[time-nuts] signal from DirecTV

[SAIDJACK at aol.com]

Hello Andrew,
 
unfortunately I am not sure what you mean by Sat signal/code  frequency.
 
The local STB PLL generated 27MHz on the video signal will be derived from,  
and locked to the PCR time stamp inside the MPEG stream of the  broadcaster.
 
The broadcaster will likely use an in-house frequency standard to generate  
this, but it is entirely up to them what they are using. My comment was that  
this signal was not very stable from what I have seen.
 
If you are interested in the RF frequency of the Sat signal, things get  very 
complicated because the Sat signal is mixed with an LO at the LNB, and so  
not knowing the LO offset error inside the LNB you would have to hack into  the 
LNB to get the RF frequency of the Sat. This is not as simple as using a  
27MHz bandpass: even the IF is in the 800MHz to 2GHz range, and the RF is  
somewhere above 30GHz I think.
 
bye,
Said
 
 
In a message dated 9/22/2008 09:50:01 Pacific Daylight Time,  novick at nist.gov 
writes:

Said,

If I measure the output of the STB, am I not just  measuring the PLL in the 
box?

You mentioned in your original post that  the outputs of different STBs 
behave differently.  If I'm looking for the  frequency offset and stability of the 
satellite signal/code frequency, then it  seems like I need to tap off of the 
signal at the antenna input.  Maybe  with a 27 MHz bandpass to get rid of the 
modulation information?

Thanks  for any thoughts on this.

Andrew 



At 02:30 PM 9/19/2008,  you wrote:

Hello  Andrew,

you can find the NXP chips on most any TV capture card  for PC's. Philips 
also used to make and sell large eval boards, but they are  only available for 
customers as far as I know.

You may be in  luck to find an embedded capture card on mouser etc. that uses 
one of the  NXP chips.

Some set-top boxes (such as Directv's older units  with CVBS inputs) also may 
have them built-in.

Lastly many of  the DVD-based video recorders will have them, especially if 
these are from  Philips/Magnavox.

Alternatively, you can probably wire it up  fairly quickly (since you are 
only interested in the LLC signal (27MHz clock  output), but I think you would 
have to have a micro initialize the chip via  I2C.

Good luck,
bye,
Said

In a message dated  9/19/2008 11:35:09 Pacific Daylight Time, novick at nist.gov 
writes:

Hello!

I haven't had a lot of time to look into this...is there a kit board  for 

any of the SAA chips?

Did you layout a circuit?


Thanks for any help!


Andrew Novick

NIST

novick at nist.gov

303-497-3378



>Message: 2

>Date: Sat, 10 May 2008 17:51:53 EDT

>From: SAIDJACK at aol.com

>Subject: Re: [time-nuts] Pulling a signal from DirecTV

>To: time-nuts at febo.com

>Message-ID: <d2b.2580607a.355772f9 at aol.com>

>Content-Type: text/plain; charset="US-ASCII"

>

>Yes, the frequency accuracy is not very good.

>

>We generated 27MHz out of the CVBS coming from a Philips Directv  STB.

>

>To do this, just hook up an NXP video decoder to the CVBS/YC  signal (such  
as

>SAA7111, SAA7114 etc) and that will give you a line-locked  27MHz.

>

>

>Significant medium term drift, measurable on 1/10Hz if I  remember  
correctly.

>Jumps every so often ( a couple of times per hour) to re-sync.

>

>Depends also on the algorithms and PLL inside the STB,  different  vendor's

>units all behave differently from what I could see.

>

>bye,

>Said

>

>

>In a message dated 5/9/2008 08:42:08 Pacific Daylight Time,  novick at nist.gov

>writes:

>

>Does  anyone have experience getting a measurable frequency  (in phase with

>the  broadcast FQ) from a consumer DirecTV box?

>






 
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