Posts by David G0MRF

    Hmmm. Am I the only one who is a little sceptical about this project?
    I recall hearing the same optimistic plans about amateur radio onboard the ISS.

    The reality turned out to be some very expensive patch antennas on Columbus and the 2m / 70cm being used 99% of the time for NASA publicity via schools contacts, where the amateur radio contribution is sometimes invisible.

    Hi Frank.

    Sometimes an earth loop will cause 50Hz sidebands. It's a difficult issue, but having a single point earth or disconnecting an earth can resolve the issue. Trial and error?

    OK Uli. Thank you. Sounds like a group order could be a good idea. ?
    Has anyone tried this particular TCXO to see if it has the annoying digital jumps as part of the correction routine?
    I have had this problem so many times now and it seems to be the lower cost TCXOs that all suffer from it.

    I've tried the Fox and ECS products in the same price category and they all have the same issues.

    For my upconverter, I think I will have to go from a 3 Euro to a 10 Euro product to stop the 130Hz jumps.

    Certainly a learning process. 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 ..._._ . .



    G8UGD

    Hi Adrian.
    I use one of those amps on a regular basis and it needs about 170mW for full output.

    I did a demo at a local club a while back and forgot to put an attenuator in the drive. When I tried to send some CW the trace on the screen, which should have been a single line looked more like the PSK beacon. On SSB it looked rather like the image in your post. Easy to fix though, just turn down the drive until it looks and sounds right. The really nice thing about all these SDRs is that you have your very own Spectrum Analyser to check the signals. Are you going to Milton Keynes tomorrow?


    73 David

    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

    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)


     


     

    Quote

    For mrf21045, my bias voltage is 2.7-3.0, 0.55-0.9a at 24v, and 42DB is output when 30DB is input

    So you have 12dB gain? 42dBm out for 30dBm input.

    I wonder if 50W output is possible, perhaps the internal matching is not so good at 2400. (28V and 14.7dB gain at 2200MHz on datasheet)


    David

    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


       

    Upconverter: First test.


    LO and upconverter board mounted in enclosure.

    Input at 432.510 MHz at 0dBm

    Output apx at 2400.0091 into frequency counter.

    So far so good. Testing output power / conversion gain / linearity in the morning


    73 David


     


    Hi Thomas.


    This is the last press release I can find from ESA Education office. Dated May 23rd.


    "After having started its in orbit commissioning, since a few weeks the ESEO mission has been experiencing an anomaly. The educational path of the ESEO students however continues.

    The ESEO AMSAT-UK radio payload was successfully activated in the morning of 12 April 2019, and it started transmitting its payload telemetry. These data were received by many radio amateurs around the globe.

    Unfortunately, a few hours after the AMSAT-UK activation, ESEO suddenly started to behave anomalously, repeatedly sending the same notification message to ground, which normally should have been sent only once. The continuous use of the radio transmitter to send these notifications, in combination with the AMSAT-UK activation, led to a temporary discharge of the battery when the spacecraft was in eclipse. This under-voltage then triggered the protections to automatically shut-down the AMSAT-UK payload.

    A clear reason for the anomaly has not been identified yet, but the most accredited hypothesis is a possible radiation effect on a memory cell, which in principle could be recovered through an automatic reboot of the on-board computer (data handling system), that cannot however be anticipated.

    In the meanwhile, until this malfunction is resolved, ESEO cannot receive tele-commands and its in-orbit commissioning cannot continue."


    End quote.


    Current status: On 31st August the OBDH system reset following a low battery watchdog. This stopped the continuous transmissions and put the satellite back into safe mode. At present, telemetry is being received on 70cm and the attitude control system is being investigated. Commands are being successfully sent to ESEO and temperatures and battery voltages are back to nominal values.


    Speculation: After the platform checks have been completed it would be reasonable to assume the S band ( 2.1 + 2.2GHz commercial spectrum) system will be checked so that the science data from the student payloads can be gathered and downloaded via TU Munich.

    Thanks


    David

    Looks neat so far with upconverter PCB using 120mA at 12V now final ERA2 has been installed 'dead bug style'.
    Oscillator operates from 5V regulator on back wall of enclosure. Not sure it will look so good after all the wiring is added.


    Water bottles these days have a new meaning, but this 'old school' version provided an easy method of assessing the performance of my "high stability 10MHz source" bought at a radio rally a couple of years ago.

