[Elecraft] KPA500 mobile?

[Wes Stewart]

I am reminded of when I (actually my employer and you taxpayers) bought a 
shielded room to enclose "my" RF laboratory.  This was modular, 16' x 20' x 10' 
and composed of 2" thick particle board, clad on both sides with tin-plated 
sheet steel.  Because I needed to be able to move a rack mounted test position 
with a table top in and out, I specified a four-foot wide door.

The door was constructed similarly with a brass frame around the door and was 
prehung in a brass jam and massive hinges.  It was installed using a forklift to 
position it while the fasteners were tightened.  The jam had a continuous 
channel around the periphery that housed a double row of beryllium-copper finger 
stock backed up by conductive foam.  The door frame had a brass "knife-edge" 
around the periphery that drove into and was pinched by the finger stock in the 
jam.

On of the specs that I remember was 120 dB of isolation at 10 Ghz.  We measured 
this by setting up a source with a horn antenna on a tripod outside the room 
with another horn and LNA into a spectrum analyzer inside the room.  We 
normalized the path with the door open and the horns aligned and then closed the 
door and measured the difference.  It made 120 dB, but just barely; this is not 
a trivial achievement.

To drive home the necessity of maintenance, the vendor engineer said, "Watch 
this."  He took a dollar bill out of his wallet and laid it across the finger 
stock and then closed the door.  I don't remember the exact number but it was 
yuge; the attenuation went down 30 or 40 dB just from breaking the connection of 
the knife edge with the finger stock over the width of a dollar bill. (For what 
this room cost, he should have been using a c-note.)

Wes  N7WS



On 4/14/2017 1:33 PM, Jim Brown wrote:
> On Fri,4/14/2017 1:13 PM, KENT TRIMBLE wrote:
>> The assumption has always been that the driver and passengers are riding 
>> inside a Faraday Cage 
>
> There are HUGE holes in that assumption in the form of non-metallic parts and 
> paint preventing contact between metal parts. An enclosure forms a Faraday 
> cage ONLY if it is continuous. and ONLY if all conductors penetrating it have 
> either a feed-through to the enclosure or, if a shielded conductor, the shield 
> is bonded to the enclosure at the point of entry.
>
> Modern vehicles have lots of paint between metal parts. When I used Hamsticks 
> on my Volvo S80, I had to bond the mount to the trunk, and I had to bond 
> around the trunk hinges.
>
> 73, Jim K9YC
>
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