Si5351A with TCXO Update

Just a few days ago, I finally received some of the TCXO parts that I've been planning on using with the Si5351A Breakout Board. I had no problem using one on the remaining prototype circuit board that I have, and at first glance it appeared quite stable and also very close to the nominal frequency (my correction factor for this one was only 8 Hz at 10 MHz).

Direct comparisons are always the best way to do things, so I ran the Si5351 with TCXO through my thermal chamber at the same profile that I did in the last test in my initial blog post. Rather than write a whole new blog post, I updated the original post to keep that data together, which will be handy for future reference. Go forth and look at the update at the bottom of the original post. Thanks!

13 thoughts on “Si5351A with TCXO Update”

  1. My two Si5351 kits have arrived in perfect shape. Very nice kitting job. Just had eye surgery so won't be assembling them for a week or so. Will first turn one into a general purpose DDS for the bench but the 2nd I plan to use as the LO, BFO and transmit osc in a QRP transceiver. I'll post progress on QRP-tech group. I'm experienced at SMD assembly at the bench. I have a Rigol spectrum analyzer, a HP 8640b, tektronix scope, DMM's, freq counters, HP lab power supplies . . .etc. . so will be able to use the SI5351 breakout boards in various projects. Years ago when an engineer at TRW I had some pick'n'place machines for SMD pcb assy controlled by the old PDP-11 minicomputer. Wish I could find one of those on the surplus market.

    Thanks for your very fine work and contribution to us ham radio homebrew QRP folks.

    Gene, W5DOR

  2. FB Gene,

    I look forward to seeing what you can do with the Breakout Board, and will try to remember to keep an eye on qrp-tech.

    Thanks for your support!

  3. I want to use the Si5351 board as a general purpose signal generator for troubleshooting receivers. Do you think I could amplitude modulate the output by feeding an audio sine wave into the VDDO pin? Is the I2C interface fast enough to do a rudimentary frequency modulation?

  4. I haven't tried amplitude modulating the output using VDDO, but it seems like it should work in principle. It would be worth trying. As far as FM goes, that approach may work but would be fairly bandwidth limited, I would think. My current version of the Si5351 library for the Arduino can switch frequencies in about 4 ms, but I had a contributor figure out a way to do it in about 500 us. I do plan on trying to change my code to support this speed boost at some point in the future.

  5. If you want to do FM with the Si5351, your best bet may be the Si5351B, which as a voltage control pin to pull the XO.

  6. The board arrived in the mail today. Don't see any way I can isolate and connect to the VDDO pin It appears to be connected beneath the IC. Earlier today, I thought of synthesizing AM by just generating three frequencies, carrier and +/- sidebands with carrier at 4 MA, sidebands at 2 MA, using a resistive combiner. Might work.

  7. I don't see any mention of TCXO in the library, how do I set it up in the example? Does the load capacitance setting matter?

  8. You don't need to do anything special if you are using a 25 MHz TCXO. Until recently, you had to select either 6, 8 or 10 pF load capacitance although it seemed to make little difference when using the TCXO. However, there is an undocumented register setting for 0 pF load C, and you can set that in the latest version of my library.

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