[Moon-net] Cavity question RX1AS PA 144Mhz

[Oene Spanjer]

Hello All,

I am building a RX1AS design PA right now and it has a half wave
tube connected to the anode as resonator.
This tube has a diameter of 55 mm and the lenth of the total
resonator including cooler is 53 cm.
The housing is 170mm by 170mm.

I want to use a 40mm tube so the whole impedance of the resonator
will change. I think it is going upwards.
Now my question is what effect will this be ??  Too much mismatch ?
and do I need to lenthen or shorten the resonator to get it in resonance ?

I want to keep the same housing distances, but my feeling tells
me that it should change also with 40mm tube, because the whole line
can be seen as coax.

Maybe it is best to use 55 mm tube instead, but I was just curious and
cannot find any software that calculates it for me
The tube used will be a GS-35b 
The info I refering to,  is at www.pa3csg.hoeplakee.nl/GS35-2M/GS35-2M.html

Thanks in advance !

73 and have nice summer holidays !
Oene
PA3CWN