Radio Intermediate Frequencies

the IF

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: I believe a Direct Conversion design, which eliminates the need for an IF, : makes separating the modulation from the RF signal quite simple. Direct : Conversion uses demodulation rather than envelope detection, so the signal : is baseband audio straight out of the mixer. A simple low pass filter (RC) : will prevent RF from affecting the following audio stage(s). If one wishes, : wideband and narrowband audio filters can be switched in/out for "music" and : CW.

Don,

While direct conversion has the advantages that you mention, it also has some serious disadvantages. One of the biggest disadvantages is that Direct Conversion Receivers suffer from large DC offsets caused by self-mixing of the LO (i.e. LO couples into RF signal.) Most of the solutions to this problem are not very elegant -- they involve calibration/trimming/etc. It's also difficult to prevent the coupling of the LO into the input signal, because of the way the mixers, themselves are typically designed (I've only worked with CMOS mixers -- this may not apply as much to Bipolar designs.)

Joe

The problem you describe is certainly possible with a poor design, such as using a single diode mixer and not using an isolation stage between the signal input and the mixer. But these are avoidable.

More importantly, the OP asked about methods (I assumed modern ones) that do not use an IF. Direct Conversion can easily provide good results, just as a superhet can provide good results *if properly designed*.

Don

they do a MES with a built-in lens, it could give a semi-realistic headlight beam.

aaa size batteries are about the smallest worth connecting to an incandescent lamp.

if you were to use white leds (which are smaller) and a more complex setup like the "joule thief" LED driver which uses less energy, you could use button cells, (like used in watches and hearing aids) to power it...

you could use button cells with the torch bulbs but it'd use them up quite fast and they are more expensive.

there's also SMES bulbs which are about half the size of MES. and even smaller ones too...

I am glad I checked back on my post T H A N K S. I also recently downloaded still another simulation package, although not as easy to use as CircuitMaker yet it's seem Ok,

Anybody using B2 SPICE v5?