Posts by OZ2OE

    Hi Mike,

    I find it interesting that you mention QSB on the QO-100 beacon signals - and I have heard that commented before. Can you specify how much QSB you see? Like many others I also use the beacon signals for checking my setup, making ajustments, improvements etc., But I find the signals quite stable with variations less that half a decibel or so. (I have ofcourse seen greater variatinon during very heavy rain, but that is not something that happends often)

    Maybe we could find a time on the satellite to exchange observations?

    73 Ole OZ2OE

    Hi Roland

    I have also been wondering about the way SDR Console defines SNR and how this affects the SNR number we read off the screen. I found an explanation on Simons webpage:


    Noise Floor

    A few weeks previously a reasonable logic was implemented for measuring the noise floor. Purists will not be happy - they rarely are, but it works for me.

    Take the output from the SDR radio, ignore 15% of the bandwidth at the high and low end of the output to avoid the ant-alias filtering, and we're left with a healthy 70% of the signal. Now sort the FFT bins by value, take the mean of the lowest 10% and that's the noise floor.


    Reading this doesn't fully explains the changing values vs. changing display bandwith, but at least it shows a different approach to "defining" noise level - hi.

    For what it's worth, I see the introduction of SNR reporting on satellite signals as a step forward. So thanks for putting that into SDR Console - even if noise bandwith is "undefined" and displayed numbers seems too high.

    73 Ole OZ2OE

    I also measure 3 dB lower signal on upper beacon, but then noise floor is 2 dB lower around upper beacon, so SNR is not too different between the two.

    Furthermore with my 85 cm dish, noise floor around upper beacon is only raised 2 dB above system noise floor, which means I see both transponder noise and a large contribution from system noise. A bigger antenna may have exactly same signal/noise ratio on both beacons.

    By the way interesting how mark/space is inverted on upper beacon compared to lower. I guess this is to put space frequency on lower at exactly 10489,500 MHz and at the same time have space on upper at 10490,000 MHz?

    73 Ole OZ2OE


    I'm using signal from the CW beacon as a mean for testing short term stability of my reference frequencies. Looking at the 5 sec dashes on a waterfall, I see straight lines (vertical on my SDR setup). But when the frequency scale is expanded to something like 100 Hz per cm - or more - the line is not always straight and with sharp edges. Sometimes - depending on stability of the reference - I see either wobble or fuzzy edges. This is not a strict measurement of stability, but it gives an visual indication, especially when comparing various references. (note that setting of the FFT BW must not be too narrow, as this will integrate/mask short term variations)

    Ofcourse the CW beacon itself has to be stable and clean - and it is - otherwise you don't know what is measured. I don't know just how stable the beacon is, but when I compare to other carriers (test transmissions) on the satellite, I almost never see signals as stable.

    Using this method I have tested OCXO's from KVG, Telequartz, TDK but also cheap TCXO's from the internet and a Rubidium standard. Clearly the best was an old TDK OCXO, followed by the Rubidium with OCXO's from KVG and Telequartz marginally worse. The cheap TCXO was very bad, but even this gave perfectly sounding SSB reception. Stability is only critical for certain modes!

    Ufortunately I have no Leo Bodnar to compare with.

    73 Ole

    For me the maximum solar interference will be on the 13'th at 11:57 local (09:57 UTC). Interference is also observable 2-3 days before and after the max. event. Last time - half a year ago - I observed something like 5-6 dB increase in background noise looking 500 kHz below the transponder. This time I will watch the effect inside the transponder BW, which will be different due to transponders own noise floor.

    73 Ole

    Hi all

    I have measured about 2 dB higher gain on the "4W" than on the "8W" amplifier. I believe it is due to difference in loading impeadance of the two active devices - which are visibly different. When designing amplifiers you can chose to maximize Pout or Gain - or have some compromise in between. I believe there is a reason for the two versions to exist.

    73 Ole

    Hi Mike, G0MJW - my dish is a 60 cm TRIAX with f/D 0.6. My measurements does not show that the POTY is better without the dielectric lens - on the contrary, as others have reported. When I assemble my next POTY, I'll measure the lens effect more closely.

    My Y-factor measurement was done on POTY both with and without dielectry lens. I make these measurement on the LNB+feed combination alone - so no dish involved. Ideally the Y-factor should not change from narrowing the beamwidth, as long a the LNB sees either cold sky or hot ground within the actual beamwith. I believe the small reduction in Y-factor with the lens is due to losses in the dielectric material. (theoretically could also be due to changes to side-/backlobes)

    73 Ole

    The POTY also have a 10 GHz "side". I have measured LNB performance with the original LNB feedhorn and with the POTY feed on the LNB - after cutting off the original horn.

