Posts by SM7PNV

    Great! Thank you for sharing.
    I have a module I have not built yet so nice to get some outside validation that it works well.
    I will use a 1.6mm PCB and manually cut 50ohm stripline with a scalpel to my SMA edge connectors as the module seems to be made to have a 1.6mm PCB between its pins and the ground-plate.

    How much heat is it generating for you?

    I guess your big heat-sink is little bit overkill at 0.4W ?


    //Harry

    I have modified a couple of them to run from a OCXO.
    They were very clean after the mod.


    I know that some TCXOs are not ideal in their frequency corrections and I guess that is what some people have gotten bitten by.
    If a TCXO would be used I would recommend the Abracom lines, I use them myself with good result in HF WSPR applications.
    See here for a good investigation by Jason Mildrum / NT7S
    https://nt7s.com/2016/04/si535…akout-board-tcxo-upgrade/


    73

    //Harry

    Very clever to use the original cover!

    On the other hand for lowest noise figure it is hard to beat having the antenna directly in on the gate of the the first amplifier.
    The best LNB option in my view would be to find a low cost "slim" LNB with a fitted dielectric lens that is a PLL unit and preferably using a 25MHz crystal for easy conversion from 10MHz.
    I'm on the hunt for a suitable unit and have a couple of slim LNB in transit.


    It's great that Oscar 100 forces us to build for microwaves.
    I find it really enjoyable trying to figure out how to build a station in the smartest way and I guess so does a lot of other Ham.
    Lots of great ideas and builders on this forum.
    Fun times! :-)

    Yes, I agree on that as well. I have some experience with both OCXOs and GPS modules.
    I run my downconverter from a 10MHz OCXO that I convert up to 25MHz and send up to the LNB and that seems to me is the way of doing it. A TCXO can also be used and is probably good enough especially if it sits in the rack and feeds the 25MHz remotely.


    In my view a OCXO don't really need constant GPS adjustments like in a GPSDO to keep it on frequency.
    It is nice to have but the drift is so low it is probably OK to just adjust it once a year just for crystal aging.
    If you do have the means to build or construct an GPSDO with a OCXO then by all means go ahead and do it but it might be overkill in my humble opinion.
    The OCXO I use is a rather affordable module and when I look at it's drift using either a Rubidium standard or a warmed up HP Z3805 the drift is so low, we are talking fractions of PPB for the most time that I don't have the skills to build anything to try to correct that without actually worsening the drift and jitter.
    Of course it can be done as evidenced by the HP Z3805 but for myself an OCXO that I re-calibrate once a year if needed is good enough and much smaller and easier to deal with (my HP Z3805 needs 48 hours of warm up to be really useful).
    But each to his own and other people will of course have other needs and opinions.


    73

    //Harry

    The GM-201 however is a bit wobbly, sounds a bit like aurora. So personally nothing I can wholeheartedly recommend.

    Hmm that is odd.

    I have tried out at least five of these and never had anything else than clean signals. I have run both with 25MHz injection and unmodified and they look and sounds clean to me?? Listen to the MP3 I just recorded with an unmodified unit. It obviously drift but sounds clean to me. Is this how yours sound or is your worse 08-May-2019 18h59m34s - 10489.331 MHz, USB.mp3.zip?


    73

    //Harry

    Nice :-)
    I guess you used a DC to DC converter to increase the voltage from the 5V on the USB bus because I cant get my GM-201 to work below 7.3V?


    Hi Peter.
    I don't have an answer to why they choose to use a square instead of a circular wave guide.
    But I cant see why it would be more expensive to manufacture?
    The wave guide seems to be cast alloy so the manufacturing cost would be the same regardless of shape. Maybe it was more convenient to put a flat PCB on top a flat side of the wave guide?

    For code to program the Neo GPS, this could be suitable : https://github.com/HarrydeBug/1009-GPS_Derived_RF_Generator


    It is written for Arduino and ATMega328 but could be adaptable to the ATTiny.
    On the other hand if you want it to be super easy - you could change from ATTiny to ATMEGA328 so you can use the code directly.
    It will only increase your BOM cost with a euro or two but make it radically faster as the code already does exactly want you want to do (set the GPS timing output to a fixed output frequency at each startup)


    73

    //Harry

    Hi IZ2EEQ
    I don't have an answer to your question but rather a few comments.
    Comment 1 - Neo7 GPS and jitter.
    I think the Neo7 is not suitable directly as a source for injection locking a LNB. I have a lot of experience with the Neo6 line and also tested a Lea8-T and they are very jittery on the output.
    The Lea8-T is specifically made for timing applications and therefore have a more advanced TXCO compared to the simple oscillator in the regular Neo6 GPS modules. But they are both way to jittery for use as a reference.
    I have not tested the Neo7 line but I would imagine they are not much different.
    Even if you use an output frequency that is an integer from the internal 48MHz oscillator the frequency corrections are very jumpy and random in both short and long time scales. 24MHz is a good output frequency for these as you avoid fractional division spurs but even at 24MHz they are super jittery.


    Comment 2 - Why not use a 25MHz TCXO for your Starcom LNB ?
    I would recommend the Abracon ASTX-H11 series of TCXO, they are available in 25MHz frequency and not to expensive. They have built-in electronics that counter-adjust the frequency drift of the built in quarts and are really nice TCXOs.
    They have an absolute precision of 2.5ppm but drift due to temperature changes is lower, around 0.5ppm.
    If you have it in the shack and feed the 25MHz on the coax the resulting frequency drift should be quite low and "good-enough".

    73

    //Harry