[amsat-bb] Need some information

Sat Jun 17 23:00:44 UTC 2017

>  Given the proliferation of low power, narrow-bandwidth digital modes...
> I'd think that there should be some discussion about expanding beyond
> CW and SSB for use on the linear transponder satellites.

Off topic, but we are getting close to launching QIKCOM-2 which will have a
DTMF uplink with APRS and voice downlink if the FCC would ever finish the
filing of the API submitted back in Nov 2014.

This will let simple HT's with only a DTMF keypad participate in APRS.and
two-way contacts.
http://aprs.org/qikcom-2.html

We are also delivering PSAT-2 which will have the same thing, but a better
voice module and a secondary payoload of a PSK31 transponder like is on
PSAT.  Again, only if the FCC will finish processing  the API that was
submitted back in 2015.

http://aprs.org/psat2.html

I hate to make such announcements until it is actually in space and
working, but Im working 12 hour days for months trying to finish and it is
working GREAT on the bench.

As some of you may remember, I have been an advocate of using DTMF for more
practical  communications applications for years...since EVERYONE has an HT
that will do it.  (except modern Baefengs - Needs a 16 digit DTMF memory to
be useful)
http://aprs.org/aprstt.html

Bob, WB4APR

On Sat, Jun 17, 2017 at 1:26 PM, Mac A. Cody <maccody at att.net> wrote:

> Hi Paul,
>
> The AMSAT website can provide a lot of the information thatyou need.
> An overview the operational satellites can be found on the AMSAT Live
> OSCAR Satellite Status Page(http://www.amsat.org/status/). There are
> hyperlinks to additional information for many of the satellites listed
> below the Name column on the left of the web page.  Additional
> information and links can be found on the Communication Satellites web
> page (http://www.amsat.org/?page_id=177)
>
> Essentially, a linear transponder receives signals at a specific center
> frequency with a bandwidth of tens of kilohertz.  It then retransmits them
> at a different center frequency with the same bandwidth, sometimes
> inverting
> the frequency band along the way.  The frequency inversion helps to
> mitigate
> the effects of Doppler shift.  For example, CAS-4A receives at a center
> frequency of 435.220 MHz with a bandwidth of 20 kHz.  The signals are
> retransmitted at a center frequency of 145.870 MHz and the frequency band
> is inverted.
>
> It is by agreement that the communication modes used to communicate through
> the linear transponder satellites are CW (Morse code) and SSB. This is
> done to conserve bandwidth usage and power utilization accorded to a
> particular transmission.  Theoretically, you could transmit FM, or any
> other modulation, through a linear transponder, but you would become quite
> unpopular for using up the bandwidth of the transponder with an
> 'unacceptable' signal.  You can also become unpopular for transmitting too
> strong a signal into the transponder, as your signal will be accorded most
> of the power the transponder uses to transmit, thereby reducing the power
> available for the other signals.
>
> (On a soapbox for a moment:  Given the proliferation of low power, narrow-
> bandwidth digital modes that have become available, I'd think that there
> should be some discussion about expanding beyond CW and SSB for use on
> the linear transponder satellites.  End of soapbox and queue up those who
> disagree...)
>
> Right now, there are effectively only two FM satellites: SO-50 and AO-85.
> While Lilacsat-2 has an FM repeater, it is not always available.  There
> are a couple of FM satellites that should be launched this year, so the
> outlook for FM birds will be better in the future.  There are also APRS
> digipeaters available of the ISS and NO-84, which you can communicate
> with using a 2M FM handheld connected to a computer, tablet, or smart
> phone.  Some handhels have APRS capabilities built in.
>
> I hope I've answered your questions sufficiently.  Hope to hear you on the
> FM satellites soon!
>
> 73,
>
> Mac / AE5PH
>
>
> On 06/17/2017 08:57 AM, Paul Ecker wrote:
>
>> I am trying to get back into working Satellites again after a hiatus of
>> about 7 years. In trying to catch up, difficult to sort out the current
>> landscape of what can be worked. So a couple of probably dumb questions
>> for
>> you guys who seem very much on top of the entire subject.
>> - So where or how can I get a complete list of all the Sats that are
>> currently workable with a full duplex FM HT setup?
>> - in reading about the new CAS 4A &4B, it says they have linear
>> transponders and it lists VHF and UHF frequencies for up & down-link. So
>> is
>> linear transponder a code word for SSB, can't be worked using an HT?
>> - What exactly is a Linear Transponder?
>>
>> Tnx & 73
>> Paul
>> kc2nyu
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> _______________________________________________
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> expressed
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> AMSAT-NA.
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