    For a 25 to 60 degree temeprature change this Murata oscillator drifted 6 kHz at 1967.5 MHz. Probably no more than a big crystal and a TTL inverter housed in a large metal can. Buyer beware !!

    Oh well, the ECS TCXO may have digital jumps, but it does compensate very well and stays within 200Hz .......Another couple of bits in its A to D converter and it would be much better.


    So with 10 days to go before setting up the demo station, it's time to get these parts into a box and wired up to the Spectrian PA.

    Perhaps a test by this weekend?



    In the words of Homer Simpson.....Dooh !
    Yes, of course, how can 393.5 be an integer. There are so many settings I just selected INT-N and didn't check the rest.

    OK, I will find the PICKit and try again.

    I've already found a rather ancient ovened 10MHz oscillator module, But at 40mm cubed I just hope it does not draw more power than my PA. (hi)


    Thanks, adjusted for +2dBm and done...... David


    And the not so good:
    The local oscillator is operating, but looking at the signal on a FUNcube dongle shows a couple of issues which need to be improved.

    Firstly, the TCXO is manufactured by ECS and is available from Mouser. While it holds the frequency stable over a period of time it has internal correction that uses a D to A converter. This produces frequency corrections as 130Hz jumps in frequency every time it drifts outside a preset limit. Not too bad when warmed up, but not pleasent when starting from cold or if mounted in the same box as a power amplifier. If anyone can suggest a 7 x 5mm 10MHz TCXO that is not 'digital', please let me know. The spectrum of the LO is shown below on an image from SDR#. The signal on the left is the ADF4351 with the TCXO 'jump'. The signal on the right is a reference signal from a signal generator on 1967.5kHz.

    The second, lesser problem, is spectral purity. I have used integer N operation to minimise spurs and hopefully improve noise performance.

    Unfortunately, the carrier appears to have odd bursts of 'phase noise' or interference that extends +/- 90Hz from the carrier. Beyond 90Hz the signal is very clean, so I'm not sure what this can be. I have copied the register settings from the Analog Devices software below. If anyone has a better performing set, please let me know. This is not visible on this SDR sharp image, so it may be an intermittent issue that will go away with proper shielding and supply line decoupling.


    73 David (Yes...I know. I wouldn't get frequency jumps with GPS locking ! )



    More steps forward and some steps back. - Here is the 'good'.

    I managed to programme the 12F629 with the code from G7DOE adapted for 1967.500MHz using interger N as suggested by Remco.

    The Chinese pickit-3 put up a small struggle, but I finally got the 'build successful' and 'verify' responses from the free MPLab-X software telling me that the software had been loaded into the processor.
    It took some time before I managed to get the synth board to lock as, for some reason, the data is not transferred successfully when power is applied. What is needed is that after power has been applied the MCLR pin near R11 on my board needs to be momentarily connected to ground. After the voltage comes back up, all is well and the 'lock' LED on the synth board is illuminated.

    Frequency is good (see later) power output is also good at 0dBm. The programmed level was +2 dBm but I've assumed this is measured as the total from both outputs rather than just the one that I'm using. Finally I replaced the drifting 25MHz crystal with a 10MHz TXCO. So what could go wrong?..........


    73 David


     


     


    The upconverter board is 90% complete and only one minor issue has been found so far, - a missing coupling capacitor.

    The board uses 2 bandpass filters, I thought I would use different types to evaluate performance.

    Filter A in the image below is the popular SF2124E. It has 6 connections: Input, output and 4 ground pads. Importantly, there is no DC connection from input to output, or from input or output to ground. This means you do not need coupling capacitors and I have a direct connection from the filter to the input of the ERA2 that follows it.

    The second filter (B) is a TDK DEA252450BT. It has 4 connections including grounds that take up the entire length along the sides of the device, making it easy to fit to the board with a regular soldering iron. Unfortunately this device has a DC connection between all of the pins. This property means I need to add a coupling capacitor between the output of the ERA2 and the filter input. I think I have some 100pF 0402 caps somewhere. There is just about enough room to squeeze one in if I remove about 1mm of copper track.


    Next task. Programme the PIC12F629 and attach the Local Oscillator module. Then some measurements and fitting the the final ERA2.


    73 David