I have been following this discussion for a number of months now both on the Eagle discussion group and on AMSAT-bb. I don't want to add to the noise on amsat-bb but do have an opinion. I want to hear the satellite as well as possible so if that means abandoning 2.4 Ghz as a downlink, I can live with the decision. I am not happy with the prospect but I realize that you can't fight physics. I do plan to borrow a spectrum analyzer and examine how bad the situation is around my house in Tucson. Before we lost the L1 transmitter and the dish antenna on AO-40 I was hearing the bird very well with a minimal antenna and poor noise figure down-converter. The AO-40 S-band downlink took a huge hit when all we had was the S2 transmitter and the helix antenna. I have spent the best part of 15 years selling S-band as the satellite downlink of choice to satellite users so it is very hard to now have to start selling another answer, but so be it.
My BIG concern is giving up the L-band uplink without a fight based on the assumption that at some time in the future we may lose the band due to a system that has not even been fielded yet. While the Galileo system will probably be fielded, let's not give them the benefit of the doubt. Even if it is fielded we do not automatically lose the allocation. It looks to me like our potential for interference is relatively minor compared to the real issues that they face on the E5 links in the radiolocation band where there are aircraft transponders, DME transponders, DME interrogation links, Link-16 Data Links and numerous other radio navigation emitters and radars. I personally don't think that they will even notice us. I have seen one or two places where they are selling the Safety of Life services as being jam resistant and these capabilities are spread out among all of the downlinks.
Since L-band only involves a receiver on the satellite and antenna space that could also be shared with other receivers if necessary (with well designed stacked patch antennas or feeds), I think that an L-band receiver should be flown (unless we lose the allocation prior to launch). In making this statement I am assuming that the cost of adding an L-band uplink is not excessive. I think we should plan on using the band and then turn off the receiver if we lose the allocation. It is part of our responsibility to use and defend our bands to the best of our ability and the L-band uplink is very valuable to us. Many of us have existing equipment and are L-band terrestrial or EME users and we need L-band on the satellite to help defend our rights to the band. Have a back-up or alternate uplink in case we do lose L-band at but plan to fly and use it as long as possible. We can inform our members that the band is at risk and then it is their choice if they invest in new L-band equipment. We should make it be the government (not AMSAT) that takes away our access to this band.
There are my thoughts. I will happily adapt to whatever decision that AMSAT's management and the Eagle design team make. I am looking forward to seeing many of you at the TAPR/DCC conference next weekend.
Larry Brown, W7LB