Posts by DJ0MY

    SWL - markro92: When I try to receive the beacon (with version .16 and Pluto) I manage to get a stable and nice constellation, but as soon as LDPC worker is activitaed the constellation frequently loses lock and nothing is streamed therefore to VLC.

    Could this be a CPU issue? (its a i5 3rd generation)

    Thank you Marcel. That sounds like great improvements in the pipeline. Do you think that by ading the 16 bit processing path you may have slightly less quantisation noise which could potentially lead to a slightly improved RX performance with SDRs >8bit....???

    Or am I misinterpreting something?


    73, Oscar

    I had my equipment running over the last 24h for this experiment.


    My hardware was a GPSDO disciplined Pluto SDR as RX for the IF.

    And a LNB also GPSDO disciplined.


    GPSDO was a dual channel Leo Bodnar unit programmed for 25MHz (for the LNB) and 40MHz (for Pluto) outputs.


    The SDR-Console measured peak-to-peak drift was +/-26Hz over 24h.

    See attached EXCEL graph below.


    73 de Oscar


    SWL - markro92 Are there any plans to intoduce somewhere in the GUI a simple MER display ? (Modulation Error Rate in dB)


    I think that whould be very useful for people that are tweaking their hardware, RX, antennas, LNB etc. to "measure" some kind of relative improvements or changes. Similar to the hams always giving MER reports when using Minitouner hardware... :-)

    For those of you whom my modification is too complicated and just looking for a "classic" way of using this Twin LNB only as a single LNB with externally fed 25MHz reference via one of the spare F-Connectors, here is a nice page by EA3CNO explaining how this could be done for exatly this same LNB type. (its in Spanish, but you can use Google Translator and/or the photos are rather self explainatory)


    https://ea3cno.wordpress.com/2…b-con-referencia-externa/


    73, Oscar

    Last weekend I modified the Octagon Twin LNB Green. The main problem is that the version with the two cristals that the original poster added here is no longer available. Most of the versions sold today use only one central Xtal for both PLL sections of the LNB.


    Since the idea was to use this LNB for DATV and for NB I modified it to have one output working with the internal Xtal reference for low phase noise (important for DATV on the WB transponder). At the same time I wanted to be flexible regarding the connected DATV RX and therefore it was desireable to have an output in a frequency range able to be received by am ordinary SAT TV RX.


    On the other hand I wanted to have good stability by means of external stabilisation for the NB transponder.

    Based on the good experience with my VENTON LNB single cable inyection solution (invented and heavily promoted by Remco PA3FYM) my target was to have the same advantage with this LNB.


    So I had to come up with a creative solution to cover both use cases - optimized for WB and for NB at the same time.... :-)


    Here is what I did:


    The one side of the LNB is running the PLL chip on a 24 MHz Xtal (original 25MHz Xtal was removed with hot air gun).

    This results in an IF frequency for the WB transponder of around 1130Mhz...(+/- Xtal tolerance)


    To avoid the other PLL being fed also by the 24MHz reference part of the Xtal PCB traces were cutted and partially removed.

    (see photo)


    The rest of the circuit is the typical PA3FYM approach. Cut the power trace from the F connector to the meander line and 330 ohms resistor leading to the voltage regulator. A 120pf+330nH parallel circuit blocks the 25MHz reference but lets the current pass to the voltage regulator to power the future "NB transponder" section of the LNB.


    Then only add a 120pF + 330nH LC resonant circuit as a filter for the 25MHz reference and use a short enamelled wire towards the inyection point of the PLL dedicated for the NB transponder....


    That"s it...now one side works for NB (with 25MHz reference injected in the shack via one of the many diplexer / triplexer circuits found here on the forum). And the other side works well for good quality DATV reception.


    Hope this will be useful for you.


    73, Oscar

    The stability may be better with a non-tunable one and any frequency error can be corrected through adjusting the pluto offset setting. This setting is held in flash and retained on power cycles.

    Hi Mike,


    sorry for hijacking this old one :-)


    When you say "pluto offset setting" which is held in flash:

    Do you refer to the reference frequency command that you use via the serial terminal?

    The same commands you use when you change e.g. from 40MHz to another reference frequency?

    If so, does that have actually sufficient Hz resolution for very fine offset tuning? Or is there a seperate command for offsets?

    (I didn't come across in internet)


    I am just working on another project where it could come very handy to store a fine offset in flash.

    (rather than correcting it externally, like e.g. in SDR-Console instead).


