[Moon-net] Cavity question RX1AS PA 144Mhz

[Conrad G0RUZ]

The approximate impedance can be calculated from 138log10*(1.08* D/d). All
you need to do to preserve things is keep the ratio of the diameters the
same. Basically the inverse of what F1CXX did, in this case the box could be
made 124 mm x 124 mm, but I personally would not do it. The whole cooling
arrangement will be compromised, there will be more stray capacitance and
the tuning may become more critical. F1CXX did the right thing, his looks
like it won't fall over :-)

73

Conrad G0RUZ




-----Original Message-----
From: moon-net-bounces at list-serv.davidv.net
[mailto:moon-net-bounces at list-serv.davidv.net] On Behalf Of Oene Spanjer
Sent: 20 July 2007 11:22
To: Moon-Net; Moon
Subject: [Moon-net] Cavity question RX1AS PA 144Mhz

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
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