Posts by David G0MRF

    Hello all.
    Two months on from my original post and I have learned a lot about oscillators and the Pluto Ver D

    I am currently midway through my mission to make the Pluto stable, on my 3rd oscillator and as yet, it is still not suitable for narrowband modes, but I am making progress. The following info (saga) may be of interest.

    My objective is to make the Pluto stable enough for narrowband digital modes so I can keep it compact and take it /P without having to use my Leo Bodnar external clock. Original issues were the crystal supplied is 25ppm and drifts. Let the saga begin:

    1) Original 40MHz 25ppm crystal oscillator fitted by Analog Devices. These drift both in the short and long term. On receive only in 'the shack' they stabilise after about 15 mins and can be useful for long term monitoring of the digital signals on .540.
    Unfortunately, when you go to transmit, the board heats up and the oscillator drifts making TX signals unreadable and when you go back to RX, decoding (at 739MHz ) is impossible as the oscillator cools down. On the rev D this oscillator has an enable and disable pin.
    This oscillator had to go. Surprisingly, using 2 soldering irons, the oscillators can be removed in 10 seconds. Remember if you are extracting the oscillator, you don't have to worry about killing it. A large blob of solder on each side and 2 irons will melt the solder on all 4 pins at the same time and the oscillator will lift out in seconds. No hot air or Kapton required but a microscope or magnifier is an advantage to see if the solder is molton.

    2) Purchased 2 Epson 40MHz TCXO from Digikey. Part number TG2520SMN 40.0000M-ECGNNM3. These are 500ppb (0.5ppm) 1.8V oscillator modules and were suggested as suitable replacements. They are slightly smaller than the original part, but were fitted fairly easily. As it was late in the evening, the Pluto was switched on and FT8 signals from .540 were quickly seen and began decoding after a minute or so. I watched for about 10 minutes, all seemed well and I went to bed. The next morning I could see a page full of decodes but they had stopped around 7 hours after I started the Pluto / WSJT-X. The waterfall on SDR Console contained no signals from QO-100 and a reboot of the system gave a message about possibly insufficient USB power or a non-functioning oscillator. As the USB power was fine I checked the new oscillator and found that it had failed after 7 hours.

    3) After looking at the circuits for Rev B and Rev D Plutos, I found two possibilities for the oscillator failure. The first is that A.D. have fed DC to the enable pin on the rev D. This was measured as 1.8V. However, the Epson data sheet is clear that there is no enable function on the new oscillators and that Pin 1 should be left floating or be connected to ground. - It should not be at 1.8V. I removed a 1k resistor from the board to make pin 1 'float'. The second possibility for the failure could be the extra circuitry on the rev D board. On the rev D, the oscillator drives the AD9363 but is also connected to U17, the external clock buffer, which adds extra load to the oscillator. (R99 in series with C157). I decided to leave this intact in case I needed it later.

    Eventually I decided not to disconnect the ext osc buffer and left the circuit unmodified. I then fitted the second Epson TG2520 oscillator and hoped this would work.

    4) You get what you pay for !!
    The second Epson oscillator (About 3.5 Euro) has been working for a few days without failure and the Pluto is functioning again.
    However....The performance of the oscillator, although within specification, is completely unsuitable for communication using any sort of narrowband mode. - Let me explain.
    A high performance TCXO for communications should have good long term and good short term stability. Typically you would expect the TCXO frequency to change very slowly over its temeprature range e.g. -40 to +85C. So perhaps 500ppb off at -40 or +85C and something between these limits across the rest of the temperature range.
    With a cheap TCXO, such as this Epson device, the response is very different. When you switch on, the frequency quickly drifts just like a 25ppm or worse crystal. What happens next can be seen in the image from the lower QO-100 beacon shown below. Somewhere in the device, a temperature sensor detects the change and it also senses that the frequency is about to exceed the 500ppb limit. To compensate for this, internal circuitry quickly applies a correction (DAC?) which causes the frequency to rapidly swing in the opposite direction. This process happens again and again with any change in temperature. The result is that the output frequency is always within 500ppb. - So the long term stability is fine. However, the short term stability is terrible, with the frequency moving 400ppb at frequenent intervals. This short term stability variation makes FT8 etc completely undecodable. On the image you can see the oscillator suddenly moving 200Hz lower in frequency. At 739MHz this is just over 300ppb. This is well within specification, but makes the oscillator unsuited for narrowband use.

    4) Next step.....Yet another Oscillator. This time an IQD crystal surrounded by good old temperature compensated capacitors. I'll let you know how it performs. (About 20 Euros)

    73. See you /P sometime, Pluto allowing.

    Thank you Andreas Detlev and Frank.

    At the moment my Pluto takes 15 minutes from cold to stabilise on 739MHz (FT8 decode). I can imagine 2.4G takes even longer.

    I will have a try and replace the oscillator with a TCXO. Then go /p. Opening and closing the car door is a good test.

    Thanks for the suggestions. I'll let you know how I get on.

    73 David


    Does anyone have a suggestion for an 'in stock' replacement TCXO for a Rev D PLuto?

    It seems that despite the other improvements the standard crystal oscillator didn't get an upgrade.

    I do have a Leo Bodnar unit, but don't want all that extra kit when I go /P.

    73 David G0MRF

    Just spotted this new product from RFMW.

