Posts by PA3FYM

    Yep, that's the way to go. First try to determine the gain value by putting it in hold mode and then check the difference between h1 and h65535 and do the math as described in Lars' document. This gain value is related to the Δf/ΔV ('k' of the reference oscillator).


    To check quickly if it locks, choose a short filter time constant, e.g. 16.


    Very important is to reduce noise at the ADC input. Solder the capacitor, 10M and 3k9 as close to the ADC input pin as possible. Here I soldered them ON the Arduino board. Also add an (extra) elco at the Aref pin to GND. It all helps.


    Personally, for me this is a non issue and endlessly discussed in the past on other bands, with and/or without the use of transverters.


    There is almost nobody having a real logarithmic S-meter (the S-meter is very often derived from the AGC voltage).


    I use the ARRL-method with odd numbers. In case of doubt, the QSO-partner earns an extra point ; -)

    Quote

    People who recently made QSO with me (Hi Remco!) have probably noticed the same behavior - there are some very polite people on QO100 who did not comment to me when they needed to adjust the RIT more than 500Hz over one QSO.


    From the QO-100 beginning I use my transceiver (FT-857) in 'split mode', which is more convenient than using the RIT.


    I consider it bad operating practice when a QSO partner 'discovers' he/she is drifting and aligns his/her frequency according to his/hers perception so that I've to retune into the signal and (sometimes) miss information as a result.


    My recommendation (which seems abject in the amateur satellite community) is, when one persistently wants to monitor him-/herself, tune the RX frequency while drifting and not the TX frequency.


    Bottom line: you're not in QSO with yourself but with somebody else,

    (although practice often proves people are in QSO with themselves: "Ooohhlaaa", "1, 2, 3 test", "Probaaa" ; -)

    @G0KTZ When you remove the connector from the Airspy, is there something else connected to the IF-port of your LNB?


    If the answer is 'yes' (because you said the noise level dropped around 25 dB) try to load the 'disconnected connector' with 50 Ohm. The open line can be an open 1/4 lambda stub (or uneven multiples of that) for 739 MHz.


    I had this during a /P operation and somebody wanted to connect his Minitiouner on the IF-out port of my transverter. I connected the cable, the noise level decreased drastically, but when the cable was connected to his Minitiouner everything was ok.

    Indeed, that's what we discovered too, i.e. 'more' dielectric gives more gain, i.e. the opening angle narrows. For me it works best when I somewhat under illuminate the dish , i.e. the -10 dB angle is around 80 - 83 degrees instead of the 'goniometric correct' 90 degrees. The rocket LNB gives me around 80 - 83 degrees.


    Edit: 'goniometric correct' is related to a f/D = 0.6 (<-- 'normal broadcast') dish

    Haha .. no problem.


    The trick is to 'not shortcut' the 25/27 MHz REF to GND via the 'meander line' (which is a choke for the IF-freq range but not for 25 MHz) to GND (via mostly 78M06 & decoupling caps) and to 'short cut' the REF signal (through the series resonance, a la OH2AUE) to the PLL-chip.

    In the shack the same applies as can be seen here. (<-- old fashioned pencil drawing, but what the heck ... ; -)


    Edit: Check ... the mention in part 2 (sorry, I read across that)

    DJ0MY Oscar, when you reinvent the wheel, at least cite your predecessor(s) AND publish the right values: it is 120 pF and 330 nH (Thomson's formula for resonance)

    My wheel was invented in Dec 2018 and re-published on 8 April when I experimented with a very cheap LNB (which I still use), see this picture.

    DL1GNM That's peculiar because most LNB's have huge gains (due to the use of crappy coax intended for it's primary use: the reception of TV broadcast, not a CW- or PSK-beacon ; -) in the (claimed) order of 50 - 60 dB. This amount of gain almost HAS to compensate losses in the receiver?


