[R-390] Signal Generator Impedence Questions

[David Wise]

Roy Morgan beat me to the punch in saying that the GR1001A
"impedance matching adaptor" was nothing more than a 40 ohm
resistor.  The connector assembly it's embedded in costs
about 100x what the resistor did.

But I want to take issue with your statement that the
1001A does not have a calibrated attenuator.  It most
certainly does, unless early production omitted it.
To get 150uV (assuming it's terminated right), using
the CARRIER control you set the meter to the SET CARRIER
line, then set the step attenuator (MULTIPLIER) to 100uV,
and set the vernier (OUTPUT) to 1.5 .  Simple.

73,
Dave Wise

> -----Original Message-----
> From: Roy Morgan [mailto:roy.morgan at nist.gov]
> Sent: Thursday, June 02, 2005 12:00 PM
> To: Barry; R-390 at mailman.qth.net
> Subject: Re: [R-390] Signal Generator Impedence Questions
> 
> 
> 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 --
> 
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