In article , wrote:
Don Pearce wrote:

On Mon, 01 May 2006 13:58:50 GMT, (GregS) wrote:

In article ,
wrote:

2 GHz at 12 GHz is 16.67% which is narrow. Don't tell me that there
is no filtering at all. A circulator or isolator has a usable bandwidth
which keeps out of band noise out of the amp. One of my KU band
receivers is aboard the ISS.

Audio is true broadband, from DC to whatever the upper limit is set
at by the design and limitations of the components if it is DC coupled,
and from less than 100 Hz if its AC coupled.

Not only that, but at low to DC freqs., the noise increases dramatically
of most devices. When looking at op-amps I have to often look at DC drifts,
which is the largest noise.

greg

Tell me about it. I've had to design baffling into a system before now
to control air currents that were causing cyclic temperature drifts.
Generally in an audio amp, though, there is sufficient DC feedback to
render this a non-problem.

d

--
Pearce Consulting
http://www.pearce.uk.com


In our analog receivers the DC offset was measured, and a 18 bit ADC
was used to trim the offset to keep it to about a millivolt from
wherever it was set. Some external decoding required a fixed DC offset,
and this was available from the front panel. We also had a 63 dB range
in the output level control, digital with accurate .1 dB steps. This
was on the Microdyne 700 and 1620/1670 series telemetry receiving
equipment.

I forget how this got into this, but I once built a 20 bit, well I don't know how many
bits, but I overlapped two 12 bit stages, and used discrets like a successive
approximation register, and op-amps and got at least 20 bit offset correction.
A/D D/A, but was interesting.

greg