> -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of [EMAIL PROTECTED] > Sent: Monday, September 22, 2008 10:52 AM > To: [EMAIL PROTECTED]; time-nuts@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. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.