MY QO100 SETUP

  • PA3FYM I test' my 'chip PL902191 driving at 1MHz from NEO7M and producing 25 & 27MHz. The generated signals have less jitter that the 1 MHz but it is still too high the jitter to be used directly. I try to cascade at 25MHz with PL902167 and if this fails, I want to make a PLL at 25MHz. But it seems the arduino PLL is the best solution waiting for the 390 and 4046 that I have order and the new release from you.

  • SV1BDS I was not satisfied with the results in my contraption (i.e. Philips 10 MHz TCXO with LS86 phase detector @1 MHz using a Ublox producing 1 MHz and cleaned with a dedicated jitterblocker).


    On receive jitter was still present and a LOT of phase noise. Most signals sounded like there was aurora ; -)


    Weighing the ingredients time, homebrewing, components, result and satisfaction I went for the Lars GPSDO.


    Less time, less components, cheap, good result and satisfied : -)

  • PA3FYM I searched for PL904 and I see that no one selling them. For Lars gpsdo there is no need to use a NEO7 I think a chiper NEO6 is suitable as it produces 1 pps. Also I will try to lock a 25 MHz VC-TCXO using one more /5 divider on the HC390 to provide the 5MHz and 1MHz required. As you know the software is any reason that it will not work?

  • PA3FYM I searched for PL904 and I see that no one selling them. For Lars gpsdo there is no need to use a NEO7 I think a chiper NEO6 is suitable as it produces 1 pps. Also I will try to lock a 25 MHz VC-TCXO using one more /5 divider on the HC390 to provide the 5MHz and 1MHz required. As you know the software is any reason that it will not work?

    Of course any (proper) 1 PPS GPS-rx can be used. There is always jitter on the 1 PPS (due to propagation/atmospheric issues etc) but that is 'smoothened' inside the GPS-rx. Also in the Lars software the PPS jitter is handled.


    Concerning your 25 MHz VC-TCXO, the software does not know you are applying another 5 MHz source (i.e. 25 / 5) but I think you need some fiddling concerning the time constants and 'gain' for the software PID-loop. I reckon your 25 MHz VC-TCXO has a higher 'k' (i.e. Δf/ΔV) than 'the average' OCXO. But these parameters can be entered in the software. Bear in mind the software (read: the filtering) was designed for a reference source with intrinsic short term stability (like an OCXO) but I am very curious how it'll perform with your 25 MHz setup.


    Important tip: solder the RC-network (3k9 / 1 nF) as close as possible at the analog pin. I soldered the 1 nF directly on the Nano board

  • SV1BDS , PA3FYM , I'm following your conversation regarding the Lars GPSDO with great interest as I'm hoping to do something similar myself. So, Remco, like George I'm very interested in seeing your updated code!

    Given that 10MHz oscillators are much more plentiful than 25MHz, what would you think about building the GPSDO for 10MHz and using a clock multiplier like NB3N502DG to get 25MHz?

  • GI8RQI I know somebody using that clock multiplier but did not get satisfactory results concerning phase noise & jitter (have to ask him precisely what 10 MHz ref he used).


    The only thing which works fine* with me is the setup as published in my first posting ever at this forum: an ADF4001 locked in conjunction with a low noise 25 (or 27) MHz VCXO GPS locked.


    *fine = low phase noise, stability, precision AND accuracy, see picture below :


  • Hi,

    I tested some so called 1N5711 blue diodes that has been bought from eBay. They go up to 500MHz, others (red) go up to 1500MHz and give some signal at 3GHz. The red has 2 pF. The blue ones have a voltage drop of 325 mV and the red one has 650 mV.

  • SV1BDS ... Good question.


    From my quick & dirty analysis it doesn't make a difference as the whole thing is edge triggered.


    I have to dig deep into the ATmega328p datasheet to find out if the 'delay' between the 20% vs 50% duty cycle generates an intrinsic 'phase offset' (which will be compensated anyway).


    Code
    1. _____|----|_____ (50% duty cycle)
    2. ________|-|_____ (20% duty cycle)
    3. . .
    4. . .
    5. |dT| Question: delta T matters ?