Richard Hosking wrote in message
. au...
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.

Thanks

Richard


When I was very poor, I built a spectrum analyser. It took an eternity,
albeit much was learnt. By far the costliest and most time consuming lesson
was finding I hadn't a hope in hell of meeting a decent performance without
enclosing every circuit block in it's own screened casing, each with
extensive 'cleaning' of the incoming power and control lines. Even the power
supply transformer had a mu-metal screen to reduce magnetic field effects.
regards
john