Bodnar GPS locked external oscillator info sought please?

Is there still a benefit from using the likes of a Bodnar GPS disciplined frequency standard as the LO on the Kiwis? I am not sure if firmware updates to the Kiwi have made this moot. Can any age Kiwi be modded to take an external oscillator, and if so where might I find some guidance? Is there a preferred frequency for the external oscillator to be run at? Many thanks for any help here. I hope this is the appropriate section for the query.

Comments

  • Thanks, I admit I failed to find that discussion, however, I don't see any photo in the antenna switch discussion I managed to find showing the pad to connect the external oscillator to. Also, do I need to somehow disable the internal oscillator when using a Bodnar? Thanks again. Perhaps this modification is worthy of a dedicated section with a detailed run through?

  • this may apply, depending on what you want tthe ext. XO for...


  • You will find the 'External ADC clock?" slider control on the bottom left of the Kiwi's Admin->Config page.

  • edited February 6

    Photos of the Antenna Switch

    https://forum.kiwisdr.com/uploads/Uploader/5f/492f44efb5a272d715c5219da67b44.pdfare fuzzy but do show one of my Kiwis with an attached Bodnar coax:


    The coax shield has been stripped back and tinned so that it can be soldered a couple of places for mechanical strength and some silicone sealant (or something, I forget) added for strength. The other end goes to a panel mount SMA or SMB connector on the enclosure LAN-end plate.

    Nothing else is needed since the switching gets taken care of by Kiwi HW

    Glenn n6gn

  • Ah OK, so you can disable the stock oscillator by software, that's very good, thanks I hadn't noticed that option.

  • Thanks again, I have managed to solder a miniature Teflon co-ax to the pads, and place an SMA socket in the front panel, I appreciate your advice and PM's.


  • edited February 12

    I wonder what the range of the ext. clock can be? Is it limited to 66.66

  • If it isn't exactly 66.660000 MHz I think there will be frequency error. Isn't having a correct clock the whole point?

  • I'll have to review the schematic before I refine my question.

  • If it isn't exactly 66.660000 MHz I think there will be frequency error. Isn't having a correct clock the whole point?

    As the exact frequency of the external clock can be entered via admin interface / config tab, I guess that there is some tolerance and no need to hit the 66.660000 MHz exactly (as long as the external clock is stable, of course).

  • That's my understanding. The internal code has a value it calls "clock frequency" and if that matches actual external input then there is no error.

    When I first tried an external Bodnar reference on a KiwiSDR a few years ago, there was a few-Hz error at upper HF, even with correct values the IQ vector rotated when tuned exactly to NIST / WWV transmissions over a line-of-sight path. However John very quickly corrected this error and since that time if the numbers match the external HW, the polar display sits within a few degrees over both short and long term, generally consistent with short term accuracy accuracy of the Bodnar operated in an imperfectly controlled environment..

    I've not played around with picking different but correct external clock values, not least because values requiring more digits, e.g. 66.660123, generally have higher divide numbers within Bodnar or similar SiLabs based GPSDO references so also have higher spurious levels but I suspect it will work. Low (even) integer divide numbers tend to produce better spectra so staying with the standard value works pretty well.

    It's possible that, say, 66.000000 MHz even could work and if one has a clean and precise source there that things still work OK. How far one can go from this value is in question since internally other processes, not just frequency may also depend on having an absolute value. I suppose that is a question for JKS.

  • My bad, on looking at what the bit of debris in the photo was that I had left by the crystal oscillator I noticed the xtal frequency was not 66.66 MHz but 66.666 Mhz, so corrected the pen marking ;) The debris was just a bit of flux residue from when I cleaned the soldered area.


    I'm wondering if the external oscillator solder pads match one of those tiny button type mini coax sockets, I forget their name, but I think I have some. I could then use one on my other Kiwi and utilise another of the coax cables I bought in its entirety, which have an SMA female bulkhead socket one end and one of the tiny pop on button connectors at the other, instead of butchering them. That would make a more sanitary installation than my cack handed soldering of the coax direct ;)

  • As shown on the schematic, that "do not load" (DNL) position is for a U.FL connector (Hirose) https://en.wikipedia.org/wiki/Hirose_U.FL

  • Thanks, those are the ones, I got a few thinking to use one for my Pluto SDR, again for an external GPS locked LO. I ended up doing the direct coax connection as on my Kiwi as a U.FL wouldn't really fit the pads left on removing the tcxo.

  • How can I split the output from one Leo Bodnar to several Kiwi SDR's please? For 10MHz I use a commercial 75 Ohm box, not sure what's best to use for 66MHz? Thanks.

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