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RE: [linrad] 10.7 MHz mixer question...
- To: Linrad
- Subject: RE: [linrad] 10.7 MHz mixer question...
- From: "Leif ┼sbrink" <SMTP:LEIF.ASBRINK@xxxxxxxxxxxxxxxxxx>
- Date: Sun, 09 Mar 2003 12:50:42 +0000
Hi Oleg and All,
> I have a little question regarding 10.7 MHz mixer (that is built
> on three 74HC4053).
> What do the capacitors (C101,C102 470pF from the mixer
> arms to ground) do ?
These capacitors improve IP3. They also reduce higher order
spurious responses of the mixer.
The transformer (TR13) is an inductance at high frequencies
and when the switch opens the current that was going through
it has to continue. If there is no load, the voltage will
rise to force current into the 4053, something which will
lead to a voltage transcient at the 4053. This large
voltage will cause nonlinearity and ultimately clipping in
the 4053. The rather big capacitors will absorb the current
without much variation of the voltage.
Leif / SM5BSZ