[HIham] ISS Crossband repeater
Ron Hashiro
rhashiro at hawaiiantel.net
Fri Jan 9 09:55:24 EST 2009
Ando Richard wrote:
> Ron AH6RH,
>
> I can transmitt and hear you/others on the VHF uplink (145.99, PL67).
>
> But I do not hear anyone/myself on UHF downlink (437.800).
>
> Any ideas about this?
>
> Richard WH7HZ
>
>
>
>
Good morning Richard. Thanks for the email. I'm glad you gave it a
try, as we had KH6DAD, WH7QR and N6NCT as newly successful hams making
contact on the ISS reverse crossband repeater last night on the 65
degree pass starting at 9:10 pm. I understand WH7GG, KH6CPU and
yourself also tried but looks like you didn't make it in. I hope you
don't mind if I share the answer with the EARC and HIHAM reflectors, so
others will gain the insights.
It seems for whatever reason you did not get a good signal up to the
ISS, as I didn't hear you on last night's pass. And, you probably
didn't hear the ISS very well or very long.
First off, assuming you are using a vertical antenna, you'll need a
location or situation that you can transmit unobstructed from the
horizon to the maximum elevation, and back down to the other side, or at
least as much of the pass as possible. The exact line in the sky that
the ISS traces varies based on these parameters.
1) If it's a south-to-north pass (ascending), or north-to-south
(descending).
2) Whether the pass is towards the east or west. It's rarely directly
overhead, and we tend to get two consecutive passes (one to the east,
one to the west) about 90 minutes apart.
3) The elevation of the pass.
--------
Since the orbit of the ISS is inclined 51 degrees, on a directly
overhead 90 degree pass, for an ascending pass it'll trace a line from a
bearing of 231 degrees, to directly overhead, to 51 degrees on the other
side. You pretty much saw that when you saw the ISS visually when we
did the Jamboree On the Air back in November and also contacted Richard
Garriot. Anything to the East or West will appear to be coming off the
side of that line, going up to a maximum elevation, and going down --
again, off to the side of the line just painted above.
Similarly, for a descending pass, the trace in the sky is 309 degrees
down to 129 degrees. And, being east or west means being off to one
side or another of this line.
If you want to see the effect by getting a list of azimuth (compass
bearing) and elevation for a given pass, use the pass predictor on the
website www.issfanclub.com. Then use a compass (or Google Earth or
Delorme Street Atlas or my favorite Delorme Topo Maps) and see where
these compass bearings point to in your neighborhood. Don't forget to
adjust for magnetic declination, if you're using a compass.
For example, I know for the location I'm using that looking out square
into the street in front of me is bearing 211 degrees. So, 90 degrees
left and right are 121 and 301 degrees (which is the bearing of the
street in front of me), and behind me is 31 degrees. So, I estimate
where 45 degree increments (1/8 of a circle), 22.5 degree increments
(1/16), and 10 and 20 degrees variances of these points are. Even with
an Arrow beam antenna, if you're within 10 degrees, it's good enough.
The satellite is moving anyways, so you'll need to periodically move the
beam antenna.
Similarly, I know how high 90 degrees is, and half of that is 45
degrees, and half of that is 22.5 degrees. It gives you an idea where
to look.
If you're using a vertical antenna, of course, you can't steer it
(unless you tilt it). If it's a low pass, you want to use a gain
antenna to get as much signal out towards the horizon. The ISS is 1,200
miles away when it appears over the horizon, and about 220 miles when
directly overhead.
If it's a high pass and you're not going to steer it by changing the
orientation during the pass, use a unity gain (quarter wave) antenna --
because it sends and receives a lot of it's signal going upwards as well
as towards the horizon.
If it's a high pass and you use a Diamond NR73 which is a vertical gain
antenna, you can hand tilt the antenna so that the maximum radiation
which comes off perpendicular to the antenna is pointing to where the
ISS is located -- but be careful you don't run more than 7 watts, or
you'll get an RF safety exposure problem. If you attempt this, remember
to hold the mag mount base, and not the loading coil of the antenna.
Not only will you cut off the signal, you'll expose your hand to
excessive RF. BTW, I saw Honolulu Electronics had these in stock for
about $70 (mag mount not included) a couple of weeks ago.
--------
Next, you should, if possible compensate for doppler on both the
transmit and receive. If you don't do it for VHF uplink, it isn't so
bad as the max doppler is 3.3 kHz and you won't lose out on the middle
half of the pass. But, if you didn't compensate for it on UHF downlink,
your usable time in the middle is only 30 seconds. You wouldn't hear
anything before, or afterwards, as your receiver would probably pick up
a 5 watt UHF signal, 280 miles away that's off freq by about 3 kHz or
less. Anything more off frequency, and you won't hear it. If you
compensate for doppler on the downlink to keep it where your receive can
hear it, you would add another 90 seconds. So, this is not an item to
ignore.
