--- In [email protected], "Daniel Jackson" <[EMAIL PROTECTED]> wrote: > > "Have you already considered 7360's or 6AR8's as demodulators?" > > Well I have looked at the 12AU7 and wondered if it would go up high in > HF. But two Pentagrid convertors seem most likely. > > I will will get my RCA Tube handbook and llo at the 7360's and 6AR8's. >
Actually, I HAVE thought about 6AR8's in a hybrid I/Q receiver. Just for the heck of it. By hybrid, I mean using a "modern" DDS to generate the necessary LO signals, and using tubes for the rest of the circuitry. Or most of the rest, anyway, depending on what a final design might look like. Somebody will complain that this doesn't achieve some number or other (usually IP3) that could be achieved with <fill-in-the-blank>. So what? For anything that includes the human ear and brain as part of the system (such as a strictly CW/SSB receiver) "numbers" alone don't tell the whole story since, to the audio processing centers of the brain, all distortion products are not created equal and some are actually preferable. I guess that wouldn't be strictly a "Software Defined Radio" though. More of a "Wetware Defined Radio." :-) :-) :-) For something headed for a DSP, however, tubes MIGHT not be the best choice. NOTE: 7360's were developed for military applications while 6AR8's were intended for consumer applications. Both feature two plates and beam-controls that allow switching the electron flow (once it has passed through the grid and the screen) to be switched between the plates based on an external signal. Usual mixer operation is to feed the RF signal to the grid and the LO signal through a transformer to the beam-control electrodes and take the output from the two plates via another transformer. The tube is thus working as a switching-mode mixer rather like many "modern" topologies. BTW 7360 data is in the Transmitting Tube Handbook while 6AR8 data is in the more-familiar Receiving Tube Handbook. Note that 7360's are a lot more scarce and expensive than 6AR8's. 73 de K8QN
