re single chip receiver for fsk john ackermann x jra law daytonoh ncr com wrote my next project is to come up with an if detector module for fast to kb sec packet radio use no fancy modulation scheme just wide fsk for use at or mhz i m a bit familiar with the motorola chip but i wonder if there are newer designs that might work at higher input frequencies my goal is to come up with an inexpensive design for a receiver back end with if input on one end and an fsk demondulator on the other i m particularly interested in ways to use a higher if than do any current chips work up to say mhz with internal downconversion so a normal if filter can be used any suggestions john what you describe is very close to what i built and described in the th arrl computer network conference proceedings i built watt fsk transceivers at mhz they are essentially double conversion transverters with digital mod and demod at mhz the receiver uses the mc which is the same fsk receiver chip i used previouslyu in the mbps ghz data link i first published in ham radio and which is now also in the arrl handbook the mc which includes a vhf converter section could also be used at these speeds there is a newer and perhaps slightly improved design of this the mc if i remember rightly while using this would have let me reduce the external if count on receive it didn t really offer all that much help on transmit so i didn t bother with it the radios i built were first designed and built for kbps in a mhz channel but later reduced to half that these kbps radios actually have done quite well in across the bench tests at kbps and speed is pretty much a function of filter design handling the data stream is another matter entirely some of the existing radios are currently deployed on hilltops in a beacon test mode while there is not yet end end two way data flow due to lack of resources to debug software for the digital hardware mio also shown in the cnc proceedings data is perfect copy at n gn even though the data clock is currently at about half speed the a kbytes of the test text chapter of isaiah takes only a little over of a second i ve been hoping that someone would get interested enough to step in and get involved in writing code to make the whole thing usable borland ide environment with remote debugging possible as mentioned in the proceedings but to date a couple of us have been on our own and running low on resources of time money and energy if anyone in the sf bay area wants to check it out there is also a cw id after the text on the mark side at mhz from beacons on sonoma mtn and black mtn overlooking si valley the antenna is horizontally polarized i guess in retrospect my suggestions are that this is a fairly costly approach if the radios are intended for users rather than backbones and you might want to carefully consider your target if you can t arrange your paths such that you have complete line of sight i think you ll want to address the inter symbol interference caused by multipath and probably link c n budgets if paths are very far from los for more details see the th cnc i m currently working on a spread spectrum direct conversion design to address some of these problems i d be glad to help as i can with any design problems glenn elmore n gn n gn k mc amateur ip glenn santarosa ampr org internet glenne sr hp com
