Posts by g7iii

    Thinking about a minimalistic QO-100 station, RX testing proved to be successful!


    Golden Media GM-201 LNB unmodified, DVB-T stick and USB powered LNB injector. Easy copy of CW signal and probably also PSK beacon once the LNB has reached thermal equilibrium. Thing is, that the operator is also nearing rapidly thermal equilibrium.. :D

    I have successfully uplinked with an 11dBi (13cm square) Wifi panel. I wonder what weak signal modes could work under those constraints (I'm thinking EM-comms usage here) . I suspect you'd still need to GPSDO the downlink, but then again, the uBlox modules can be reconfigured to output more than 1 PPS...Not sure if they can get to 25MHz tbh


    Finally.,C2H5OH (or related to it) can help "operator thermal equilibrium" :)

    Hi David,


    Not yet, it's still on my 'todo' list, but there's quite a lot of wiring to get out to the dish (and possibly a second dish), not to mention a 10GHz feed to sort etc.


    Was hoping to this month, but looks like things might slip a little (too many inter-related projects HI!)



    73s


    Iain

    I have just realigned my 1.1M dish after storm Hannah blew through yesterday. When I say re-aligned, I mean re-mounted after an incident during the re-alignment (not related to the storm), but after it popped out the mount, I decided to remount on a smaller diameter pole to reduce a slant on the dish that I had.


    Long story short:


    1.1M Dish, Beacons 19-20dB above the noise floor, *BUT* in 500kHz B/W, gnuradio, USRP N200, Still need to tweak dish illumination and LNB skew

    One thing not to forget: Plenty of WX conditions can effect your overall loss. For example, in the early morning if the sun is on my dish, I can see the noise floor higher than at late at night.


    Then we have cloud cover. At both 'ends' of the "QSO" (or Beacon Uplink site, or GHY Downlink). Let alone rain drops on the dish, at either ends! Here in the UK they are threatening hail today, so that might well be an interesting effect!



    Which brings up something else I've been thinking about over the last few weeks...Would weather reports from key sites (Bochum, QARS, Es'hail Satellite Control Centre, GHY etc) on the Upper Beacon be useful ?


    I know there's times I've gone "Where did 6dB go ?! I had 14dB SNR last night, what's changed in 7 hours!", so gone fiddling with the feed position to no avail, and *then* find out its windy and raining in Bochum, or looked up at the sky here! Ditto with Goonhilly.


    (If you are comparing your system to the Beacons, and/or GHY's SDR, then you need to make sure you are aware of local conditions at each site)


    If there's interest in discussing WX and other environmental effects, we can start a new thread (I really just wanted to point out that the WX can effect these measurements on this thread, having been caught out myself)



    73s


    Iain


    (and as if by magic, 5 minutes after I post this, the great attenuator from the sky comes down in liquid form...British Weather, have to love it!)

    DH2VA :Dish is 1.1M


    Power is a bit debatable. P.A is one of those 8 Watt "Wifi boosters", fed by a four watt version (my 100mW USRP hasn't got enough puff to push the 8W one into transmit mode [needs 400mW] , and I am *not* doing SMA soldering), but there is some debate as to whether the 8W versions are 8W or 4W as they have a 4W part.


    After that, there is a 5m run of Aircell 7 at present, so ~1.8db loss (I have plans to cut that run to <1m), so currently power to the dipole is probably either ~5.28W, or ~2.64W.


    For a Carrier, I am hearing myself 6-7dB above my filter noise floor (6kHz wide, -3k/+3k complex bandpass) with the dipole. With the reflector, that improved to 10-11dB above the filter noise floor)


    In the same filter, the LB peaks at about 16dB above the filter.



    73s


    Iain

    Hi All,


    Well all of these are wonderfully made. I've never been good mechanically, but yesterday I added a 2.4GHz "feed" to my LNB downlink. Highly complex and expensive (not!), and note the "super expensive" adhesive as you can see from the picture.


    Originally I only had the dipole (6UKP from one of the FPV drone guys, but cut to 2400MHz for me). Reflector (<2mm diameter copper wire from the junk box) added ~4db S/N for me through the transponder, position of both reflector and dipole element a compromise to prevent impact to the downlink signal.


    Probably going to add extra yagi's at 90, 180, 270 from the existing one, but for multiple uplink capability rather than phasing them together



    73s


    Iain

    DK2ZF : Things are being worked on :) [RWM style, in assembler, along with other code :)]. Although how to embed a callsign in an MSF or DCF time-code is another question :)


    Or maybe a parallel carrier a hundred, or even just tens of Hertz away, as SDR Filters are so good these days


    Oddly enough here in G land, they changed the regs so that rather than saying you have to identify after a specific amount of time, they now say 'when convenient ' or some such phrase, such that it actually isn't a legal requirement to identify every 15 minutes as it used to be.



    My uplink antenna is only an 11dBi flat panel, and running a couple of Wifi boosters (4W followed by an 8W, although I have my doubts the 8W is truely 8W), but interesting I'm 3dB above the transponder with you, that's interesting.


    And indeed, two way QSO's are certainly not off the table, Just I have an interest in timing and ranging, and QO-100 give us such a platform for experimentation :)



    73s


    Iain

    Hi Folks,


    Having finally got around to wiring it all up, I have built an experimental time station built around a MKU-LO-8-13 from Kuhne (to generate the signal) , and a Beaglebone Green SBC (to control PTT and C&C for any required frequency changes etc)


    The MKU-LO-8-13 is locked to the same GPS house reference as the rest of my station. The Beaglebone Green is fed a PPS (Pulse Per Second) from the same house standard (which is aligned to the start of the UTC second) to one of it's real-time units. That real time unit, then keys the transmitter for 100msec.


    It will be on-air, when I am:

    o I am testing

    o Developing modulations such as MSF, DCF, TDF, IRIG etc to provide a Time of Day signal, not just a 100ms PPS

    o Developing the ground software to measure the round trip delay


    It is currently on 2400.060MHz uplink (10489.560 downlink, just inside the CW portion of the bandplan, although that can be adjusted if needed.


    Reports will be gratefully received, however it is very narrow, and very weak, but you can hear it using the Goonhilly downlink. I am hoping to provide gnuradio flowgraphs that may be able to be used for 'one way ranging' of the spacecraft, as well as to set your own clock (once I get those bits written - Tonight was about getting the hardware working and the keying working correctly!)


    Rumours of a paper or a presentation at the AMSAT-UK colloquium can not be confirmed or denied, until I get some interesting results :)



    73s


    Iain

    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...