Category Archives: Amateur Satellite

WA5VJB Cheap Yagis — Wood Boom

A couple of weeks ago, I started working on a version of the DL6WU Yagi that I might be able to get going for this weekend’s Moonbounce activities. I cut and mounted all the elements, but frankly, the feed system is a bit more complicated than I would like so I didn’t get it finished. On the other hand, I have constructed the so-called “Cheap Yagi” of WA5VJB before, and its feed is very, very simple: the driven element is a hairpin and the coax is soldered directly to it. Nice, neat and simple. So, I surfed on over to here:

WA5VJB Cheap Yagis — Wood Boom

And started cutting some copper-bronze welding rod to lengths. But something disturbed me: the length of the elements weren’t monotonically decreasing. In particular, director 4 was only 11 inches long, but it was surrounded by directors which were 12 inches long. That struck me as bad. Very bad. So, I tried to search for the original article that these antennas were based upon, and found a scan here:

The original article

Close comparison of the dimensions for the 11 element 70cm antenna reveal that director 4 should be 12″ long as well. So, that’s what I cut. Tomorrow, I’ll drill the holes, hot glue the elements in place, and then solder the feedline to it. And, maybe I’ll try to test record a pass of AO-51 or something to ascertain that it basically works.

Bruce, VE9QRP on his qrpTracker

Bruce, VE9QRP has been experimenting with using a small Atmel controller to implement the Plan 13 algorithm that provides satellite tracking and Doppler calculations (the same algorithm that I use in my own Python code). It seems silly to drag a laptop into the field to do Doppler tuning when a couple of dollars worth of silicon can easily do the calculations necessary to provide full Doppler tuning. Wouldn’t it be awesome if your rig could do this “out of the box”?


httpv://www.youtube.com/watch?v=TP_fq_frqKw

Upcoming Balloon Launch: Arizona Near Space Research

Another one of those nifty amateur balloon launches is scheduled for next Saturday, February 6:

The vehicle will be a 1200g helium-filled latex balloon. The expected burst altitude will be 90,000 feet or higher. The flight is anticipated to last about 2.5 hours from launch to touchdown.
Payload: In addition to ANSR flight computer/cross-band repeater and beacon packages, the balloon train will carry student-built packages containing a variety of scientific apparatus as well as digital cameras to photo-document the flight.

The posting includes links to the APRS tracking pages where you could monitor the flight over the Internet.

Arizona Near Space Research | Promoting science and education by exploring frontiers in amateur radio and high altitude balloons..

A pass of SO-50….

I hadn’t worked SAUDISAT 1C (aka Saudi Oscar 50, or SO-50) in quite some time. My recollection was that it was a trickier satellite to work than AO-51, and this pass proved that my recollections were correct. I had significant problems with deep fades. Still, I managed to exchange calls with WD9EWK, K0KU, and N7EDK. Here’s the recording.

(I was working this with my TH-D7A HT and my Arrow Antenna).

2010-01-03-SO-50-FM, recording of WD9EWK, K0KU and N7EDK

DK3WN SatBlog » XW-1 SSTV

More fun on HO-68!

During a low elevation pass, Mike DK3WN and Henk, PA3GUO made the very first SSTV contact via HO68 – linear transponder. Images were transmitted between the two radio stations in Germany and The Netherlands. Signals were transmitted to HO-68, which was 1200km above earth and about 8000km distant from the radio amateur stations.

Check out the pictures!

via DK3WN SatBlog » XW-1 SSTV.

HO-68 in SSB mode

I don’t really have the hardware to effectively transmit to satellites in linear transponder mode. To really make it straightforward, you probably would like to have a computer to handle the Doppler tracking and antenna pointing, and a full duplex SSB transmitter (or a pair of ordinary ones). That’s more than I am willing to invest at the moment, but with my little FT-817, you can actually receive these birds pretty easily, using my ever present Arrow antenna and just tuning by hand. So, that’s what I did this morning: here is my recording of HO-68. It begins with a bit of the CW beacon, then shows me tuning around to try to find SSB signals. Sometimes, the tracking is pretty good, but later in the recording, my next door neighbor began mowing his lawn and running a leaf blower, and it was hard to hear (I need to use my over the ear headphones instead of these earbuds I’ve used for FM passes). Anyway, here’s the recording:

