Converter 739 to 144 MHz tiny style

  • Hello Sat-Fans !


    Update : After some requests, I offer some semiprofessional, homemade PCBs for this Konverter now on ebay.

    Look at : https://www.ebay.de/sch/armin_graewe/m.html


    After my converter "oldschool style" I developed and build another simple, more up-to-date converter 739 MHz to 145 MHz with just 3 active RF-components. I named it "NB-Converter tiny".

    It works excellent for receiving Oscar100 NB transponder with a 2m RX.


    I wrote a complete report and building instruction for it.

    You can find it at : https://elektronik-muenster.de/viewtopic.php?f=17&t=34


    Sorry, german language only.

    But there are lots of pictures an shematics also for download so everyone should it find interesting.

    In other case "deepl" helps :-)


    73s

    Armin DF1QE

    I still know at which end to grip the soldering iron :)

    Edited once, last by DF1QE ().

  • Just a remark on the harmonic content of the LO: it is irrelevant.

    Any mixer is non-linear (otherwise it would not mix) on its LO port. Some mixers work even best when being driven with a square wave on its LO port. Filtering is only required on the IF and RF ports but be careful: to make the mixer work to its specs, all ports need to be terminated with 50 Ohms broadband. This is not true for most filters outside their passband as they reflect the blocked signals back which then can generate additional spurs in the mixer. Special reflectionless filters exist but its usually better to have some broadband isolation between the mixer port and any frequency-dependent component.

  • Hello Achim !

    Thanks for your comment.

    About the LO harmonic I agree. In some older RF SDR designs they even use just switched mixers with digital components.

    But anyhow it also mixes with the harmonics, so an input filter on 739 makes sense to keep unwanted products away.

    And about the output matching : That's why I attached the diplexer and the dump resistor to the mixer output.


    73s

    Armin DF1QE

  • I have been considering prototype-ing something like this with a few changes:

    • To be fed from the IF output, not external power supply;
    • Allow it to be fed from 18V;
    • 18V DC power from the IF output passed-through to the input;
    • 144 MHz filter removed, or changed for 1335 MHz (1335 = 740 + 595 MHz)

    This way, one would have an in-line converter that I can put in-line between LNB and sat receiver, and which will convert the WB passband to a frequency range the sat receiver accepts. Because the sat receiver supplies 18V, the LNB would switch polarity.


    I'm contemplating trying this but I have some JOTA projects to finish and those have a deadline.



    Speaking of receiving the WB converter: does anyone have data on the chips used in DVB-S2 sat receivers? I wonder if they can be programmed to receive 740 Mhz instead of the "minimal" 950 Mhz, or if there is a hardware restriction preventing this.


    I have tried if I could re-build the openatv image to remove the 950 MHz limitation but the bitbake recipes have a considerable build time and the build doesn't succeed in one go..

  • Hello Jan !

    Thanks for your comment.

    Well as I wrote at the end of my report I am about to do the same.

    So we will see who is first :-) ....

    The DC feeding and feedtrough from a receiver is a really nice idea.

    May be I will implement that as an option.


    73s

    Armin

  • Most diode mixers are switches, on or off. Driving them with a square wave is exactly what they need. If you want to be really cheap and get from 739MHz to 2m all you need is a mixer, an LO source and an attenuator on the output. Performance will be .... well, it would be better with a filter or two.


    The LO source could be a cheap packaged unit, a packaged 600MHz oscillator costs €5. If you insist on 145MHz then pay big money for an si560 or similar and control it with the BATC board.


    DVB Tuners and lower IFs. Yes, or course, if you get the right one. This is what the Minitiouner does, IF from 144MHz to 2.7 GHz.


    Mike