Beiträge von g7iii

    I can now get it to track well enough that FL Digi can decode the Lower Beacon (which I could not do before).


    Still some drift, and it's still 1-2k off, but that's just a static offset. Probably I need to play with the numbers a little more, and not be so impatient!


    Have grafted the Upper Beacon decoder on, No success as yet, but it may still be drifting too much for the decoder, and/or I need to remove the 1k5 offset. I may just modify the decoder to take the input from an audio device, and route the audio feed via jack and run both flowgraphs to make things easier to debug.


    Drift is much less on the Upper beacon as well, so I think it's just fiddling with the numbers and getting the beacon in the correct frequency space for the decoder. Well I hope at least!



    Iain

    Hey Wouter,


    How far have you got with this ? I've been a bit tied up with work lately, but I'd be very interested in your results with the Costas loop. I've been trying with FFT and the Argmax block, but with limited success. The major issues I've been fighting are:


    a) There is always a 'loudest' bin even when the carrier is off - Thresholding and the interleaving the loudest bin with the threshold out to a external script is how I solved that.

    b) I use RPC from a python script to send the correction back to the FlowGraph. It's difficult to get/send enough updates quick enough for fldigi to reliably decode the CW, or for the GNURadio PSK400 decoder to decode the PSK400 beacon.



    73s


    Iain

    DL3DCW : Is your code available yet. I'm trying something similar in Gnuradio, but running into performance issues when I scale to the level that fldigi needs (Probabaly me trying to be too clever!)


    I'd like to compare the techniques, and maybe get some ideas as to what you are doing differently to me



    73s


    Iain

    Hi Edson,


    I will probably not be quite ready for uplink until the weekend, but will try and listen out for you this week, I'd like to test FLdigi's AFC myself (as well as a carrier tracking algorithm of my own in GNU radio) It's a shame FLdigi doesn't support PSK400, and it's AFC doesn't work in CW mode!


    73s


    Iain

    For my 1.1M dish, here in UK, I do the following


    0) Connect a cheap satellite meter in line

    1) Find 28.8 East (Astra et al). I Confirm by checking BBC News (V) and BBC Four(H) get a locked front end, but it's pretty obvious it's 28E2.


    2) Nudge the dish towards south until the satellite meter stops screaming at me :)


    (and I did this in the dark last night when I lost the bird!)


    But that might not work for others - 28.8E is very strong for me

    @db6rs: That will depend on the mode. People have already managed to get 100mW-200mW to work on CW, 500mW on SSB. Considering SSB requires ~6db more, that fits within the ball park.


    For a first *guestimate* take how much less S/N your chosen digital mode needs over CW, and calculate from that, that should give a good idea.


    However, you must take into account the antenna used. The 100-200mW CW station was using a 50x60m dish. the 500mW SSB station had a 1.2M dish


    Also, we don't know exactly what will happen when more folks start to use the transponder, figures may change if it gets very busy, It will be fun finding out...

    pe1chl : Oh wow! "Inverted Sideband" I'm guessing that was the ROT13 of it's day (IE absolutely useless) ? During these times in the UK, the independents (ie *NOT* the BBC [aka 2LO once upon a time when they where 'amateur'!] were just starting, and very regulated


    I'm sure google has some of the test cards that you probably received! I say resurrect something similar!


    73s


    Iain

    Well, this thread is probably going to end up as technically useful as the Sat Humour thread, and maybe no-one out side of the UK will recognise the image or the joke, but,I have heard it suggested to use Wednesdays UTC as an 'Experimenters Day'.


    Well in any case, any G's, M's, or 2E's recognise the attachment ? :) Or at least something similar ? Do you remember the Engineering Announcements aka Ghost Programmes ? I was thinking of adding PID information for what I'm playing with on any particular Wednesday. Anyone up for generating something similar (Along with Testcards..) ?

    Hi Peter,


    Congratulations to you, AMSAT-DL, QARS, and Es'hailSat. Very appropriate considering the giant leap (Pun intended) in capability this spacecraft will bring to the Amateur community. Thank goodness NEXUS (FO-99) worked :)


    73s


    Iain

    (who must go and order the remaining uplink bits!, minor issue of an antenna to fix, the 30W PA needs something to dump it's power into, and a dummy load won't do!)

    G4SAQ : Not sure about the transponder itself, but I think there will be ~240ms RTT simply due to Geostationary orbit to consider.

    So long as you can receive one or other beacon within the passband (and it's CW), a single stick software drift connection is possible. I have some gnuradio code that does just that (although I'm using my Ettus USRPs, but the same code could be used with a dongle


    Whether a tablet would appreciate the extra overhead of gnuradio is another matter of course.


    For those interested, Basically I take 250k of B/W, Filter and Decimate around the 'beacon', then send to a FFT, measure the 'strongest' bin, calculate what that frequency is, compare against the 'correct' frequency, and send the difference back to the USRP or Frequency Translating FIR Filter (otherwise known as the Virtual Big Tuning Knob!)


    In the case of a dongle, it would need to be the FIR Filter, as the drivers in gnuradio don't let you change the frequency of the device once set without stopping and restarting the flowgraph.


    Note, my code will go down to 250mHz (Yes, milliHertz). Overkill, yes (although not for some of the experiments I intend to do), but remember that when the beacon is in PSK mode, there will of course be frequency shifts every time the phase changes to deal with. I'm hoping at least one beacon will always be in CW mode


    Iain

    Mark,


    I've not seen the 11205 beacon here in G-Land for a while (It is believed that they may have switched to a narrower beam a week or two ago). However, during the time they switched, and afterwards, I could see an increase in the noise floor while they were testing the NB and WB P4A Transponders.


    The fact that you can receive beacons of _something_ suggests your system is good-to-go (pointing adjustments with a 2.2M dish aside, you may need to tweak things, I know I will, and I only have a 1.1M)


    I think we just have to be patient now, for the spacecraft to be handed over to the operators, and then some time after that P4A testing will begin. I'm sure Peter and Achim will keep us updated as and when there is something to tell



    73s


    Iain