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2 for the group.

Hi All,
         I  am *NOT* a digital Ham - in fact, those that know me are aware that I'm THICKER than the two proverbial short planks so I hope someone with a bit more brain capacity than I have will help me.

I have two questions for the group.

Question 1.

Is there ant reason why I can't transmit a modulated carrier (FM) on the 145.900Mhz uplink of AO-16 and receive CW on the SSB/CW? downlink of 437.026Mhz ??.

Question 2.

I am 'TOTALLY' blocked by mountains re: the ISS and PCSAT  and do *NOT* have 9600bps gear for AO-51 ... however, I can receive AO-16.

Can I use the UPW - (PSK modulation) - program to transmit APRS data on the uplink and will that be received on the USB downlink ?? ... and be forwarded to the internet via an APRS station ??.

I have attached the UPW file for perusal by anybody who has a few more braincells than LA2QAA and is able to advise.

(There are currently no "normal" 1200bps sats - I am trying to find a 'satellite' use for an IC-E91 D-Star transceiver ... no D-Star repeaters in Norway ... as mentioned, I'm totally blocked by mountains re: the ISS).

I would be very grateful for any advice and/or (sensible) suggestions please.

73 John.   <la2qaa@amsat.org>
Announcing UPW - Uplink to Pacsats for Windows

by Douglas D. Quagliana, KA2UPW
What is UPW ?

UPW is a computer program for amateur radio operators who want to transmit a position report through one of the orbiting PACSAT satellites into the Amateur Position Reporting System (APRS) network using only a radio and a sound card. Although anyone can use it, it is intended mainly for travelers who are out of range of the regular APRS network and satellite experimenters. UPW will send an AX.25 packet with an APRS position report containing latitude, longitude, course, speed, and an optional comment. UPW requires a computer, a sound card, and a radio transmitter. A TNC is not needed nor is the special Manchester/PSK satellite modem. UPW does the work of the both using specialized computer software and digital signal processing techniques.

This documentation assumes that the reader has some familiarity with Amateur Radio ("ham radio"), the Amateur Position Reporting System (APRS), the amateur radio PACSAT satellites, and the Global Positioning System (GPS).

The existing ASTARS APRS radio network is a collection of amateur radio stations on 144.390 MHz which transmit, receive and repeat information such as the position of a car, the leader of a race, current weather information, and short text messages. Many areas of the country which have some APRS activity are linked together via the Internet. Thus, any amateur radio operator within radio range of any piece of the APRS network can transmit a packet and reasonably expect that it will be seen by most of the rest of the APRS network via radio and the Internet.

Common pieces of information that mobile amateur radio operators frequently transmit include their current position (the current longitude, latitude as received via GPS), course and speed. This allows other amateurs, friends, or relatives to know exactly where the mobile amateur is and which way he is going.

Assuming that at least one other radio station in the APRS network can hear the signal, the mobile amateur's information will be forwarded out to the rest of the network and the Internet. However, in some parts of the country, there isn't another amateur station within radio range to hear the mobile amateur's transmission. While traveling in these "black hole" areas, their information can not reach the outside world. This is one area where UPW can be used to get the information out.
Where can I download UPW ?

Click here to download UPW Version 1.07B, which is the latest version as of this writing (3/2002). Version 1.07B removes the requirement for a GPS provided the user knows their latitude and longitude.
Why use UPW?

UPW allows any properly licensed amateur radio operator with a computer, a sound card, and an ordinary two meter FM transmitter to transmit a Manchester encoded AX.25 packet containing an APRS style position report to an orbiting amateur radio satellite. When one of the appropriate 1200 baud pacsat satellites is in view, the satellite will retransmit the signal from UPW back to earth. Any ground station that hears the repeated packet from the satellite can then retransmit the packet into the APRS network allowing other amateur radio operators throughout the network to receive the original position report from UPW. It's important to note that the original amateur running UPW does not need any elaborate satellite reception equipment.