    73, Oscar DJ0MY

    He explains it also here why the SNR cannot be zero:

    https://www.sdr-radio.com/s-meter



    Note:

    When no signals are present with the SNR display it is quite normal to see a SNR reading. This is because Noise is the mean (average) whereas Signal is the peak value, so even in a quiet part of the band there will be a difference between the peak and mean. To see this yourself change the Smoothing algorithm to None (Ribbon Bar, View, Spectrum, Smoothing). The default smoothing is very good at eliminating noise.

    You see the same effect with a 'normal' receiver which has a S meter - even on a quiet band it will be moving and following peaks in the noise.

    Roland wrote: The SNR should be ZERO with no signal and should not change according to the zoom level!


    This was already discussed long time ago on the SDR-Radio support list after Simon introduced the SNR feature into the S-Meter. It seems that it is not a bug, but a feature :-)


    However, the change when zooming seems indeed a bug, hi hi...



    73, Oscar DJ0MY

    RIT gibt es im linken RX Fenster ein bisschen weiter unten (auch XIT)....

    Aber wahrscheinlich nur bei "sendefähigen" SDR Typen, z.B. Pluto SDR.

    (Du hast nicht geschrieben was für ein SDR das ist)


    73, Oscar

    Do I interprete it right, that in the mixed mode segment 2700Hz BW limitation is suggested for "normal mixed modes", but that this does not apply for the "special purpose" use, as nothing is mentioned ?


    The only remaining question would be, what qualifies for "special purpose"....? And should this be done in agreement with AMSAT?


    Oscar

    I reckon more than 1700 POTY's (kits) have been made. So there is potential activity enough. Furthermore there must be an RF incentive (i.e. make stuff for 2.4 GHz narrow band) to become active on the NB transponder. Making stuff for 2.4 GHz uplink seperates boys from men ; -)

    I guess there could be a significant percentage who built two POTY feed kits.....for example myself I got two of them (one bought spontanously at Friedrichshafen Fleamarket). Using one on my permanent dish and one for my portable station :-)


    And I am still missing one important QSO in my collection - that's with DB2OS himself, hi hi


    73, Oscar

    Would be indeed interesting to have some weak signal mode 2.4GHz QRP TX...is there a design perhaps already existing somewhere?

    Would be also cool for APRS positioning like applications, e.g. from a driving car into a QFH helix or a patch on the roof.

    Or for amateur baloon payloads, etc.


    73, Oscar

    Maybe of interest for OM/YL still looking forward to modify a Pluto SDR for NB use, but are afraid of the hardware mod...


    Hi DG2SBL,


    based on my experience the internal TCXO is quite accurate and has only a very tiny drift...something like 100-150Hz during warming up or in-between transmissions.


    Specially noticable when operating outdoors at cool temperatures (bigger temperature differences than indoor use). But I also noticed the drift indoors.


    I think for SSB work this is fully acceptable and almost not noticeable. I used it in the past at home with and without GPSDO.

    Now I use it only for my portable station and always without GPSDO, since I do not want to carry so much equipment, hi.


    The external 10MHz reference + GPSDO is therefore only required if you really want to be "rock solid" on frequency.


    73 de Oscar DJ0MY

    They are two Russians - conversation very roughly like this:


    They guy asks the other:

    "Hello, hello

    "How much are you running - a Kilowatt?"

    "A hundred"

    ""Blah, you are going well - should we go there or stay here?"

    "we can go there...away and see further"

    "OK lets go pilgrim.."


    73 de Oscar DJ0MY

    You have a clever son. This looks a neat solution for the SMD challenged.


    I would advise against using the tunable TCXO. The stability may be better with a non-tunable one and any frequency error can be corrected through adjusting the pluto offset setting. This setting is held in flash and retained on power cycles. Also be aware some TCXOs tuning voltage moves the frequency in discrete steps so you will find setting it exactly not to be possible for those devices.


    Mike

    Hi Mike,


    thanks for your suggestions.


    I was not aware that the Pluto could also permanently store correction settings in flash. I thought it would always rely on external software to do so. But you know - some hams like to turn knobs and not hack something into a console. hi hi:)


    The tunable version is widely in use (as it was widely propaged by Sigi DG9BFC) with no bad experience so far as compared to its fixed frequency counterpart.


    I am using it since August this year in my Pluto openly wired (see photos attached) and once tuned to the right frequency it never had to be retuned so far. Also the tuning is really smooth and sounds very analog style - therefore no discrete steps in this model noticeable as it seems...


    Oscar