HI

I was wondering in general, how best to create some VERY effective
shielding between some equipment

for example, I wanted to stack my powersupply ontop of a tuner

while each are in metal enclousures and properly"" grounded i wanted
to go further


what is the best way?? would a thin sheet of lead (i'd encase in a
rubber coating) or a sheet of copper?


or would the only way be to say get some copper tape and wrap the unit?


thanks

The first and most important step is to heavily filter all conductors
entering and leaving both units. This is important because all wires act
as antennas, efficiently radiating and receiving the interference -- it
doesn't matter how good the cabinet is if you have ways for interference
to get through it. Filtering can be simple or difficult depending on
what lines you're filtering, and doing a really good job requires
considerable skill and knowledge. For the tuner, you can't filter the
differential antenna current at the frequencies you want to receive, so
you'll have to put it far away and heavily filter the common mode current.

In addition to heavily filtering all conductors entering or leaving, you
need to enclose each unit in its own secure box. Any decent conductor
(e.g., copper, aluminum, or steel) will do for MF and above. The
important thing is that it can't have any holes or slots except small
ones, and even those will degrade the shielding. This means that all
seams have to be sealed with multiple screws or rivets and/or RF
gasketing material. Any large holes like one for a meter should be
covered with screen which is solidly connected all around its perimeter.

Those are just some of the basics. EMC is a challenging discipline, and
doing a really good job of isolation generally requires skill and
knowledge beyond that which most amateurs have.

Roy Lewallen, W7EL

ml wrote:
HI

I was wondering in general, how best to create some VERY effective
shielding between some equipment

for example, I wanted to stack my powersupply ontop of a tuner

while each are in metal enclousures and properly"" grounded i wanted
to go further


what is the best way?? would a thin sheet of lead (i'd encase in a
rubber coating) or a sheet of copper?


or would the only way be to say get some copper tape and wrap the unit?


thanks

The very first thing to do is to stack the PSU on top of the tuner and
check to see if further precautions are really necessary.

I very much doubt that they will.

If there IS any interference, it will be picked up wherever in the
shack the boxes are placed and the only solution will be to change the
type of power unit.
=====================================

At HF most of the interference you're going to get from box to box is
either conducted along some wires connecting them or radiated by some
large metallic structure (the power cord, the house wiring, etc) that
is connected to wires coming out of the boxes and then picked up by the
antenna.

Although Roy has excellent points about what you need to do to get
solid EMI shielding, you can do a lot without plugging the holes in the
boxes.

Reg is right about the first step. Do you need extra measures at all?

The second step is plugging the BIG leaks, which would involve doing
things like filtering the unshielded cables coming in and out of things
(ferrites on the power cord, for example). Your boxes already have
some shielding by virtue of the fact that they're in metal enclosures
(I assume).

If you are having problems with, say, a switching PSU and you think
it's leaking in to the tuner, try this. Replace the antenna and
feedline with a good, shielded dummy load. Then see if there's any
change in the noise in your RX between setting the PSU on the tuner and
setting it elsewhere.

Dan

Le Fri, 11 Aug 2006 02:57:00 GMT,
ml a écrit :

HI

I was wondering in general, how best to create some VERY effective
shielding between some equipment

for example, I wanted to stack my powersupply ontop of a tuner

while each are in metal enclousures and properly"" grounded i wanted
to go further


what is the best way?? would a thin sheet of lead (i'd encase in a
rubber coating) or a sheet of copper?


or would the only way be to say get some copper tape and wrap the unit?


thanks

You must first try to stack the supply on the top of the tuner and hear
what append.

If it is HF EMC, Roy and Dan give you some advices for that.

If it is 50 or 100Hz, only mu-metal will do something. With copper or
metal, you will only get Foucault's current in the shield, and those
currents will make a new EM field on the other side of the shield.
Successive metal shields can even be a very good mean to transport at
distance a low frequency magnetic field. So, only mu-metal will be
effective in that case.

