[amsat-bb] Station decisions re. upcoming Geosync bird

John Toscano tosca005 at umn.edu
Thu Mar 24 04:17:47 UTC 2016

Details on the satellite are still quite sensitive, but details on ground
station requirements are much more readily discussed due to the lack of
ITAR restrictions there.

One approach to the ground station would be to add a 5G and a 10G
transverter to your existing radios, using them for IF radios. Though many
5G and 10G transverters use a 144 MHz IF, some are available with a 432 MHz
IF. Getting one of the two transverters with a 432 MHz IF and one with a
144 MHz IF would probably facilitate full-duplex operation, unless you have
two 144 MHz IF radios available.

This sort of approach might be preferred by an operator who plans to add
those two bands to BOTH terrestrial and satellite operation. But if you
were adding these two bands for satellite use only, there is significant
opportunity for financial savings. You only need a 5G transmitting
converter and a 10G receiving converter. On the receiving end, a modest
satellite dish and an inexpensive LNBF designed for for satellite TV will
convert the satellite downlink to a signal somewhere near 700 MHz, which is
easily within the RF range of many software-defined radios. The ground
station team has been hoping that an under-$20 satellite TV PLL-LNBF
coupled with an inexpensive RTL-SDR dongle MIGHT suffice for the heart of
the 10G receiver. For the uplink, it is possible that a $300-ish HackRF One
SDR (which can transmit at up to 6 GHz), coupled with appropriate filtering
and a suitable power amplifier might form the heart of an inexpensive 5G
transmitter. The ground station team is looking at other, more expensive
solutions, as well, and we can't yet promise that the rock-bottom-price
solutions will work until they have been well-tested.

In any event, digital modes are going to be the order of the day, so if you
are using a pair of all-mode radios as IF's, they will need to support a
digital interface to a computer. That's one of the reasons why we are so
excited about the possibilities of SDR to get us from RF to digital data
and back at affordable prices.

\I hope that helps at least a little bit.

John Toscano, W0JT/5

On Wed, Mar 23, 2016 at 7:44 PM, Peter Klein <pklein at threshinc.com> wrote:

> I've been casually following the discussion of the upcoming geosynchronous
> satellite.  I currently have a Mode B , J and A analog setup that I've used
> on Oscar 10 and 13, and on some LEOs. This includes crossed Yagis on 2m and
> 70cm, and an all-mode radio for those bands.  LEOs and flying mailboxes no
> longer interest me, so in recent years that setup has only been used for
> occasional terrestrial VHF SSB/CW, plus local repeater activity.
> I will need to make some decisions on my general station setup soon.
> Antenna space is limited, and I want to take the possibility of the geosync
> bird into consideration.  From what I've read and seen on video, the
> uplinks and downlinks to the satellite will be microwave.  The satellite
> track will make a figure-8 pattern in the sky, but I don't know how large
> that pattern will be at my location. My 144 and 440 MHz antennas will not
> be compatible with the new bird.  But will the 144/440 radios be useful,
> perhaps as an IF after the digital gymnastics happen in a converter?
> So, my questions:
> - Are any "dummy" Keplarian elements available for the geosynch bird's
> planned (or likely) orbit? That would let me do some "what-iffing."
> - If the above are not available, could someone tell me the approximate
> range of azimuth and elevation I might expect from CN87 (Seattle area)?
> - What is the physical size of the required dishes?
> - Will the radio for the new bird be self-contained, or require another
> radio as an IF?  If the latter, what frequency band or bands are being
> contemplated for the IF?
> If I've asked things that are too sensitive to discuss right now, let me
> know and I'll shut up.  :-)
> 73,
> --Peter, KD7MW
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