I don't know a standard but I can tell you that you don't need to measure it and how to do it if you still want to.
Quoting MIL-STD-461E para. 4.3.2.1: " Minimum performance of the material shall be as specified in Table I. The manufacturer's certification of their RF absorber material (basic material only, not installed) is acceptable." And from the appendix para. 40.3.2.1: "It is intended that the values in Table I can be met with available ferrite tile material or standard 24 inch (0.61 meters) pyramidal absorber material." Table 1 is as follows: Frequency Minimum absorption 80 MHz - 250 MHz 6 dB above 250 MHz 10 dB Measuring absorption is conceptually easy. Aim two antennas at a bare metal surface. Drive one and receive with the other. Record transmit and receive levels. Place absorber on bare wall and repeat measurement. The difference in dB is the absorption. This is a very easy test to do at microwave frequencies where you can use a high gain horn, because you can put the receive horn in back of the transmit horn and be in a back lobe and minimize antenna-antenna coupling. But this doesn't work at 80 MHz with a biconical. My advice would be to get what the mil-std says and rely on the manufacturer certification. If you insist on checking performance at 80 MHz, here is my non-standard and esoteric advice - I welcome other practical and perhaps more ingenious approaches. Make the following measurement in the unlined (bare-walled) chamber: Set up two biconicals at random positions in the room but at least one meter apart from each other and well away from walls (following mil-spec guidelines for antenna separation from walls and ceiling and floor). Apply 0 dBm into one antenna and record received power in other antenna. Do this while sweeping the biconical range, 20 - 200 MHz. You will see large variations in peaks and valleys due to room reflections. Repeat this measurement after you have lined the chamber. If the variations between peaks and valleys has decreased by the amount listed In Table 1, you have a successful installation. A slightly more sophisticated version of this test is to use a paddle to stir the room with the spectrum analyzer in a max hold mode, and record until all sharp dips are gone. Repeat this with the room lined. The level at each frequency should then be down by the mil-std table 1 value assigned to that frequency. Final advice. Tiles are expensive but they take up less room. If you are retrofitting a small chamber, you may have to go with tiles to retain enough empty volume to perform testing. The tiles are spec'd from 30 - 1000 MHz. Since the mil-std takes you above 1 GHz, you need the hybrid tiles with cones glued on to give you anechoic performance all the way to 18 or 40 GHz (assuming you go the tile route). Ken Javor on 1/11/02 2:32 PM, [email protected] at [email protected] wrote: > > Can anyone point me to a reference for measuring the absorption of anechoic > material to verify the requirements as specified in MIL-STD-462D? > > Thanks, > Susan Beard > > > ------------------------------------------- > This message is from the IEEE EMC Society Product Safety > Technical Committee emc-pstc discussion list. > > Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ > > To cancel your subscription, send mail to: > [email protected] > with the single line: > unsubscribe emc-pstc > > For help, send mail to the list administrators: > Michael Garretson: [email protected] > Dave Heald [email protected] > > For policy questions, send mail to: > Richard Nute: [email protected] > Jim Bacher: [email protected] > > All emc-pstc postings are archived and searchable on the web at: > No longer online until our new server is brought online and the old messages > are imported into the new server. > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
