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Micro908 info

Micro908 Information and Files (rather old now)

Whilst I think that my AMQRP Micro908 is a brilliant piece of kit, its accuracy at higher frequencies has always been slightly suspect. When I added a DDS60, it was even worse. I was hoping that v6.0a of the AA908 software would bring about improvements but this was not so. See the following posting to the Micro908 reflector:

http://www.applegate.org/pipermail/micro908/2007-February/000929.html

A few other people reported similar findings.

I therefore decided to take some more readings. Using the debug mode, I extracted a series of data points from my unit for 50 ohm, open, short and 274 ohm terminations at 7, 15, 30 and 60MHz. The results are encapsulated in the spreadsheet given below:

RawDataAnlaysis180207v3.xls

I hoped that these readings would point to a clearly duff channel which I could replace/fix. However, this doesn't seem to be the case. What I see typically is that for a given connection scenario, the "low reading" channel, increases which frequency, whereas the "high reading" channels decrease. I would expect the high reading ones to go down since the output of the DDS60 falls with increasing frequency but I wouldn't expect the "low reading" ones to go up. I have put some of the graphs below - there are more in the spreadsheet.

UPDATE 24/2/07- I have now taken some further readings with a 100MHz scope, a spectrum analyser and a calibrated power meter. From these I have found that

a) The DDS60 output is clean (harmonics at 45dB below the carrier)

b) The reflectometer is splitting the output from the DDS across a 50ohm dummy load properly

c) The values measured by the Micro908 VF channel track measurements taken by an accurate power meter connected to the output. See graph below:

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I would be interested to see what the readings would be for an accurate Micro908.

In order to gather data, the process is:

a) Connect to the Micro908 via TerraTerm in the usual fashion

b) Go to the AA908 config menu and select Debug Monitor

c) Fix the appropriate load to the Micro908 and set the dial to the required frequency. Every time you change the frequency, the debug information is written to TerraTerm over the serial link.

d) Once you have the load and frequency correct, clear the buffer on TerraTerm by going "Edit -> Clear Buffer". This should also clear the screen. Hit return and the Micro908 will send a set of debug info to the screen. Copy all the data - you might need to scroll up to get to the beginning.

e) Open a copy of the above spreadsheet and paste in the information over the data already present. Note, it needs to be in text format.

f) The graphs should then automatically update themselves.

Any problems - let me know. If you have an accurate Micro908 and wish to share the results, I'll be happy to upload another spreadsheet here. Please email me at