Bill Fuqua wrote:
> If what you say is true then no resonant circuit has Q.
>
Not quite. It's true the formula is either X/R or R/X and at resonance
Xc and Xl are equal. But the formula says to use EITHER Xc or Xl, not
both which would be zero at resonance.
73
Roger (K8RI)
> In series resonance Q= Xc/R or you can use inductive reactance. they
> are equal at resonance.
> In parallel Q=R/Xc
> 73
> Bill wa4lav
>
>
> At 09:58 PM 4/8/2010 -0400, TexasRF@aol.com wrote:
>
>> Q=X/R in a series circuit or R/X in a parallel circuit. Since at resonance
>> there is 0 ohms X in the series circuit or infinite X in the parallel
>> circuit, The Q would be 0 as in zero.
>>
>> No flywheel action here.
>>
>> In a real world case, say 15,000 vdc and 5A plate current, the plate load
>> impedance would be about 1700 ohms. There would probably be 100 pf from
>> plate to cathode which is about -58 ohms at 27 MHz. So, looking into the
>> tube,
>> there is a parallel circuit of 1700 ohms resistive and about 58 ohms
>> capacitive. The Q is 1700/58 = 29.
>>
>> The series equal is 2 -j58. The antenna would need to look like 2 +j58 for
>> a match. That is not a very friendly number so more help is needed.
>>
>> I will leave the rest of the design work to others.
>>
>> 73,
>> Gerald K5GW
>>
>>
>>
>>
>> In a message dated 4/8/2010 5:50:05 P.M. Central Daylight Time,
>> dezrat1242@yahoo.com writes:
>>
>> ORIGINAL MESSAGE:
>>
>> On Thu, 08 Apr 2010 17:09:08 -0400, Ron Youvan
>> <ka4inm@tampabay.rr.com> wrote:
>>
>>
>>> By adjusting the antenna length to be resonate at the exciter's
>>>
>> frequency the antenna
>>
>>> is that "tank circuit," it's just lossy by the radiation resistance. A
>>>
>> variable coupling
>>
>>> capacitor is not necessary.
>>>
>> REPLY:
>>
>> Upon further consideration, if the antenna impedance matched the
>> tube's plate load impedance, wouldn't the Q be just one? I think you
>> still need the simple LC tank circuit for the flywheel effect.
>>
>> 73, Bill W6WRT
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>> _______________________________________________
>> Amps mailing list
>> Amps@contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
>
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|