How to access the Kenwood D700 on ISS in
cross band repeater mode
By Miles Mann WF1F
MAREX-MG News www.marexmg.org
The Cross Band repeater on ISS is only operational during specific published
events such as Field Day and Cosmonauts Day. ARISS will post the operation
schedule on the AMSAT and other web pages and on the SAREX mailing lists
Kenwood D700 System
The Kenwood System uses a transceiver that has a built in packet modem
and also supports “Cross-Band Repeater” mode. This system
is located in the Service Module.
The Kenwood model D700 supports two Amateur radio bands: 2-meter FM (144
– 146 MHz) and the 70 centimeter FM (435 - 438 MHz). The built-in
modem or TNC supports 1200 and 9600 baud data rates. The D700 system is
connected to one of the 4 Amateur Radio antennas mounted outside of the
Service Module. The typical power output of this system is 5, 10 or 25
watts. Only 1 mode can be in operation at a time. When it is posted that
Cross Band repeater mode is operational, please configure your station
accordingly.
Cross Band Repeater Mode
When configured for Cross Band operation, the D700 will act like a typical
Amateur radio repeater.
The two big differences with Cross Band Repeater on ISS are:
• The Space Station is moving at 17,500 mph
• You need to transmit on 437.800 MHz, and receive on
145.800 MHz. Your transceiver will need to support Cross Band operations.
You do not need to have a FULL-Duplex transceiver.
Contact from Home
To work ISS from your home, you should have at least the following Amateur
Radio equipment:
• A Dual band 2-meter & 70 cm FM transceiver with an output
rating of 25 to 50 watts. Check your manual to make sure your radio can
transmit on 437.800 MHz.
[Note this is aimed at USA Hams since their 70cm FM
rigs are designed to operate between 440-450 MHz. QSO’s can be made
through the Cross Band repeater by stations running at little as 2 watts
output on 70cm rather than the 25 watts quoted. The repeater system is
designed assuming a FM deviation of 5 kHz is being used. In Europe 2.5
kHz deviation is commonplace so if you can do so then set your rig to
the wider setting – Trevor M5AKA]
• A Dual band Omni-directional antenna (2m and 70 cm
) or small beam.
• A short run of good quality coax (RG-213, 100 feet
or less).
• Optional, Tracking software on your PC
Doppler Shift
The ISS Space Station is travelling around the Earth at over 17,500-mph
(28,000 Kph). This great speed will make radio signals appear to shift
in frequency. This phenomenon is called Doppler Shift. Many of us have
radios that are Channel locked. This means you cannot make any fine tuning
adjustments to your receiver or transmitter's frequency.
Most Mobile and HT radios cannot make any frequency changes less than
5 kHz channel steps (lets hope that radio manufacturers will add 1 or
2 kHz channels steps in the future). The Doppler shift the 2-meter band
is approximately Plus 3.3 kHz and Minus 3.3 kHz. This means that a radio
on ISS, transmitting on 145.800 will drift from 145.803.3 through 145.796.6
during a 10 minute orbit pass. The good news for the 2-meter band is that
the FM mode is a bit forgiving and you do not need to be exactly on frequency.
Most radios will accept a 3k frequency error without very much signal
degradation.
Doppler on 437.800 MHz
The Doppler on 437 MHz is much greater than on the 2-meter band. The
Doppler shift on 70cm is Plus 10 kHz and Minus 10 kHz. This means that
a transmitter on 437.800 will drift from 437.810. through 437.790 during
a 10 minute orbit pass. To compensate for Doppler, you need to predict
what frequency the Repeater-Receiver is on and then transmit on the correct
uplink frequency. It is actually easier than you may think.
This is simple chart showing the Doppler shift for 437.800 for the ISS
Min Date Time Elev
Range Doppler(Hz) UP Freq
1 15Jun2006 0748 4 1731
+10,349 437.790
2 15Jun2006 0749 9 1350
+10,293 437.790
3 15Jun2006 0750 16 977
+10,111 437.790
4 15Jun2006 0751 31 624
+9,525 437.790
5 15Jun2006 0752 67 366
+6,977 437.795
6 15Jun2006 0753 50 434
-1,815 437.800
7 15Jun2006 0754 24 742
-8,347 437.805
8 15Jun2006 0755 13 1105
-9,820 437.810
9 15Jun2006 0756 7 1483
-10,204 437.810
10 15Jun2006 0757 2 1865
-10,331 437.810
Note at the beginning of the pass the Doppler is +10,349 Hz. This means
that if you transmit on 437.800, that 10 kHz of Doppler shift will be
added to your frequency which will put you on 437.810 MHz. To compensate
for the Doppler shift you need to do the Opposite correction and transmit
on 437.790. The 10 kHz Doppler correction will put your signal close to
437.800 MHz.
This process is hard if you are using manual tuning VFO’s, however,
its very easy if you pre-program in “Channels” with the correct
split band frequencies.
