On Tue, Feb 21, 2012 at 10:33 AM, Ken Alexander <k.alexan...@rogers.com>wrote:
> Hi All, > > I'm not sure what kind of parameters you'd like to be able to adjust > Brian. > I don't think there are any besides frequency (tuning) and possibly preamp gain. > I think that if you put a good filter at the antenna jack and get rid of > the AM broadcasters then your Flex can easily do the rest. > The Flex has its own filters that get in the way. If you bypass the front-end filters and feed the signal directly to the QSD you need to provide the functionality of the front end filtering externally. Oh, and you need a way to command the radio to bypass the built-in front-end filters. > > I have already built a lowpass filter that cleans the longwave band of any > AM broadcast interference. A bandpass filter is more difficult to do; it's > not as forgiving of variations in component values so trimmer capacitors > would have to be added to get it set up correctly, which makes it more > expensive to build. > > It seems to me one only benefits from a bandpass filter if one lives in > parts of the world where Loran-C is still operating, or where the longwave > broadcast band is still active, i.e., not North America. Otherwise, the > lowpass filter lets you hear EVERYTHING below 500 kHz. > > Anyway, I'm building a few lowpass filters as soon as I get the rest of > the components I need; one for me and one for a list member I've been > corresponding with who is going to give me some feedback. I'll be glad to > make more if they work out well. The bandpass filter too, but that'll take > a little longer. > Sometimes old technology suffices. Think "tunable RF" receivers that predated superhets. Lastly, since I have no real interest in operating in the 600m band, most of this discussion is moot for me. I was just thinking that it might be easy to spider-web wind a coil and use a two-gang 365pF variable to tune it and use that as your preselector with suitable loose coupling so as not to kill the Q of the resulting LC circuit. (One can get amazing Q out of a spider-web wound coil of Litz wire tuned with an air-variable.) And if you need more Q, make a second, identical stage. Heck, you can use mutual coupling between the two coils for coupling the stages. Makes me think of the old "wave couplers" used back in the spark days with early crystal detectors. What's old is new again. :-) -- Brian Lloyd, WB6RQN/J79BPL 3191 Western Dr. Cameron Park, CA 95682 br...@lloyd.com +1.767.617.1365 (Dominica) +1.916.877.5067 (USA) _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flexradio.com/ Homepage: http://www.flexradio.com/
