JR: Your use of the quad mixer with 455 kHz is no doubt something I as well as others hope you get a chance to document. I feel that such a circuit will be very popular. I will go look up the SA612/602 mixers you are planing on using in the Ten-Tec RX320D. Ten Tec makes some good things.
(SA602 = NTE Device Number: NTE7164 IC-Linear, Double-Balanced Mixer & OSC this is what I pulled up out of my NTE software: this idea of a balanced mixer / oscillator on a chip interest me.) You seem to like the idea of these things as marketable future products and perhaps the largest selling group could be the shortwave listeners. I also feel that a simple receiver that can give general coverage will be a good seller also. A good and stable vfo design in that case is the thing to look into. I am looing into both ideas and I hope to compile all I learn into a text for not just myself but everyone interested. I have the time to explore the circuits and draw them up. And I will not charge for the text since people such as you and others are giving me ideas for it. If you have figured out pretty much the way to match things to most 455 Khz ceramic filters then good. I will look at the 602 version from NTE and see whats up there. Or in a board design let say.. Perhaps a high impedance preamp and a potentiometer will make the device more easily matched to most radios if it is viewed as a rf voltage and sampling probe rather than a perfect rf match. So long as the input impedance of the quad detector board is way higher than the tap point in the recever circuit it should then work with every 455 kHz radio. The potentiometer is merely a load which is very high (50 to 100 kohms) and in parallel to a lower impedance in the receiver i.f. chain. The potentiometer merely doesn't seem to be there load wise to the receiver; but the preamp obtains a signal according to the level the pot is set at. A short length of cable can go from the tap point to the quad board of perhaps 1 to 2 feet at most if the board is in a box outside of the receiver. And maybe a 500 to 1000 ohm resistor is between the tap point and cable to offset and isolate the cable from loading the tap point. I think you could figure out what I mean and maybe use it sometime, but a preamp seems called for in this sort of an idea as an rf voltage sampling amplifier. I will draw up a diagram here soon of what I mean. After having looked at the phase shift coil that Rick Campbell used, it appears to me that if the same coil was used to split off a 455 kHz signal with a mixer and crystal offset about 98 kHz from 455 kHz perhaps an even simpler circuit can be made for 455 kHz. I will have to draw up a circuit diagram to better explain it but the logic of it came to me yesterday and so I will explore it. Folk could look at it and then decide if it seems like something to try. (Maybe a very simple device; if I continue to look at it.) I will try to keep and sort through my notes and once I have the story down fairly well I will write it all up in a text with diagrams. Wolfgang is explaining to me the importance of phase noise being reduced especially in the case of using DRM software. He is telling me that the reduction methods in the circuits will not come cheaply. I will have to review the handbooks and text to re-read up on oscillator phase noise and jitter. I have math and formulas from the manufacturers of single package type block oscillators that define the paramaters of jitter and noise. I understand oscillator design and how to calculate the capaciitive load of the oscillator circuit on the crystal so I am good there. I should also include in my notes the ideas of crystal and vfo circuit designs so the load is understood. I think I am now getting the picture of the whole idea of whats required depending on the type of SDR software and so the receivers and i.f. boards should be compatible as much as possible with all SDR software and even DRM. I do have some digital circuits that I have found but I am looking at the basic ideas first of all using as much analog ideas as I can to begin with; in the rf sections of the SDR receiver scheme. Rick Campbell's little circuit showed me an analog way to do this, and that surprised me in that it was defining pure radio and audio signals as we know them to be without mysterious TTL type clock or divider circuits to have to study up on. Dan _____________________________________________________________________ Call Anyone, Anytime, Anywhere in the World - FREE! Free Internet calling from NetZero Voice Visit http://www.netzerovoice.com today! Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/soft_radio/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
