Ham receives ISRO Mars Orbiter

Ham receives ISRO Mars Orbiter

On Wednesday, September 24, the Indian space agency ISRO successfully put their MOM spacecraft into Mars orbit, the first country to have achieved this on the initial attempt

Radio amateur Paul Marsh G7EYT/M0EYT received the signal from the Mars Orbiter Mission spacecraft and tweeted: "S-Band downlink from MOM spacecraft now on orbit @ Mars! Great signal with Doppler; congrats to ISRO - good job".

An image of the MOM signal can be seen at
http://pjm.uhf-satcom.com/twtr/mom_240914.jpg

UHF-Satcom
Web http://www.uhf-satcom.com/
Twitter https://twitter.com/uhf_satcom
Yahoo https://groups.yahoo.com/group/amateur-DSN

BBC News report
http://www.bbc.co.uk/news/science-environment-28268186






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I have serious doubts that:'received by radio amateur'. What was the aperture used on RX and how big is it? Why is there no picture of the RX antenna?

What is the integration time? How was doppler coorected for? What do the on-offs look like? Is the LNA cooled? What is the G/T ?

Lots of legit questions to ask...

Answers??


Chip W1YW

 

This web page seems to answer your questions - http://uhf-satcom.com/sband/ If not, you could get on Twitter at the links provided and ask him!

These folks are either quite serious about monitoring satellites and space missions or seriously delusional. Based on the number of people and the equipment discussed, I'd say they are very serious.

 

I'd say there is no evidence that this is true at all. And, of course, I did look.

The gain needed, for example, is not manifest in the helices they show. I know very well the size of the apertures needed.

This is not a 'satellite' it is a 'space mission'. Detecting satellites is trivial compared to detecting a Martian orbital insertion.

Also you have to have sufficient SNR on the doppler to PROVE the orbit insertion. And the doppler has characteristics that will be unique to insertion for a given height above Mars. Absolutely no evidence of that.

None of this is manifest in the meager data shown. No hardware shown.

Nada.

Also, why is it incumbent on ME to provide those queries? They have made an extraordinary claim and they know they have to show the system and the data to back it up.



73
Chip W1YW

 

I was prepared to call BS too but then I looked up comms system on that satellite.
"Communications are handled by two 230-watt TWTAs and two coherent transponders. The antenna array consists of a low-gain antenna, a medium-gain antenna and a high-gain antenna. The high-gain antenna system is based on a single 2.2-metre (7 ft 3 in) reflector illuminated by a feed at S-band. It is used to transmit and receive the telemetry, tracking, commanding and data to and from the Indian Deep Space Network"

Then I looked up what EME stations on the 13 cm band usually have and it seems they run similar power and 3-5 meter dishes and that's just to make a half million mile round trip. That satellite is a bit over 139 million miles away and I can't imagine those little helicals being anywhere close to the gain of a 3 or 5 meter dish.

Then I looked up the Indian Deep Space Network that satellite is designed to connect to:
The network consists of a fully steerable 18 metres (59 ft) and a 32 metres (105 ft) DSN antenna which improves the visibility duration when compared with the existing ISRO Telemetry Tracking and Command Network (ISTRAC).

Yeah. I'm with Chip. I doubt India spent $13,000,000 on that network if they could have spent $130 on some helicals. Granted, much of the size is so they can Tx back to Mars. But still. I don't see those little helicals Rxing that signal.

 

How well does the moon reflect radio signals?

 

Not well at all... very little gets reflected back.

I would think if this guy picked up signals from the Indian mars spacecraft that he had to be using much more than just that little helical antenna shown on his website. He didn't really state the antenna that he used. Those helical antennas he had on his website he only described as using them for satellite reception... which is far different then picking up a signal from a mars orbit.

 

To the GREAT W1YW

Hi,

>I have serious doubts that:'received by radio amateur'.

Run the numbers, its very simple to estimate the path loss and you can see that even a small 3ft antenna with half decent LNA will work nicely.

