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How 2 Cross Band, ISS repeater



ISS Amateur Radio Status: June 15, 2006

How to Access the Kenwood D700 on ISS in Cross Band
Repeater Mode

By Miles Mann WF1F,

MAREX-MG News	www.marexmg.org

Manned Amateur Radio Experiment

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.

Only 1 mode can be in operation at a time.  When it is
posted that Cross band repeater mode is operational,
please configure you station accordingly.

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 you 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 difference 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.
•	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 traveling 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 10k
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 preprogram 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, 5k 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 

( 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 down link
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 down link.  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.


Attritional “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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