Dominique

Dominique Michel wrote:
. . .
If it is 50 or 100Hz, only mu-metal will do something. With copper or
metal, you will only get Foucault's current in the shield, and those
currents will make a new EM field on the other side of the shield.
Successive metal shields can even be a very good mean to transport at
distance a low frequency magnetic field. So, only mu-metal will be
effective in that case.

That's absolutely right, although you might get by with a good layer of
steel for mains-frequency shielding. I was thinking only of RF
interference. If you're having problems with mains-frequency hum from
the power supply transformer's field or the field from the conductors
between the transformer and the filter, you'll need some highly
permeable material. Steel might be adequate, but mu-metal is better.

Roy Lewallen, W7EL

What are the pro's and con's of lengenthing a mobile antenna? I have a
travel trailer that I would like to operate from with a mobile vertical
antenna off the back bumper. I standard 8' Huslter type mobile antenna
would be poor with most if its length running parallel the back side of my
aluminum framed trailer body. Would it be benefitial to add about 15 or
so feet of mast to the antenna below the coil? Would an additional 15 feet
of mast below the coil prevent me from tuning to resonance with the
adjustable whip on top? If so, any suggestions as to materials to do
so?

PS: I'm only planning on operating 75M and maybe 40M.

Ed K7AAT

In article 20060812010400.61fa4a39@localhost,
Dominique Michel wrote:

Le Fri, 11 Aug 2006 02:57:00 GMT,
ml a écrit :

HI

I was wondering in general, how best to create some VERY effective
shielding between some equipment

for example, I wanted to stack my powersupply ontop of a tuner

while each are in metal enclousures and properly"" grounded i wanted
to go further


what is the best way?? would a thin sheet of lead (i'd encase in a
rubber coating) or a sheet of copper?


or would the only way be to say get some copper tape and wrap the unit?


thanks

You must first try to stack the supply on the top of the tuner and hear
what append.

If it is HF EMC, Roy and Dan give you some advices for that.

If it is 50 or 100Hz, only mu-metal will do something. With copper or
metal, you will only get Foucault's current in the shield, and those
currents will make a new EM field on the other side of the shield.
Successive metal shields can even be a very good mean to transport at
distance a low frequency magnetic field. So, only mu-metal will be
effective in that case.

Dominique

what is mu metal?

ml wrote:

what is mu metal?

Doing a google search is a good skill to know. This would be an ideal
opportunity to learn it.

Roy Lewallen, W7EL

On 12 Aug 2006 01:02:27 GMT, Ed
wrote:




What are the pro's and con's of lengenthing a mobile antenna? I have a
travel trailer that I would like to operate from with a mobile vertical
antenna off the back bumper. I standard 8' Huslter type mobile antenna
would be poor with most if its length running parallel the back side of my
aluminum framed trailer body. Would it be benefitial to add about 15 or
so feet of mast to the antenna below the coil? Would an additional 15 feet
of mast below the coil prevent me from tuning to resonance with the
adjustable whip on top? If so, any suggestions as to materials to do
so?

PS: I'm only planning on operating 75M and maybe 40M.

Ed K7AAT


Ed, I am assuming you are operating from a fixed location as the
height would exceed that of many bridges on the highway.

Can you get to the roof of the motor home easily enough? If so, I
would mount a bracket on the roof with a quick-disconnect on it. Then
when you reach your location, you can just climb up and mount the
antenna there fro the duration of your visit. Then when mobiling,
move the antenna back to the bumper.

I have operated a lot of mobile 80 and 40 meters. First of all, don't
expect miracles, especially on 80 meters. The placement of either
antenna on the center of the roof of my car has always been noticeably
better than the bumper mount version. I now drive a van and the
antenna is mounted on side of the van. Again, it is much better on
the roof and tunes more easily there too. However, i cannot drive
with it on my roof (I use Hamsticks).

As for your specific question, I don't know the answer, but if you can
find a piece of extension to test it with temporarily, such as a piece
of copper pipe, you might get an answer at an inexpensive cost.

Good luck,
Buck
n4pgw

--
73 for now
Buck
N4PGW