I did some progress on a solution based on the circuit SI5351 to have something feeding the SDR and the LNB . With the designed I used, I arrive to the conclusion that the performances are insufficient for a high power transmitter. The stability in frequency is good, but I have spurious lines at -40, - 50dB. I gave more explanation at the bottom of this post.
I don't know if SATSAGEN is a reliable analyzer. If you switch 10 dB in between, all lines must decrease by 10 dB.
I have to finish my clock generator and measure with a HP Spectrum Analyzer.
The main issue with the W3PM based design is the usage of fractional-N mode for the correction of the Si5351a output frequencies.
There have been several discussions showing that a clean output cannot be realized when using an Si5351 in fractional-N mode (as required for the frequency corrections with this design).
An Si5351running with integer mode is able to generate 25MHz and 40Mhz with a signal quality that is good enough for QO-100 operation.
73 Jean DJ0VL
I'm preparing to join the QO-100 party after many years or QRT ( the FT847 still looks beautiful but needed a good dusting ) and have a Pluto Rev B to stabilise. I've been looking at this thread about the various options and problems in obtaining certain TCXO's. I came across a 40MHz Kyocera device in a similar package on Ebay today for about £10 and wondered whether anybody here has had any experience using this device. The part number is KT2520K40000DAW18TAS
The spec' looks pretty comparable to the Abracon TCXO : 2ppm (not as good but maybe good enough?) , 1.8v, 10K, 10pF load imp, clipped sinewave output etc.. Phase noise looks slightly better at -86dBc/Hz at 10Hz
Here's the full data sheet https://media.digikey.com/pdf/…20K40000DAW18TAS_Spec.pdf
I'd be interested to hear any thoughts on this device. Once it arrives, I'll feed back my experience of trying to use it.
For those which still need a replacement for the original Pluto TCXO and can no longer find the ABRACON ASTX-13-C-40.000MHz-I05-T
you can replace it by the ABRACON AST3TQ-T-40.000MHZ-28 with some advantages.
The only disvantage is that it costs a bit more. I am using it in two Plutos and works perfectly.
the ast3tq does not work with 1.8v i guess (it is a 3.3v unit) and there is NO CLEAN 3.3v insidfe the pluto
but you can now get 40 megs 1.8v with 0.5 ppm from epson
the astx13/asvrtx13 is now out of stock but the epson works identical
sidenote DO NOT USE THE 1.8v at the front (close to usb connector) ... use the solder lug between fpga and trx chip named 1p8v_clk!!!
the 1.8v at the front is a bit "dirty" while the 11.8v clock voltage is superclean
there is a reason why AD mounted a special low noise voltage chip in front of the xo (now tcxo) and that power chip only powers the clock and nothing else ... wh9le the 1.8v at front powers different things (and so is a bit noisy)
Information here saying the AST3TQ-T-40.000MHZ-28 "does not work on 1.8V" is not correct.
I have it connected to the original tcxo 1.8V and it works perfectly. Please read component data sheet before posting incorrect information.