Subject: Re: Wideband gain measurement
From: "John C. Price"
Content-type: text/plain; charset="US-ASCII"
NNTP-Posting-Date: Wed, 09 Oct 2002 15:51:18 GMT
Organization: AT&T Broadband
Date: Wed, 09 Oct 2002 15:51:18 GMT
Thanks again to everyone for the helpful comments. I think I will manage to
get what I need with a home made attenuator and the scope. Right now I am
stuck because my signal source stinks, but I will get something better soon.
Yes, what is a phase angle voltmeter? Sounds a lot like a lock-in, but
maybe no phase locked loop in it, so you need a healthy reference signal?
And what is a vector voltmeter, such as the HP 8405A? Same thing?
By the way, 1000 G-Ohm resistors show frequency dependence even at 100 Hz,
due to distributed self capacitance. You can read about it in Electronics
Letters, vol. 38, p.413 (2002), but beware that the author is unreliable.
Being new here I cannot resist thanking Mr. Hill for his book. Changed my
life when I was an undergraduate.
On 10/9/02 8:48 AM, in article IkXo9.24957$Fz.email@example.com, "Ban"
> "John Woodgate" schrieb im Newsbeitrag
>> I read in sci.electronics.design that Ban wrote
>> (in ) about 'Wideband gain
>> measurement', on Wed, 9 Oct 2002:
>>> you can greatly increase the accuracy with a precision adjustable
>>> and your scope as a display.
>>> generator>input amp>Channel1
>>> output amp>attenuator>Channel2
>>> now adjust the generator that the amp is in a linear region without
>>> overload, high enough out of the noise and hits a horizontal line(90%) on
>>> the screen.
>> Before you go on, disconnect the amplifier and attenuator from the scope
>> and connect the generator, at the output level setting you have just
>> found, to BOTH channel 1 and Channel 2. Adjust the channel gain controls
>> until the two traces exactly co-incide. You have thus eliminated any
>> error due to channel gain difference from your measurement.
>> Then re-connect the amplifier and attenuator to channel 2 and go on to:
>>> set the attenuator course to-30dB and adjust the fine scale until both
>>> traces are of equal height. Write down the value, it corresponds to the
>>> of your amp.
>> Regards, John Woodgate, OOO - Own Opinions Only.
> John, thanks for this excellent extension!