Reception of 4M signals
How and What does transmit 4M?
4M transmits on 145.980MHz with 1W of RF power
The antenna gain of 4M has an average gain of -10dBi in all directions, with smooth peaks at +3dBi and some narrow deeps at -30dBi
4M transmits its data using JT65B, which is basically a 65-FSK, modulating the carrier in SSB with tones approximately comprised between 1200 and 1600Hz
The JT65B sequence is followed by an ‘analog’ sequence in which you have
- A tone that can have 400, 420, 440, 460 or 480Hz and that indicates what type of message was sent in the JT65B sequence
- A tone at 250Hz
- A tone which value is comprised between 500 and 3000Hz, which indicates the temperature following the equation:
- Tone frequency= 500 Hz +12 Hz/°C (T+50), with T in °C
- A tone of 1300Hz represents thus:
- (1300 – 500)/12 – 50 = 16.666°C
- A tone at 300Hz
- A tone which value is comprised between 500 and 3000Hz, which indicates the voltage at input of the 4M electronic following the equation:
- Voltage: 500 Hz+0.1 Hz/mV *V
- A tone of 2100Hz represents thus:
- (2100-500) x 10 = 16000mV, which is also the maximum value to be expected.
- A no transmission period of 2seconds
Each tone has a duration of 2s.
A SSB mode generates tones that are dependent of the tuning of the receiver, the fixed tones at 250 and 300Hz are there to allow computing the offset of the receiver. If the second tone is measured at 310Hz for example, it means that your receiver is offset by + 60Hz, the value should be substracted from the analog reading.
The whole sequence lasts exactly 60s.
As the Onboard computer clock may drift during the mission, the JT65B may not start on second 0 of the UTC minute.
This one minute sequence is repeated 5 times to produce a 5 minutes cycle.
The description of the 5 sequences is as follows:
(the greeting messages have been replaced by ——- )
You have, in column order:
- C1: The time that is used by WSJT + manual offset (the field that is in the lower left of the window to the right of the time display)
- C2: (Tech info)
- C3: Signal to Noise
- C4: Clock shift dT with respect to WSJT time (in seconds)
- C5: (Tech info)
- C6: (Tech info)
- C7: The message itself (meaning see below)
- C8: 1
- C9: 0
- C10: The value of the manual offset. (0.0 in this example) between -59.5 and +59.5 s
What do the messages contain ?
- LX0OHB-4M0167 : call sign. The last 4 figures are the mission elapsed time in steps of 5 minutes. 167/12 = 13.917 Hours in this example.
- 160V271A +18C : 16.0Volts, 0.217A, +18°Centigrades, field is always 13 characters in length, with ‘V’ at 4th position, ‘A’ at 8th position and ‘C’ at 13th position.
- R9 SW4RFJZ : « Gamma receiver » or radiation dosimeter : always begins with R, and counts exactly 10 characters, the last three ones being filled up with spaces. There are two sensors, the results of which are being sent alternatively. This field may take the value: RNODATA.
The following picture shows a typical decoding sequence using WSJT 10.0 release 4336a which has special features for this mission. All versions of WSJT will nevertheless work although we recommend using this version that can be downloaded at:
What do you need to receive 4M?
The minimum requirement is
- Antenna that is orientable in Azimuth and elevation like this setup:
Figure 1Antenna (Joachims antenna 2x8Elts LNA ferom SSB.de)
- The antenna should have a minimum of 12dBic gain and followed with a LNA of 1 dB NF max. During the first day, 4M can be received with a lower gain antenna.
- A receiver with SSB mode
- A PC equipped with sound card
- An AF cable connection between PC and receiver.
- A sound recorder: like spectrum Lab: http://dl4yhf.darc.de/spectra1.html
With this minimum setup, you can receive the signals and record them so as to send them to the 4M team
In addition of the above, you can decode the signals in the JT65B sequence.
This requires the installation (simple and foolproof) of WSJT. It is a strong wish to have the PC connected on the Internet, so as to have the PC clock reasonably synchronized.
The use of WSJT requires a little knowhow, although it is sufficiently well designed as to minimize the hurdle.
It is best to get acquainted to it before starting.
However, the basic rules must be obeyed:
- Set the level of the AF gain of the receiver so as to have the level between -10 and +5dB on the spectrum window. Alternatively, use also the digital gain adjust scale that is located just to the right (without legend) of the clock of the spectrum window.
- Make sure the command window indicates that your audio setup is working properly. Refer to the manual for reference.
- In the “mode” tab”, check the JT65B mode
- In the “decode” tab, check only: No shorthand decode and no deep search
- In the “save” tab, check: “save none” or “save decoded”. The lates will generate .wav files that you can send to the 4M team
- Click on “monitor”, this should turn the box in green.
- At this stage, adjust the levels accordingly as described above.
DO NOT TUNE the receiver during reception, but set your receiver frequency according to the Doppler tables provided below.