On receive, you start with 437.810, then change to 437.805, then
437.800, 437.795, 437.790. It moves quite quickly in the middle. If
you don't change the frequency in the middle, it's over in 30 seconds.
On transmit, you start low at 145.987, 145.988, 145.989, 145.990 -- and
proceed to 145.991, 145.992, 145.993. If you only have 5 kHz, then you
transmit on 145.985, 145.990, 145,995 respectively.
You can read more details at:
http://ronhashiro.htohananet.com/am-radio/spacecomm/getting-started-iss.html
http://ronhashiro.htohananet.com/am-radio/spacecomm/doppler-and-the-iss.html
Look closely and study the graph. You'll begin to see and understand
how short the usable time is without compensating for doppler.
--------
Lastly, you should be using as much power as you have to make the
contact. You COULD do it with 5 watts, but 50 watts (for example) would
overcome a lot of misgivings of not doing doppler compensation.
Remember, the ISS repeater needs to hear your signal well and clearly if
it's going to repeat it. If it hears mush, it will repeat mush -- which
we don't want. If you use a beam antenna such as the Arrow crossband
satellite antenna, you'll get a double advantage of improving your
transmit and receive.
http://www.arrowantennas.com/146-437.html
It would be best if you could do 1 kHz increments on the VHF uplink for
doppler compensation, with good transmit power and an antenna, as then
you'll get the cleanest signal into the ISS crossband repeat, and you'll
get clean audio coming down on the downlink. If you don't get into the
ISS repeater very well (not enough signal strength, poor audio from
being off frequency), then you'll get a poor audio signal coming down.
And, if you don't tune for doppler, you could possibly be heard by
others, but you won't hear yourself or others calling you except for the
middle 30 seconds.
Then, the golden rule of amateur radio then takes place. If you can't
hear 'em, you can't work 'em.
Even is you have the most basic of equipment, it's worth the try. Eric,
NH6TY and Rick, KH6OM have mastered these techniques using vertical
antennas -- I believe the antennas are outdoor. I believe they're using
5 kHz doppler correction on both the VHF uplink and UHF downlink.
They're consistently on earlier and later in the pass. I belive they're
running 50 watts.
Hope this makes the picture of what's happening clear for you. Think of
it as the amateur version of perfecting a golf swing. Understand one
element at a time, then bring it all together.
There's more usable passes. There is a chance that the astronauts will
come on during these passes on Saturday and Sunday, as they tend to come
on during the weekends and during their lunch time which is between 3
and 4 in the morning our time, and these passes are during their waking
hours.
Date Time Azimuth Elevation
---------------------------------------------
Aos: 2009/01/10 05:43:36 330.0 0.2
Max: 2009/01/10 05:48:49 70.2 33.8
Los: 2009/01/10 05:53:12 127.2 -0.0
Aos: 2009/01/10 20:28:24 227.1 0.0
Max: 2009/01/10 20:33:40 339.0 47.6
Los: 2009/01/10 20:38:20 34.0 -0.2
Aos: 2009/01/11 06:10:06 307.8 0.2
Max: 2009/01/11 06:15:00 225.4 28.7
Los: 2009/01/11 06:19:31 158.9 -0.0
Aos: 2009/01/11 19:19:53 199.2 0.0
Max: 2009/01/11 19:24:49 118.3 26.2
Los: 2009/01/11 19:29:23 53.4 -0.0
Aos: 2009/01/12 05:01:11 327.5 0.0
Max: 2009/01/12 05:06:27 74.1 41.5
Los: 2009/01/12 05:10:56 130.7 -0.1
Aos: 2009/01/12 19:46:05 230.6 0.0
Max: 2009/01/12 19:51:21 334.3 38.7
Los: 2009/01/12 19:55:55 31.7 -0.0
Aos: 2009/01/13 05:27:45 305.2 0.0
Max: 2009/01/13 05:32:42 223.9 23.5
Los: 2009/01/13 05:37:03 162.5 -0.1
Aos: 2009/01/13 18:37:24 202.7 0.1
Max: 2009/01/13 18:42:39 105.8 30.2
Los: 2009/01/13 18:47:03 50.8 -0.1
Aos: 2009/01/14 04:18:45 325.2 0.1
Max: 2009/01/14 04:24:00 81.7 51.2
Los: 2009/01/14 04:28:33 134.2 -0.1
Aos: 2009/01/14 19:03:41 234.1 0.0
Max: 2009/01/14 19:08:57 332.2 32.0
Los: 2009/01/14 19:13:25 29.4 -0.0
Give it a shot, and good luck!
Ron H, AH6RH
EARC Education Committee Chair
More information about the HIham
mailing list