Tuesday, 16 July 2013

DATV-Express Phase plots

Here is my first attempt at measuring the phase noise of the Fractional-N
synth used by the ADRF6755 PLL/Modulator. The light blue trace at
the bottom is the base reference for the Agilent E4406A used to make
the measurements. However it is at 50 MHz so not that representative.
In fact at frequencies below 10 KHz and above 1 MHz it looks as if
the phase noise from the Agilent may well be dominating the plot.
These plots were done using John KE5FX's PN software.
The results are within a few dBs of the equivalent trace in the Analogue
Devices data sheet.  The above trace has spur removal activated. There
were 3 main spurs within the loop filter bandwidth that I could see.
The first was at 50 Hz (UK mains frequency), the next at 150 Hz and the
last at 5.5 KHz, this last spur is probably related to the divider/charge pump
in the PLL as it changes with frequency in a very predictable manner.
None of the spurs exceed the manufacturer's data. All these traces were done
at 1.2 GHz to match figure 27 in the data sheet. The ADRF6755 was silicon
revision 4.


  1. Is the DATV-Express still on schedule for sale in October?

    I'm planning on attending the TAPR conference in Seattle in September.

    Mike KM7MH

  2. Hello Mike. It is not looking good for October. There is nothing
    major holding us up, things are just taking a bit longer than we
    hoped. The current issue is that some noise from the PSU appears
    to be getting into the output.

    What tends to happen is that nothing much seems to be happening and
    then suddenly everything happens at once so I am not ruling October
    out completely.

    - Charles