    Amplifier from 3D RF Energy Corp

    Amplifier, Pallet, 2.4 to 2.5 GHz, 250 W, 32.5 dB, 32 V,, 72 x 34 mm, LDMOS

    It's a 250 Watt LDMOS PA priced at $400. Although it says 'CW' the graphs show it has reasonable linear performance and it should be possible to optimise it as access is given to both the driver and the PA gate voltage supply.…1-Source&utm_medium=email

    Datasheet is here:…5M9X2S250-1_datasheet.pdf

    73 David

    Hello Andreas

    The Skyworks data suggests that the device has a maximum power dissipation of 1.25W.
    I do not really see how they can claim "4W Output" other than that is the maximum saturated output with everything on or slightly over the limit. Looks like it may be just acceptable at 500mW but even then the response is not ideal. Probably a device to avoid.



    Hello all.
    Thanks for the QO-100 Challenge yesterday.

    Does anyone have an example of the correct format for a QSO in cabrillo format?
    I have a log from N1MM+ but I'm getting error messages when I try to upload.

    The format produced by N1MM+ is:

    CREATED-BY: N1MM Logger+ 1.0.9450.0

    QSO: 2.3G PH 2022-02-19 1802 G0MRF 59 001 IO91 SP5EXA 59 002 KO02

    but it creates an error message

    FYI My grid locator is IO91

    Any thoughts appreciated. 73 David

    The AMSAT-UK International Space Colloquium will be held as an online Zoom Webinar on Sunday 24th October 2021

    The Colloquium will run from 10.45 BST (11.30CET) to approximately 16.00 BST. (17.00 CET) A full programme of the event is detailed below.
    You don’t have to be a member of AMSAT-UK to attend, and the event is free of charge.

    This year’s colloquium will be in the form of a Zoom Webinar. It’s easy to use, simply register at the address below, and follow the instructions which will arrive by email.

    Please register before the 24th , or join live at

    The 2021 colloquium will also be streamed via YouTube.

    The event will be hosted by members of AMSAT-UK and formally opened by our Chairman, Martin Sweeting, G3YJO.

    Each presentation will be followed by a 5 minute Q+A session, which will allow those viewing via Zoom, to pose questions to the speakers.

    All times are BST which is CET - 1hr.

    10.30 BST (11.30CET) Webinar web site opens.

    10.45 - 11.00 Official opening by Martin Sweeting, G3YJO.

    11.00 - 11.30 IARU Amateur Satellite co-ordination Hans Blondeel Timmerman PB2T

    11.30 - 12.00 AMSAT-DL Peter Guelzow DB2OS

    12.00 - 13.00 Lunch break

    13.00 - 13.30 Robert Bankston KE4AL President AMSAT North America

    13.30 - 14.00 STAR-XL: AMSAT-UK Payload – An updated OBDH for Nanosats
    Phil Bladen, Sam Lane, Chris Bridges

    14.00 – 14.30 STAR-XL: X-Band Upconverter & Dual Band L/X Patch Antenna for Space
    Patrick Hope, Marcel Friesch, Chris Bridges

    14.30 - 15.00 Iain Young G7III - QO-100 using a SkyQ Dish

    15.00 - 15.30 David Johnson B2Space Presentation

    15.30 - 16.00 Satellite Operating from 57 Degrees North. Peter Goodhall 2M0SQL

    16.00 - 16.05 Announcement of G3AAJ Trophy – G3YJO.

    16.05 End of Colloquium

    16.05 - 16.35 AMSAT-UK AGM

    17.30 Onwards. Informal session. Q/A and audience participation

    SITAEL and the ESA Education Office are excited to announce that you have been selected for attending the second “lessons learned” workshop on ESEO, the spacecraft mission developed in collaboration with student teams from across Europe, which is scheduled to take place
    19-21 October 2021.

    (Plenty of material for 3 days) Should be a good educational experience.

    Hi Joseph.

    Tracking the moon should not be too problematic. It moves very slowly and there are many EME tracking programs that will do this automatically.
    Even with manual controls it should be possible to gently, nudge the rotators and watch the signal levels.

    Not so different from the old Oscar 40 with the 2.4GHz downlink where you needed to make very small adjustments every 10 minutes or so. - Will be good if it happens and much easier than 10GHz from LEO.



    Oh dear. So much for my Geography Stefan. 5000km is rather more than I imagined.
    Looking at the footprint, it's about 70km or so out to sea. But I think the cliffs at St Johns are very high.
    It may be possible on 2.4G, but I know when I point my LNB towards the ground the noise on 10G increases substantially.
    Perhaps leave that test to one of the locals. I know there is someone there who chases all the transatlantic possibilities on LEO Sats.
    Merry Christmas + HNY

    Hallo Hartmut,

    Ich hatte die gleichen Bedenken, dass mein IC 9700 einen Aufwärtswandler antreibt, der 40 mW Eingang für 25 W Ausgang bei 2,4 GHz benötigt.

    Ich habe eine Länge von RG58 verwendet, die einen Verlust von etwa 10 dB aufweist, gefolgt von einem 20-dB-Dämpfungsglied am Aufwärtswandler.

    Jetzt kann ich den 9700 auf 25 W auf 70 cm einstellen, um ein schönes Signal bei QO-100 zu erhalten.

    Wenn ich versehentlich versehentlich die volle Leistung übertrage, wird der Konverter übersteuert, aber nicht beschädigt.

    Sorry for the Google Translate.... 73