The signal may be weak and NOT audible to hear, but the spectral window can show you that:
The “sync” vector should be around 1270Hz, or double click on the spectral line to align the search window on the frequency. Uncheck “freeze”
In the above case, this is a perfectly decodable signal.
If you intend to have long hours of decoding, you may wish to have “freeze” and AFC checked.
The search window (in green on top ) reduces to 50Hz, check also AFC. Please note that the above copy of the screen depicts a correctly set input audio level (do not account for the -20dB value read)
Full setup (experts)
In addition of the above, you install (if not already done previously) the NTP monitor that keep your PC sync’ed.
Meinberg has a good tool: (please note that this software must be left running on your PC permanently)
As an expert, you may also install the JAVA client, that will send automatically the decoded messages to our website:
Login or register, then download the appropriate version in the ‘download’ section.
Unzip the file in a folder of your choice, then run 4Mclient.exe
Configure it (very simple operation) by filling in the fields:
The client will look at your “decoded.txt” file every minute, and if there is a new message, will automatically send it to our server.
If you login to the server, you will see your messages and the messages of the other stations coming in.
How to send your data?
- send a request (blank E-Mail, no attached files) to E-Mail address, taking care to put in the subject of your mail, like this:
We will send you FTP credentials where you can upload your WAV files:
- Create for each day, or if you change your frequency, a new folder on the FTP server with a folder name Yyyy-mm-dd-4M-yourcallsign-locator-WAV-145.980 (where 145.98XX is the REAL displayed frequency on your receiver)
- use WAV format, 11025s/s, 8 or 16 bits
- DO NOT USE MP3, only wav format
- send the ALL.TXT file (that you find in the WSJT directory ) to email@example.com , taking care to put in the subject field of your email, exactly like this:
- If you wish to send some decoded WAV files of WSJT, that you find significant, proceed as above changing ALL to WAV and DO NOT FORGET TO ADD THE TUNING FREQUENCY OF YOUR RECEIVER AS INDICATED ABOVE
- if you use the 4M java client, it is done automatically, otherwise, proceed as above. At any rate, send the tuning frequency of your receiver with the ALL.TXT as indicated above.
Pointing the antenna
There are several ways to point your antennas to 4M:
- Going to our website (“Tracking” tab), enter your geographic position, you will then get a table with 1 minute steps that give you Az, EL, Range. Clicking “select”, then CTRL-C, allows you to paste it in a text file. As the apparent movement is slow, manual pointing of the antenna every 10 minutes or so will do.
- Using satellite tracking programs, then the following TLE’s are to be input and should do:
Use this TLE up to 27/10 1200UTC
1 99999U 14298.79728009 .00000066 00000-0 00000-0 0 00006
2 99999 030.6553 295.6956 9746689 147.2577 071.9585 00.10600338000010
The following set is to be used after the flyby from 28/10 1200UTC onwards
1 99999U 14301.79728009 .00000000 00000-0 00000-0 0 00009
2 99999 049.9434 067.2017 6639865 045.9865 124.5019 00.06612018000010
Between 27/10 and 28/10: aim at the Moon following WSJT Az, El !!!
You can check the success of your tracking software by comparing with the animations that are in the ‘multimedia’ tab of moon.luxspace.lu
Tuning the receiver.
The receiver is to be tuned to the frequency of 4M +/- the Doppler shift and your receiver’s frequency errors.
The Doppler changes very slowly and is mainly due to the rotation of the Earth. The following figure gives the variation to expect up to the flyby. Note that the Doppler does not vary more than 450Hz during the whole visibility, so tuning the receiver so as to place the sync vector at 1400Hz at the beginning of the pass, will allow you to not tune the receiver during the pass duration, which lasts at least 9 hours, depending on your latitude.
The signal will be affected by QSB during the reception If you can alternate polarization, try to use choose the opposite one
The following graph gives the expected variation of signal strength during the passes While the antenna of 4M has an average gain of -10 dBi, it has smooth peaks at +3dBi, and some sharp deeps at -30dBi.
The following is a typical zoom:
Alternating polarizations may help as described below:
The above graphs are typical and based on the antenna pattern computation of 4M when integrated on the 3rd stage of the launcher.
The period of the QSB as well as the deep value will exclusively depend on the angular rotation speed of the last stage and its orientation. This is unpredictable.
It is to be noted that the above integrates the sun, galactic and ground noise, but not the man made noise. If you are in a noisy location the S/N figure may unfortunately be lower.
The simulations above are made on the basis of 12dBic antenna gain and 1dB LNA noise figure.
Please note that the signal will be usually quite weak, barely audible by ear. Rely on the spectral display.
Word of notice
Be ready before the launch. The trip to the Moon lasts only 96 hours.
Try your procedures beforehand so as to be QRV in time.
As you can imagine, we are eager to receive the first reports, on the launch day, please send a text (SMS only, NO MMS) to +86 155 107 46989 or email immediately your first all.txt to E-Mail address. For wav files, please follow the procedure described in a previous chapter.