What attenuator are you using ?
-100dBm is a lot of attenuation.

Rene

Richard Hosking wrote:
Many thanks for the replies
That has given me some ideas for a start

Richard


Richard Hosking wrote:

Dear all
I want to design a DDS board which has attenuators on the output to
provide a low level output (-100dBm)
I have a venerable HP8640B which can give a calibrated output to -137dBm
To achieve this HP have gone to extraordinary lengths to shield the
oscillator attenuator/output amp circuits and any control lines - I
note there are at least two stages of bypassing/low pass filtering
with an intermediate shielded section

My question is: how do I get data and power lines into my DDS chip (in
a shielded enclosure) and prevent RF leakage out which will limit the
useful minimum level out from the DDS board?
I presume I will have to use a buffer of some sort for the data lines
and extensive bypassing on the power lines. I want reasoanbly quick
update speeds for my DDS, which is a serial port, which will mean data
rates in the MHz region.