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Old 30th Nov 2017, 7:08 pm   #19
G0HZU_JMR
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Join Date: Sep 2010
Location: Cheltenham, Gloucestershire, UK.
Posts: 3,077
Default Re: Attenuators - theory and the design of.

If you had a source of 50R in series with 50pF and a load that looked the same then one novel way to make a 'flat' attenuator would be to cancel each 50pF cap with a series -50pF cap. This would require an active circuit to create a -capacitor that looked like 'minus' 50pF in series.

Then use a conventional 50R resistive pad (10dB?) in the middle. In theory at least you would end up with a flat frequency response and flat phase and about 10dB attenuation. There would be limitations in terms of signal handling/linearity and bandwidth and it might be tricky to keep it all stable but if active circuits are allowed then this will work across a fairly wide RF bandwidth (in theory at least).
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Regards, Jeremy G0HZU
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