This is a repost of the:

PCSAT FREQUENCY COORDINATION REQUEST:The mission of our PCsat is unique in the Amateur Satellite Service as it
is designed to support the text messaging and position tracking needs of
mobiles and handhelds only and links into the terrestrial internet system.
As such, the link margins to user OMNI antennas require downlinks in the
2 meter band.

For international operation, we will need a frequency(s) in the agreed
Satellite sub band of 145.8 mhz. This frequency can hopefully be shared
with a number of other UI digipeating satellites in work… But we also
hope to use the exclusive North American Continent wide 144.39 APRS frequency
for occasional downlinks of brief one-line text pages to remote mobile
travelers. The following design summary should provide the background.

UPLINKS AND RECEIVE GAINS: Up and downlinks fall into several different
classes based on ERP and receiver antenna gain as shown below. The column
labeled Standby-receive gain is for the user who is not aware of, nor
optimized for satellite reception. For example, an HT in a pocket, or
a mobile parked under trees.

ERP ERP Rcv Rcv Rcv
UHF VHF UHF VHF STBY
USERS (W) (W) dBi dBi dBi Applications
——— — —- — — — ——————————
HANDHELDS 3 5 3 3 -6 Sailboats, Hikers, Wilderness
MOBILES 70 100 5 5 -6 Boats, Remote Travelers
HOME STNS 700 1000 13 13 Not intended for PCsat

NETWORK
IGATE RCV 7 5 Omni Internet receive site
MSG NODE 70 100 Internet to user UPLINK site
COMMAND 700 1000 13 13 US Naval Academy Ground Station

MISSIONS: Since several other amateur satellites have provided imaging
and file store- and-forward for the last several years, PCsat concentrates
on the current trend towards personal real-time wireless messaging using
UI digipeating. In this context, the following list prioritizes these needs.

1) Handheld/Mobile message uplink to Internet (emergency and routine)
2) Handheld/Mobile message downlink delivery from Internet
3) Handheld/Mobile to Handheld/Mobile real-time communications
4) Nationwide Bulletin delivery to all users
5) Handheld/Mobile GPS position tracking to internet
6) GPS tracking of buoys, telemetry devices, wildlife, expeditions
7) Other UI digipeating applications (TBD)
Message Store-n-forward (limited special applications only)

FUNDAMENTAL ASUMPTIONS:

1) Optimum ALOHA CSMA channel efficiency is about 18% due to collisions
2) VHF links have a 9 dB advantage over UHF links (Omni to Omni)
3) 1200 baud AFSK has a 7 dB advantage (measured) over 9600 baud FSK
4) T/R delays render 9600 only twice as fast as 1200 for short bursts
5) UHF uplinks require wide bandwidth to avoid Doppler (- 4 dB)
6) UHF downlinks require user tuning throughout pass (not desired)
7) There are available off-the-shelf handheld and mobile radios now
that can serve as stand-alone digital satellite transceivers

REQUIREMENTS/CONSTRAINTS Design Drivers: The following are some of
the obvious first-order alignments of requirements to hardware and
Frequencies. From these, then, we determined the optimum trade-offs to
arrive at our final design and frequency requirements.

1) MSG delivery to HT in Standby requires best possible downlink
(1200 baud VHF). Igate uplink is relatively unconstrained.
2) MSG receipt from HT requires best possible uplink (1200 baud VHF).
Downlink to internet is relatively unconstrained.
3) Continent wide Bulletin Delivery requires downlink on existing
dedicated terrestrial APRS frequencies (144.39 in USA and 144.8
in Europe (both 1200 baud).
4) HT/Mobile real-time messaging requires same up/downlink baudrate
5) GPS HT/Mobile tracking is relatively unconstrained.
6) Low power GPS tracking devices requires best uplink (1200 baud VHF)
and the uplink must not be used by any other satellite uplink to
avoid unintentional interference to other systems.
7) Other UI digipeating applications should be crossband full duplex
and should use same up/downlink baud rates
Store-n-forward (rare) is unconstrained with equal baud rates
9) Spread of applications among multiple receivers to minimize
Collisions is desired.
10) Redundancy and Backups are desired.
11) UHF downlinks are of little value due to poor link budget and doppler
12) UHF Uplinks can work without Doppler tuning with a 30Khz Satellite RCVR
13) KISS applies (Keep it Simple, Stupid)

HARDWARE ALIGNMENT: Using the above as the basis, we chose a pair of
dual-port KPC-9612 TNC’s to satisfy as many of the above requirements as
possible. Each KPC-9612 can cross relay from either of its two inputs
to its two outputs. Since we only have two transmitters on VHF for best
downlink, we output both the 1200 and 9600 baud data to the same transmitter
(with appropriate PTT/DCD cross strapping). ALthough we need two 2m
downlinks, two 2m uplinks and two 70cm uplinks, we have gone ahead and
penciled in some obvious suggestions, so that the uniqueness of the choices
is quite obvious.

USERS UPLINK TNC DOWNLINK
—————- ——- ———— ———————
KPC-9612 #1
HT-to-HT 145.825 ——> 1200 Baud -*—–> 145.825 (ITU Subband)
\ / |
/ \ |
Mobile-to-Mobile 435.250 ——> 9600 Baud -*

KPC-9612 #2
Low Pwr Trackers VHF-V2 ——> 1200 Baud -*—–> 144.39 (over USA )
\ / |
/ \ |
Igate Paging UHF-U2 ——> 9600 Baud -*

Notice that the Igates monitor both downlinks to capture every packet
Heard and feed to the worldwide APRServe internet linked network.

Our AMSAT/ITU Frequency request is:

1) VHF-A = 145.825 as a shared international UI digipeating frequency

2) VHF-B = 144.390 downlink over North America Only. This frequency is
already dedicated for APRS by TAPR, ARRL, AMSAT and their Canadian
counterparts. Downlink on this frequency even though it is outside
the Gentlemen’s agreed satellite sub band is a unique opportunity
welcomed by all current users in North America.

3) VHF-C = Any 2m satellite uplink frequency hopefully not shared with
any other satellite uplink so that we do not QRM any other sats.
We have no objections if this frequency is another satellite
downlink. This will be our command uplink channel and reserved
special uplink channel for very special world interest events.

3) UHF-A = 435.250 for all 9600 baud 50w mobiles.

4) UHF-B = Any other 20 KHz frequency in the 435-437 MHz band.

Bob Bruninga, WB4APR@amsat.org

amsat or called The Radio Amateur Satellite Corporation

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