# VCXO measurements

Harald Welte laforge at gnumonks.org
Sun May 9 20:12:49 UTC 2010

```As Christian has just pointed out, 0.228Hz/LSB is a better approximation,
and I've re-computed as follows:

So this means the voltage control slope is 500/2750 = 0.228 Hz / LSB
Converting this into ppb: 0.228 /.026 = 8.769 ppb / LSB

Based on this, the ideal value for AFC_SLOPE according to the measurements
should be 229.   I haven't tested that, this is just my thinking:
0.008769 * 32768 = 287

Also, to give you some idea what this means in terms of
"Hz carrier frequency / LSB":

Center of GSM 900 between UL and DL: (960+880)/2 =  920 MHz
overall multiplication factor for mid-band GSM900: 35.38
resulting theoretical slope: 8.07 Hz / LSB

Center of GSM 1800 between UL and DL: (1710+1880)/2 =  1795 MHz
overall multiplication factor for mid-band GSM900: 69.04
resulting theoretical slope: 15.74 Hz / LSB

--
- Harald Welte <laforge at gnumonks.org>           http://laforge.gnumonks.org/
============================================================================
"Privacy in residential applications is a desirable marketing option."
(ETSI EN 300 175-7 Ch. A6)

```