What consequence for 75 Ohm output into 50 Ohm input ?

How should I recalibrate a HP 3336A 75 Ohm output signal generator (
with better than .2 dB output resolution ) for use into 50 Ohm DUT's ?

Thanks
Peter.

 

Perhaps the simplest thing is to make a 75 ohm to 50 ohm T matching network
with a fixed attentuation.

Ian

 

There are commercial L-pads to convert from 75 to 50ohm,with enough
bandwidth and low VSWR for much higher frequencies.
This generator only goes to 21 Mhz,IIRC.

 

Well, I mean : how should I read the ( in 75 Ohm output calibrated ) dBm scales
when the HP 3336 generator's 75 Ohm output is inputted into 50 Ohm devices ?

I guess there is a calculating factor for it.
VSWR will be 1.5 ( right ? ) i.e. 4% power transfer loss.
Is it as simple as that I can multiply the output scales with a 100/104 fraction ?

Peter.

 

(Peter) wrote in

A commercial L-pad should have the db loss marked on it,or in the datasheet
that originally came along with it.
Then you just subtract the db loss of the L-pad from the output db's.

 

We called them "min-loss-pads" years ago

Frank

 

If you terminate a 75 ohm generator with 75 ohms, the open circuit output
voltage will drop by 6db right? Now if you terminate the same generator with
50 ohms the open circuit output should drop by
7.9588 db. The difference (7.9588 - 6) = 1.9588db.
bg

 

75 ohm gen >----[ 43.3 ohms]--------o---------->50 ohm DUT
|
86.6 ohms
|
///

use a 43.3 ohm resistor in series and a 86.6 ohm in shunt to gnd...







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Then use a power meter to determine the output level and L-pad loss.
If you use SMD resistors and a PCB,you ought to achieve a decent BW.