2009-12-30-HO68-SSB, recording by K6HX in CM87 using an FT-817 and hand tuning

Bounced a signal through HO-68

This morning I got another chance at HO-68, the newest Chinese amateur satellite that was operating in FM mode. I wasn’t sure what the problem was: I had the PL tone setup right and the signals seemed strong enough. On this pass, I fought to try to find a slot to transmit, and finally at the end of the pass, confirmed that I was indeed able to get into the bird. I made the following recording of the pass, and you can hear me in the downlink twice near the end of the recording, calling (without response) to VA7VW and W7JPI. The satellite was actually configured to turn off its transponder while it was still high in the sky here (it is on for a pass over Europe, the North Pole, and then down over the states) so I think I was the last person active before it went off.

2009-12-29-HO68-FM, recording by K6HX in CM87

Chinese Amateur Satellite XW-1 launched, beacon has been heard…

This morning, a quick check of my email and blog roll indicated that the Chinese had launched XW-1, probably the most interesting amateur satellite to launch this year (sorry SO-67).    It carries a payload with both linear and FM transponders, and it seems to have a higher orbit than current LEO satellites.    It should orbit around 1200km, whereas the popular AO-51 has an altitude of  only 700-800km, which should translate into a significantly larger footprint.

A couple of amateurs have recorded MP3s of the CW telemetry downlink already.

Here’s one.

And another.

Satpack: Arduino Satellite tracking and doppler tuning

Bruce, VE9QRP has a nice video demoing his qrpTracker code (open source) running on an Atmel AVR microcontroller and tracking the Doppler of a cubesat as well as AO-51. Nifty.

httpv://www.youtube.com/watch?v=XgNcCGXeRyw

Addendum: Back in January of 2008, I acquired my (then) new FT-817, and one of the first projects I did was to use my own implementation of Plan 13 to automatically tune the radio to follow a satellite’s Doppler shift. Here is my first recording of the (recently defunct) satellite LO-19.

How to use Python to predict satellite locations…

Occasionally I get to talk to hams who are just getting into using amateur satellites, and many of them ask the quite reasonable question “How do I figure out when the next pass occurs?”. For most of them, I suggest that they simply use a program like predict, which is probably what most people expect from a satellite prediction program.

I used just such a program for quite a while, until I first worked NH7WN in Hawaii, myself standing in my front yard, he standing on a beach in Hawaii, and I asked myself the quite normal question: “How often can I work Hawaii from here in California?” The (frankly excellent, don’t get me wrong) predict program didn’t provide a convenient way to answer that question.

Faced with this, I decided to write my own code for satellite prediction, so I could easily adapt it to answering questions like these. Because I like Python, and find it convenient for scripting applications, I chose Python as the implementation language. The algorithm I used was James Miller, G3RUH’s Plan 13 which was originally written in BASIC, and was relatively easy to port. I ended up creating a simple Python library implementation of Plan 13, which I’ve used for all my own satellite prediction needs. The nice thing about Python is that it has a bunch of useful libraries you can use (I used the sqlite3 library to build a database of orbital elements, and urllib to download them automatically from celestrak), and it’s been quite adaptable.

Still there were a few warts with it, and I haven’t had the chance to tidy it up. But recently I discovered that the PyEphem library includes a lot of the same functionality, and with a better version of the orbital model that I implemented. And, it’s pretty easy to use. As an example, here is a small chunk of code that figures out the next three passes of the ISS, using the current (for today) orbital elements. Even if you aren’t an amazing programmer, you can probably figure out how it works. 

