Date: Fri, 7 Mar 1997 18:03:52 GMT From: rdkeys To: Multiple recipients of list Subject: Greetings fellow regenerator lover. > Corne, > I'm forwarding your message across town to Bob and > will let him answer you himself. Thanks for writing and I > hope you enjoyed Bobs photo tour! > > Best 73 > /John I will see if I can get him some info together. There are several folks that have asked me for regen info, lately, so I am making up some master sets of basic information that I have found to be the best of the available literature. I am also bouncing this info along to the Glowbugs mailing list. Perhaps Conard should add Corne to the list if he is not there, for a time and see if it is helpful to him. If he has an interest in regenerators, I am sure he will be most welcome. Bob > >From: Corne Janssen > >Subject: NA4G's homebrew firebottle gear > > > >Hi John, > > > >Are there any schematics available on NA4G's homebrew projects? > > > >I am especially interested in Bob's "very hot super-duper 2-tube > >signal-slicing regenerative receiver". > > > >Greatings, > >Corne. > >-- > >Oce Nederland B.V. name: Corne Janssen > >P.O. Box 101 email: cjan@oce.nl > >5900 MA Venlo > >The Netherlands Corne.... Nice to run into a fellow regenerator lover. Although I don't have specific schematics for the sets I build, because I build from a generalized schematic tradition as a craftsman of old would do, I will outline the parameters that you need to follow, and if you wish, I will follow up with a letter and the hand-drawn schematic of that particular set, plus some other info that may be of use on regenerators. First, and most important, the loosest coupling possible is required for any regenerative receiver. I use a 1 turn link and no more for link coupling, and if I can, make that variable to reduce it further. Good coupling of a 1-turn link only needs about 1-2 inches of coupling, but any amount that does not give reduced selectivity or make the detector overload on strong signals or pull in frequency is fine. That particular set has a 1 turn grounded link wound around the bottom of the coil. The alternative is a small grid coupling capacitor (and I mean SMALL). On mine I use a pair of aluminum plates of 1/2 square inch spaced 1/8 inch apart as the maximum size antenna coupling capacitor. Anything more is TOO much. That value, by formula, comes out to about 1pf or close to it. Second, and equally or slightly less important, is the use of a high value grid leak and a low value grid capacitor. Typically, old style regen receivers used 100-250pf for the grid coupling capacitor and a 1-3 meg ohm grid leak. I use a 10-20 meg ohm grid leak and a 10-20pf capacitor, rather than the older values. It works much better and does not load down the tuned tank, and thereby maximizes the selectivity. This is how I can cut the sideband off a sideband signal, easily, with a regenerative receiver. I am always suspect of a coupling cap greater than 50pf and a grid leak less than 5 meg ohms. On my tank circuits, I prefer to use the largest number of coil turns possible and the smallest tuning capacitance and padding capacitances possible (usually a single plate 25pf tuning capacitor is more than plenty, and the band edge setting capacitor is only about 10pf variable. That maximizes the tank inpedance, reducing the loading effect on tank Q, and generates larger voltages across the detector grid circuit. Third, use a LARGE value of throttle condenser to control the feedback. I use a 365pf throttle condenser with a series rf choke and an appropriate feedback tickler coil for the 36 vdc plate voltages that I use. I adjust the regeneration feedback by the number of turns of tickler such that the set will just begin to oscillate with about 250pf of throttle condenser. That way regeneration is easy, smooth, and the transition is not subject to a pop into oscillation. That makes the selectivity optimized for right on the edge of oscillation. One can use tapped electron coupled oscillator (Hartley style oscillator) detectors, but I prefer tickler circuits, usually, myself. Fourth, I use choke coupling or transformer coupling (when I have the requisite 3:1 to 9:1 audio interstage transformers available) into the audio stage. Usually, the transformers are not available so I wind up with a 10-100h choke coil (any value greater than 10h will do fine) and a coupling capacitor suited to pass low frequency audio (around 0.1 to 1.0ufd). I find it advantageous to tune the audio choke with a parallel capacitor of anything from around 0.01 to 0.05 ufd to make the choke resonate at the tin can headphone frequency of choice (anywhere from 300 to 1000 cycles). The audio stage uses a grid leak of around 10K-470K (check for optimum value --- i.e., loudest signal with least distortion although distortion on CW is not bad and actually helps to make the signal easier to hear and copy). The headphones, if not transformer coupled, are choke coupled in a similar manner out of the audio stage. I prefer old style tin cans with large diaphrams of about 3 inches in diameter (7cm or so or larger is best). But, if you want to hear the maximum selectivity, use good high quality 600 ohm phones that will work down to 300 cycles or less, and you can actually hear the passband narrow down to that level, on the edge of regeneration. I find one stage of audio is usually plenty sufficient for earsplitting volume on W1AW and the locals and great for DX copy of QRP out to 1000 miles or more. Two stages of transformer coupled audio will require some means of uncoupling the antenna still further to reduce the signal. That can be good as it tends to further increase selectivity and reduce detector overloading. The use of a volume control is not necessary, but could be done on the second audio stage. Usually audio stages are run wide open and the rf input is changed to accomplish volume control in regen receivers. Fifth, use a metal panel or mount the parts at least 6 inches behind a non-metal panel (i.e., bakelite or acrylic plastic or such). The farther behind the panel you put things, the less hand capacity is present. Also, use insulated couplings where possible, and ground the dial mechanism and the capacitor rotor shafts. I use both types of panels, but like the old style plain black panel and wooden baseboard. That particular set was mounted on a 3/8 inch plastic base mounted on rubber stoppers, and a 1/8 inch black acrylic plastic panel with a thin sheet of grounded 1/32 aluminum behind the panel to reduce hand capacity effects. All the RF parts were mounted on the back edge of the base. That is how I build them...... basically, use a pattern in mind and optimize the design, in hand, as it is being built. The schematics are not at all critical and have been around since the 1920's. The art and craft of it is making the parts work together to give an optimized design for the components at hand. I usually use the above ``Rules of Thumb'' as they are called and that makes for a fine regenerative receiver, that is stable, sensitive, and selective. I am still amazed at how well these things do work, even today. 73/ZUT DE NA4G/Bob UP rdkeys@csemail.cropsci.ncsu.edu p.s. Our Glowbugs mailing list is currently free, and you can get it by sending an email to ws4s@infoave.net who is he listowner, and he can help you with further particulars.