[HamSat] Re: HamSat Digest, Vol 7, Issue 3

[Lowell White]

Thanks, Jim, for a clear and informative note.

Hopefully I'll be on the bird before long.

73 de 
Lowell White
K9LDW


*********** REPLY SEPARATOR  ***********

On 8/3/2004 at 4:00 AM hamsat-request at mailman.qth.net wrote:

>Send HamSat mailing list submissions to
>	hamsat at mailman.qth.net
>
>To subscribe or unsubscribe via the World Wide Web, visit
>	http://mailman.qth.net/mailman/listinfo/hamsat
>or, via email, send a message with subject or body 'help' to
>	hamsat-request at mailman.qth.net
>
>You can reach the person managing the list at
>	hamsat-owner at mailman.qth.net
>
>When replying, please edit your Subject line so it is more specific
>than "Re: Contents of HamSat digest..."
>
>
>Today's Topics:
>
>   1. AO-51 Operation Notes (Timothy Pickett)
>
>
>----------------------------------------------------------------------
>
>Message: 1
>Date: Mon, 2 Aug 2004 20:25:50 -0400
>From: "Timothy Pickett" <timp at speednetllc.com>
>Subject: [HamSat] AO-51 Operation Notes
>To: "Hamsat Mailing List" <hamsat at mailman.qth.net>
>Message-ID: <03a001c478f0$6de73690$0200a8c0 at dad>
>Content-Type: text/plain;	charset="iso-8859-1"
>
>The 67 Hz PL tone must be transmitted continuously for a station to be
>heard through the FM repeater.
>
>Unlike previous similar satellites the Echo PL tone decoder both turns on
>the downlink transmitter and gates the
>audio path. The tone must be present on a signal for the audio to get
>through. If a signal without a tone captures the receiver no audio will
>get through the decoder chip and the satellite will be transmitting a
>signal without modulation. If that condition persists for 10 seconds the
>transmitter will go off until it again hears a signal with PL.
>
>Multiple uplink signals can mix and cause no clear PL tone to be present
>at the decoder. During this time no audio is being repeated. What has been
>reported as a 'dead carrier' is usually a result of this condition.  It's
>not a carrier with no modulation on the uplink, but no valid PL on the
>uplink because of mixing, resulting in no audio passing through the
>satellite.  May we again note this is just like a terrestrial FM PL
>controlled repeater?
>
>The PL decoder chip easily detects PL tone of 1 Khz deviation and is
>quite forgiving. It is neither necessary or desirable to increase the
>deviation of the PL tone you transmit above the nominal values. It will
>not work any better.
>
>It is possible to turn off the PL function. But there is no COR (carrier
>operated relay) in the satellite. So without the PL function to control
>when the transmitter is on it would have to be on all the time. In the
>first few orbits in this mode, the B transmitter has been on about half
>the time. If it was on all the time it would have to be operated at a lower
>power level. There is only so much DC power available in the satellite
>and it is a zero sum game one orbit at a time. One of the major advantages
>of the PL control mode is it keeps the transmitter off when not in use and
>therefore allows it to be at higher power when in use.  Of course another
>is the satellite will not re-transmit signals not intended for it.  It is
>not
>possible for the PL tone to turn on the transmitter but not gate the audio.
>
>We are watching the power usage closely and considering how to modify the
>software to allow higher transmitter powers when adequate DC power is
>available, and not pull the battery down to far for Echo to make it
>through the next eclipse, and not go to deep into the battery capacity,
>etc. This three week (aprox.) trial period is for the purpose of
>measuring these performance parameters (and of course having some fun with
>this
>cool bird).
>
>The trial move of the voice downlink frequency to 435.300 MHz does not
>limit Echo in any way or change the number of options available for
>various modes.  All three Echo transmitters are frequency agile in their
>bands.  435.225 MHz was initially chosen and coordinated with the IARU on
>the assumption GO-32 was not active.  The reactivation of that satellite
>required Echo to move.  435.300 MHz was suggested by the IARU frequency
>coordination group.  If feedback from users around the world indicates
>this is a usable frequency we will complete the coordination process and
>continue to use it.
>
>The power level of the B transmitter on 435.300 MHz has been at about.5
>Watts for a couple of days now. This is as high as we can go in the
>current mode without over stressing the batteries near the end of eclipse.
>
>There is no beep generator in Echo so it is not possible to send a
>courtesy tone type beep when a valid PL goes away.  We put the idea of
>sending a short 9k6 digital packet from time to time on the voice downlink
>on our todo list.  It would have to interrupt any voice repeat going on at
>the time for about half a second due to the switching that it would entail,
>but at first glance seems doable.
>
>There is nothing wrong with the sensitivity of the uplink receiver.  In
>fact if anything it is too sensitive.  In any event it cannot be
>changed.  There is nothing about the orientation that is causing a
>reduction of sensitivity on the uplink.  The uplink antenna is for all
>practical purposes omni-directional.
>
>Jim White, WD0E
>
>
>
>------------------------------
>
>_______________________________________________
>HamSat mailing list
>HamSat at mailman.qth.net
>http://mailman.qth.net/mailman/listinfo/hamsat
>
>
>End of HamSat Digest, Vol 7, Issue 3
>************************************