VK3AQZ Si5351 drift test

[@Magikflame]

Update re. the BPSK modulation present on the PPS output pin from the uBlox GPS module: I mentioned the use of a Costas Loop in my previous comment - not needed. I read one single sentence somewhere online that set the ball rolling for me - feeding a BPSK through a frequency doubler also doubles the phase, so 180+180=360* in other words it cancels out thereby removing the modulation. I removed the XTAL from the si5351 board and fitted a 0.1uf capacitor to XTAL pin 'a' as per the datasheet, I set the NEO-M8 module to output 12MHz and feed it into a simple single transistor frequency multiplier 2n2369a with a collector tank circuit tuned to 24MHz which drives the si5351 and in the Arduino IDE just put 24000000 into the line of code that specifies the frequency and it works great !! Rock solid and a quiet carrier with the si5351 outputting 144-146MHz in quadrature and I use clock 2 for the BFO/CIO which goes to the SSB board. I tried connecting the GPS board directly to the si5351for comparison and although the frequency was rock solid you could clearly see/hear the modulation that is present. I had a 56 ohm resistor connected at the PPS pin of the GPS module to apprx 1 meter of RG174, at the si5351 end I had a 100 ohm resistor in series with the 0.1uf cap connecting to XTAL pin-A I set the GPS to output 12MHz and in the Arduino sketch set the same frequency and load capacitor to 10pf and got the best results for that test. I also have the same NEO-6M as you use Lou and will try the above with that module too and look forward to seeing if I get the same results. Bottom line: for less than £10 sterling and just a few components you can have GPS precise frequency for your rig and/or test equipment. Looking forward to your next video Lou, you really inspire me with your projects! 73 de 2e0iiz

[@vk3aqz]

Hi, yes, thank you for all that. Currently in the desert travelling. Hope to be back in civilisation soon. Cheers and stay healthy.!

[@theDaftman]

Would love to see more on the signal generator please. How its put together and code used.

[@vk3aqz]

There is more here on the generator. Give me your email and I can send the code and circuit. Cheers, kzbin.info/www/bejne/jnLRlqashZhjbZosi=LjUOqvc3urpKYkou

[@radio655]

Beautiful equipment. One bonds much more with test equipment that was self made, isn't it? The counter does not have an external clock input to connect the GPS permanently?

[@vk3aqz]

Hi Jan, no the counter just has an ordinary crystal oscillator and no external locking input. I guess it would not be hard to phase lock the crystal oscillator with a varicap driven from a phase detector locked to a GPS or TCXO (when there is no GPS signal). But I don't use it often and generally just check it's accuracy when I need to. Thanks for the compliment on my homebrew equipment. Thank you, and take care, Lou.

[@galileo_rs]

Feed the Si5351 with a 24MHz output from the GPS module ...

[@vk3aqz]

My GPS does not seem to put out any signal more than 16MHz.

[@galileo_rs]

@@vk3aqz That's strange, my M8 has no problems with 24MHz. Try feeding it with 12MHz (internal clock is at 48MHz so anything that is a division of 2^n should be low jitter).

[@galileo_rs]

Or at least the M8 one is at 48, check your model.

[@vk3aqz]

@@galileo_rs Hi Dragan, yes, my GPS is a NEO6 - M. I did have a NEO 7 but it was a fake one from China and refused to accept any changes from the UBLOX software. It just sat in default with 1PPS output. Yes, your idea is good in some applications. I did have an earlier Si5351 locked to a PAL subcarrier system (Rubidium clock) I had from a TV PAL SPG unit. But it was not small or portable so I now just use the GPS and calibrate my frequency counters. The other issue I have here is that in the room (metal roof!), my GPS signal cuts in and out, and during those times, I lose lock. On my transceiver I now use a TCXO to drive the Si5351 and it stays within 1Hz no matter what happens with any GPS source. So I just check that with my PAL clock, or a GPS from time to time. I should point out that the whole idea of publishing this video is to let others know that if they use an Si5351 without due care to environment effects, it will not be accurate. Some believe that these devices are very accurate when in fact they can drift with temperature, for example when they go outside on a very hot or cold day. So that is the purpose of the post.

[@Magikflame]

​@@vk3aqz The Si5351 itself only does the arithmetic, it is the oscillator module that clocks the Si5351 on the board itself that is the cause of the drift. I have both the Neo-6m and Neo-8m and the 6m does put out higher than the datasheets specified 1KHz, but anything over 10MHz is pushing it - the waveform looks very poor. The Neo-8m however is fine right upto 24MHz, It will not go any higher than this and I beleive I have a genuine module according to the data I can see filled in the Ublox Ucentre evaluation software connected to the Neo-8m, the 6m however returns no manufacturer fields, they are all blank, so I guess I got a fake too. You will need a 'costas loop' to get rid of the BPSK modulation that is present on the timepulse pin on the Ublox modules. There are higher priced modules within all of the various series with the suffix 'T' that are meant specifically for timing applications, it would be interesting to see if the phase modulation is present on these modules also. When I purchased the two modules I noticed the 'T' versions were apprx 10x the price! The GPS boards as received had pin 7 soldered to ground, I connected it to the 3.3v VDD which enables pins 5&6 which you connect 27R series resistors to the centre two pins of a USB socket, data&clock (and ground, the +5v pin can be used if desired to power the whole board as it has a 3.3v regulator) then you have a USB interface without the need for an RS232 adaptor, that said now I hve found more uses for them I find I can have a much longer RS232 cable than I can with USB. If it's any help Lou, my Neo-6m needs to be on a window ledge, whereas the Neo-8m will work just fine just about anywhere indoors or out. 73!!