Hello, Check this out, http://www.ets-lindgren.com/CASSPER.cfm, it does a good job of ambient cancellation at 3 Meters. Ken Hall
From: [email protected] [mailto:[email protected]]On Behalf Of [email protected] Sent: Wednesday, January 28, 2004 2:20 PM To: [email protected]; [email protected] Subject: Re: OATS Measurement In a message dated 1/28/2004 3:15:35 PM Central Standard Time, [email protected] writes: The method Dave Cuthbert mentions can work it some cases. I have tried a variation on his method which is to use a combiner for the two signals rather than re-radiating the ambient. The problem is that it doesn't give you a very deep null if the ambient has significant multi-path components, which was the case at my site in the mountains. While it is possible that the radio station could be exactly on the EUT emission frequency, it very rarely is. Most of the time I've seen this problem, it can be solved by simply reducing the measurement bandwidth to sort the two signals out. Of course this only works on narrow band signals and you get a peak reading rather than quasi-peak, but there is a work around. I have successfully argued on occasion that the reading can be adjusted by the same ratio of peak (at the same RBW) to quasi-peak levels of a similar emission from the EUT measured in the clear. Brent DeWitt I have been experimenting with an OATS that from above looks a bit like a B-2 bomber. The EUT sits where the cockpit is, and the antennas ( identical ) sit at the wing tips, they are 90 degrees apart. I'm writing a software module that takes 2 scans at the same time, and has the ability to rotate one plot 90 degrees. I'm hoping that the EUT related emissions will be similar, the Ambients, quite different. Where the sun comes out in Chicago, I'll be able to test this and see what real data actually looks like, over what I hope I see. Anyone else ever try this? Derek N. Walton Owner, L F Research EMI Design and Test Facility Poplar Grove, IL 61065