#!/usr/bin/python

import sys
import math
import ephem

iss = ephem.readtle("ISS (ZARYA)",
	"1 25544U 98067A   09270.78646569  .00012443  00000-0  87997-4 0  6860",
	"2 25544  51.6377 140.0905 0009007 135.9273 312.2213 15.74420558622113")

obs = ephem.Observer()
obs.lat = '38.0'
obs.long = '-122.0'

for p in range(3):
	tr, azr, tt, altt, ts, azs = obs.next_pass(iss)
	while tr < ts :
		obs.date = tr
		iss.compute(obs)
		print "%s %4.1f %5.1f" % (tr, math.degrees(iss.alt), math.degrees(iss.az))
		tr = ephem.Date(tr + 60.0 * ephem.second)
	print
	obs.date = tr + ephem.minute

Running it produces a dump of times, altitude and azimuths for three passes. Here’s a resulting run.

2009/9/28 04:12:18 -0.0 268.5
2009/9/28 04:13:18  1.4 257.6
2009/9/28 04:14:18  2.4 244.9
2009/9/28 04:15:18  2.5 231.3
2009/9/28 04:16:18  1.8 218.3
2009/9/28 04:17:18  0.4 206.7

2009/9/28 17:27:22 -0.1 169.1
2009/9/28 17:28:22  2.1 159.4
2009/9/28 17:29:22  4.0 147.1
2009/9/28 17:30:22  5.2 132.6
2009/9/28 17:31:22  5.1 117.1
2009/9/28 17:32:22  3.9 102.7
2009/9/28 17:33:22  1.9  90.7

2009/9/28 19:00:26  0.0 227.2
2009/9/28 19:01:26  3.8 226.9
2009/9/28 19:02:26  9.2 226.4
2009/9/28 19:03:26 17.8 225.3
2009/9/28 19:04:26 35.8 222.0
2009/9/28 19:05:26 80.4 152.7
2009/9/28 19:06:26 37.7  57.0
2009/9/28 19:07:26 18.5  53.3
2009/9/28 19:08:26  9.6  52.2
2009/9/28 19:09:26  4.1  51.8
2009/9/28 19:10:26  0.2  51.5

I did notice that this simple program may not work properly if the ISS is currently visible from your location, but I am sure that with just a little more work we could figure that out. I’ll probably port my existing software to this framework, because it also includes a bunch of useful functions (like figuring out when the sun rises and sets, and other fun things) which would be a pain for me to add. So here’s my radical suggestion: if you need to compute the location of satellites, write some scripts of your own using pyephem! It’s the homebrewer way. 🙂

Addendum: A few more minutes of work added some more interesting outputs…

#!/usr/bin/python

import sys
import math
import ephem

iss = ephem.readtle("ISS (ZARYA)",
	"1 25544U 98067A   09270.78646569  .00012443  00000-0  87997-4 0  6860",
	"2 25544  51.6377 140.0905 0009007 135.9273 312.2213 15.74420558622113")

obs = ephem.Observer()
obs.lat = '38.0'
obs.long = '-122.0'

for p in range(3):
	tr, azr, tt, altt, ts, azs = obs.next_pass(iss)
	print """Date/Time (UTC)       Alt/Azim	  Lat/Long	Elev"""
	print """====================================================="""
	while tr < ts:
		obs.date = tr
		iss.compute(obs)
		print "%s | %4.1f %5.1f | %4.1f %+6.1f | %5.1f" % \
			(tr, 
			 math.degrees(iss.alt), 
			 math.degrees(iss.az), 
			 math.degrees(iss.sublat), 
			 math.degrees(iss.sublong), 
			 iss.elevation/1000.)
		tr = ephem.Date(tr + 20.0 * ephem.second)
	print
	obs.date = tr + ephem.minute

And some output:

