[R-390] Signal Generator Impedence Questions

[Roy Morgan]

At 02:23 PM 6/2/2005, you wrote:
>The GR1001A doesn't have a microvolt meter.

To Barry and all,

I have both information and experience with the GR 1001A. (I thought I had 
a manual in digital form, but I find I do not.) I'll provide more details 
later, but in short:

  - The thing was meant to be operated with a 40 ohm series output resistor 
to create a generator of  50 ohms source resistance.  For the RF Level Set 
meter, Output mulitplier, and Output Variable control to give you a correct 
indication, the end of any cable needs to be loaded with 50  ohms.  With 
the end of the cable not terminated, you get twice the indicated output.
  - They provided one 50 ohm load that was also a voltage divider (I think 
it was 10:1). Use of that thing let you be quite confident of the actual 
voltage at the input of the receiver (or whatever) with little effect from 
the actual receiver (or whatever) input impedance.

>  In reality, I was guessing at 150uV by setting the output level to 100uV 
> and setting the adjustable attenuation control to 150%.

You did just the right thing *IF* you loaded the end of your cable with 50 
ohms, *and* used a 40 ohm series resistor at the generator.  (And avoided 
the one attenuator setting that is not 10 ohms source impedance.)

>  Kludgy, but probably not too far from accurate
>(if it is in calibration which I'm sure it isn't).

It may be closer than you think.

More later.

Roy

- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
7130 Panorama Drive, Derwood MD 20855
Home: 301-330-8828 Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-948-6213
roy.morgan at nist.gov --