7A22/7A13, was RE: 475 instead of 475A?


Craig Sawyers <c.sawyers@...>
 

The 7A22 has a sensitivity of 10uV /div and has built in high and
low pass filters. The maximum bandwidth is limited to 1MHz. The
differential input will allow you to look at ballanced as well as
unbalanced signals. It is well suited for audio work.
I'll second that John! Used in differential mode, it will also give a CMRR
of 10^5 at 10uV/div to 10mV/div with matched probes (P6055). This falls to
10^3 for 20mV/div - 10V/div. There is a variation with frequency and ac/dc
coupling, but the above a typical figures in the audio range. There is a
basic dc offset control to measure signals on DC, with a range depending on
sensitivity.

I'd also add the 7A13 diffential comparator. This has a poorer CMRR than
the 7A22 of around 2x10^4 and only goes to 1mV/div. But you can offset the
effective dc threshold of the measurement with a comparison voltage up to
(effectively) hundreds or thousands of volts with digital readout (depending
on range selected) - so slow waveforms riding on DC (like power supply
ripple) can be looked at without the amplitude and phase distortion
introduced by ac coupling (of course you can ac couple instead if you wish).
It has the advantage of going to >100MHz in the right mainframe.

Oh, and with a mainframe, you can also get a 7L5 audio frequency spectrum
analyzer. These are still quite expensive, going for around $500-800
typical; however, option 25 that adds a tracking generator so that you can
do swept frequency responses. If you are *really* lucky you might find the
version that comes with log sweep too. The 7L5 has digital memory, so you
don't need a storage scope to view the trace on slow high resolution sweeps.

All in all a mainframe wins every time for flexibility and upgradeability.
The only disadvantage it is relatively heavier and larger than a 475 and if
portablility is an issue that might be a significant consideration.

Craig

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