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 _______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb