[Amps] low pass filter fail

[Ian White]

>
>##  Do you really require a LP filter ?  

Nope - you should only need to attenuate the harmonics of the driver
signal, so a harmonic notch filter should be fine. (Any non-harmonically
related spurious signals must be coming from the driver, and should be
removed before the reach the PA.)

>You could also use a .25 wave long
>coax stub..with far end shorted.   You can also add additional stubs
etc.
>Paralleling caps is the real answer to your exploding cap problem.  2-4
caps
>in parallel  would be the ideal ticket.   Your typ 2m ant will only be
resonant
>on
>its 3 and 5th harmonic.   You can make stubs that will kill odd
harmonics if I
>remember correctly. W2VJN has a good book on stubs.
>

A ready-made design is right here:
<http://www.ifwtech.co.uk/g3sek/swxfiltr/swxfiltr.htm#2.>

Trim the stubs to length in the usual way, and stretch/squeeze the
inductor for minimum VSWR. The 5f stub causes a slight increases the
minimum VSWR, but you probably do need that notch at 720MHz. A version
made with RG142/RG400 ("Teflon RG58") handled 1.2kW with no problems. 


73 from Ian GM3SEK