    I own a FT-857 (technically identical with a FT-897) but mine doesn't go to 739 MHz (stops at around 480 MHz, if I remember correctly <-- will check this later)

    DL5RDI I think it is even worse. A DXCC-compliant contact needs to be a two way QSO. When using a remote receiver it's not a 2-way QSO (when I understand the DXCC-rules correctly).


    Receiving 10.5 GHz myself I can't enforce whether somebody receives my signal via a remote receiver/WebSDR. So I can't get punished for invalid contacts, is my opinion.

    Yes, you can do that, but it's wise to calibrate it with a known source.


    What I do, when I don't have a power meter attached, is measure the reflected voltage, then the forward voltage (connect the coupler reverse) and then RL = 20.log(Vr/Vf)

    SV1BDS I have no in depth knowlegde concerning the real parameters of the tpx (however, some people on this forum have ;; -) but from the ITU user requirements it is possible to do some calculations. If these calculations meet reality is difficult to say, Formally the link budget is part of the ITU/IARU satellite coordination procedure. However, my experience in a former life is that when these coordination parameters are violated/exceeded there is no strict enforcement regime 'because the bird is in the sky'.


    So, 34 dB might be plausible. What I know when the tpx sensitivity was maximal, there were more situations the AGC of the tpx was activated. Nowadays this happens rarely.

    SV1BDS George, it is not 'that simple' (because you/we? see the noise floor +5 dB 'in Greece'). Suppose -in your situation- the tpx gain will be decreased with another 5 dB, you will see (with your setup) 0 dB tpx noise.

    In other words, you can't see an increment due to the tpx.


    So the noise of the tpx will be the same as your system noise. However, these 'noises' are not correlated, but ... add up stochastically, meaning you've 3 dB more noise (system_noise + tpx_noise = 2 = +3 dB). That means that the detoriation of weak(er) signals is more than 3 dB (refer to the 'noise figure formula' of a receiving system).


    The tpx gain ('noise') is set up in such a manner that the given user requirements of the link budget (dish size, or better ... G/T, see ITU ES'hail-2 document) are met.


    (I commented a few times about this on this forum, but can't find it now .. ; -) Iirc the ground station requirements are around 75 - 80cm dish diameter in the 'average coverage area' (<-- my words) when the uplink power (using the same diam dish) is around 5 - 10 Watts for 20 dB C/N @ 2.5 kHz.


    So, if you use a 1.6m dish you receive these 5 - 10 W uplink with 26 dB C/N, and an increment of the tpx noise. As a consequence, with this 1.6m dish you can reduce your uplink power with 6 dB : -)


    Summarized: dish size around 75-80 cm diam, and 5 - 10W uplink power has to produce 20 dB C/N in 2.5 kHz BW 'averagely'.


    Having monitored the tpx since the beginning I think the reduction of 10 dB (in two steps, first 4 dB and then 6 dB) is a good choice and heeds the formulated requirements and ... improves dynamic range : -)

    DB8TF Florian, the Doherty concept makes that when the 'main' amp is above saturation, a second (or 'peak') amp 'helps'.


    Mostly the main amp part is in class AB and the peak amp in class C.


    So, the overall efficiency is better compared to a balanced ('push pull') amp.


    Say AB has 60% efficiency and C has 80% efficiency (modern LDMOS can have these efficiencies) means that (push pull) 0.4 + 0.4 = 0.8 / 2 = 40% is dissipated, whereas

    (ideally) in a Doherty setup 0.4 + 0.2 = 0.6 / 2 = 30% is dissipated (so 25% less).


    In contrast to a push pull, where the phase difference between the two halves is 180°, the phase difference in a Doherty amp is 90°.


    Assume the input splitter of your amp is of a 'rat race' type and that 90° ports are

    selected, the output combiner must also have this 90° phase shift (but then in the opposite direction).


    Looking at the output circuit, you marked a 90° delay line from which I strongly conclude it is a Doherty setup (!)