[time-nuts] manual request: Austron 2201A

Magnus Danielson magnus at rubidium.dyndns.org
Thu Jul 19 19:12:16 EDT 2007

From: "Rob Kimberley" <rk at timing-consultants.com>
Subject: Re: [time-nuts] manual request: Austron 2201A
Date: Thu, 19 Jul 2007 21:40:32 +0100
Message-ID: <!&!AAAAAAAAAAAYAAAAAAAAAOYAZyOzV8ERq+LmT45ypI7CgAAAEAAAAHNkDDJzE/pPgmlezQHl6CkBAAAAAA==@timing-consultants.com>

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.


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