While the APRS network covers large areas of the country, it is not everywhere. There are many places where there is no APRS activity, no RELAY stations, and no way to get an APRS message into the network. In cases where there isn't another station within radio range, an amateur radio 1200 baud pacsat satellite can be used as digital repeater to relay the packets. Each satellite can see portions of the earth thousands of miles across and everyone within the footprint can use the satellite as a digital repeater. This idea is known as ASTARS. More information about ASTARS is available at


There are some technical restrictions on the use of the satellites: the satellites are in low earth orbits ("LEO"), and the radio signal sent to the satellite must be correctly modulated. The satellites only receive 1200 baud AX.25 packets modulated using Manchester modulation. Because of the low earth orbit, the satellites appear to rapidly rise, pass across the sky and then set. A satellite can only be used during the time when it is overhead in the sky, between the time when it rises and the time when it sets. Usually there are three passes in the morning and three in the evening. Each satellite pass lasts about fifteen minutes, and they are separated by about ninety minutes. Additionally, the satellites only repeat a certain kind of signal.

Since an ordinary TNC can not generate the Manchester modulated signal which the satellites are expecting, a separate Manchester/PSK modem is used. An additional cable is used to connect the Manchester modem to the TNC disconnect header. Proper installation of the modem sometimes requires minor surgery on the TNC, cutting traces on TNC circuit board and/or soldering a twenty pin disconnect header to allow access to the TNC data signals. Many amateur radio operators are hesitant to perform the necessary modifications. UPW greatly simplifies satellite communications by replacing the TNC and the special satellite Manchester/PSK modem with a computer and a sound card.
What does UPW do ?

UPW performs all of the work that would normally be done by a Manchester modem and a TNC: the generation of HDLC flags, zero bit stuffing, NRZI encoding, CRC calculations, Manchester modulation, and sending the push-to-talk ("PTT") signal to the radio.

UPW starts by accepting GPS NMEA data from a GPS receiver. (This version of UPW expects that the GPS NMEA data will be on COM1.) UPW scans the incoming NMEA data for the $GPRMC string and extracts from it the latitude, longitude, course and speed values. These are reformatted into an APRS style packet with an optional comment from the user. This information encoded into an AX.25 packet which is then modulated into a Manchester encoded signal.

UPW raises the DTR pin on COM1 as the signal to turn on the transmitter, plays HDLC flags for a short period of time for the transmitter to stabilize (TXDelay) and then plays the Manchester signal out of the sound card.

If one of the 1200 baud Pacsat satellites is overhead, it receives this signal and retransmits it on a different frequency in the seventy centimeter band using PSK modulation. A different amateur radio ground station on the earth with a PSK modem can receive this signal, demodulate the packet, and insert it into the APRS network either via a connection to the Internet or by retransmitting it on two meter FM as a regular APRS packet. However, the user of UPW need only transmit the Manchester signal on the two meter uplink frequency.
Quick Start Guide

The following items are required for use with UPW:

a computer running Windows 95 or Windows 98. The computer must have a sound card and a serial port (COM1) but does not need to be particularly fast.

optional GPS receiver which outputs $GPRMC strings (regular 4800 baud NMEA) (you can now enter your latitude and longitude directly, so the GPS is not required.)

a two meter FM transmitter or FM transceiver tuned to one of the satellite uplink frequencies (all four frequencies are equivalent and should work equally well). The radio should be set to FM siplex. All of the 1200 baud pacsats share the common uplink frequency of 145.900 MHz.

Satellite Uplink frequencies


























Cabling including sound card to radio microphone cables and associated "push-to-talk" circuitry to connect the GPS receiver to the computer and turn on ("key up") the transmitter (This circuitry can be as simple as a single transitor with a few resistors and diodes.) Recent issues of CQ/VHF (see December 99) and QST have featured such circuits.

satellite prediction software with up to date orbital elements. A future versio of UPW will perform the satellite predictions, but for now, you must compute the times with a separate program. Satellite prediction software is available from AMSAT


Up to date orbital elements are available at




Although slightly older element sets will probably still work, the orbital elements should be less than a month old for best results.

