See this: «The coils should be "along side" the resistor in parallel, not wrapped around the body of the resistor»
http://www.kk5dr.com/ampbuilders.htm Parasitic chokes: In fig.16, you see a parasitic choke. Much has been written about these chokes, much debate, and much conjecture as to what makes an effective choke to suppress parasitic oscillations in an HF amplifier. The basic theory of choke operation is as follows; The HF fundamental energy passes freely through the choke turns, but any VHF energy "sees" a very high impedance in the coil, and must then pass through the resistor which rapidly attenuates the RF to a level that can not sustain an oscillation in the tank circuit. I have experimented in the types of coil material and found that Ni-Chrome® is a little TOO lossy when used on 10 meter band, but it does prevent parasitics. I found that Stainless Steel wire is a good less lossy material to use, and will not "rob" the amp of 10 meter RF energy. The "old" practice of using flat copper strap, is a total waste of time, and will not prevent parasitic oscillations at all. Don't use it! Another "old" practice is to wrap the coils around the body of the resistor this is also a poor approach. My design of parasitic choke is; About 4 turns of stainless-steel 18ga wire, about 1/4 - 3/8" inside diameter. Silver solder the coil across the a 2-3 watts carbon resistor, 50-150 ohms, or a 100-200 ohm "flame-proof" metal film resistor. The coils should be "along side" the resistor in parallel, not wrapped around the body of the resistor. The reason for this is that I believe the VHF RF "sees" a higher impedance than the old method. I have tested this theory, and it seems to hold up. The wire I used is what is known as "Aviation safety wire", used to secure parts on aircraft. This wire is very flexible and very high in Nickel content. If the coils heat up to much on 10 meter operation, remove one turn from the coil. --- [EMAIL PROTECTED] wrote: > > > Jose wrote: > > >Do you really mean > > ->Tinned or enameled? > > Tinned, but either would work. > > ->Wrapped or wound? > > Wrapped, but wound expresses it well. > > ->Times or turns? > > Now I think you're kidding me. > > > Steve WD8DAS > > [EMAIL PROTECTED] > http://www.wd8das.net/ > ------------------------------------------------ > Radio is your best entertainment value. > ------------------------------------------------ > > > -----Original Message----- > From: Jose HF Silva <[EMAIL PROTECTED]> > To: Discussion of AM Radio in the Amateur Service > <[email protected]> > Sent: Sun, 3 Feb 2008 9:14 pm > Subject: Re: [AMRadio] The Viking II is FINALLY > starting to work > > > > > > > > > > > Hi, > > Do you really mean > > ->Tinned or enameled? > > ->Wrapped or wound? > > ->Times or turns? > > 73 de Joe / CT1AXG > > > --- [EMAIL PROTECTED] wrote: > > > > > I noticed a type-O mistake in my earlier comment > > about parasitic > > suppressors. I wrote: > > > > >I haven't found it to be critical. I generally > use > > the solid tinned > > >wire that radio shack sells on a small white > reel, > > wrapped three or so > > >times around a 2-watt carbon resistor. The > > resistor is usually 47-ohm > > >or thereabouts. > > > > but I meant to write: > > > > >wrapped three to six times around a 2-watt... > > > > > > Steve WD8DAS > > > > [EMAIL PROTECTED] > > http://www.wd8das.net/ > > ------------------------------------------------ > > Radio is your best entertainment value. > > ------------------------------------------------ > > > > > > > > > ________________________________________________________________________ > > More new features than ever. 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