On 2021-07-08 11:47, Max via groups.io wrote:

Sounds like rf maybe coming in through the mike cable. The bigger
problem is the fact that none of the jacks (mic, keyer, antenna, etc.)
are grounded to the case BEFORE entering the radio. AS is, I'm not
sure if the case does much shielding at all. Sorry to say it, but this
part is a bad design!

** I disagree. Vehemently. Connectors should NOT be individually grounded
to the case. The case should be grounded to the ground plane in one spot,
and one spot only.

If you ground the case in multiple places, you risk causing RF currents
to flow through it. This can cause the case to act as an antenna, rather than
as a shield. For low level audio, it can cause "ground loops". Same deal.

- Jerry KF6VB

On Jul 11, 2021, at 14:41, gareth.paley@... wrote:

?I'd agree with it coming through the mike cable. Just added this electret fist mic from Amazon to mine (??) which doesn't appear to have a shielded cable. This LCD screen became corrupted on speech peaks and sometimes locked in TX which didn't happen with an electret element soldered directly to a mic plug. I'm running an end fed half wave on 20m but there's an RF choke on the coax just before it enters the shack which should block any RF, never-the-less RF was getting in through because as soon as I put a 22nF cap across the PTT and ground pins on the back of the mic socket it cured it. I seem to remember this being pretty standard practice even on CB's and the like.

M0WWS

<Screenshot 2021-07-11 192944.jpg>

Presuming that the case is all encompassing, then in the theoretical sense, the currents must flow on the outside of the case. ?Due to RF skin depth those currents won¡¯t be very deep. I¡¯m not sure exactly how deep. ? ? ( ? I suspect physical reality differs slightly due to imperfection)

?

However, the typical view of the conductive faraday cage is that there won¡¯t be currents on the inside surface and therefore there can be no potential differences between one point on the inside surface and another. ? ? ?

?

I had never really thought about that before. ? RF currents have a skin depth. ? I would encourage debaters to address how this electromagnetic theory applies to their position.

?

?

On Jul 12, 2021, at 01:46, Jerry Gaffke via groups.io <jgaffke@...> 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.? My first guess would be to expect it
to decrease linearly with with frequency, but it instead decreases with the square root of the frequency.
And can be quite significant way down at 60Hz.

So if you have a 200 amp service entrance for electrical power into your house, the copper conductors
are often big flat pieces of copper to increase the surface area available.? A round conductor of the
same amount of copper would have considerably higher resistive losses.

Jerry, KE7ER


On Sun, Jul 11, 2021 at 11:53 AM, Gordon Gibby wrote:

Presuming that the case is all encompassing, then in the theoretical sense, the currents must flow on the outside of the case. ?Due to RF skin depth those currents won¡¯t be very deep. I¡¯m not sure exactly how deep. ? ? ( ? I suspect physical reality differs slightly due to imperfection)

?

However, the typical view of the conductive faraday cage is that there won¡¯t be currents on the inside surface and therefore there can be no potential differences between one point on the inside surface and another. ? ? ?

?

I had never really thought about that before. ? RF currents have a skin depth. ? I would encourage debaters to address how this electromagnetic theory applies to their position.

?

?

Amazing !!

On Jul 12, 2021, at 01:46, Jerry Gaffke via groups.io <jgaffke@...> 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.? My first guess would be to expect it
to decrease linearly with with frequency, but it instead decreases with the square root of the frequency.
And can be quite significant way down at 60Hz.

So if you have a 200 amp service entrance for electrical power into your house, the copper conductors
are often big flat pieces of copper to increase the surface area available.? A round conductor of the
same amount of copper would have considerably higher resistive losses.

Jerry, KE7ER


On Sun, Jul 11, 2021 at 11:53 AM, Gordon Gibby wrote:

Presuming that the case is all encompassing, then in the theoretical sense, the currents must flow on the outside of the case.? Due to RF skin depth those currents won?€?t be very deep. I?€?m not sure exactly how deep.???? (?? I suspect physical reality differs slightly due to imperfection)

?

However, the typical view of the conductive faraday cage is that there won?€?t be currents on the inside surface and therefore there can be no potential differences between one point on the inside surface and another.?????

?

I had never really thought about that before.?? RF currents have a skin depth.?? I would encourage debaters to address how this electromagnetic theory applies to their position.

?