Demo station for AMSAT-UK colloquium

  • Testing of the low level upconverter is now complete.

    Gain was lower than expected. It seems the insertion loss of the 2 band pass filters increases near 2400MHz.

    Also, the ERA-2 output stage needed better earthing before it was unconditionally stable.

    Eventually, I swapped the ERA 2 for a slightly higher gain MMIC, A VNA-25 from Mini Circuits.

    Now, linearity is very good and 10dBm on the input at 70cm produces 10dBm output at 2400MHz.


    Now I just need to wire up the 12V PSU to the drive, Spectrian amplifier and the fan.

    In 'other news' A Venton LNB arrived this morning. - Thanks Mike and Heiner. Not spent long looking at it, but how do you remove the dielectric lens?


    73 David


       

  • In 'other news' A Venton LNB arrived this morning. - Thanks Mike and Heiner. Not spent long looking at it, but how do you remove the dielectric lens?

    You need to take a firm grip and pull it off, slightly sideways seems to work. The lens is glued on. You might find it easier if you heat up the metal first to soften the glue. When I demonstrated this at Harwell the LNB owner looked very concerned, then relieved.

  • 2 days to go, but it's all coming together.
    Firstly, thanks Mike + Remco for the confidence to pull the Venton apart. I'll fit the lens to the POTY in the morning.


    Also, the upconverter box is now complete. - It works well into a dummy load but will benefit from tidying up some wiring after the weekend. I'll connect it to the radio and antenna tomorrow and try a QSO. I hope the PA heating the TCXO is not too much of an issue.
    Set up time starts Friday 17.30. Hopefully G0AUK ( AMSAT UK ) will make an appearance for testing shortly after. QSL cards available.
    The convention demo runs 08.00 to 16.00 Sat and 8.00 to about 15.00 Sunday (UTC)


     


     

  • PA3FYM

    Thank you for all the advice during the last 6 weeks. The ADF4351 seems to have lower spuri now it's running in integer N mode.

    FYI. I discovered that the combination of the 4351 board and the 12F629 circuit does not like a slow rise time supply voltage. My bench PSU had a 70% fail record where the data would not be loaded correctly into the 4351 registers at switch on. However, with the upconverters internal SMPSU, which has a faster rise time, the data is always transferred correctly and the board correctly locks.

    Just one of the many problems found and solved during this 'journey'

    73 David

  • Sunday evening and the AMSAT colloquium (and RSGB convention) is finished for another year.

    The QO-100 demo station worked very well and was visited by many of the conference attendees.

    At the end of a couple of days there were 70 QSOs in the log representing 21 DXCC countries.

    What impressed me was the interest from people who are mainly involved in the HF or VHF aspect of our hobby.

    You know it's going well when the conversation goes beyond looking at the screen and listening to QSOs, to asking about ways of getting onto QO-100 and the cost and the source of different pieces of hardware. The head of Yaesu UK took a particular interest in the dual band antenna feeds.
    Pictured below is Slade 2E0SQB at the microphone working stations on a busy transponder, with Jim G3WGM managing the exhibts and talking to visitors at the AMSAT table.


    73 David ..._._ . .



  • I discovered that the combination of the 4351 board and the 12F629 circuit does not like a slow rise time supply voltage. My bench PSU had a 70% fail record where the data would not be loaded correctly into the 4351 registers at switch on.


    Congrats on the colloquium, Especially with the scheduling these days it is impossible to attend (I suspect attendance from would-be JOTA people is quite low; the VERON moved the event to November for a reason). Anyway..


    Looking at the source code, there is quite a bit that can be done to improve reliability: use of the brown out detection, putting a delay loop at the beginning, perhaps send a few dummy bits before clocking in the real data (so that there is no confusion because of the direction programming).


    The code I wrote for the attiny85 (published elsewhere on the forum) also carefully uses delay_us(1) to let things settle and to make sure signal ordering is OK. I also use a very low clock of the mcu; the PIC code I saw uses the internal 16 MHz oscillator. I'm not interested in programming speed, I'm interested in reliable, correct initialization.


    Now the dust from the colloquium had settled, perhaps worth another poke?

  • ATTiny13a is too much to bit-bang an ADF4351, 13a is sufficient imho. No delay_us(1) but a 'nop' suffices.


    Here's my clock in routine: