[GPS_Standard] Question abt. LTC1485

[Bert, VE2ZAZ]

Hi Helmut,

The LTC1485 is used as a front end in this circuit to interface with various
type of OCXO's. It will work with input swings as low as 100mV (single
ended). The common mode rage of up to up to +12V includes a +2V offset of
your signal. So I do not see why your TTL signal would not trigger the
receiver in this chip. Did you install a resistor in R1? For a TTL signal,
you should not. Did you actually measure your swing at pin 6, while your
input signal is connected?

Indeed, if you use a 10MHz TTL signal to drive the board, you may want to
try to skip the LTC1485 stage...

Regards,

Bert, VE2ZAZ

----- Original Message -----
From: "Helmut Bayerlein" <helmut.bayerlein at fen-net.de>
To: <gps_standard at mailman.qth.net>
Sent: Sunday, January 21, 2007 10:28 AM
Subject: [GPS_Standard] Question abt. LTC1485


Hello @all!

Now I've ready built my GPS standard. But I have problems with the input
circuit LTC1485. At pin 6 (A) is a digital signal of abt 4V, but no output
signal at RO. When looking into the data sheet, I found the description of
RO
pin (output): if A>B by 200mV, RO will be high. If A<B by 200mV, RO will be
low.
Because B is at ground and A is TTL level, RO will never change its level.
Is
this correct? Is this LTC1485 really necessary?

Thanks for Your help!

73 de Helmut, dc3yc
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