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Kenneth Gonsalves | 10 May 17:06

digital freedom in iitm?

hi,

at today's lug meeting I wanted to give a live demo of digital  
mapping with gps after my talk. But I found that I just could not  
acquire any satellites within the IIT campus. Max lock I could get  
was 15 seconds. The moment I left the campus, my instrument behaved  
normally. This leads me to wonder if IITM is blocking gps. If so,  
why? There are countries like China and Cuba where mapping by  
citizens is illegal - but the last time I looked, IITM was in India.  
so wtf?

--

-- 

regards
kg
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http://nrcfosshelpline.in/code/

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Zico | 10 May 17:31

Re: digital freedom in iitm?

On Sat, May 10, 2008 at 9:08 PM, Kenneth Gonsalves <lawgon@...>
wrote:

> hi,
>
> at today's lug meeting I wanted to give a live demo of digital mapping with
> gps after my talk. But I found that I just could not acquire any satellites
> within the IIT campus. Max lock I could get was 15 seconds. The moment I
> left the campus, my instrument behaved normally. This leads me to wonder if
> IITM is blocking gps. If so, why? There are countries like China and Cuba
> where mapping by citizens is illegal - but the last time I looked, IITM was
> in India. so wtf?
>

*WOW!! Jammed the system???*

--

-- 
Best,
Z
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Saripalli Siva Prakash venkata phani | 10 May 18:14

Re: digital freedom in iitm?

hi,
i think its some problem with your device....
iitm doesnt waste money in crap like that.... :)

On Sat, May 10, 2008 at 9:01 PM, Zico <mailzico@...> wrote:

> On Sat, May 10, 2008 at 9:08 PM, Kenneth Gonsalves <lawgon@...
> >
> wrote:
>
> > hi,
> >
> > at today's lug meeting I wanted to give a live demo of digital mapping
> with
> > gps after my talk. But I found that I just could not acquire any
> satellites
> > within the IIT campus. Max lock I could get was 15 seconds. The moment I
> > left the campus, my instrument behaved normally. This leads me to wonder
> if
> > IITM is blocking gps. If so, why? There are countries like China and Cuba
> > where mapping by citizens is illegal - but the last time I looked, IITM
> was
> > in India. so wtf?
> >
>
> *WOW!! Jammed the system???*
>
> --
> Best,
> Z
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Shakthi Kannan | 10 May 18:22

Re: digital freedom in iitm?

Hi,

--- On Sat, May 10, 2008 at 8:38 PM, Kenneth Gonsalves
<lawgon@...> wrote:
| But I found that I just could not acquire any satellites
| within the IIT campus.
\--

1. Did you walk with your device outside the building or did you try
it from inside? You are not going to get consistent signals from
inside the building. You could try to go near the window(s).

2. Which device are you using? What is its Time To First Fix (TTFF)?

3. What was your TTFF [1] when you received the signals?

4. How many satellites did you receiver pick, when it did?

I doubt if IIT-M has GPS jammers.

SK

[1] http://en.wikipedia.org/wiki/Time_to_first_fix

--

-- 
Shakthi Kannan
http://www.shakthimaan.com
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Kenneth Gonsalves | 11 May 03:41

Re: digital freedom in iitm?


On 10-May-08, at 9:52 PM, Shakthi Kannan wrote:

> --- On Sat, May 10, 2008 at 8:38 PM, Kenneth Gonsalves
> <lawgon@...> wrote:
> | But I found that I just could not acquire any satellites
> | within the IIT campus.
> \--
>
> 1. Did you walk with your device outside the building or did you try
> it from inside? You are not going to get consistent signals from
> inside the building. You could try to go near the window(s).

from MIT, Chromepet to IIt gate I had perfect signal. On the flyover  
opposite IIT gate, I lost the signal, but got it back at Madhya  
Kailash. Again lost the signal on entering the campus. Both before  
the meeting and after it, I walked around outside and tried to  
acquire. For about 15-30 seconds I was able to acquire 3 satellites.  
After that nothing. Again from tenet building to the exit gate, no  
signal. When I left IIT and reached Raj Bhavan I got the signal back  
and was getting 5-6 satellites all the way back to Chromepet.
>
> 2. Which device are you using? What is its Time To First Fix (TTFF)?

garmin 72. In Chennai, cold start takes about 2 minutes for a fix.  
Warm start is about 30 seconds. Bangalore takes a little longer. In  
Ooty it is less than a second.

>
> I doubt if IIT-M has GPS jammers.
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Sivasankar Chander | 11 May 15:59

Re: digital freedom in iitm?

