Well this is a good idea, use two simple quad diode mixers. I wrote before in thse columns that I tried this in the sixties of the former century with Germanium diode quads but these diodes were not fast enough then, nor were the Si ones. I selected them on equal voltage on conducting because that determined the carrier suppression. The 90 degrees phase shift is on VHF much easier obtainable then on HF. Just take a quarter wave coaxial cable. Take into account the velocity factor, so about 1ft+. And with the now available thin coaxial cable it will be much smaller then with RG58 or59 of those days. We used a griddipper to determine the quarter wave. For transmission we also needed a 90 degrees shift between the 2 audio signals. That was very difficult and was realised with a complex RC filter with many poles and zeroes of non standard values. If I had enough time I would give it a try.
--- In [email protected], "Alan Melia" <[EMAIL PROTECTED]> wrote: > > I have watched the comments about 2m operation and wonder if there are some > other possible solutions? The multiplexer/ switching mixer chip is not fast > enough for 144Mhz mixing but diode ring mixers are readily available at that > frequency. So then to generating the quadrature LO at 144Mhz....its a bit > fast for easy logic....but if you used the standard quad circuit used at hf > and mixed I and Q up in phase you would generate a 144MHz quadrature LO > signal. The problem is obviously the extra mixing stage and birdies but > these should be easy to avail and the second mixer could be used to sweep > the signal over a wider portion of the band (DDS??) the alternativeis to mix > down and then do the quadrature bit, which might be a lower parts count. I > have no idea which would work out best though.....any ideas if a "direct > conversion" 2m RX would be worth doing like that?? I suspect the "IF" vesion > with some IF gain would be perhaps better. > > Alan G3NYK >
