This weekend I was supposed to be off to North Yorkshire for a weekend dog agility event. Unfortunately due to a family emergency we were forced to change plans. So yesterday I found my self at home and in between doing some much needed odd jobs I had the chance to get out the 2 meter YAGI and capture a couple of passes of those Russian navigation satellites I blogged about last week.
Each pass lasted the best part of 15 minutes from the first faint signal acquisition to finally losing it as it sped out of range. Below is an except from the first pass at around 10:00 UTC. The signal is clear and the different tones used can be clearly distinguished. These captures should prove useful for testing any decoder.
Russian Parus Satellite 27-11-2011 by nerdsville It is quite fun standing with the antenna and pointing in the direction where I expecting the satellite to appear and then once the signal is acquired then fettling it during the pass to maintain the best signal strength.
Not sure what my neighbours are making of all these antics, perhaps I should try to find that extension cable so I can use headphones to monitor the pass rather than letting it blast out the laptop speaker! It must look odd me standing there waving an huge antenna about and receiving strange foreign voices (from the ARISSat-1 satellite) and now this weird ‘morse code’
At the weekend I attended a dog agility show in the depths of Cambridgeshire, there is always a lot of waiting around in between runs and so I was sat in the foggy car park. To pass the time I had taken along my PRO-26 scanner. I monitored amateurs on GB3PY and GB3OV chatting about the tropospheric ‘lift’ they were experiencing, found a few taxi firms complaining about the fog, some hospital paging but it was pretty boring.
I was idly scanning around when I happened across a strange signal on 149.9375Mhz. I could hear a definite doppler shift in the tones so it was a satellite. Checking my pretty useless 9th Edition UK Scanning Directory the frequency was identified as being in the Russian radio navigation and satellite beacon band.
Over the last couple of days I have done some research and discovered it is the Russian Parus Navigation System which dates back to the 1970s. The transmission was in fact on 149.940Mhz but I had the scanner set on 12.5kHz stepping. I have been trying to track and capture more of the signals but had been hampered by a persistent source of interference at home, but did get some audio
These satellites are very easy to receive on a handheld scanner though obviously you’ll get better results on an external antenna. The tx power is about 10 watts (+40 dBm) so with a 140dB path loss on an overhead pass (alt = 1000 km) you’ll get about a microvolt in a zero-gain antenna, which is enough to hear.
The VHF frequency carries the time data and orbital parameters for the current and other satellites. There is a second transmission on around 400MHz- its in an 3:8 ratio with the VHF carrier frequency. This is unmodulated- i.e cw. It is used to measure the Doppler shift, to determine when the satellite is dead abeam the observer. The transmitted time, and the orbital data, tell you where the satellite was in the sky when that happened- or, put another way, if you know where the satellite is relative to you, then you know where you are- well, you’re somewhere on a line at right angles to the satellite’s track. You then wait for another satellite, and obtain another poition line- and where they cross, then bingo- that’s where you are. Hope that makes sense!
Parus could give you a fix in 1-2 hours; and had an accuracy of 100m anywhere on the earth’s surface. Okay that’s poor compared to GPS, but in the 1970’s it was revolutionary.
It isn’t just Doppler that determines the receiver bandwidth, although you do take it into account. Most satellites have a much higher FM deviation than a normal narrowband FM transmission- the NOAA met sats are about 19kHz deviation I think- and these nav sats are higher too, but not that much. But for decoding, you do need to resolve the 7kHz second markers which a narrow filter won’t easily do.
There is also a lot of information about the Soviet space program on the Zarya website
I would like to decode these signals at some point, providing I can sort out reception. I have found a number of historical guides and projects in addition to the articles linked to in the thread above.
As I mentioned in yesterdays post, this weekend saw a couple of well timed passes of ARISSat-1, today had two which seemed to offer the possibility of decent results.
So the setup again was I’d have the PRO2006 in the spare room on the loft mounted discone to capture any SSTV images and the Yagi with the Alinco DJ-X10 in the garden to capture the CW beacon. The first pass yielded rubbish results from both setups, the beacon was very faint (I suspect I haven’t got something quite right for receiving the SSB/CW modes) but as I lost signal at the end of the pass I switched the Alinco to FM on 145.950MHz and got a really strong signal!
The decision was made! For the second pass I decided not to bother with the beacon and get a FM capture with the Alinco.. well glad I did got a cracking full 5 minutes of voice and three sstv images, including a beautiful one of the blue marble!
