[R-390] Measuring Sensitivity - divider correction

[Roy Morgan]

R-390 folks with GR 1001A generators,

I made an error in my email about making a divider to ensure getting the 
right voltage into a receiver:

I wrote:
> > Here is what I suggest,
> > Make up a voltage divider with a 50 ohm resistor and a one-half ohm
> > resistor in series from the input to ground.
...
> > - It will divide the voltage at it's input by 100.
...
> > The voltage at the antenna terminals will be one hundredth of the panel
> > indication.

Barry wrote:

>Roy,
>
>I'm curious about this voltage divider.  If the voltage at the output end of
>the cable when terminated in a 50-ohm load is 1/2 the value set on the
>generator's controls, then is it correct to say that the voltage at the
>connection between the 50-ohm and 1/2-ohm resistors is actually
>one-two-hundredth the value shown on the controls rather than
>one-one-hundredth?


Indeed, Barry is right (and has confirmed it by actually measuring some 
voltages!)  Thanks to him for pointing this out.

The GR-1001A produces one half the panel indicated voltage if its output is 
properly terminated.  SO:

Make a 50:1 divider to load it and deliver one hundredth of the panel 
indication by  using a 50 (or 49) ohm resistor in series with a ONE ohm 
resistor (for a division ratio of 51:1 (or 50:1).

Then use the 40 ohm series unit on the generator with the 100 micro volt 
multiplier setting, and the divider at or close to the receiver, and divide 
the indicated output voltage by 100.  The generator is easy to read and 
deliver from zero to 2.0 micro volts by using the "OUTPUT" variable control.

There, I expect this is right now.

Roy


- Roy Morgan, K1LKY since 1959 - Keep 'em Glowing
13033 Downey Mill Road, Lovettsville, VA 20180
Phone 540-822-5911   Cell 301-928-7794
Work: Voice: 301-975-3254,  Fax: 301-975-6097
roy.morgan at nist.gov --