper. It decreases exponentially as you go deeper.

What I find curious is that at 60 Hz, the skin depth is 8.4mm. That's 6 orders of magnitude lower
in frequency, but only 3 orders of magnitude larger skin depth
 

Gahhh,

So according to that calculator, skin depth is inversely proportional to the square ROOT of the frequency.


On Mon, Jul 12, 2021 at 08:23 AM, Jerry Gaffke wrote:
So according to that calculator, skin depth is inversely proportional to the square of the frequency.
[email protected]
 

Yes it locked up with "TX:14.225.00" etc displayed on the second line of the LCD except some of the characters were garbled with nonsense patterns. A capacitor across the PTT line and ground on the back of the mic connector fixed it.

I also have an additional relay connected to the PTT to key up my linear (as per N6QW see attached ) which I guess doesn't help, but the amplifier wasn't plugged in at the time so it only took 10 watts of RF coming in on the PTT line to screw it up.

M0WWS?

Scan.jpg

 

I've got some info stored away of using a plasma based vacuum coating system (homebrew), and it might be a great way to coat the interior of cases with a transparent but conductive coating.? From what I've seen, the coating isn't 100% transparent, but you can easily see through it and it's still quite clear.? I'd think that would be something to consider for cases, if someone wanted to build such a system or had access to one.

There was also a discussion some time back about using a conductive plastic in 3-D printing that would make conductive cases for good shielding.

Another little point I've learned related to this topic - there is a copper-arsenic alloy is silver-like? in appearance, and has conductivity very close to silver itself.? The only problem with that alloy is that it is not very flexible, and is hard to work with (and it required precise and accurate control of the proportions of copper and arsenic to make it).? The ancient Mayans and some other groups used to make that alloy for decoration (they made all sorts of alloys, based on appearance and cultural ideas about metals at that time).? I've forgotten the actual proportions of each element, but it was like a few percent of arsenic, the rest copper.

If we could somehow manage to make wire with a coating like that but that was usable (flexible/bendable), it would be very useful!? Maybe some way to deposit a thin coating on a copper wire.? it would be cheaper than silver or silver plating, that's for sure!

Bob
N4FBZ

On 7/12/21 5:59 AM, georges bery wrote:
Gordon,
Gathering back memories from engineering school .
Skin effect is frequency related as well as power and conductance dependent .? At DC no skin effect is present . increasing the frequency will lead to a migration of the AC currents at the periphery of? the conductor .
With this phenomenon comes the need to improve conductance of the outer layer to be able to transport the energy needed for your purpose. One of the most obvious examples of this is the L-band cable used to connect the statellite reception antenna to the demodulator . The LNB (low Noise Block convertor) in front of the mirror is the actual antenna , polarity selection and first intermediate frequency downconvertor, it produces a low power radio signal in the 900Mhz to 2.7 Ghz range . Millions of instalations worldwide needed a cheap way of connecting this from the rooftop to the living room so a cable with a steel core is cheap as the center conductor can be used as pin for the (#*&!@) F connector . However steel is a poor conductor altough its mechanical qualities are welcome , So in comes copper cladding the core and skin effect . Good quality RF high power cable are therefore thick often silverclad as silver is the best conductor and hollow when you go to very high power at very high frequency.
Faraday cage is another kettle of fish. here you are talking of equipotential surfaces .When you surround something with a conductive layer there is no electron flow inside as there is no difference of potential between different points of the surface. It works both ways and is at its best when the conducting surface is solid . Often compromises are made to save material costs or to provide cooling and mesh is used instead of solid sheet or conductive paint loaded with metalic oxides or graphite to make acceptable Farady shields inside plastic cases.
73
Georges
HB9EFN
John Cunliffe W7ZQ
 

Robert,

Simple conductive shielding paint will do the trick. Easy to use and apply.
This is just one of many products available. I use it in many applications.



John

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