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

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.

Thanks

Richard

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.

Thanks

Richard

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.

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.

I read in sci.electronics.design that Rene Tschaggelar
wrote (in ) about 'Shielding
data lines to RF circuits', on Thu, 1 Apr 2004:
What attenuator are you using ?
-100dBm is a lot of attenuation.

No, it's only 1 dB of attenuation from -99 dBm. 100 dB is a lot of
attenuation (or gain).
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

I read in sci.electronics.design that Rene Tschaggelar
wrote (in ) about 'Shielding
data lines to RF circuits', on Thu, 1 Apr 2004:
What attenuator are you using ?
-100dBm is a lot of attenuation.

No, it's only 1 dB of attenuation from -99 dBm. 100 dB is a lot of
attenuation (or gain).
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

John Woodgate wrote:
I read in sci.electronics.design that Rene Tschaggelar
wrote (in ) about 'Shielding
data lines to RF circuits', on Thu, 1 Apr 2004:

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


No, it's only 1 dB of attenuation from -99 dBm. 100 dB is a lot of
attenuation (or gain).

Got me John,
So how to get -99dBm, considering the DDS outputs in the
order of 0dBm.
Are there any decent digital step attenuators around ?
The better switches available at minicircuits have an isolation
of 80dB when off, their analog Attenuator has a range of 55dB.
In 2 stages then ?

Rene

John Woodgate wrote:
I read in sci.electronics.design that Rene Tschaggelar
wrote (in ) about 'Shielding
data lines to RF circuits', on Thu, 1 Apr 2004:

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


No, it's only 1 dB of attenuation from -99 dBm. 100 dB is a lot of
attenuation (or gain).

Got me John,
So how to get -99dBm, considering the DDS outputs in the
order of 0dBm.
Are there any decent digital step attenuators around ?
The better switches available at minicircuits have an isolation
of 80dB when off, their analog Attenuator has a range of 55dB.
In 2 stages then ?

Rene

I read in sci.electronics.design that Rene Tschaggelar
wrote (in ) about 'Shielding
data lines to RF circuits', on Thu, 1 Apr 2004:
John Woodgate wrote:
I read in sci.electronics.design that Rene Tschaggelar
wrote (in ) about 'Shielding
data lines to RF circuits', on Thu, 1 Apr 2004:

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


No, it's only 1 dB of attenuation from -99 dBm. 100 dB is a lot of
attenuation (or gain).

Got me John,
So how to get -99dBm, considering the DDS outputs in the
order of 0dBm.
Are there any decent digital step attenuators around ?
The better switches available at minicircuits have an isolation
of 80dB when off, their analog Attenuator has a range of 55dB.
In 2 stages then ?

Yes, it's often the simplest solution.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk