Posts by DJ0MY

    VERY IMPORTANT NOTE:


    Like with all HF PSK based modes it is very important for high data throughput in VARA not to overdrive your transmitter and hence create significant IMD products degrading your modulation.


    There are plenty of tutorials on the internet explaining how to setup your station for e.g. PSK31 mode by watching the ALC meter of your radio very carefully. If you apply those settings to VARA, it should be working just fine and produce clean signals.



    Find below two spectrum examples that I have taken live from QO-100:

    One OM over-driving his TX in VARA mode and creating significant sidebands and resulting bad IMD as well as unequal amplitudes of the three PSK carriers of that VARA speedlevel.


    Also as a reference see below how a clean signal looks like in comparison with more or less equal amplitudes of the three carriers and no overdriven sidebands.


    73 de Oscar DJ0MY

    I wonder if the circular waveguide (22mm Cu tube behind the mount) could be shortened without any performance issues? Shorter tube would make the total feed assemply look a bit more compact....(more for optical reasons than anything else, hi hi)


    It is randomly extended anyway by the various connected LNB types, so I guess that total length is perhaps therefore not overly critical?


    73, Oscar DJ0MY

    Inspired by this thread I did some experiments this morning.


    Now, this is what I call an umbrella dish, hi hi :):love:


    I was using a "professional" umbrella type dish. Its basically an old "portable" Inmarsat Telephone for the former Inmarsat-B service.


    I tried it with the POTY feed and constructed quickly yesterday evening a 3D printed mount for the central strut for replacing the original L-Band helix.


    I have the impression that the antenna is underilluminated with the POTY.

    (120cm diameter with F/D around 0.35)


    RX SNR was a few dB down from my usual 80cm dish and comparable to my small camping dish.


    Also the effect of my 3D printed mount on beam pattern is unclear.

    I printed with 30% infill, so I have still lots of air inside, hi)


    But due to very narrow beamwidth it is very hard to adjust and do the directional fine tuning. (my 40cm camping dish I can adjust easily within 10 seconds, hi hi)....


    Also the mesh size of the wires woven into the fabric net have a hole size of 5x5mm, which is not great for 10GHz.


    On the TX uplink I assume also due to underillumination my SNR with same power was 2-3dB lower than with my 80cm offset dish (seen in the background).


    Last but not least I also tried to optimize the focal point (I could slide the Feed forward/backward with my mount) and focal point is very critical...moving 0.5cm forward/backwards from ideal point already cost you some SNR dB.

    (again here it seems that my smaller dishes are less critical)


    So in my view, despite being nice to look at and it was fun experimenting with, I think this is not really a great antenna for real portable use. I would rather go for the typical camping-dish approach.


    73 de Oscar DJ0MY

    I am very sorry, I need to correct my earlier too optimistic results (70Hz slow drift / 30 minutes) with the TXC 7N type.


    When I did my initial tests there was no wind and overcast sky with constant outside air temperature.


    Today I did another longer term test and the LNB was in plain sunshine and it was a bit windy with varying wind speeds. I had the LNB without the outer plastic case (just metalic part) in the plain wind.


    After initial warmup the TCXO oscillated mostly up/down (this time audible) within 1-2 minutes in a range of around +/- 50Hz with sometimes some slower drift of the average center frequency of up to +/- 150Hz over longer period of time, e.g. 10-20 minutes.


    Since this setup is intended primarily for my portable station I am still OK with it.

    But my initial impression was definitively uch bettter.


    Not sure if this would improve with the outer plastic case mounted. Maybe some additional thermal isolation can't hurt. I will keep monitoring the performance.


    73 Oscar DJ0MY

    @DL1GNM: Please have a look to the earlier document from DD1US here in this thread.


    He uses it in an Octagon and instead of 27MHz he uses 26 MHz and with the resulting LO frequency he ends up around 1110 MHz IF (with a few slightly odd kHz, but that can be corrected via calibration in case of receiving with an SDR)


    This shifted LO has the advantage that it can be directly used for DATV also as that resulting IF can be directly received with a SAT-TV receiver.


    73 de Oscar DJ0MY

    Hi Roberto and all,


    yes I was still using the speed limited demo mode. Will try the licenced high speed mode later. Also ARDOP mode with 2000 lead delay later...


    In the attachements you see the Winlink status message box during the mail transfer connectng to your Winlink server.


    Also the very first testmail sent to myself.


    Great system for future emergency communications and very remote areas within the footprint of QO100


    73 de Oscar DJ0MY

    SV1BDS Yes TXC, sorry. Corrected my text above.


    I did not use voltage control. I just connected it to GND and satisfied with result.

    The feature is not well documented in the datasheet (no required voltage range given)


    73 de Oscar

    Roberto,


    my WINMORE.INI did not have those two parameters, so i added them manually.

    I am therefore not sure if they are really understood and applied by the Winmore TNC modem software.


    I tried with analog receiver (like last attempt yesterday) and with 1000 / 10 and 2000 / 10, but I hear no difference in my transmission.


    It sounds as if the break time between two connect packets is always the same default length...no matter what I set in the INI.


    One time (first try) the connection with your server suddenly happened, but then your server was sending packets to me with too short intervals and my TX was never keying PTT (maybe because the break inbetween was too short and the modem was detecting that the frequency was busy) or only after many retries from your server my TX was ocasionally keying.


    So either still the parameters are not right or the software ignores them because they are too long?


    Hmmm, not sure what else to try....


    73, Oscar DJ0MY

    Now D75F was replaced by an TXC - 7P-25.000MBP-T

    (7N types were not on stock at Digikey)


    This is the CMOS version. Just added a 10nF at the supply voltage pin against GND and a 1nF cap for coupling into one of the the PLL chip Xtal traces.


    Works like a charm and is very stable. Just had it running for the last 30 minutes on the CW beacon frequency with my Airspy SDR and had hardly around 70Hz very slow drift during that time.


    I am very satisfied now with the alternative TCXO.


    Thanks to David G0MRF for hinting us into this direction.


    73 de Oscar

    Hi Roberto,


    I will try to change the parameters in the INI and try to connect your server tonight.


    I think the delay with Winmore mode could work.


    I am not sure if ARDOP would work, because my understanding is that leader length is only the initial tone market before the synschronization starts and the data is sent?


    I think this should not have an influence on the delay between one ARQ burst and the next? (or maybe I do not fully understand the protocl, hi hi)


    Hope to have success later.


    73 de Oscar DJ0MY

    Hi,


    I now fixed my supply issue and restored the 3.3V and also added a missing 10nF at the TCXO 3.3V pin to GND. But unfortunately still moving around with similar symptoms.


    I just removed it from the LNB and will try one of those TXC types.

    In the attachement you see a picture of my faulty Connor Winfield TCXO.

    Maybe that helps to narrow down the faulty batches.


    Seems that coding is more likely to be Year / Week.

    (therefore opposit as to the proposed above)


    73 de Oscar DJ0MY

    Roberto, it seems indeed that the ARQ timing of all those modes is not suitable.


    Aven ARDOP whcih has built in latency ARQ timing negotiation is not able to cope with this long latencies.


    My last attempts were actually with fully analog TX and RX !

    Going fully to analog I could hear the start of your reply e.g. in ARDOP mode, but the modem already started transmitting next packet while you were transmittting the connect acknoledgement.


    Sorry, but it seems that all three modes are ARQ timing wise not suitable for QO100.

    Or perhaps both sides need to move to to fully analog radio to improve latency even more.


    Testing split mode does not really help because all three modems (Winmor, ARDOP and VARA) do not seem to support full duplex links. They switch off the RX decoder during transmission.


    Maybe we need to talk to one of the modem authors to introduce a special long ARQ delay version for QO-100 and SDR use?


    Sorry for the negative testing results...


    73, Oscar DJ0MY

    Hello Roberto,


    excellent idea (I was expecting this to happen some day, hi hi).

    Is your server now running 24/7 ?


    I just tried to connect several times using RMS Express with Winmor modem to your server and there was no reply. (I was "spot on" on TX and RX with my GPSDO reference)


    On HF the software works very well. My signal sounded OK on the downlink and my signal should have been sufficiently strong (close to upper PSK beacon level).


    Or was your server just down?


    I tried both .635 and .600 (because on the Winlink list your server is listed as 10498.600 - not .635). But no luck.


    73 de Oscar DJ0MY

    It would be great to find an official way on how we could have faulty D75F's replaced

    (I guess Connor Winfield will not talk to non-professional users?)


    And/or to find and list here suitable / working TCXO alternatives for 25MHz that could be used instead.


    Those TXC 7N look interesting. Were they already confirmed to give smooth analog compensation instead of jumpy digital compensation? (but suggestions for any other working types would be highly appreciated by many hams I guess)


    73 Oscar DJ0MY

    There are still some OM that prefer to feed the GPSDO signal via external cable.


    This mod is very simple....just follow the disassembly steps as above until you hold the PCB in your hands.


    Then unsolder the XTAL as described above.


    Now there are two options:


    1. Use a small coax pigtail

    2. Use a short and round bulkhead (those types fixed with a nut) SMA jack


    I opted for No. 1 since I had a short RG316 SMA pigtail still in my junkbox. (but I have seen an OM on twitter that placed a SMA jack exactly at the same position were I guided my cable through the case)


    If you opt for the pigtail I suggest using one of the two round indentations in the LNB case to drill your hole and passing the cable. Do not foget to make also an aligned hole in the outer case, before soldering the coax to the PCB.


    Now with the pigtail threaded through one half of the outer plastic case and the LNB case, just connect the two pins of your coax (or the SMA jack) to the two pins of the removed XTAL. I passed the cable through the two XTAL holes and soldered them from the bottom side of the PCB.


    For the VENTON the polarity does not seem to matter as both XTAL inputs are "floating" against ground....both ways seem to work well.


    With this MOD the PLL locks with less than 0dBm 25MHz signals from the GPSDO into the pigtail without any problems.


    I had to use some scotch tape on the bottom side of the PCB and XTAL compartment to prevent shorts of the braid against ground. So you may want to measure for this after assembly.


    73 de Oscar DJ0MY



    Note:

    TCXO mod to be published hopefully soon.

    I just finished to modify my second VENTON LNB for portable use with a D75F this morning and just gave it a test run on the 40cm portable dish....its a 25MHz type that I just bought a few weeks ago from a DL ham on eBay.


    I was very astonished to find its also drifting very slowly up and down within a 1-2 KHz range over a period of lets say 1-2 minutes....its just drifting in this narrow range, so obviously some kind of "regulation" is still happening.


    But I have another perhaps related problem:


    I generate the 3.3V for the TCXO from the LNB PLL chip voltage via a series resistor and a 3.3V zener diode. I used a wrong resistor value, because initially I thought the internal LNB supply voltage to be 6V, but only realised later that it actually has 5V.


    So as a matter of fact now my input voltage at the D75F is below spec, around 2.9V....


    I need to find a suitable SMD resistor the next days to modify again and obtain a supply of around 3.3V to remain within the specified limits.


    So now after reading this brandnew thread here I am totally uncertain if my issue is a faulty D75F or if it is just related to my too low voltage supply - any opinion on this anyone?


    Unfortunately, I cant read the markings anymore, since I mounted it upside down, stuck to the PCB. (would require total dismounting)


    73 de Oscar DJ0MY

    I am also using 25MHz and 10MHz combination since many weeks without problems.


    Now, I also tried to do 25MHz and 600MHz combinations, which also seems to work.


    The reason is to use the 600MHz as LO for a passive minicircuts mixer and output the mixer to my 2m radio (and receive QO-100 then around 139 MHz, wich most 2m rigs cover without any problems).


    The problem was that 25MHz and 595MHz (for direct RX on 144MHz) combination does not seem to be possible to configure,


    73, DJ0MY

    PA3FYM sorry Remco - seems I was too much in a hurry when entering the capacitor values. (Mr. Thomson still applies today)


    Will edit it in my text....


    You were actually cited - see my "Mod part 2" post above - I learned the parallel circuit trick from you (hence you were cited by me). But not the serial LC circuit one (which I picked up as an idea originally from OH2AUE's work).....so I hope one citation should be sufficient. :)


    Thanks for all the good work Remco. LNB works like a charm now...