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Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 08:27
by sudarshan
No data rate (the data rate was "-"). It seemed like just the carrier signal on the downlink. I guess the lander won't send data to any old donkey who asks for it?
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 08:31
by Mort Walker
UlanBatori wrote:Pingreji pls: what is an up signal and what does -141 dB mean? Compared to 1 watt? And is that the source (because receiver power should depend on solid angle of capture), hain? Like if I got this much power with this much area, and I know it came from this source, then the omni-directional source should have a power of... ??
-141 dBm is power in decibels per miliwatt reference. It is the power at the receiver of the ground station after passing through filters, low-noise amplifiers and down converters.
antilog(-141/10) = 7.94E-15 mW or 7.94E-18 Watts.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 08:37
by Mort Walker
sudarshan wrote:No data rate (the data rate was "-"). It seemed like just the carrier signal on the downlink. I guess the lander won't send data to any old donkey who asks for it?
It means one of two things. One, the transmitter and/or antenna on Vikram was destroyed. Two it could mean that Vikram is transmitting, but it is below the noise floor of the ground station receiver due to Vikram's antenna being pointed somewhere else.
The noise floor, as a rough rule of thumb is -174 dBm + 10log(receiver bandwidth). A receiver with 1 Hz bandwidth has a noise floor of -174 dBm and at 1 KHz it would be -144 dBm. See:
https://en.wikipedia.org/wiki/Johnson%E ... uist_noise
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 08:42
by sudarshan
It was briefly at -115 dB (around the time of suryag's post saying to "go check on the website"). At that time I was so excited about the dB value, that I didn't notice the data rate or whether the downlink signal was just the carrier or actual data. Didn't get a screengrab either. Kicking myself for it now. We'll see if it comes back.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 08:42
by SSSalvi
Right now ( 0820 IST ) Goldstone is transmitting 11 kw @2.1 GHz using ant#24 to CY2. Data rate is not there in status panel.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 08:44
by arshyam
sudarshan wrote:It was briefly at -115 dB (around the time of suryag's post saying to "go check on the website"). At that time I was so excited about the dB value, that I didn't notice the data rate or whether the downlink signal was just the carrier or actual data. Didn't get a screengrab either. Kicking myself for it now. We'll see if it comes back.
Screenshots please, saar

. I am also trying to monitor it to see if anything changes. Will share if I spot something.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 08:46
by prasannasimha
The plane sune wavd is the carrier wave. The modulated wave pic is tge data transmission occuring.
No terrestrial telescope has the resolution to even image Apollo landing sites and can only be imaged by LRO and now Chandrayaan.
This is dictated by optics. Our largest telescope does not have the two point discirimination capability to even image the Apollo lander let alone the much smaller Vikram so lets not have flights of fancy.
The signals we are getting can be still due to a wrong lock. We have to see. Even if ruggadized ( all satellites undergo thermoacoustic testing) we need to see of the lander rolerated the unscheduled hard landing. Getring just some communicarion on itself would be big as we would get the crucial data wrt what happened in the last phase.
There is no self righting mechanism for the Lander so we will not be able to kick and jiggle it open . The 0eople at ISTRAC have salvaged previous missions but problem for reorientation is that the lander is on a surface so refiring will not help . They will be thinking of out of the box things. If lander awakens it will be an Apollo 13 type of thing of problem solving pr more like Hitens salvage.
The
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 08:57
by arshyam
sudarshan wrote:It was briefly at -115 dB (around the time of suryag's post saying to "go check on the website"). At that time I was so excited about the dB value, that I didn't notice the data rate or whether the downlink signal was just the carrier or actual data. Didn't get a screengrab either. Kicking myself for it now. We'll see if it comes back.
Per this tweet (not sure how genuine it it is, it claims to be a bot that monitors NASA's DSN site):
Deep Space Network
@dsn_status
2h2 hours ago
DSS 24 carrier lock on Chandrayaan-2 Lander
Frequency: 2.2846GHz
Signal strength: -138dBm
IDLE OFF 1 TURBO
https://twitter.com/dsn_status/status/1 ... 9194380289
The Goldstone antenna name is indeed DSS 24.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:01
by suryag
Speculation from an armchair satcomm(am a cellular RF engineer by training) as to what is being trained
1. On the Uplink frequency the DSN transmits tone and data(some inane data not like asking to send pictures) because it doesnt know if the receiver is good, we dont want the lander to transmit at high power and exhaust the battery if the DSN is not getting any good signal
2. Once Tone and data is received by the receiver the receiver tries to initiate comms by transmitting tone
3. The DSN looks for a tone on the DL
4. Once power above noise floor is measured(noise floor is very subjective and based on link budget, so we dont know what Vikram's noise floor would be configured at the DSN receiver) then freq errors, phase drifts are measured to see if this is indeed coming from the intended party or some background noise
5. At this point if the receiver parameters are good the DSN may transmit another separate command to start receiving some data because you now know that the lander can transmit something meaningful and will not rail on TX power and exhaust batteries
What ISRO engineers might do is
1. collect the data from Madrid/Goldstone where tone was being seen at, check the parameters and lock the azimuths of the antennas(?) because i see that the DSN azimuth was changing which i believe is their attempt to try different orientations to get through
2. Once they lock the azimuths they can possibly transmit at higher power around the same time and orientation and get something back
literally, the chances are slim but miracles often happen on the RF side. I just want to hear "Bengaluru this is goldstone we have your bird" this was the dialogue in that johnny walker mars mission video
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:05
by arshyam
Thanks for the explanation saar. Any idea on what that tweet I posted above means? What's a carrier lock - is it a lock on to an incoming signal?
