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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/XPJM2VNJ23APUTIYP3QWWSTSW7PVSWWB/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "XPJM2VNJ23APUTIYP3QWWSTSW7PVSWWB",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/XPJM2VNJ23APUTIYP3QWWSTSW7PVSWWB/",
    "sender": {
        "address": "k0vty (a) juno.com",
        "mailman_id": "69d7c9bb693a4435bee46454dd0afb25",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/69d7c9bb693a4435bee46454dd0afb25/emails/"
    },
    "sender_name": "joseph Murray",
    "subject": "[amsat-bb] Re: Sequencer",
    "date": "2007-03-12T21:11:17Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "This issue might best include VOX and full duplex in a round table on\nHEO.\n\nJust in case\n \nJoe  K0VTY\n====================\nOn 12 Mar 2007 14:18:32 -0500 [email protected] writes:\n> On Mar 12 2007, Edward Cole wrote:\n> \n> >At 05:15 AM 3/12/2007, Stargate wrote:\n> >>Is a sequencer needed when using a 160w switchable preamp from \n> ARR?\n> >\n> >Let's analyze this:\n> >\n> >You send a voltage to run the preamp.  It needs voltage to switch \n> to \n> >Tx mode.  When RF from your transmitter arrives it switches over to \n> \n> >bypass the preamp.  I would guess if you turn off the power to the \n> \n> >unit, it can't operate correctly, so how is a sequencer going to \n> >help?  I have not owned one of these units so not familiar with \n> their \n> >power wiring.  If you have two 12 volt power contacts then you \n> might \n> >run the preamp separately from a sequencer.\n> \n> Sequencers don't have to only apply/remove DC power in a set \n> sequence. In \n> fact, in the general case, a sequencer has a series of switch \n> contacts that \n> are enabled in the proper order and disabled in the opposite order. \n> The \n> switch contacts could be configured as NO (normally open) or NC \n> (normally \n> closed). These can either provide and remove DC power, or short the \n> \n> pre-amp's own PTT circuit to ground to take it out of receive mode \n> (or, \n> depending on the model of preamp, maybe +12 is PTT instead of GND). \n> The \n> Down East Microwave sequencer has a DPDT relay for each of the \n> sequence \n> stages, so you get two independent NO and NC contact sets to play \n> with as \n> you wish.\n> \n> If (like the ARR models) the preamp has built-in bypass switching, \n> one \n> issue that remains is how quickly and completely the preamp gets \n> switched \n> out of the transmit path. If slow to switch, and/or if the isolation \n> is \n> insufficient, a spike of RF may still enter the very sensitive \n> preamp and \n> fry it. With a sequencer, you can (usually) select whatever \n> switching delay \n> is needed for the isolation relays to reach a fully switched \n> position, and \n> you also get to pick the isolation relays themselves, with attention \n> to \n> power dissipation and degree of isolation needed. I believe that ARR \n> says \n> that the built-in RF-sensing relay is good for up to 160 watts, but \n> a \n> sequencer with a separate isolation relay could basically allow you \n> to use \n> 1.5 kW, if you had an awfully darn good reason to use so much power, \n> ;) \n> that is.\n> \n> On my 144, 222, and 432 bands, I have an RF Concepts \"brick\" \n> amplifier with \n> an internal preamp and RF-sensed automatic switching. On 144 and \n> 432, these \n> are \"soft keyed\" (i.e. keyed by sensing RF). On 222, which is done \n> with a \n> transverter instead of directly out the back of my FT-847, I went to \n> the \n> effort to \"hard key\" the amp/preamp by using its PTT input (which I \n> had to \n> re-configure as PTT to GND instead of PTT to HI). Both \"soft\" and \n> \"hard\" \n> switching methods work OK, but on 144 and 432 it is best to briefly \n> pause \n> after keying the mic before you start talking, to insure that the PA \n> is \n> switched in, and when you unkey, you have to hope that the person on \n> the \n> other end pauses briefly before responding because it takes a \n> noticeable \n> amount of time for the amp/preamp relay to switch back to receive \n> mode. \n> (The delay is intentional, to prevent relay chattering.) On 222, \n> since the \n> radio, transverter, and external PA/preamp are all hard-switched by \n> their \n> own PTT signal, the send/receive cycle is much smoother, no excess \n> delays, \n> no chance of relay chattering if the loudness of your voice drops \n> low for a \n> moment, etc. So I definitely prefer the \"hard keyed\" method of \n> operation. \n> One of these days, I will get around to modifying the 144 and 432 \n> amps for \n> hard keying also...\n> \n> On 902, 1296, 2305, and 3456 MHz, my transverters were built with \n> split \n> Tx/Rx, which makes it simpler to connect a preamp (if needed) to the \n> Rx and \n> a power amp to the Tx, and of course you need a T/R coax relay \n> external to \n> the transverter. So far, because my PA's on these bands are low \n> power, I \n> hard-key the T/R relay but it is not sequenced -- radio PTT = \n> transverter \n> PTT = T/R relay PTT, all at the \"same\" time. When I move up to the \n> high-power class of operation, I will install a sequencer on each. \n> We have \n> local folks here who have had the experience I am trying to avoid, \n> namely \n> simultaneous switching works ok at low power, but add in some REAL \n> output \n> power and things fry if not sequenced. These bands have PA's of \n> 40-120 \n> watts waiting to be integrated. (This is for terrestrial work, not \n> satellites, by the way, as you can probably figure from the high \n> powers and \n> non-satellite bands/sub-bands mentioned...)\n> \n> 73 de W0JT\n> AMSAT-NA LM#2292\n> _______________________________________________\n> Sent via [email protected]. Opinions expressed are those of the \n> author.\n> Not an AMSAT-NA member? Join now to support the amateur satellite \n> program!\n> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb\n> \n> \n",
    "attachments": []
}