Paul Burridge wrote:
On Thu, 12 Feb 2004 01:51:41 GMT, "Pete KE9OA"
wrote:

Hi Paul,
I just finished it this evening......................it is a
good piece of equipment, and worth the money. Tomorrow, I will do more
in-depth testing. It appears to have resolution to 6 digits, which is good.
It consists of a pair of 9851 DDS chips, with a 1496 being used as a direct
conversion detector. I think I am going to build another one, so I can use
one at home and one at work.

Thanks, Pete. Resolution is one thing, accuracy is another. Do you
have a proprietory instrument within calibration to compare it
against? I want to believe in this kit.

N2PK's website (www.qsl.net/n2pk) gives exhaustive information about
measurement accuracy, standards and comparisons with professional VNAs.

When used correctly (a necessity for any VNA), N2PK's instrument is so
accurate that he had to go to extreme lengths to find any real
differences from commercial equipment. For example, the measured signal
magnitude tracks a 'standard' step attenuator to better than 0.1dB over
a 90dB range... but which is in error, the VNA or the attenuator? At
those levels of performance, it's almost impossible to tell.

Bottom line: you'll hardly ever need to worry about accuracy as such,
only about using the instrument correctly.

The only minor drawbacks are a small amount of thermal drift (because
this is a DC-coupled system) and the possibilities of responding to DDS
harmonics and spurs; all of these are very thoroughly documented.

If it works as advertised then
it's a significant breakthrough for those of us who feel reluctant to
part with 20,000 quid for a piece of relatively infrequently-needed
test equipment! Please report back here when you've had the chance to
check it out properly and let us know how it performs...

Having had one running for about six months, I can confirm it's
excellent. Far from being infrequently-needed, it has become one of
those instruments I couldn't possibly manage without!

Read the documentation and you'll see exactly why.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)

http://www.ifwtech.co.uk/g3sek