"Frank" wrote in message
news:VPqbe.902$0X6.797@edtnps90...
Thanks again Ed. From everyone of your posts I learn something new.

The MIL-STD-461E requirement for absorbed is a 10 dB return loss at 250
MHz.

Assume you would test the chamber return loss with a tuned dipole having
free space return loss 10dB.

Again, the 250 MHz verification of return loss is measured with a horn
antenna, typically a double-ridged model like the ARA 2020 or the EMCO 3106.

A newer technique is to use ferrite tiles, especially on the floor. They
are less than a half-inch thick, and perform much better at low
frequencies. And the cost is about $100 / sq ft. I like to think of my
walls and ceiling as covered with $5 bills, and the floor carpeted with
$10's.

Your anechoic chamber is never really perfect; however, it becomes "good
enough" when you run out of money.

I have heard of the ferrite floor tiles, and are probably a much better
solution than inverted pyamids fitted into the floor mounted pyramids.

Before I installed the ferrite floor tiles, I had considerable problems with
resonances, starting around 7 MHz and continuing through about 150 MHz,
associated with the chamber XYZ dimensions. After the ferrite installation,
the resonances have nearly disappeared.


I did a lot of analysis to figure out what was required, but never got to
finish it, on account of being laid-off! Nobody ever seems to want to
spend the money to get it right.

You can write that on your chamber wall (but management will be ****ed).

OK, just for trivia's sake. If the antenna base was cylindrical, painted
grey crinkle, had a 6-position range switch and a brown bakelite top
insulator, it was an Empire VA-105.

Describes it perfectly

But, if it was almost a cube, painted battleship grey, had a black front
panel and an 8-position range switch, it was a Stoddart 92138-1 (that
number is a hazy memory). Both were passive antennas. The Empire was used
with the NF-105 receiver,

That was the one I used, now you mention it I remember the model number as
the NF-105


So you're older than dirt too? g


--
Ed
WB6WSN
El Cajon, CA USA