[amsat-bb] Need some information

[Mac A. Cody]

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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