Date/Time (UTC)       Alt/Azim	  Lat/Long	Elev
=====================================================
2009/9/28 04:12:18 | -0.0 268.4 | 34.9 -145.6 | 335.6
2009/9/28 04:12:38 |  0.5 265.0 | 34.0 -144.5 | 335.7
2009/9/28 04:12:58 |  1.0 261.3 | 33.2 -143.4 | 335.9
2009/9/28 04:13:18 |  1.5 257.4 | 32.3 -142.3 | 336.0
2009/9/28 04:13:38 |  1.9 253.4 | 31.4 -141.3 | 336.2
2009/9/28 04:13:58 |  2.2 249.1 | 30.5 -140.2 | 336.3
2009/9/28 04:14:18 |  2.4 244.7 | 29.5 -139.2 | 336.5
2009/9/28 04:14:38 |  2.6 240.2 | 28.6 -138.3 | 336.6
2009/9/28 04:14:58 |  2.6 235.7 | 27.7 -137.3 | 336.8
2009/9/28 04:15:18 |  2.5 231.1 | 26.7 -136.3 | 337.0
2009/9/28 04:15:38 |  2.4 226.7 | 25.8 -135.4 | 337.1
2009/9/28 04:15:58 |  2.1 222.3 | 24.8 -134.5 | 337.3
2009/9/28 04:16:18 |  1.7 218.1 | 23.9 -133.6 | 337.5
2009/9/28 04:16:38 |  1.3 214.0 | 22.9 -132.7 | 337.7
2009/9/28 04:16:58 |  0.9 210.2 | 21.9 -131.8 | 337.9
2009/9/28 04:17:18 |  0.3 206.6 | 20.9 -131.0 | 338.1

Date/Time (UTC)       Alt/Azim	  Lat/Long	Elev
=====================================================
2009/9/28 17:27:24 |  0.0 168.7 | 19.0 -118.4 | 346.7
2009/9/28 17:27:44 |  0.7 165.7 | 20.0 -117.5 | 346.4
2009/9/28 17:28:04 |  1.4 162.5 | 21.0 -116.7 | 346.2
2009/9/28 17:28:24 |  2.1 158.9 | 22.0 -115.8 | 345.9
2009/9/28 17:28:44 |  2.8 155.1 | 22.9 -115.0 | 345.6
2009/9/28 17:29:04 |  3.5 151.0 | 23.9 -114.1 | 345.3
2009/9/28 17:29:24 |  4.1 146.6 | 24.9 -113.2 | 345.0
2009/9/28 17:29:44 |  4.6 141.9 | 25.8 -112.3 | 344.7
2009/9/28 17:30:04 |  4.9 137.0 | 26.8 -111.3 | 344.4
2009/9/28 17:30:24 |  5.2 131.9 | 27.7 -110.4 | 344.1
2009/9/28 17:30:44 |  5.3 126.8 | 28.6 -109.4 | 343.9
2009/9/28 17:31:04 |  5.3 121.6 | 29.6 -108.4 | 343.6
2009/9/28 17:31:24 |  5.1 116.4 | 30.5 -107.4 | 343.3
2009/9/28 17:31:44 |  4.8 111.5 | 31.4 -106.4 | 343.0
2009/9/28 17:32:04 |  4.3 106.7 | 32.3 -105.4 | 342.7
2009/9/28 17:32:24 |  3.8 102.1 | 33.2 -104.3 | 342.4
2009/9/28 17:32:44 |  3.2  97.9 | 34.0 -103.2 | 342.2
2009/9/28 17:33:04 |  2.5  93.9 | 34.9 -102.1 | 341.9
2009/9/28 17:33:24 |  1.8  90.2 | 35.8 -101.0 | 341.6
2009/9/28 17:33:44 |  1.1  86.9 | 36.6  -99.8 | 341.3
2009/9/28 17:34:04 |  0.4  83.8 | 37.4  -98.6 | 341.1

