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could VFO frequency be below IF ?

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July 20th 06, 03:45 AM posted to rec.radio.amateur.homebrew

tim gorman tim gorman is offline

tim gorman is offline

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First recorded activity by RadioBanter: Jul 2006

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could VFO frequency be below IF ?

wrote:

hi,

I'm experimenting with my superhet. My IF is 8mhz (cause I have 8 mhz
crystals for IF filter). I first experimented on 40m. VFO was 15mhz. At
design time I'm using 3 meters long wire as an "antenna" (and I'm
sitting in my basement). I heard different european stations (EA5FKX,
RW6XE, UR4GI etc) which are several thousand km-s away. Pretty amazing
for such "antenna"!

So I decided to go for 20m band. I had an option to set my VFO either
to 6mhz or 22mhz. I first went with 6mhz. But for my disappointment I
heard nothing but the band noise.

So I'm confused now - is it because the short "antenna" or am I wrong
thinking that VFO 6mhz + IF 8mhz should give me 14mhz?

any ideas?

The frequency schemes should work fine. Be sure you don't have a high pass
filter somewhere between your vfo and your mixer. I don't know what kind of
mixer you are using but if it is an active mixer then there could easily be
some kind of filter involved. That's why I like diode ring mixers with
resistive pads between the vfo and the mixer - it gives you a good
termination for both the mixer and the vfo and there isn't nearly as much
to worry about.

tim ab0wr

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