From: "Rob Kimberley" <[EMAIL PROTECTED]> Subject: Re: [time-nuts] manual request: Austron 2201A Date: Thu, 19 Jul 2007 21:40:32 +0100 Message-ID: <!&!AAAAAAAAAAAYAAAAAAAAAOYAZyOzV8ERq+LmT45ypI7CgAAAEAAAAHNkDDJzE/[EMAIL PROTECTED]>
Hi Rob, > I agree. When I looked at the Quantic numbers you gave me, I sort of hit a > mental block - not logical to me. > > Meinberg's current GPS antenna has following characteristics > > 10 MHz LO > 35.4 MHz IF > 12V - 18VDC Power > > http://www.meinberg.de/download/docs/manuals/english/gpsant.pdf > > For more info. Lower cable damping at lower frequencies allows for longer cable runs. Very handy when considering putting GPS receivers into underground telecom bunkers. Fiber link is also a very good thing in those cases. Both is a must if you want to play in that leage, and Meinberg wants that. Now, If you look at the Zarlink GP2015 GPS Frontend chip you will find how well it fits with this scheme. You apply 10 MHz to the chip, it PLL locks a 1,4 GHz VCO and mixes down with that (1575,42 - 1400 = 175,42 MHz), then it goes for a filtering round and then comes back for the second mixer at a tenth of the VCO frequency, i.e. 140 MHz (175,52 - 140 = 35,42 MHz) again goes out for a filtering-round (through a SAW filter) and back in for a mixdown with 31,11 MHz (actually 280 / 9 MHz) producing a 4,309 MHz signal which is then sampled at 5,714 MHz (actually 40 / 7 MHz) producing 1,405 MHz carrier frequency in the 5,714 Msamples/s 2-bit datastream. The Meinberg trick can be done by simply put one frontend chip in the antenna and another in the receiver. Both is fed the same 10 MHz clock but you pick up the signal after the 2nd mixdown stage and transport that IF over the cable and then toss in it at that place in the receivers frontend. The AGC there will automatically compensate for cable damping which happends around the 3rd mixdown. The HF part of the frontend in the receiver it just kept as dead functionality. Same goes for the 3rd stage in the antenna. Fairly clean and simple. Cheers, Magnus _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