Date/Time (UTC)       Alt/Azim	  Lat/Long	Elev
=====================================================
2009/9/28 19:00:26 |  0.1 227.2 | 23.8 -137.4 | 345.3
2009/9/28 19:00:46 |  1.2 227.1 | 24.8 -136.5 | 345.1
2009/9/28 19:01:06 |  2.4 227.0 | 25.7 -135.6 | 344.8
2009/9/28 19:01:26 |  3.8 226.9 | 26.7 -134.7 | 344.5
2009/9/28 19:01:46 |  5.4 226.8 | 27.6 -133.7 | 344.2
2009/9/28 19:02:06 |  7.2 226.6 | 28.6 -132.8 | 343.9
2009/9/28 19:02:26 |  9.2 226.4 | 29.5 -131.8 | 343.6
2009/9/28 19:02:46 | 11.6 226.2 | 30.4 -130.8 | 343.3
2009/9/28 19:03:06 | 14.4 225.8 | 31.3 -129.7 | 343.0
2009/9/28 19:03:26 | 17.9 225.3 | 32.2 -128.7 | 342.8
2009/9/28 19:03:46 | 22.2 224.7 | 33.1 -127.6 | 342.5
2009/9/28 19:04:06 | 28.1 223.6 | 34.0 -126.5 | 342.2
2009/9/28 19:04:26 | 36.1 221.9 | 34.8 -125.4 | 341.9
2009/9/28 19:04:46 | 47.7 218.5 | 35.7 -124.3 | 341.6
2009/9/28 19:05:06 | 64.1 209.2 | 36.5 -123.1 | 341.4
2009/9/28 19:05:26 | 80.5 149.1 | 37.4 -121.9 | 341.1
2009/9/28 19:05:46 | 66.7  71.9 | 38.2 -120.7 | 340.8
2009/9/28 19:06:06 | 49.6  60.7 | 39.0 -119.5 | 340.6
2009/9/28 19:06:26 | 37.4  57.0 | 39.8 -118.2 | 340.3
2009/9/28 19:06:46 | 29.0  55.1 | 40.5 -116.9 | 340.1
2009/9/28 19:07:06 | 23.0  54.0 | 41.3 -115.5 | 339.8
2009/9/28 19:07:26 | 18.4  53.3 | 42.0 -114.1 | 339.6
2009/9/28 19:07:46 | 14.9  52.8 | 42.7 -112.7 | 339.3
2009/9/28 19:08:06 | 12.0  52.5 | 43.4 -111.3 | 339.1
2009/9/28 19:08:26 |  9.5  52.2 | 44.1 -109.8 | 338.8
2009/9/28 19:08:46 |  7.5  52.0 | 44.7 -108.3 | 338.6
2009/9/28 19:09:06 |  5.7  51.9 | 45.4 -106.7 | 338.4
2009/9/28 19:09:26 |  4.1  51.7 | 46.0 -105.1 | 338.1
2009/9/28 19:09:46 |  2.6  51.7 | 46.5 -103.5 | 337.9
2009/9/28 19:10:06 |  1.3  51.6 | 47.1 -101.9 | 337.7
2009/9/28 19:10:26 |  0.2  51.5 | 47.6 -100.2 | 337.5

Addendum2: As another example of what can be done, consider the command line voice synthesizer that is included in Mac OS. Using the os.system command, you can have your computer speak voice updates almost as easy as printing them. For example:

#!/usr/bin/python

# Mac OS includes a voice synthesis command called "say".   It's pretty
# easy to make a simple program like this that will use voice to announce
# the current position of the satellite.   With a little work, you could
# easily make it announce the altitude and azimuth repeatedly during a pass.

import sys
import os
import math
import ephem

iss = ephem.readtle("ISS (ZARYA)",
	"1 25544U 98067A   09270.78646569  .00012443  00000-0  87997-4 0  6860",
	"2 25544  51.6377 140.0905 0009007 135.9273 312.2213 15.74420558622113")

obs = ephem.Observer()
obs.lat = '38.0'
obs.long = '-122.0'

iss.compute(obs)
if iss.alt < 0:
	os.system('say The ISS is not currently visible.')
else:
	os.system('say "The ISS is at altitude %d, azimuth %d."' % \
		(int(math.degrees(iss.alt)+0.5), int(math.degrees(iss.az)+0.5)))

Here’s an example of the voice it outputs:
Voice synthesis example

Recently Launched Cubesat Frequencies

Andrew, VK4TEC posted this list of frequencies for four recently launched cubesats. Archiving for future reference. I’ve added links to some relevent info for each.

ITUpsAT1 is on 437.325 MHz CW ITUpSAT1 is a student-built Turkish satellite.
UWE-2 is on 437.385 MHz, 1200 bps Ax.25 packet Universität Würzburg Experimental-Satellit2
BEESAT is on 436.000 MHz CW using the call DP0BEE
SwissCube is on 437.505 Mhz CW using the call HB9EG/1More info.