RadioBanter - View Single Post

March 2nd 06, 02:20 PM posted to rec.radio.amateur.homebrew

wrote:

hello,

I'm building my first reciver. I can't choose what kind of mixers
should I use. I have read that diode ring mixers are far superior
compared to dual gate mosfet mixers.

Is this true for both - first (RF / VFO) and second (IF / BFO) stages?
Or is there any real difference at all?

thanks

Hi

If you think the situation in short waves today:
Russian and their previous satellite country jammers are quiet
Local broadcast is nearly completely in FM
Propaganda is no more effective to transmit in short waves
Commercial data is practically in Internet. and in satellites
Marine communication is in satellites.

All this means less cross modulation products in first mixer than some
sixteen years ago
Atmospheric noise in sw is much higher than the noise of modern front
and mixer stage
Advantage of diode mixer is marginal
IGFET mixer is simple and advanced solution for DIY project.
IGFET mixer doesn't need any front amplifier stage.
A selective band filter in front of mixer is superior to broadband
transformers
I am using loosely coupled 3 stage band filter tuned by variable triplet
air capacitor
3 coils for low end of sw and 3 coils for upper end of sw.
Coils are DC selected by small reed relays
KISS

If you are constructing premixer then I recommend DBM to keep birdies
in low levell
For IF/BFO my recommendation is also DBM or "semi DBM"
For both of those DBM solutions I recommend you to Google a nice
advanced component MC1496.
In some Motorola handbooks and ARRL handbooks are examples for MC1496 as
DBM, product detector and balanced modulator.
It is mostly used in single ended circuits in RF meaning and balanced
for DC

73, Risto OH2BT