When i responded to your original email, I ignored the in/out more/less
capacitance because you said that you could get 1.5 kW out. That means
you can get a match. That email didn't make it to the list because it
had the wrong "from" address. Here it is again
When I play with this design, it appears that 5 uH
for the inductor at 3.8M is just too low.
Rp 1000
Cstrays 20 p
Ctune 410 pF
L 5 uH
Cload 1660 pF
Those values seem to agree with what you described.
Raising the Inductance to 7 uH
Ctune 267 pF
Cload 990 pF
Which seems more like a typical 75M tank.
None of this varies very much with Rp. The tune
cap and tank inductor mostly define the resonant
frequency, the load cap defines the match between
antenna and Rp.
I'm using a graphical smith chart program
for this analysis...much easier than any of the
other things I've tried. You don't even need to
understand smith charts, just move the component
values around until the line hits center of the
chart.
jeff, wa1hco
ka1mwp wrote:
> Comet CV05c - 650n/5
>
> Hooked up to a GME LC200 inductance meter
>
> Watching the capacitance as I turn, not that it matters..
> The issue is why does the amp need LOTS AND LOTS of capacitance :)
>
>
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
> On Behalf Of Roger
> Sent: Saturday, October 17, 2009 10:45 PM
> Cc: Amps@contesting.com
> Subject: Re: [Amps] tank calculations - need input
>
>
>
> ka1mwp wrote:
>
>> Well, I can see turning it clockwise lowers the value...as I sit here
>> and double check...
>>
>> Out is increasing value (CCW) it gets looser and opens the plates...
>>
>>
>>
> That's backwards to mine. Does the screw have right or left hand
> threads. If CCW would be backing the screw out it's pushing the plates
> closer together. The screw should be held in place so it can only turn
> which pushes or pulls the plates in the opposite direction you'd think
> the screw would be moving.
>
> 73
>
> Roger (K8RI)
>
>> -----Original Message-----
>> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com]
>> On Behalf Of Bill, W6WRT
>> Sent: Saturday, October 17, 2009 7:05 PM
>> To: Amps@contesting.com
>> Subject: Re: [Amps] tank calculations - need input
>>
>> ORIGINAL MESSAGE:
>>
>> On Sat, 17 Oct 2009 16:49:39 -0400, "ka1mwp" <ka1mwp@comcast.net>
>>
> wrote:
>
>>
>>
>>> its with the vacuum cap out all the way (max
>>> capacitance) and
>>>
>>>
>> REPLY:
>>
>> That's backwards. All the way out (unmeshed) is minimum capacitance.
>>
> Is
>
>> that
>> leading you the wrong way?
>>
>> 73, Bill W6WRT
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>>
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>>
>>
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