Here are my results after building an RFC for my 2xGS35B amp:
Progress on testing the choke:
2 series resonance dips in the 30MHz spectrum. 1st dip at 7.1MHz and
second at 14.3MHz, clean above and below. Tested on grounded Al plate
with coils normal (vertical) to the plate. Removed Form 2 Coil 1.
Reduced L to 274uH and moved resonances up 1+ MHz. Success!
Reactance at 1.8MHz = 3099 Ohms
Tomm, KD7QAE
KD7QAE wrote:
All,
I just finished sacrificing 12" of Teflon bar stock to the 2xGS35b
project this evening. The result is a 320uH inductor in 2 sections. I
will sweep the unit tomorrow at work and report back with the resonance
story. The basics are as follows:
Wire: 24AWG
OD of coils: approx. 39mm
Form 1: Coil 1: 25mm
Form 1: Coil 2: 27mm
Form 1: Coil 3: 49mm
Form 2: Coil 1: 26.5mm
Form 2: Coil 2: 24mm
Form 2: Coil 3: 18mm
Form 2: Coil 4: 27mm
The coils are parallel (against conventional wisdom) Center to Center
separation: 85mm. It certainly looks cool. I plan on adding a HV
capacitor and relay at the connection point if necessary to switch out
~1/2 of the inductance if necessary.
Tomm, KD7QAE
k7fm wrote:
>It has been stated that winding two solenoids rf chokes end-to-end will in
>effect make one rf choke, so that they must be at right angles.
>
>That statement is only true if the rf chokes couple. But, it is possible
>for them not to couple. How? Wind them in opposite directions. Then,
>coupling will be minimal.
>
>I just wound two solenoid rf chokes in line, separated by about 1/4".
>Measured the resonance of the first rf choke before winding the second.
>Then, wound the second with more turns, so I could look for a different
>resonant frequency. The resonant frequency of the first was unaffected by
>the additional solenoid wound end-to-end. Then checked the resonant
>frequency of the second coil. It was right where it was supposed to be.
>
>I then measured the inductance and they added.
>
>So, it is possible to make rf chokes on one form for the purpose of avoiding
>resonant frequencies.
>
>The problem with resonant rf chokes is that the hi Q creates fireworks.
>There may be another solution, and that is to use resistance wire for the rf
>choke. It is common to install a glitch resistor in the high voltage line.
>If you wind an rf choke with the correct resistance wire so that the desired
>resistance is equalled by the wound rf choke, then you can eliminate the
>resistor. Whether the choke Q would be low enough to not worry about
>resonances I am not sure.
>
>That is a project for another day, to wind such a choke and get the Q meter
>out - but I do not have neough desk space to do that at the moment.
>
>73, Colin K7FM
>
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