Lash up Direct Conversion Receiver

[pwdrive]

I must admit Lawrence I am a bit nuts, but would never have thought to attempt this!

cheers Mark

Hi Mark, it's nothing complicated, it is basically a mixer as you would find in any valve/transistor superhet followed by a broadly tunable IF (there is no IF amp as such) in the form of a regenerative detector which tunes a much narrower band of frequencies than the traditional regen receiver would tune, this makes the designing and building the regen detector which is always the critical bit a lot easier and you can then end up with a constant tuning rate and good regen frequency stability irespective of the band selected to tune.
If using an unganged oscillator you also have the option of the usual Flo = Fs + IF or the less popular Flo = Fs - IF (down to a limiting frequency) which can sometimes be a help on strong unwanted images, choose the IF to suit, at present the test receiver is running on an IF center frequency of 2.25 Mhz, the regen detector tunes plus or minus 250 Khz either side of the center frequency ie: 2 to 2.5 Mhz, this means that you can tune the whole of the SW spectrum in nice easy to manage 500 Khz chunks with a stable regen det. the tuning rate and stability of the regen detector remain unchanged which ever frequency range you want to tune.
Ie: to tune the 40 meter amature band (7 - 7.5 Mhz) the Osc can be set to 9.5 Mhz or to 5 Mhz the regen detector tunes from 2 to 2.5 Mhz therefore the difference frequencies are 7 to 7.5 Mhz which is what we want to listen to.
Try it sometime, valves or FET/Transistor, makes no difference. You can get good results without an RF amp if you want a simple job.

Lawrence.