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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/ATCXENGL6EOVGP7UELUFIKX5YU3X3NT2/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "ATCXENGL6EOVGP7UELUFIKX5YU3X3NT2",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/ATCXENGL6EOVGP7UELUFIKX5YU3X3NT2/",
    "sender": {
        "address": "maccody (a) att.net",
        "mailman_id": "b6473a44d40d4c91b7f8bb74bef3b879",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/b6473a44d40d4c91b7f8bb74bef3b879/emails/"
    },
    "sender_name": "Mac A. Cody",
    "subject": "[amsat-bb] Making the linear satellites more accessible",
    "date": "2017-09-09T23:08:35Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "First, thanks to those that replied to my question about the level of\nactivity on the linear transponder satellites.  What was saidwaspretty\nmuch what I suspected.  I was just looking for some verification from\nothers before expressing some thoughts about making the linear satellites\nmore accessible to amateur radio operators.  I apologize up front for\nthis lengthy posting.  Please accept it in the spirit of experimentation,\nreducing the level of congestion on a few satellites, and possibly\nincreasing the ranks of the amateur satellite community.  I'm sure that\nthere will be those ready to step forward and correct me on any of the\nassumptions or statements that I make.  Please be understanding.\n\nThere are currently two FM repeater satellites (three, counting the\nsporadicly active LilacSat2).  SO-50 and AO-85 are heavily used, with\nfrequent congestion.  Meanwhile, there are a dozen linear transponder\nsatellites that are relatively lightly used with bandwidth for multiple\nsimultaneous channels.  I understand that it makes sense to launch linear\ntransponders, rather than FM repeaters, due to the better utilization of\nresources.\n\nIn my estimation, the relative lack of utilization of the linear birds,\ncompared to the FM birds, is the cost barrier for the radio equipment\nrequired to be able to work them.  The added challenges of finding other\nstations in the band and stricter Doppler accommodation also exist, but\ncan be mastered with practice.  Allow me, though, to confine my comparison\nto voice-mode communication only, for reasons I'll explain shortly.\n\nA pair of inexpensive hand-held FM transceivers and a pair of Yagi antennas\n(or an Arrow or Elk antenna) are all that is needed to successfully work the\nFM birds.  In fact, that is what I'm using right now.  An expenditure of\nabout $200 is needed, possibly less.  On the other hand, to properly work\nthe linear birds using voice requires an SSB transceiver (if capable of\nfull duplex operation), or that and another SSB receiver, otherwise.  The\nattendant expense appears to approach $1000, possibly more.\n\nOne suggestion is to work the linear satellites using CW mode. While this\ncould definitely be less expensive, it exchanges one barrier for two others.\nThe first is the need to know Morse code.  The second is the apparent \nlack of\nregard that many in the satellite operator community appear to exhibit \nfor CW\noperations on the satellites.  The cause appears to be a lack of discipline\nby some CW operators in both power management (signals hogging the \ntransponder\npower or 'flipping the bird') and signal frequency management (failing to\nproperly compensate for Doppler shift, thereby encroaching on other QSOs).\nBoth of these discipline problems occur at the expense of the SSB operators\nresulting a lot of public ire towards CW ops - Ironically, I also hear that\nsuch discipline problems also occur with some SSB ops, too. Consequently, I\ndon't see CW ops as a particularly viable solution to lowering the barrier\nto using the linear birds.\n\nI also don't see allowing other digital modes on the linear birds to be a\nviable solution either.  Most digital modes are propagated via SSB \ntransceivers.\nThis raises the cost bar once again, which doesn't solve the problem.  There\nare a few digital modes, such as Hellschreiber, that don't ride on SSB, but\nthey are not popular and would exclude QSOs with voice-mode operators.  The\nclosest may be the successful use of OpenDV and an appropriate digital\nmodulation scheme.  That is all still very experimental.\n\nWhat I propose, then, is the use of well-disciplined DSB (double sideband)\nmodulation as a means of lowering the cost bar while providing \ninteroperability\nwith SSB voice stations that are working the satellites.  What I mean by\n'well-disciplined' DSB is as follows:\n1) Baseband audio bandwidth sharply limited to 2.5 KHz, resulting in RF\nbandwidth or 5 KHz. This would realistically enable three to fifteen\nsimultaneous 'channels' depending upon the linear bird being used.\n2) Power output would be limited to just a couple of Watts.  This is all \nthat\nis really necessary to access the linear birds in most situations.  It\nwould reduce the possibility of signal interference.  The cost of the PA\nwould be relatively low.\n3) The RF oscillator would be accurate and computer controlled (e.g. Silicon\nLabs Si570), which would enable active Doppler compensation via software \nwith\nCAT control (e.g. gpredict).\n\nCurrent SDR technologies already enable inexpensive, multi-band receiver\nsolutions.  The desired sensitivity and selectivity of the SDR receiver\nultimately drives the receiver cost.  The performance of the receiver, then\ndepends upon the budget of the station builder.  Solutions for every\nbudget are now available, ranging from dirt cheap hardware derived from\nRTL-SDR dongles to more capable devices (e.g. SDRplay, AirSpy, FunCube\nDongle).\n\nAt the sacrifice of some bandwidth, the following advantages can be had with\nusing DSB modulation:\n1) DSB modulation is relatively easy to achieve.  The band-limited audio\nis fed into a double-balanced mixer, bandpass filtered for harmonics, and\nfed into a PA for transmission.  The resulting hardware is comparatively\ninexpensive to construct and to tune.\n2) Sideband inversion caused by some linear birds is no longer an issue.\nHaving both sidebands present in DSB modulation means that the correct\nsideband will always be available for reception.\n3) Interoperability with SSB stations would be maintained, as DSB modulation\nis a superset of SSB modulation.\n\nThanks again, for reading this long posting.  I'm sure that there will be\nthose that will consider my suggestions to ill-advised, or even outright\nheresy!\n\n73,\n\nMac Cody / AE5PH\n\n",
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}