Current information on which 1200 baud pacsat satellites are currently operational and in digipeater mode. Current information and information from the AMSAT News Service can be obtained from


The latest bulletin is available at

Step 1: Verify that the sound card is operational.

Connect a speaker or headphone to the audio output jack on the soundcard and use the Windows recorder program to play any recording or .WAV file. The recording should sound clean, clear, and undistorted. If not, adjust the volume in Windows or consult your sound card's documentation. UPW absolutely requires excellent audio from the sound card. In particular, the audio must not stutter.
Step 2: Build the cables.

There are two cables. The first cable must carry audio from the sound card speaker output jack to the radio microphone input jack. The sound card end of the cable will probably use a standard mono 3.5mm jack. Check your soundcard documentation to be certain. The radio microphone end of the cable will be specific to that brand and model of radio. Pinouts and wiring diagrams for many popular radios are available at




Note that this web site is describing TNC-to-radio connections not soundcard to radio connections.

The second cable connects various pins on COM1 to the GPS receiver and also to the "push to talk" (PTT) circuitry on the radio. This allows UPW to use only one serial port on the computer while still receiving GPS signals and sending a signal to the two meter transmitter to "key up." This also means that there are two connections to the radio: the first connection from the soundcard and the second connection from COM1 to PTT.

COM port pin	9pin  25pin
------------	----	-----	
RXD		2	3
DTR		4	20
signal ground	5	7

from the Computer
RXD               ---- to GPS receiver
DTR               ---- to radio PTT via single transitor circuit
Soundcard speaker ---- to radio audio input
signal ground to both GPS receiver and radio.

UPW will raise the DTR signal when the transmitter needs to be turned on. The exact method of converting this signal into the appropriate signal for turning on the radio will vary depending on the type of radio used. Many radios have a PTT pin built into the microphone jack on the radio. Some radios require that the PTT pin be shorted to ground to turn on the transmitter. In this case, a simple single transistor circuit can be used. Examples of this type of circuit have appeared on the Internet and recently in QST and CQ/VHF magazines.
Step 3: Obtain satellite rise and set times.

Since the PACSATs orbit the earth in low orbits (LEO), they are not always visible from a given location on the earth. Instead, they appear to rise and to set at certain predictable time. The exact times can be calculated with a satellite prediction computer program. Using one of these program with a current up to date set of orbital elements, obtain the satellite rise and set times for either AO-16, LO-19, or IO-26. These are also known by the names PACSAT, LUSAT, and ITMSAT and are object numbers 20439, 20442 and 22826 respectively.

UPW can be used to send a signal to any one of these three satellites but only when they are above the local horizon. This usually happens approximately three times in the morning and three times in the afternoon. A future version of UPW will calculate this times automatically. Note that the digipeater functionality of the satellite is not always turned on!
Step 4: Connect the cables to the soundcard first, then to the radio and finally to COM1.
Step 5: Connect a GPS receiver to the cables going to COM1.
Step 6: Start UPW.

Click on "Start" in the lower left corner of the screen. Click on "Run", and enter the path to the UPW.EXE program. Press enter.
Step 7: Enter user information into UPW.

If you haven't registered, you will need to enter your FCC assigned amateur radio callsign, select the satellite to be used, and adjust TXDelay as needed for your radio (Note: more TXDelay is not better! It should only be as large as necessary.) You can also enter a comment, but this is not required. Once you register, UPW will save and remember this information each time it is restarted.
Step 8: Click on the "Get NMEA" button.

