8033	2013-01-05 07:10:35	jor	Torroid question for L-C tuner
Message	Date	From	Subject
Bill, You understand my question. I think your conclusion is right, for a closed magnetic ring field in the torroid the damping should be high and if power is put in the coil the loss will be high and Q factor low. In case with a straight air coil tuner the magnetic field is more open, spread in space and the shorted coil part probably act as a metal reflector on one end. The loss will be match lower and not affect the Q factor so match. If one torroid coil is used in the L-C tuner than a winding should not be shorted. Self-resonance frequency of the unused coil part should not be fell in the wanted frequency range. For QRP 5 watt power the voltage is low and not a problem A torroid make the coil attractive small. I am also thinking to experiment with a ferrite 43 torriod and mill a 1 mm air cap split in the ring to prevent surtuation. May be than les winding are necessary and the size can be kept small. Thanks every one for the input. Joris van Scheindelen PE1KTH
8035	2013-01-05 07:10:35	jor	Torroid question for L-C tuner
Bill, You understand my question. I think your conclusion is right, for a closed magnetic ring field in the torroid the damping should be high and if power is put in the coil the loss will be high and Q factor low. In case with a straight air coil tuner the magnetic field is more open, spread in space and the shorted coil part probably act as a metal reflector on one end. The loss will be match lower and not affect the Q factor so match. If one torroid coil is used in the L-C tuner than a winding should not be shorted. Self-resonance frequency of the unused coil part should not be fell in the wanted frequency range. For QRP 5 watt power the voltage is low and not a problem A torroid make the coil attractive small. I am also thinking to experiment with a ferrite 43 torriod and mill a 1 mm air cap split in the ring to prevent surtuation. May be than les winding are necessary and the size can be kept small. Thanks every one for the input Joris van Scheindelen PE1KTH
8036	2013-01-05 09:55:45	William Carver	Re: Torroid question for L-C tuner
Shorted turns, in both toroid and air coil, will have larger current in that short than the current at the coil terminals. If that short is PERFECT, no loss from those higher currents, then inductance changes but Q is not affected. But there is resistance in the turns, resistance in the switch contracts. So in the real world there must be some Q loss, and power loss in that loop....primarily switch contacts I think. As I said in previous post, I melted some substantial-size contacts of a heavy switch of high reputation when I accidentally shorted turns in an airwound coil. So shorting turns, even in an airwound coil, produces loss that may be capable of melting the contacts of receive-sized switches with 5 watts. Better to avoid shorting turns...just change taps...and try to avoid self-resonance and higher voltages that even QRP could produce in the unused open-circuit turns. Magnetic materials with specific properties are not always easy to obtain. Making a mm gap (breaking core?) may be difficult. Of course you are aware of powdered irons...loss in -6 are low over most of HF range, or -10 if you are 14 MHz and above. But more turns. I would be interested in your experiments and results with -43 (or "modified" -43 cores!) at power levels of a few watts. Bill On Sat, 2013-01-05 at 13:22 +0000, jor wrote: > > Bill, > > You understand my question. > I think your conclusion is right, for a closed magnetic ring field in > the torroid the damping should be high and if power is put in the coil > the loss will be high and Q factor low. > In case with a straight air coil tuner the magnetic field is more > open, spread in space and the shorted coil part probably act as a > metal reflector on one end. The loss will be match lower and not > affect the Q factor so match. > > If one torroid coil is used in the L-C tuner than a winding should not > be shorted. > Self-resonance frequency of the unused coil part should not be fell in > the wanted frequency range. For QRP 5 watt power the voltage is low > and not a problem > A torroid make the coil attractive small. I am also thinking to > experiment with a ferrite 43 torriod and mill a 1 mm air cap split in > the ring to prevent surtuation. May be than les winding are necessary > and the size can be kept small. > > Thanks every one for the input > Joris van Scheindelen PE1KTH > > > > >