Posts by DH2VA

    Probably none.. just unprecise specs given by the manufacturer. As an example, if you have a 50 ohm output but don't load it at all with a terminator, you may have 3.3Vpp. But if you attach a 50 Ohms termination, the signal will be reduced to 50% just because of the resistive divider (50 Ohms in the source, 50 Ohms in the termination). So you end up with 1.65Vpp.

    Next: what does the 32mA setting actually mean? We don't know, it could be just an internal current setting. 32mA vs. 16mA should be 6dB in power level.. it is not.

    Next:

    Output power level (measured at 10MHz, fundamental power channel):

    Fundamental power level means although you have a square wave they only quote the power in the 10 MHz component, not in all the harmonics. So again something to be corrected for. Why do they quote it that way? Unknown..

    Bottom line: if you can measure it, do it. Adjust for the required PLUTO p-p level with a proper AC block and 50 ohms termination before you connect and enjoy.

    DD0KP yes, the 10G lens has no effect (shouldn't). I0LYL I suspect either the adapter to be wonky or the way the N/SMA connectors were fixed to the reflector. It's just out of curiosity, the return loss and 'twist' at 2.4g looks fine to me.

    pardon the question, but why do the two measurements differ so vastly? It is certainly fine for 2.4g but I don't understand the rest of the behaviour. Do you have pictures of the two setups?

    The drive setting will only have an effect if the clock is terminated with 50 ohms.
    Your dBm to Vpp conversion assumes sinewaves with a rms to peak (crest-)factor of 2xsqrt(2)=2.818. A squarewave has a crest factor of 1, so 1Vrms=2Vpp (p-p is 2x amplitude).

    Hello and welcome to the forum!

    Check the forum for 'LNB wobbling', I think yours is a classic example. Other might comment to this but I think this is due to a really cheap/bad crystal. It might go away with external injection but maybe not. Chances are that another LNB will have a better stability so given their low price, just dump this one for a better one and never look back. :)


    73s Achim

    The idea to correct the TX by the data obtained by locking the beacons is tempting, but cannot be done:

    The RX correction (in a minimal system) corrects for the sum of LNB and Pluto instability. This cannot be disentangled. In addition, I think the Pluto does change its temperature (up) when transmitting. Not as hard as no PA is included but measureable.


    I did the TCXO change myself as well and was surprised to see little effect, but this is because I use the AMSAT-DL upconverter V1 (70cm to 13cm) due to long and tiny cables here and the resulting TX frequency drift originates now in the upconverter LO, which is currently free-running and this does heat up on TX. As the upconverter has an external 10 MHz input, I already got myself a OCXO on Ebay (15 Eur) which should get rid of the drift. This will need to stay powered 24/7 though as warming up takes some time..

    Hi Oliver,

    actually if it weren't for the aluminium of the DK2DB filter, you can use it as a hammer.. it is big, heavy and well made. These type of filters (as duplexer variant) were used in many Packet Radio interlinks in DL (those were the times..).

    CN0417: this one (and the G0MRF SDR driver amplifier) have integrated bandpass filters, so no additional filtering required. See a plot from the CN0417 datasheet here:



    I would guess the bandpass from G0MRF looks similar as they are both SAW type filters.

    73s Achim

    Doing absolute dbm measurements is all but trivial. A good indication of noise performance is to wave your hand in front of the feed. A good system should have a noise temperature of ca. 150K (give or take) when pointed to the sky, your hand has 300K. Easily detectable.

    1. RF band pass filter is always a good item but the CN0417 have one inside so it would be better to have a band-pass behind the last PA (but then you need a stronger one) - I have the same point and not sure how to fix.

    Just one remark on the filtering in general: a bandpass filter is required to get rid of any spurious emissions of the SDR (and there are plenty). You can (and should, see later) add this at a low power stage. Follow-up stages will then only generate additional emissions because of their non-linearity. Driving them -3dB (or even -6dB) from max helps a lot but even when driven hard, a normal bandpass will not help you here. The IM3 (3rd order intermodulation) will be directly next to the signal itself, so it will pass though the filter anyways. Another possible additional generated emission would be the 1st harmonic (at 4.8 GHz) but as the TX feed will likely have little to no matching there the amount of radiated power on 4.8 GHz will be low. This can easily be fixed with a lowpass if required and these are much more easy to build for higher power levels.

    The best 13cm bandpasses for hamradio (as far as know) are the interdigital filters made by DK2DB (check his shop) based on a design by my old man DL3NQ in the 1970s. They are rather big (ca. 30cm) and can handle a few dozen W of power but have a BW of 25MHz. So Q-factor of ca. 100 but unsuitable for removing IM3 of course..

    Welcome Henry !


    (this is the english section of the forum, so I reply in english that other can profit from this thread as well)


    I don't have this particular GPSDO but to me the pulseshape looks quite nice. Check again with a 50 ohm termination because I think that is what the Leo Bodnar GPSDO expects. Generally, rectangular signals for these low frequencies are better suited (some PLL chips even require them instead of sine wave inputs).

    be careful: your calculation assumes 50 Ohms load. There is no such termination in the Pluto so you have to provide the 50 Ohm resistor yourself. Otherwise you might end up with a significantly higher Vpp value.