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:05
by arshyam
suryag wrote:I just want to hear "Bengaluru this is goldstone we have your bird" this was the dialogue in that johnny walker mars mission video
Yeah, that was a very well done video. Fingers crossed onlee.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:09
by sudarshan
arshyam wrote:
Per this tweet (not sure how genuine it it is, it claims to be a bot that monitors NASA's DSN site):
That tweet might be genuine, it seems to be around the same time that suryag said to go check the site.
I've been monitoring the site so far, but now I have to knock it off and go attend to something else. I'll leave it to you other guys.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:11
by arshyam
Got it!
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:11
by suryag
Sir carrier lock means we are mostly seeing power which is above noise floor and the lock signifies that there are no runaway frequency errors or phase drifts. The tone is generally the easiest to transmit as there is generally no modulator/demodulator involved and the transmitter + power amplifier can be pre-programmed to send a sine wave without baseband(modulator/demodulator) being involved. Data transmission needs more SNR than tone, also i dont know the antenna architecture of the lander do they have 2xRX-TX antennas or 4xRX-TX antennas, but if there is no transmit diversity on the lander then you need to really hit the right orientation if it is not an omnidirectional antenna
If we indeed received tone and it is consistent it tells a lot about the health of the craft - first it didnt burn or suffer fire internally, all components are in their places along with connections, most likely the antennas lost orientation or were broken by yakherders
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:12
by arshyam
Down Signal
Type:Carrier
Data Rate: 0.00 b/sec
Frequency: 2.27GHz
Power Received: -132.38dBm (5.78x10^-20 kW)
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:12
by sudarshan
Woo hoo! -118 dB. Who's going to be first with the screenshot?
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:14
by arshyam
The power received went up to -134.19 dBM and then the down signal went off, came back for a sec and again went off.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:19
by Mort Walker
I wonder if Goldstone can switch to the higher gain antenna?
Best downlink power seen about -114 dBm.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:19
by sudarshan
OK I'm out for now.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:21
by Mort Walker
No data rates yet.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:21
by suryag
-118 is definitely encouraging
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:22
by suryag
Mort sir they have to look at the received tone characteristics before they request data
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:22
by Mort Walker
I saw -111 dBm now. A 7 dB improvement.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:25
by gauravsharma
SPACECRAFT
NAME
Chandrayaan-2 Lander
RANGE
404.77 thousand km
ROUND-TRIP LIGHT TIME
2.70 sec
ANTENNA
NAME
DSS 24
AZIMUTH
158.76 deg
ELEVATION
29.70 deg
WIND SPEED
27.78 km/hr
MODE
-
UP SIGNAL
SOURCE
CHANDRAYAAN-2 LANDER
TYPE
DATA
DATA RATE
-
FREQUENCY
2.10 GHz
POWER TRANSMITTED
11.58 kW
DOWN SIGNAL
SOURCE
CHANDRAYAAN-2 LANDER
TYPE
CARRIER
DATA RATE
0.00 b/sec
FREQUENCY
2.27 GHz
POWER RECEIVED
-110.00 dBm
(9.99 x 10-18 kW)
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:25
by Mort Walker
suryag wrote:Mort sir they have to look at the received tone characteristics before they request data
Yes, I guess they're just looking for a carrier. No data is being sent up.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:27
by Mort Walker
At -108 dBm now.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:27
by suryag
Long night for isro telemetry folks
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:29
by Bibhas
I saw -108.5 dB right now.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:29
by Mort Walker
I wonder if it actually is Vikram or is it something else (some other satellite) at 2.27 GHz.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:30
by Mort Walker
Gone now.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:31
by gashish
Here is the snapshot at 8:32pm pst
multiple image upload
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:32
by NRao
What does all this mean?
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:32
by arshyam
Here's what I saw:

Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:33
by disha
Thanks to all the RF warriors trying to get a lock on C2Lander.
Hoping for the best.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:35
by gauravsharma
On the other hand CHANDRAYAAN-2 ORBITER is sending data at the rate of 999.0 b/s with power level -125dBm to ANT26 (Goldstone)
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:35
by suryag
Sir the Madrid one was at 8 GHz that would have definitely been Vikram again the tests would be to lock the azimuth angle and checknif you see tone only when you send tone ... fingers crossed and praying
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:35
by arshyam
suryag wrote:Sir carrier lock means we are mostly seeing power which is above noise floor and the lock signifies that there are no runaway frequency errors or phase drifts. The tone is generally the easiest to transmit as there is generally no modulator/demodulator involved and the transmitter + power amplifier can be pre-programmed to send a sine wave without baseband(modulator/demodulator) being involved. Data transmission needs more SNR than tone, also i dont know the antenna architecture of the lander do they have 2xRX-TX antennas or 4xRX-TX antennas, but if there is no transmit diversity on the lander then you need to really hit the right orientation if it is not an omnidirectional antenna
If we indeed received tone and it is consistent it tells a lot about the health of the craft - first it didnt burn or suffer fire internally, all components are in their places along with connections, most likely the antennas lost orientation or were broken by yakherders
Thanks, so does this mean we are receiving tone?
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:37
by suryag
From an armchair perspective yes
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:39
by Ramnath
Was looking at the purported Bot feed on twitter.
It also had mentions about the CY Orbiter link.
Something to the effect that 7hrs ago, there was carrier lock at signal strength of -141dbm(only carrier) on dss65. Then 6 hours ago, there was a downlink ongoing at 1kbps. So the signal strength numbers of the lander don't seem to be so weak to be discounted as noise.
Re: Chandrayan-2 Mission
Posted: 10 Sep 2019 09:39
by NRao
disha wrote:Thanks to all the RF warriors trying to get a lock on C2Lander.
Hoping for the best.
In about 90 minutes.