Sunday, April 19, 2015

The Chinese- Polish- German SNA (Scalar Network Analyzer)

I had finished the SNA-JR,  because of  its size and ease of use I was very happy with it for doing basic filter testing.  There are some things that I want to do that would require a more capable piece of equipment.  I still have the PHSNA boards that I want to build someday.
Looking for something else on ebay I came across a listing for  "NWT70 frequency sweep meter 0.05-85 MHZ with 0 to 50 db attenuation" .  Looking at the description and specifications, it appears to be a SNA.  

Searching on the model number and name of the software in the listing I came up with a couple of links that look to be close to the item in the listing.

First is a Polish ham's site.
This is a SNA based on an ad9851 DDS and an ad8307  log detector similar to the PHSNA.  Good documentation including schematic ,circuit board layouts, and firmware.

The second site is from a German ham.

This is a software package that is used to control the SNA.  Looking at the  documentation in German (with considerable use of Google translate) it looks like it had most of the capabilities I was looking for.  Basic functions are a frequency scan, signal generator mode, power meter.  Additional functions included some calculators for LC values, R and LC impedance matching circuits.  Using an external Return Loss Bridge, the software has a function for measuring SWR, and correct  SWR for  the feed line. Adding a 50ohm resistor in series with the output it can compute the impedance of the device under test.  It also looks like you can add a circuit like the PHSNA measurement receiver.  There is a IF offset value that can be set that should directly display the actual frequency when in the spectrum-analyzer mode.
Looking around ebay I found several similar items that have different frequency ranges, one going up to 3.4Ghz.  I ordered the 85Mhz. version., it took about two weeks to arrive from China.  After running the internal calibration procedure, it appears that the functions I desired worked the way I would expect.  Still just starting to play with it, and looking on line for a more documentation.  But so far it looks like the PHSNA boards are going to sit around un-built for a little longer.  Will post updates as a I get more familiar with the unit.

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