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| To: | [email protected] |
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| Subject: | Re: Not LF: Opera via QO-100 |
| From: | Markus Vester <[email protected]> |
| Date: | Sun, 10 Mar 2019 08:22:13 +0000 (UTC) |
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Here's spectrogram of differential Doppler between the two 2.4 GHz uplinks, scaled to cover 16.5 hours (8:30 yesterday to 1 UT this morning). A 0.1 Hz wide diurnal variation is clearly visible, presumably caused by inclination and ellipticity of the orbit, and possibly also tidal effects from the moon. Best 73, Markus -----Ursprüngliche Mitteilung----- Von: Markus Vester <[email protected]> An: rsgb_lf_group <[email protected]> Verschickt: Sa, 9. Mrz 2019 13:28 Betreff: Re: Not LF: Opera via QO-100 Hi Luis, all, I made some tests regarding the usability of QO-100 for very narrowband modes. Over the web-sdr, we can normally stay only within a few Hz, and my own receiver using an unstabilized crystal PLL-LNC is drifting over many kHz. However it seems possible to achieve almost perfect stability using a pilot carrier, e.g. the bottom CW beacon as a reference. During the last couple of hours, I sent a Rubidium derived carrier on 2400.0512 MHz, and observed the 1.2 kHz beat frequency using SDRsharp in AM mode and SpecLab at 5.7 mHz resolution: http://df6nm.bplaced.net/VHF/QO100/eshail_beacon_AM_190309_1222.png We find some remaining instability on the order of 10 mHz or so, i.e. only about 4e-12 of 2.4 GHz. This may be due to transmit frequency variations either from my Rubidium (10 MHz LPRO), or perhaps the beacon itself (presumably a GPS-DO). Another source could be differential Doppler from lateral satellite movement between the two uplink sites (Doha, Nuernberg), although I would expect that to occur predominantly over 12 h and 24 h periods. Note that when trying to use the BATC web-sdr in AM mode for this purpose, I noticed much larger variations, which are caused by automatic samplerate adaptations following buffer fill states. So as a bottom line, it looks like Es'hail 2 is indeed usable for narrowband visual and digital modes, although coherent PSK (EbNaut) would probably still be limited to relatively fast transmissions. BTW the browsable folder http://df6nm.bplaced.net/VHF/QO100/ also contains some more pictures from my lash-up GHz hardware. Best 73, Markus -----Ursprüngliche Mitteilung----- Von: VIGILANT Luis Fernández <[email protected]> An: [email protected] <[email protected]> Verschickt: Do, 7. Mrz 2019 12:59 Betreff: RE: Not LF: Opera via QO-100 Keeping off topic ;-)
I’m also making QRP tests over QO-100 Currently using 150mW to a biquad linearly polarized antenna. Apparently Hpol works better than Vpol for unknow reasons I’m getting decodes in Opera but the WebSDR is not good enough for weak signals
There is still room for decreasing power. And using an omnidirectial RHCP antenna like cuadrifiliar helix would be also much better
I’m thinking about EbNaut over QO-100. An ADF4351 PLL can be used to generate the signal directly from GPSDO reference The Rx chain may be a problem. The downconverters in the chain may introduce phase changes. But there are I/Q downconverters to get the signal directly at baseband using just one LO
Any ideas ? This may be little bit more focused on topic. Would be amazing to transfer a message trought the sat using minimal power and small omni antennas
73 de Luis EA5DOM
De: [email protected] [mailto:[email protected]]
En nombre de mal hamilton
Hi David That is what I am doing the PLL LNB is manageable without modification for cw and ssb and most of my equipment is left on 24/7 so no warm up problems. I do have a high spec satellite RX with selectable digital or analogue reception plus various outputs, IF, BASEBAND etc. also manual frequency and parameter settings. This could be an alternative method of reception and maybe more stable than the more common LNB/DONGLE method and avoids a T bias module 73 de mal/g3kev
Hi Mal
Most of the LNBs designed for HD TV have a PLL for low phase noise. These have 'acceptable' drift for CW and SSB QSOs......Just let them warm up for 10mins before you use them. (or fit a TCXO instead of the 27 / 25MHz crystal) No set top box required. Just small dish + LNB into a dongle. Trying to get an output directly at 70cms is a bit hit and miss as you are well below the lower 750MHz limit of the LNB.
73
David
On Wed, Mar 6, 2019 at 1:56 PM mal hamilton <[email protected]> wrote:
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