[no subject]

[Leif Åsbrink <leif.asbrink@xxxxxxxxxxxxxxxxxxxx]

Hi All,

I found this question from OE8FNK:
> Q2: Anybody knows how to modify the IC-202s VXO for better 
> phase noise?

There are two problems. There are some comments in QEX Jan/Feb 2003
page 44. There is a pdf on the Linrad home page.

The relevant text is:
--------------------------------------------------------------
At 144MHz, even an IC202-- the purest commercial transmitter 
I know of-- is not good enough. It is possible to lower the 
noise floor of an IC202 by about 10dB: First, replace the 470 
ohm emitter resistor of the LO with a 150 ohm resistor in 
series with an RF choke. Then decouple the base of the first 
frequency multiplier stage for low frequencies by installing 
a 1 ?F capacitor in series with an RF choke.

Modified like this, it is just about good enough to be used 
as the LO in a direct-conversion 144-MHz receiver, but only 
if a low-level Schottky-diode mixer were used. A high-level 
mixer needs about 15 dB more LO power and would therefore give 
much higher susceptibility to LO sideband noise.
--------------------------------------------------------------

If you want to use the 144 MHz signal for a direct conversion radio
you should also reduce the gain at 144 and increase the level
on the low frequency side of the crystal filter. I do not remember
the details. Performance is at:
http://antennspecialisten.se/~sm5bsz/dynrange/rig_compare.htm

73

Leif / SM5BSZ





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