    First measurement is Y-factor (difference in cold sky/hot ground).

    Original feed: 4.9 dB

    POTY (without dielectric lens): 3.7 dB

    POTY with dielectric lens: 3.3 dB

    Second measurement is transponder noisefloor (60 cm offset dish)

    Original feed: 2.9 dB

    POTY with dielectric lens: 1.8 dB

    Noise measurements are done with averaging, so accuracy is about 0.1 dB. Both Y-factor and transponder noise floor involves other parameters than just LNB NF or antenna gain. So there is no direct one-to-one dB relation to the POTY performance.

    The degradation in performance with the POTY is measureable, but any dual band antenna is a compromise. This is compensated by only having to use one antenna.

    Anyone else with similar observations?

    73 Ole

    Rain attenuation in dB/km can be seen below. From the graph it is clear that 2.4 GHz is not much affected by rain. (except when water gets into the feed itself and ruins the matching).

    For 10 GHz it can be a problem, but then it has to pour down. There are lot of information on Sat-TV and rain attenuation on the internet. One report stating that: "For Western Europe rain attenuation only excees a couple of dB in 0.1% of time".

    73 Ole

    Hi DO1CTL - I bought a similar 1 W amplifier and took this gain measurement of the unmodified amplifier. For 2400 MHz use it needs serious modifications!!

    73 OZ2OE

    The broadband disturbances on the 4'th of April was associated with pulses having a centerfrequency of 10489,497,125 Hz - as seen on lower waterfall on this HDSDR screenshot. I have no idea what this was?

    73 Ole

    The transmission line - copper track - transforms the capacitive impeadance of the tuning flap. A quater wavelength away and the impeadance is inductive.

    So if you want inductive impeadance, you place a capacitance one quater wavelength away.

    73 Ole

    Lieber Thomas,

    ich würde mir über "driftenden" LNB erstmal nicht zu viele Sorgen machen, Du bist ja auch "Doppler-Shift" erfahrener OSCAR-User... Ich würde mir eher Sorgen um Deine 60cm Schüssel (für den Empfang) machen, die ist eigentlich unterhalb der Empfehlung für unsere Region.. da musst Du schon wirklich alles optimal ausrichten und auch einen performanten LNB haben... aber solange Du das Transponderrauschen noch siehst ist natürlich alles gut! Ein größerer Empfangs-Spiegel macht dann auch überhaupt keinen Sinn, da sich das Signal-to-Noise Verhältnis der Nutzersignale nicht verändert.. ;-)

    Dear Peter, DB2OS

    I know it's a bit out of topic regarding "Umbau Octagon", but...

    When you write that "as long as you see transpondernoise all is well" and "a bigger dish makes no difference to S/N ratio" this is not quite true :(

    I have seen this statement in other postings as well, but seeing the transponder noise floor, does not mean reception cannot be improved.

    In case of a 70 cm dish we see a typical transponder noise floor of around 3 dB - this is compared to the noise level outside the transponder bandwith. Actually what we see, is that the transponder noise - and the background noise within the transponder bandwith - are adding up and the sum of the two is 3 dB stronger than the background alone (or transponder alone if that could be measured).

    A bigger dish will receive more transponder noise, but the same amount of background noise (assuming identical LNB and antenna noise temperature). The background noise becomes less important and the S/N ratio increases. With a really big antenna, the transponder noise dominates over background noise and we can receive the satellite with up to 3 dB better S+N/N than in the "3 dB noise floor" example above.

    The noise coming from the transponder and from the background (LNB + galactic) are unrelated, so the noise power adds up in the transponder bandwith. This could also be shown on a spread sheet.

    A 3dB noise floor using a minimum size dish is in my opinion a good compromise between small setup and reduction of S+N/N ratio.

    73 Ole

    Hi George

    If you look at the xtal terminals with an oscilloscope - before removing the xtal of course - it is easy to see which is input and output of the onchip oscillator. The terminal having lower amplitude and cleaner signal is the input. Where you can inject external LO.

    73 Ole

    Robert DD4YR,

    Here is a schematic. I have changed the design from a Butterworth ( picture in my previous posting) to a Chebyshev - the schematic below. Both works fine, but Chebyshev has slightly better cutoff characteristics. I have also changed the attenuator to allow for two receivers. Both designs have 20 dB attenuation. Component tolerances are quite uncritical. Coil diameter is inner diameter.

    This have no relevance for QO-100, but I have set the split frequency at 110 MHz. The lowpass will pass any frequency from DC to 70 MHz and highpass will pass signals from 1 - 2 GHz down to 144 MHz. So this LP/HP filter can also be used for feeding reference signal to a mast mounted microwave transverter with 144 MHz IF.

    73 Ole