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{ "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/TBMMDPYF45MSHXPXLCUL7ITYAXNTUZJO/?format=api", "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/?format=api", "message_id": "[email protected]", "message_id_hash": "TBMMDPYF45MSHXPXLCUL7ITYAXNTUZJO", "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/QHOJG43IZGB5NSLKZSV62GSVA2Q5CSQF/?format=api", "sender": { "address": "oh2aue (a) kolumbus.fi", "mailman_id": null, "emails": null }, "sender_name": "Michael Fletcher", "subject": "Re: [amsat-bb] QO-100 bare minimum: GPS referenced LNB + IC-402 (read: no dish, 70cm IF!)", "date": "2019-03-01T09:28:50Z", "parent": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/34E3BIPCLZWJGCI4I5ZOZNKDPFKJYJVT/?format=api", "children": [], "votes": { "likes": 0, "dislikes": 0, "status": "neutral" }, "content": "On 1.3.2019 6:19, Dave Hartzell wrote:\n> Very cool! \n> \n> Can you elaborate a bit more on the signal chain that you have built?\n\nHi Dave,\n\na very short description: the lnb is modified for external frequency\nreferenencing and at the radio end I have a simple high pass filter\nfor the IF going to the IC-402 (or other), a low pass filter for DC\nsupply to the LNB and a simple LC series circuit to inject the reference\nfrequency (26,5 - 28 MHz is OK for reliable locking) up the IF cable.\n\nMore detail:\n\nI am using the Octagon OSLO Single LNB OPTIMA which is a PLL LNB with\nan original reference crystal of 27 MHz (poor quality, no temperature\ncontrol or even compensation). I have made an extremely simple mod to\nthis by removing the crystal and feeding an external reference\nfrequency. Most hams seek dual or more output models or drill an\nextra hole for connector in order to apply this reference, but after\nsome experimentation I finally found a stable and reliable way of\nextracting the reference frequency from the \"L band IF\" connector:\n\nhttp://fletcher.fi/27MHz_BPF_Octagon_Oslo_sized.jpg\n\nThe series LC circuit within the LNB MUST be right next to the L band\nconnector for stability. Also care should be taken in avoiding any\nshorts (Polyimide/ Kapton tape etc.). Also, the cover and all screws\nMUST be torqued down as the PCB is in compression contact, sandwiched\nbetween the bottom and cover, hence needing excellent 360 degree\nmicrowave grounding all around.\n\nWith some reliability, but still risky, you can identify this particular\nmodel of LNB by the \"3D\"-text on the box. Beware, there is zillions of\nversions on the huge market of PLL LNB's and not all are that easy\nto modify or perform well at 10.4 GHz.\n\nHere is a quick comparison test I made, using an external, radiative\nnoise source, flatness maybe +- 1dB or so:\n\nhttp://fletcher.fi/modified_lo_octagon_oslo_single_lnb_optima_oh2aue_27_02_2019_sized_annotated.png\n\nSo it is quite amazing the 144 MHz IF is also otherwise fine, but the\nPLL VCO is REALLY at it's limit of reliable locking (see the other video\non my Youtube channel \"oh2aue\". At least it just about locked at a few\ndegrees C below zero ;-) And obviously the gain is also way down\ntoo, maybe 10 dB from my 200 MHz highpass filter in the triplexer.\nHowever, the noise figure has not yet appreciable deteriorated.\n\nSome similar single ouput models others have experimented with are:\n\n\"Universal Single-LNB GOLDEN-MEDIA GM-201, 0,1 dB \"\n\"Golden Interstar Universal Single LNB GI-201 Platinum X\"\n\"Goobay 67321\"\n\nTypically I use around 40 dB of attenuation in the path in order to\nset the receiver AGC knee at a suitable point for pleasant copy. My\nattenuators have a T choke affair to bypass the LNB DC supply. There\nare also cheap commercial attenuators available, but the largest\nvalues are usually only 12 dB. Then again, homebrewing a 40 dB\nattenuator good to beyond 1 GHz is not very trivial either.\n\nThere are many models out there that have differing external appearance,\nbut contain the same electronics and vice versa: there are also models\nthat have the same external appearance but different electronics. To\nconfuse things further, the text \"PLL LNB\" does not imply that that the\nelectronics are PLL based. And vice versa, no mention of \"PLL\" does not\nmean the LNB is a DRO LO type, rather it can well be synthesized and\ncrystal controlled.\n\nIn the video I am using the Leo Bodnar Dual Output GPS Disciplined\nFrequency Reference. Obviously the supplied reference signal has to\nbe very stable and low phase noise as in e.g. the Octagon LNB above,\nthe fractional synthesis effectively multiplies by 361.1111111...\nmultiplying any residual phase noise and jitter by the same order.\n\nAt the receiver/radio end I have a very simple triplexing circuit\nfor LNB DC bias (and 22 kHz/DiSEqC as the case may be), highpassing\nthe IF from about 200 MHz up plus the 27 MHz series circuit. A lowpass\nis also recommended if your reference signal is not pure sine. I only\nhave sketchbook drawings, but here is an estetically pleasing photo of\nOH3FWG's own implementation of such:\n\nhttp://oh3tr.fi/~oh3fwg/p4a/triplexer.jpg\n\nFor my personal experimentation I have also put together a \"laboratory\ngrade\" receive system (flat group delay, flat response, impedance\nmatching for each stage, etc.). This receiver frequency selectively\nmixes down the spectra of both transponders to HF (10 - 21MHz) and\nthere is a video of this receiver feeding my Barlow Wadley XCR-30,\nmerely because I can :-)\n\nhttp://fletcher.fi/kiwisdr_eshail2_receiver_29_12_2018.jpg\n\nMore on this for inspiration at:\n\nhttp://fletcher.fi/amsat_oh_rats_eshail_2_satellite_x_band_downlink_pll_lnb_kiwisdr.htm\n\nAll this stuff is great fun, reminds me of listening to the Japanese\nlunar orbiter carrier with a paper clip some years back - and yes, there\nis a video of this on my channel too.\n\n(Freenode) IRC channels #es'hail-2 and #hearsat are recommended.\n\n/Michael, oh2aue\n\n", "attachments": [] }