You should see NMEA $GPRMC strings in the box. The "No NMEA on COM1" label should change to either "GPS not acquired" or "GPS Acquired". If the GPS signal has not yet been acquired by the GPS receiver, then wait a few minutes. Eventually"GPS Acquired" should be displayed. Transmission is disabled until GPS is acquired to prevent incorrect information from being transmitted over the air. If you continue to see "No NMEA on COM1", check the cabling connections.
Step 9: Turn on the two meter radio and set the transmitter to one of the uplink frequencies for the satellite being used as a digipeater.
Step 10: When the satellite is overhead, click on "Transmit"

You will need to consult a satellite prediction program to know when the satellite is overhead. When "Transmit" is clicked, UPW will raise the DTR signal on COM1, which should turn on the transmitter if the PTT circuitry is working. After the TXDelay, UPW will send the Manchester packet and then lower the DTR signal. This whole process will only last for a second or two. Following transmission of the packet, the transmit button is disabled for approximately thirty seconds. This is to prevent any one station from transmitting an excessive number of packets through the satellite. In reality, only one packet needs to be transmitted and digipeated by the satellite. When heard by any groundstation your packet will be entered in the APRS network for other amateur radio operators to see.

While UPW can be used by mobile stations, *DO NOT* attempt to drive a vehicle and operate UPW at the same time. While UPW can be used as a tracker, *DO NOT* attempt to drive and operate UPW at the same time. You assume all risks of using this program. The author of this program is not liable for your use or inability to use UPW.
Future enhancements

The following features are currently being considered for inclusion in the next few releases of UPW:

9600 baud uplink.

PSK receiving capability. This would allow UPW to receive the PSK downlink signal from the satellites on the seventy centimeter band.

operation on COM2 for GPS NMEA data.

options to specify the PTT signal as DTR, RTS or a pin on the parallel port.

automatic calculation of satellite rise and set times to allow for semi-automated operation.

BPSK and standard FSK modulation schemes.

APRS style one line email via 1200 baud PACSATs.


AFSK - audio frequency shift keying; a modulation scheme for sending digital data which varies the frequency of the signal to convey information. This is the method normally used on two meter FM for standard AX.25 packet.

APRS - Amateur Position Reporting System. APRS is a registered trademark of Bob Bruninga.

Callsign - a unique collection of letters and numbers assigned to a station for identification purposes. In the United States, the FCC assigns callsigns.

digipeat - to digitally repeat; to receive a digital signal and then retransmit it.

GPS - global positioning system; a collection of government satellites which send signal that can be used to determine time, latitude, longitude, course, speed and elevation information. Use of GPS requires a GPS receiver.

Manchester - a modulation scheme for sending digital data. In Manchester coded signals there is always a mid-bit transition but there might not be a transition between bits.

PACSAT - packet radio satellite; sometimes refers specifically to AO-16, but more generally refers to any satellite built and operated by amateur radio operators for "store and forward" and digipeater operations using packet radio. The 1200 baud PACSAT satellites receive Manchester coded packets on two meters and transmit PSK code packets back to Earth on seventy centimeters. Operation through the PACSATs usually requires a Manchester modem for the signal sent to the satellite and a PSK modem to receive the signals sent from the satellite. The 1200 baud PACSATs include AO-16 (PACSAT), LO-19 (LUSAT), and IO-26 (ITMSAT). There also exists several 9600 baud pacsat satellites and few at even higher speeds.

PSK - phase shift keying; a modulation scheme for sending digital data which varies the phase of the signal to convey information. This is the method used by the PACSATs to send packets down to the earth.

sound card - a device installed into a computer which allows the computer to play and record sounds.

TNC - terminal node controller; a special "radio-modem" consisting of a packet assembler/ disassembler, modulator/demodulator, push-to-talk keying circuitry. It sends and receives data from a computer over a serial port and a over a radio using the microphone and speaker jacks. The TNC performs NRZI encoding, bit stuffing, CRC calculations, and modulates or demodulates the data using audio frequency shift keying (or some other modulation scheme if the appropriate modem is connected to the TNC disconnect header.)

TXDelay - the delay from the time that a transmitter is turned on until the time at which data can be sent to the transmitter. Most transmitters can not send data immediately when turned on but instead require a fraction of a second to stabilize before they can be used to send digital data. This fraction of a second delay is called TXDelay.

Last updated: March 2002

This page has been read times since February 6, 2000.
Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author.
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