PSN-L Email List Message

Subject: Re: Help with telemetry equipment
From: "James Hannon" jmhannon@.........
Date: Tue, 11 Jul 2006 08:05:36 -0500


Each radio signal can transmit up to 8 channels of data. Each channel is assigned a center frequency per the chart below. To send data a tone either 125 Hz above the center frequency or 125 Hz below the center frequency is transmitted. A logic one or zero is signified by the tone being above or below the center frequency. Don't know which. I also have yet to find the bit rate or the exact format of the data being sent. I remember having it all figured out some years ago but can't remember. It seems from Larry's information the data is sampled to 12 bits. 


	Channel         Center freq
	   1		    680 Hz 
	   2		   1020 Hz
	   3		   1360 Hz
	   4		   1700 Hz
	   5		   2040 Hz
	   6		   2380 Hz
	   7		   2720 Hz
	   8		   3060 Hz

In looking for information I found this site that offers software to do the decoding with a sound card, not free but:
http://www.geotool.com/geoseis.htm

Jim Hannon

---------- Original Message ----------------------------------
From: Ian Smith 
Reply-To: psn-l@..............
Date:  Tue, 11 Jul 2006 13:44:17 +0100

>Hi,
>
>labview has some great demodulation software built into it as well as 
>software to interface with sound cards.  That's what I was thinking of 
>when I wondered how the signal was encoded.  Still wondering...
>
>Cheers
>
>Ian
>
>James Hannon wrote:
>
>>I would expect that a sound card would be stable enough to decode the telemetry signals. All the cards I have seen use a crystal for the reference frequency. As long as the temperature of the card doesn't vary over a wide range you will be ok. The real question is: Is there software avaliable to do the demodulation?
>>
>>As far as the radio stability is concerned: The signals are transmitted as FM so a slight mistuning of the radio will not affect the frequency of the tones. 
>>
>>Jim Hannon
>>
>>---------- Original Message ----------------------------------
>>From: ian 
>>Reply-To: psn-l@..............
>>Date:  Tue, 11 Jul 2006 06:02:30 +0100
>>
>>  
>>
>>>Hi,
>>>
>>>thanks for the link.  I wasn't able to deduce from that page how the 
>>>encoding/decoding works (call me dumb!).  Is there any other web page  
>>>that would explain it?
>>>
>>>I note your comment about stability.  Will your average radio have 
>>>similar stability or does the encoding method mean that that isn't an issue?
>>>
>>>Thanks
>>>
>>>Ian
>>>
>>>ChrisAtUpw@....... wrote:
>>>
>>>    
>>>
>>>>In a message dated 10/07/06, ian@........... writes:
>>>>
>>>>      
>>>>
>>>>>out of interest, what's the spec of how the data is encoded?  I'm 
>>>>>wondering if a sound card can decode it.
>>>>>        
>>>>>
>>>>
>>>>Hi Ian,
>>>>
>>>>       It is sent as a narrow band sine wave tone. The channel 
>>>>separation is only 340 Hz. For the center frequencies see 
>>>>http://psn.quake.net/onlinedocs/demoddoc.html
>>>>Hence the need for a precision encoder like the XR2206.
>>>>       Does a sound card to have a stability in the low ppm range? 
>>>>
>>>>       Regards,
>>>>
>>>>       Chris Chapman
>>>>      
>>>>
>>>
>>>
>>>    
>>>
>>
>>--
>>Jim Hannon
>>http://www.fmtcs.com/web/jmhannon/
>>42,11.90N,91,39.26W
>>WB0TXL
>>--
>>__________________________________________________________
>>
>>Public Seismic Network Mailing List (PSN-L)
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>>To leave this list email PSN-L-REQUEST@.............. with 
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>>
>>  
>>
>
>-- 
>
>
>
>

--
Jim Hannon
http://www.fmtcs.com/web/jmhannon/
42,11.90N,91,39.26W
WB0TXL
--
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Public Seismic Network Mailing List (PSN-L)


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