On Sun, May 11, 2008 at 7:11 AM, Kenneth Gonsalves <lawgon@...>
wrote:

> On 10-May-08, at 9:52 PM, Shakthi Kannan wrote:
>
> > --- On Sat, May 10, 2008 at 8:38 PM, Kenneth Gonsalves
> > <lawgon@...> wrote:
> > | But I found that I just could not acquire any satellites
> > | within the IIT campus.
> > I doubt if IIT-M has GPS jammers.
> >
>
> could be some experiment that is interfering with the signals.
>

Certainly odd  news. The GPS C/A receive signal is at 1575 MHz,
which can face interference from certain kinds of microwave ovens
and microwave devices. But my simple guess is that the tree cover
at IITM is causing too much attenuation of the signal from the
satellites at low elevations from the horizon. I've seen this behaviour
before from Garmin units - they need a clear line-of-sight to
the satellites for optimal performance.

-Siva
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Kenneth Gonsalves | 11 May 16:22

Re: digital freedom in iitm?


On 11-May-08, at 7:29 PM, Sivasankar Chander wrote:

>> could be some experiment that is interfering with the signals.
>>
>
> Certainly odd  news. The GPS C/A receive signal is at 1575 MHz,
> which can face interference from certain kinds of microwave ovens
> and microwave devices. But my simple guess is that the tree cover
> at IITM is causing too much attenuation of the signal from the
> satellites at low elevations from the horizon. I've seen this  
> behaviour
> before from Garmin units - they need a clear line-of-sight to
> the satellites for optimal performance.

MIT has a much heavier tree cover than IIT - but I dont have this  
problem there. And I moved into an open space and tried for around 15  
minutes. Solution is simple, can someone else try?

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kg
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http://nrcfosshelpline.in/code/

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Girish Venkatachalam | 12 May 01:53

Re: digital freedom in iitm?

On 19:29:08 May 11, Sivasankar Chander wrote:

> Certainly odd  news. The GPS C/A receive signal is at 1575 MHz,
> which can face interference from certain kinds of microwave ovens
> and microwave devices. But my simple guess is that the tree cover
> at IITM is causing too much attenuation of the signal from the
> satellites at low elevations from the horizon. I've seen this behaviour
> before from Garmin units - they need a clear line-of-sight to
> the satellites for optimal performance.

The frequency sounds too low and that would cause all sorts of
propagation problems.

I believe there are various factors at play here.

Firstly as Sivachander suggested vegetation is a big problem. And for
certain frequencies, the moisture/rain/weather etc.

Secondly GPS satellites are not geostationary (Am I wrong?). So their
orbits may not be favorable at certain times.

IOW testing it during a hot summer day and collecting multiple samples
might help.

-Girish
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Shakthi Kannan | 12 May 06:24

Re: digital freedom in iitm?

Hi,

--- On Mon, May 12, 2008 at 5:23 AM, Girish Venkatachalam
<girishvenkatachalam@...> wrote:
| Secondly GPS satellites are not geostationary (Am I wrong?).
\--

Yes. At an altitude of 20,000 km compared to 36,000 km for a
geostationary satellite. So, you need inputs from a series of
satellites to determine the receiver position.

http://en.wikipedia.org/wiki/Satellite_constellation

SK

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Venkatraman S | 11 May 16:20

Re: digital freedom in iitm?

On Sun, May 11, 2008 at 7:11 AM, Kenneth Gonsalves <lawgon@...>
wrote:

>
>
> from MIT, Chromepet to IIt gate I had perfect signal. On the flyover
> opposite IIT gate, I lost the signal, but got it back at Madhya Kailash.
> Again lost the signal on entering the campus. Both before the meeting and
> after it, I walked around outside and tried to acquire. For about 15-30
> seconds I was able to acquire 3 satellites. After that nothing. Again from
> tenet building to the exit gate, no signal. When I left IIT and reached Raj
> Bhavan I got the signal back and was getting 5-6 satellites all the way back
> to Chromepet.
>

Why do you need a GPS to go from Chrompet to IIT? :P

--

-- 
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Kenneth Gonsalves | 11 May 16:38

Re: digital freedom in iitm?


On 11-May-08, at 7:50 PM, Venkatraman S wrote:

>> from MIT, Chromepet to IIt gate I had perfect signal. On the flyover
>> opposite IIT gate, I lost the signal, but got it back at Madhya  
>> Kailash.
>> Again lost the signal on entering the campus. Both before the  
>> meeting and
>> after it, I walked around outside and tried to acquire. For about  
>> 15-30
>> seconds I was able to acquire 3 satellites. After that nothing.  
>> Again from
>> tenet building to the exit gate, no signal. When I left IIT and  
>> reached Raj
>> Bhavan I got the signal back and was getting 5-6 satellites all  
>> the way back
>> to Chromepet.
>>
>
> Why do you need a GPS to go from Chrompet to IIT? :P

http://openstreetmap.org

--

-- 

regards
kg
http://lawgon.livejournal.com
http://nrcfosshelpline.in/code/
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