Re: [Amps] FW: Â RFI Question

[m.ford]

----- Original Message ----- 
From: "Peter Chadwick" <g3rzp at g3rzp.wanadoo.co.uk>
To: "Larry Carman" <lncarman at swbell.net>; "'Brass Pounder'" <wf3j at comcast.net>
Cc: <amps at contesting.com>
Sent: Saturday, February 04, 2006 12:39 PM
Subject: Re: [Amps] FW: Â RFI Question


> Larry asked:
>> Exactly what is the composition of radar
> absorbent material and how is it applied to the metal surfaces? How does rf
> absorbent material react to different ranges of wavelengths?<
> RAM (Radar Absorbent Material) varies, depending on the application. For anechoic chambers, it's usually in the form 
> of pyramids of some foamed plastic, heavily loaded with graphite, and is pretty filthy stuff  to be touching as you're 
> setting up in the chamber. This works reasonably well dow to around 400MHz, depending on the size of the  pyramids. 
> For lower frequencies, powdered ferrite is added to the mix, and even ferrite slabs are used, placed under the 
> pyramids. It has been known for enough energy to be absorbed from a microwave transmitter/antenna in an anechoic 
> chamber for the pyramids to be heated to the point where they catch fire! Very nasty, with lots of toxic gases and 
> fumes, and carbon dirt EVERYWHERE!
> Stealth aircraft rely heavily on the reflection back to a monostatic radar being low, because the signal goes off in 
> another direction - this caused by the geometry of the various surfaces: I suspect the RAM used there is a resistive 
> material, possibly with ferrite loading again.
> 73
> Peter G3RZP
> _______________________________________________


As I understand it, the surface of the pyramids reflect the wave
deeper and deeper into the panel where they cannot escape by
reflection and are thus attennuated.

Mike k1ern