Re: [Amps] Design for plate stripline for 144 MHZ

[jeff millar <wa1hco@adelphia.net>]

Manny...

Check out the response I just sent to the reflector and Jim N9RF.

Do you have a preferred design style from http://nd2x.net or some other 
source?  The basic decisions include W6PO style with two 1/4 lines, HF 
technique style by YU1AW, or stripline style.  Mentioning DC blocking 
caps implies you're not using the 1/2 wave design like Jim (probably a 
good choice at the 700-1000W level...much more compact)

I can show you how to use the smith chart modeling software to create 
the design for the length of the line sections.  The modeling software 
works well for any type of output network.

Usually, these amps use capacitive probe output coupling at the hi 
impedance end of the line, which for a 1/4 wave design occurs near the 
tube.   YU1AW has pioneered using an inductor instead of a plate line to 
lower the impedance and enables using conventional 50 - 100 pF class air 
variable capacitors for tune and load...and they get mounted some 
distance from the tube, making for a better layout.

Assuming a stripline design, the line height is chosen mostly for 
mechanical reason to match the height of the anode ring.  Also the line 
needs enough width to carry the high currents.  The line probably should 
lie closer to the screen ring plane than the top cover to keep most of 
the return currents within the anode to screen loop.  But, the top of 
the chassis and cover forms part of the transmission line and carries 
some fraction of the  currents.  The details affect the line impedance 
used in the model but little else.

Door knob caps are a good decision.  Gimmick caps don't have good 
mechanical stability and will change value under heating more than a 
commercial cap.

this is a favorite topic of mine...hope it helps...

jeff, wa1hco

kc4mne@bellsouth.net wrote:

> Going to build a 144 MHZ amp using the 4CX800 tube. How are the dimensions and locations for the plate stripline and load and tune capacitors designed, as well as the influence of the surrounding enclosure, standoff heights, etc. I want to use doorknob caps for plate dc blocking, not the ptfe sheet method. Any help on how this is designed would be appreciated. Any software out there? 
>
> Manny
>
> KC4MNE
>
>
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