[time-nuts] signal from DirecTV

[Lux, James P]

> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of SAIDJACK at aol.com
> Sent: Monday, September 22, 2008 10:52 AM
> To: novick at nist.gov; time-nuts at febo.com
> Subject: Re: [time-nuts] signal from DirecTV
>
> 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
>

There are two flavors of LNBs, those that are locked to a reference and those that aren't. The locked ones are used for narrow band signals (e.g. SCPC, for instance)
For typical Ku band DBS, the RF frequency is in the 11-13 GHz range, with the LO being above or below that (whether the mfr want's high or low side injection).

For instance, Norsat makes a whole lot of LNBs that are PLL locked, A typical Ku LNB (1000H) has typical LO stability of 5-25 kHz (over temp). Phase noise is -75dBc/Hz @ 1 kHz, dropping 10dB/decade.  They use low side injection, so the LO is at 10-11 GHz.

Here's one with an external reference connection:
http://www.invacom.com/documents/PLLLNB.pdf which appears to take a 10 MHz input.


Note well you'll see folks talking about DRO LNBs and PLL LNBs.  In reality, they both probably use a DRO as the oscillator, but in the PLL ones, it's locked to the external reference.

Unlocked DROs are probably good to a couple MHz over temperature, and the typical DBS receiver can accommodate that much uncertainty in tuning (i.e. the signal is 25+ MHz wide, anyway)

I would imagine that one could calibrate an unlocked DRO in real time.  You could inject a 100 MHz comb or something from a quiet oscillator and then look for it in the output of the LNB.

Typical PLL LNBs run about $200-400, new. Regular old unlocked ones are in the $20-30 range.