Posts by David G0MRF

    Final update: To avoid the frequency 'jumping' observed in the cheaper Fox and ECS TCXOs, I swapped the reference crystal in the local oscillator module to a TCXO by Murata. This 3 x 5mm unit is very much better working well on CW and FT8.
    It is a reasonable cost from Digikey.
    10MHz 280 ppb. Order Number 490-18053-1-ND cost £7.99 + tax

    PCB has now been changed to allow MAR or Gali style devices to be fitted in the first stage.
    Boards and components have been shipped......Now I just have to wait for the postman. At least I will not miss the deliveries. - I'm not going anywhere :(

    While I'm waiting, I've just changed the 10MHz TCXO in my upconverter. The ECS and Fox products both had noticable jumps as they corrected for temperature change.
    This device from Murata, £7.99 from Digikey, is 280ppb and seems very much better.

    73 David

    Measuring linearity with questionable power metering ability has not been conclusive, So the board has been posted out for testing. ( Tnx Mike). Meanwhile I have ordered a batch of components and have begun making a few changes to the PCB. The major change is to the pad layout for the first amplifier. I want the layout to allow different devices to be fitted to the same board. Hopefully, it will accept either ERA or Gali devices from Mini-Circuits. This should allow any one of Qorvo PAs to be used. TQP7M9101 (250mW) TQP7M9102 (500mW) or the TQP7M9103 ( 1W ). All are available from Mouser. :)

    Thanks Ole, that gives a very good picture of the performance of the Lime mini SDR. Not running it at 100% seems essential if you want good IMD performance.
    Meanwhile, tests on the 2 stage amplifier have left some questions about which of the 2 stages are the limiting factor in the P1dB (linearity) performance. I decided that the only way to answer this was to build and test the PA stage alone and measure it's performance. Then I can select the most appropriate amplifier for the first stage.
    Pictured below is the Qorvo TQP7M9101amplifier alone. It gives me the chance to swap the matching components while looking at gain and output power. I expected some loss of performance due to the 0.8mm FR4 PCB material, but it's not as bad as it could be.

    The PA device output is internally matched to 50 ohms. However, the data sheet recommends matching on the input. Qorvo have suggested circuits for 2110-2170 and 2500 - 2700 built on microwave laminate, but nothing specific for 2.4G or the much cheaper FR4 PCB material and so a little bit of exerimentation is needed. Initial results for gain look OK at 15.2dB using 'standard' capacitors rather than any expensive RF products. Also the 15.2dB does not account for the small amount of loss in the 5 cm length of UT-086. Qorvo measued a gain of 16.5dB at 2.5G, so I'm about 1.3dB low. Actually, given the FR4 and best guess matching, that's not too bad.

    Now to look at P1dB which needs work to calibrate out all the losses in patch leads between sig gen and power meter.

    The one thing about 'social distancing' is that it gives you a little more time for projects.
    I finished placing the 22 components on the board without discovering too many errors.
    Everything fits and when I connect the board to 12V it consumes 125mA, which is as expected.

    Next I need to find a power meter to do some linearity and P1dB tests. I also need to see if the 2 matching capacitors on the input to the Qorvo TQP7M9101 are optimised values for the FR4 PCB material.

    Thanks Ole.
    This is the first time I've seen a spectrum plot for the lime. Scary number of unwanted products.
    I see from the plot that the marker is at -55dBm but the level of 2.4GHz is a little unclear. Is it around -22dBm on the scale? If so then those products are about 33dB below the wanted frequency.
    Sadly the filter choices are normally limited to whatever is available on various commercial markets. I've selected the SF2124E as it's fairly large and not too difficult to solder.

    Many thanks

    David G0MRF

    A few weeks ago I was chatting to a Lime mini SDR owner who expressed some concern over out of band spurious products and the inability to generate enough power to drive a EP-AB003 Wifi amplifier.
    My WiFi amplifier requires 175mW of drive while a recently completed DJ0ABR amplifier needs just under 200mW for 5 Watts output. There are ebay modules that are good to 100mW but driving these harder just leads to poor quality uplink signals to QO-100.
    So another project was born.
    Pictured below is a 45 x 43mm prototype PCB that has 2 stages of amplification together with a 2.4GHz bandpass filter on the input. The PA device is the Qorvo TQP7M9101 which is a 5V 250mW linear amplifier.

    The board is mounted on a small heatsink. This is not really needed for heat dissipation, more to provide a support for the 0.8mm PCB. I anticipate 200mW out with good linearity. Now to populate the PCB, see how well it works and correct any board errors.

    73 David G0MRF

    Happy 136kHz days..........
    Is JT65 the optimum JT mode for weak signals on QO-100? Just wondering about small amounts of LO drift in the TX.
    Having said that, I suppose EME has doppler shift and all sorts of multipath distortion.

    73 David G0MRF (Still Txing on 475kHz and getting wspr reports and the odd QSO from The USA)

    Hi Pete.
    Try powering the F1OPA module alone. Does it draw power from the supply? I assume it does not have a pin that you ground to transmit.
    I've just looked at the website and I can't see much detail of the circuit, but it looks like 2 MMIC amplifiers with a switched mode supply regulator. Try to have a look if there is any voltage on the MMIC amplifier supply. - Not at the devices but on the PSU supply side of the RF choke in the feed.

    I note that the Lime produces about 1mW at 2.4G and the F1OPA amplifier has a spec of -9dBm input for 100mW output.

    This means 2 things.
    1) The lime can overdrive the amplifier by 9dB.
    2) If the maximum output is 100mW, then that is probably not enough to get full power from the WiFi amplifier. My one needs 175mW for max linear output.

    If you wanted to have a chat on the phone about it, just let me know - g0mrf'at'

    Good luck. - David

    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 ..._._ . .


    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


    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)




    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)