The normal PRO2006 setup yielded nothing worthy of including here!
This weekend there are a couple of excellent daytime flybys of ARISSat-1 predicted, passing very high in the sky. Up till now I have been concentrating on the FM transmission on 145.950MHz which carries the voice messages, voice telemetry and the SSTV. The other signals from the satellite use SSB and CW modulation.
So this morning I left the loft discone and my Realistic PRO2006 with MMSSTV in the spare bedroom waiting for the pass while I took the borrowed Alinco DJ-X10, which has SSB capability, outside and using the Yagi antenna I built up last weekend had a go at getting some of the CW beacon on 145.919MHz
I got a decent signal as you can hear below, and using CWGet managed to decode some of the telemetry and the identification, but the high noise and doppler effect did cause some problems.
Well this is how it arrived, a big cardboard tube that has been sitting in my workshop since October.
Taking everything out the box, lots of metal work, but no instructions!
It was fairly logical to put together, but wasn’t absolutely sure how the folded dipole element went together and the u-shaped end pieces slotted in with no apparent fixings to hold them in place (I assume they are missing along with the instructions) There was also a piece that fitted under the antenna. I am no expert on antenna design so checked the InnovAntenna website but it was no help, lots of graphs and radiation patterns but and not one images of the actual antenna to look at! Looking at a small picture on the Waters and Stanton blog I made a guess as to how it should be put together.
I connected up a bit of coax, and screwed it a short wooden post I had. The end pieces of the folded dipole slipped in and seemed to be fairly secure but probably not brilliant electrically, so will need to secure them properly if I ever use this in anger.
It is lightweight and easy to move about, so I was ready to get going
The satellite passes are from west to east and to the south of my location. So would have to do this at the end of the garden to minimise obstuctions from houses and trees. I would be well away from my normal computer and scanner in the spare bedroom! I decided to use my Realistic PRO-26 hand-held scanner, which is a good performer and has a relatively clean unprocessed audio output (can decode pagers and ascars quite well with it)
I used an old Pentium III laptop running Windows 2000 to capture the audio. I didn’t attempt any decoding of the SSTV directly just captured the wav files so I could edit and process them later. The laptop has dead batteries but could be powered from the summerhouse mains and so with a few extension cables I could have a relatively clear view of the sky and have access to the scanner to adjust levels and could monitor the audio from the laptop!
I experimented with the first pass, at around 13:30 UTC and got a decent signal eventually, but it took a bit of trial and error as the polarisation seems to change during the pass. For the second at 15:14 UTC I set up the camera to record my efforts! The audio in the video is just being picked up by the microphone on the camera so has a lot of background noise, but as you can hear it was at times a fairly strong signal! I had my usual unattended setup going in the spare bedroom and got nothing on either pass!
I have uploaded the two audio files of each pass to Soundcloud
Here are the images decoded from the audio.. slight sync problems which I suspect is the underpowered laptop – I did have it capturing at 44.8KHz, 32 bit resolution, which was probably an overkill in hindsight!
But on the whole it was a fun way to spend the afternoon with some nice results.
ARISSat-1 is getting nearer the atmosphere but is still functional and the orbital passes have moved back into daylight over the UK so set up the gear again this week to try to get some more SSTV images. Results have been a bit poor, but did get the back end of a very nice image this afternoon clearly showing some cloud formations in the atmosphere.
Not had too much time over the last week or so to do much radio wise, but the other day while scanning around in the vhf low band found an odd signal on one of my scanners at 70.860MHz. This is the part of the spectrum that was used by the fire brigade until the introduction of the airwave system. Strangely it was a WFM signal and after a few minutes of music identified itself as BBC Radio Nottinghamshire!
Where I live isn’t brilliant for radio reception, but the BBC station is one of the stronger due to a nearby local ‘fill-in’ transmitter so I suspected it was breakthrough or some product of intermodulation. However I wasn’t sure if it wasn’t some ‘cordless headphones’ or other form of AV link or baby alarm given the proliferation of Chinese cheap and cheerful FM modules available that can operate at this frequency. That now seems very unlikely as the signal has been present continuously for days now.
To try to rule out any internally generated image I tried some of my other scanners, with different antennas and found the signal on them too. However one of them did exhibit some pager breakthrough as can be seen in the following video.
It therefore does suggest to it being an intermodulation product, but exactly what is causing it I am unsure. We have cast iron guttering on the house which has been recently repainted, so could this be caused by a rusty bolt that has been disturbed now acting as a diode?