Offset to nominal 8089.5 MHz can be non-zero. And the clock can be measured from the ground as many of you have already proven, no need to have a super precise clock on the s/c. It just has to be stable enough and I think we can all agree it is.
Posts by DH2VA
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As usual NDA.. but I can say so much that there is a non-zero offset allowed. After all, its main purpose is TV signals, not absolute frequency accuracy.
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Of course it is possible. But given the amount of work involved I believe it is not worth the effort.
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Do you know Jan King's Link budget spreadsheet? It has been a reference for quite some years now.
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Ok Achim,
you are the expert.
Please give me the solution.
best 73, tnx
Karsten
We can measure uplink and downlink frequency to a high degree of precision and we can measure the doppler (which has a 24h period). The only thing nobody (of the hamradio community at least) has measured is the actual transponder translation frequency. Is is nominal 8089.500 MHz but this is not a GPSDO. So it will have offsets and drifts.
So even if we uplink on 2400.050 MHz dead on, the CW beacon could be slightly off..
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another hint: we can measure our uplink frequency and our downlink frequency to super high precision as we can lock it to GPS, cesium and god knows what.. but there is another variable on top of doppler..
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Hi Karsten,
you forgot one component in the whole signal chain of unknown frequency accuracy.. you know which one?
Frankly, I am delighted that so many OMs can measure this level of accuracy. Hats off to you!
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I receive the beacon on 10489.550,070 Hz and on 10489.550,120 Hz in the morning.
(with GPSDO-RX)
Can this be confirmed?
Kepler elements of QO-100 show +- 20 Hz worth of doppler on 10489.550 MHz. As the beacon is generated on the ground, you have to multiply by two, so +-40 Hz over a day. Totally expected.
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It depends if the area which is uncontrolled is within the beam direction or not. For us, one would need to provide the polar diagram of the transmit antenna and derive its effective gain in the direction to the uncontrolled area. There the gain will be much lower than in the main lobe and possible even less than 0dBi. So yes, you have to give EIRP, but not with the boresight antenna gain, but with the correct one in terms of direction of interest.
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G0TKZ have you increased the AIrspy R1 gain setting for max sensitivity in the respective SDR software ? When pointing the antenna to the sky, you show see the difference if you cover the LNB with your hand (which is warm.. the sky is cold).
Only if you see this (small) difference, you will be able to see the satellite.
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Use a generous (!) amount of solder flux before heating up and the short circuits should be no more.
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DJ7GP has done measurements with wobbly LNBs. Once he extracted the crystal and supplied the crystal frequency from a clean external signal generator, the wobbling was gone. Sources tell me that there are many really cheap (as in bad) quartz crystals out there...
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For those looking to build a directional coupler, have a look at Paul Wade's article:
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Hi Pat, can't see the symbol rate setting, is it at 2000 ks/s? Also set the FEC to DVB-S2
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Hi Frank, if you clad the reflector grid with fly screen you will certainly improve the reflective properties of the dish. However you will also increase the windload to the point, where a standard offset dish of same size will be on par at wind load and in terms of RF performance even better. And with a new feed (circular), you can improve by another +3dB .
When it comes to wind, fly screen with its tiny mesh is unfortunately quite comparable to a solid sheet of metal. You can easily test this by hanging both on a 'Waescheleine' and have a look. -
2x yes (obviously..)
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DD0KP Which Harald? I think we don't know what to expect in terms of QO100 user meeting so it will be hard to do a fixed reservation for a Saturday evening dinner at some place..
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I expected to be the patch feed further out (literally flush to the holder).. seems too close to the dish to me. 1-2 dB are easily lost there. With a 1.2m dish you might be forced to check on absolute signal level rather than S/N as you will see transponder noise and the S/N will max out. Or you optimize on the increase of transponder noise relative to the non-transponder noise at (as example) 1 MHz lower.
Might be non-critical on NB signals but for WB every dB counts.
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Great job Mike! Have you tried to optimize the position of the feed in the LNB holder? I see LNB skew rotation but have you tried to shift the feed in the fixture back and forth?