You will need to review the owner's manual for your radio to learn how
to program "Odd-Splits" channel combinations and program the
following consecutive frequencies into your radios' memories.
For 5 kHz channel step radios do not try to adjust for Doppler on the
receive side. However you must adjust for Doppler on 70cm side (Uplink
or transmit side).
Cross Band Repeater Mode, 5 kHz Step Radios
Channel 1 145.800 RX, 437.790 TX
Channel 2 145.800 RX, 437.795 TX
Channel 3 145.800 RX, 437.800 TX
Channel 4 145.800 RX, 437.805 TX
Channel 5 145.800 RX, 437.810 TX
[In Europe if your radio is fitted with only narrow
filters for 12.5 kHz channel spacing then I would suggest you try setting
Channel 1 to 145.805 RX and Channel 5 to 145.795 RX – if possible
select wider RX filters instead - Trevor M5AKA]
Cross Band Repeater Mode, All mode Radios, Icom 706
Channel 1 145.802 RX, 437.790 TX
Channel 2 145.801 RX, 437.795 TX
Channel 3 145.800 RX, 437.800 TX
Channel 4 145.798 RX, 437.805 TX
Channel 5 145.797 RX, 437.810 TX
Let's assume ISS is approaching your location (QTH) and the Cross Band
Repeater is active. I am going to label the minutes of the pass from Minute
1 through minute 10.
· For Minutes 1 through 4 use channel #1 for the first 4 minutes
of the pass.
· For Minute 5, use channel #2 and be ready to switch channels
quickly.
· For Minute 6, use channel #3, The Doppler will approach Zero
for a second and then quickly swing in the negative direction.
· For Minute 7, use channel #4
· For Minutes 8 – 10, use channel #5.
For best results, use an updated tracking program, which displays the
current Doppler shift. This will assist you in determining when it is
best to change channels.
Picking A Pass
Use your computer program to select a good pass with high elevation angles.
When ISS first appears on the horizon, the satellite will be 1500 miles
(2400 km) away. When ISS is directly over your house, it is only 240 miles
(384 km) away.
Using your tracking program, pick a pass with a maximum elevation of
over 40 degrees. These are typically the best passes because ISS will
be closer to your QTH. If you were to try to call ISS when it is low on
the Horizon, you will probably not be successful. For low elevation angles,
your radio signal will have to travel along the ground, where it will
be affected by trees, buildings and hills.
When ISS is high above the trees, you will have a clear line-of-site
shot to the ISS antenna. A 1000-mile contact through the Cross Band Repeater
is easy, that is if there is nothing between you and the other station.
A good pass is only 10 minutes long. Since ISS is low on the Horizon during
the beginning and end of each pass, you will want to avoid calling during
the first two and last two minutes of each pass. This will still leave
you with a 6-minute window of opportunity.
Calling on the ISS Cross band Repeater
Before you begin calling ISS on Cross Band Repeater, are familiar with
the operations of your system and you are running the recommended power
levels.
When ISS first comes over your Horizon, there will usually be several
stations already using the Repeater. Before you transmit, monitor the
downlink and set your channel to match the predicted Doppler. Contacts
on the Repeater are usually very short.
Example:
N1WPN I copy your NH, FN 43 Please copy WF1F FN42
Boston.
Repeater Quirk
Audio Level
The ISS Cross Band repeater has an audio gain problem. It will amplify
the incoming audio too much and then sends the amplified audio to the
downlink. You must remember to speak very softly when using the Cross
Band Repeater on ISS. Strong / Loud audio signals arriving at the Repeater
will become very distorted when they are rebroadcast.
Suggestion for Icom 706 users. In FM mode, I usually set my Gain level
to 4 or 5 when running FM, and higher for SSB. When using the ISS Cross
Band repeater try values between 2 or 3 in FM.
For other FM users that do not have Microphone gain controls, just make
sure you speak softly.
FM Capture Effect
In FM, the loudest Station wins.
Your signal will need to be ON the correct uplink frequency with Doppler
correction.
Your Audio level needs to be correct.
Your Signal needs to be 6-9 db stronger than the noise at the D700 receiver.
Meet these goals and you are in.
Always use the minimal power required.
For Field day 2006, QRP 10 watts with a low gain antenna less than 3 “dBd”
Timing
You will need access to a computer tracking program or the web to tell
you when ISS is in range of your station.
NASA Tracking web page:
http://spaceflight.nasa.gov/realdata/tracking/index.html
The timing of your contact is the most important part of a successful
contact with ISS. There are many tracking programs out in the market place
today. Some programs are share-ware (STSPLUS); others cost a few bucks.
I recommend using the DOS Instant Track, program by AMSAT www.amsat.org
. This program is very easy to use and works very well with older style
computers such as 80286 style PC's. The cost of most tracking software
applications is approximately $50-100.
Additional “How to” tips can be found on the Marexmg Web page
http://www.marexmg.org
73 Miles WF1F
MAREX-MG
Until we meet again
DOSVIDANIYA Miles WF1F
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