>What was the aperture used on RX and how big is it? Why is there no picture of the RX antenna?

Why dont you read the twitter feed like everyone else on the Internet does - then you would know OM. Since you are obviously 'special' the antenna picture is at http://pjm.uhf-satcom.com/twtr/antenna.jpg

>What is the integration time?

Again, the information is presented to YOU in the FFT, take another look at it; URL http://pjm.uhf-satcom.com/twtr/mom_240914.jpg RBW 0.38Hz with an average of 1...

>How was doppler coorected for?

Hmmm the carrier is not on the same frequency as per the FFT image, why do you think it shows Doppler correction?

>What do the on-offs look like?

No idea what this means. The downlink is 999.983baud PSK with Turbo encoding so I'm not sure why that would show 'on-offs' - its not CW on 80M!

>Is the LNA cooled? What is the G/T ?

Again - See the picture of the antenna and the twitter feed - you would know about the LNA if you bothered to read it, it is a G4DDK VLNA. You can do the calcs to estimate G/T just as well as I can.

>Lots of legit questions to ask...

I would say you need to firstly do the calcs on paper OM. Just because you have serious doubts that:'received by radio amateur', does not mean you should be questioning those actually doing it in the manner that you are.

Have a nice day.

Paul M0EYT.

 

Hi Paul,

With due respect, your responses confirm my concerns that this is not what you claim.

I have no doubt you measured something. Based on my expertise on these matters, IMO this assemblage is incapable of confirming the Indian sats Martian orbital insertion.

BTW, on-0ffs refers to azimuthal and or elevation beam nods. This is done to confirm that the detected source is point like, and also not interference. It is one of several techniques used as a 'control' in the observation.


Mars and Earth have a differential Doppler shift that must be corrected for in real time. It is in excess of a fraction of a Hz...go figure it out. Go show us you have predicted the additional Doppler behavior that would be unique to orbital success.

This is your claim..it is up to you to be forthcoming on all accounts...not seeing it.

Your aperture size is.....?

You won't answer this because...?



73
Chip W1YW

 

No Paul, it will not.

But hey--let's do a BOTEC for everyone here. It is quite revealing.

Let's assume you meant a 1M dish. Your chicken wire reflector is not exactly that, but lets be a bit generous.

I note you claim a 10dB dynamic range at S-band--let's call it 13.5cm wavelength. If lucky, your aperture efficiency is roughly 70%.

So your antenna gain is roughly 25 dB.

Now for detection, I just need to beat the noise by a bit, so that means I should be able to detect the signal with, say -8dB from your plot. Thus I would need an antenna with a gain of at least 18dBi.

Get that? According to you, I could DETECT with 18 dBi for my antenna.

Needless to say, such an antenna is TRES modest at S-band. In fact, a small S-band Yagi should do the job.

That's according to your numbers Paul. I couldn't make this up.

So...are you trying to convince us that we can DETECT the Martian Orbiter with what amounts to a TV antenna Yagi?

Now the next question: what is your system temperature?



73
Chip W1YW

 

Just for some perspective Paul, that S-band Yagi would be roughly two+ feet long, and about 4 or 5 inches wide with radome.

Here's one that works at 2400 Megs....give you a good idea:

http://www.alibaba.com/product-detail/china-yagi-antenna-16-elements-18db_1963256759.html

So...shall I go listen to Mars tonight?

73
Chip W1YW

 

The first link provides a clue... http://uhf-satcom.com/copyright.html

I hope quoting an excerpt from their copyright policy isn't an infringement!

Steve
KV6O

 

Can we get Fred to can this turkey of a thread, lest it get sucked into an engine?

73
Chip W1YW

 

With all due respect, both you and especially KV6O are way off base here. As M0EYT suggests, do the link budget calculations (if you are capable of that).

 

I am not making the claims here....let him give us the numbers for HIS system.

73
ChipW1YW