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NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs Dear Elimoel A. Elias, It is unlikely that you will find a TDR instrument <italic>per se</italic> that allows you to regulate rise time of the pulse. The TDR instruments on the market tend to use the fastest rise time that the engineers could design into the instrument. You may have better luck looking for an instrument called a pulse generator. These tend to be more flexible in allowing the user to change the rise time, pulse duration, pulse voltage, etc. There are several manufacturers including Tektronix, Agilent, etc. The regular companies that deal with agricultural research equipment will not be of much help. Note that, having found a suitable pulse generator, you will need to couple it with a fast oscilloscope in order to capture the wave form. Some of the early work in TDR for soil water content measurement was done with such combinations of equipment, so you are in good company. The combination of equipment will be more expensive than a dedicated TDR instrument that combines the pulse generator and oscilloscope into one. But, it appears that you need the flexibility to pursue your research objectives. Steve At 06:50 PM 10/30/2001 +0000, you wrote: <excerpt>NOTE: To get off this list, send email to majordomo@aqua.ccwr.ac.za with the body of the message containing the line: unsubscribe sowacs [Resent] (originally sent 17/10/01) Dear list members, I am seeking a TDR instrument with regulable risetime, covering a range as large as possible. Has anyone in this list ever used, or heard of, something like this? I am familiar with a TDR instrument operating at a fast rise time, <<200 pS. I have also heard of instruments with faster rise times, <<10 pS. I am seeking an instrument with a=20 regulable risetime, covering a range as large as possible, perhaps from 10 to 200 pS. But I have been unable=20 to find any information about this. I have emailed some companies: Soilmoisture Campbell Scientific Inc. Tektronix E.S.I. Environmental Sensors Inc. but I have only received negative answers. I will be grateful for any information on this matter. Elimoel A. Elias e-mail: elias@imagenet.com.br Website:=20 <<http://elimoel.freeyellow.com/elimoel.html>http://elimoel.freeyellow.com/e= limoel.html ICQ 109845414 Tel.: +55-19-432-9458 </excerpt> ___________________ Steve Evett, Soil Scientist, Lead Scientist - Water Management Research Unit USDA-ARS, 2300 Experiment Station Rd., Bushland, TX 79012 USA 806-356-5775, FAX: 806-356-5750 srevett@cprl.ars.usda.gov, <<http://www.cprl.ars.usda.gov/programs/>http://www.cprl.ars.usda.gov<<http:= //www.cprl.ars.usda.gov/programs/>/programs/