Re: [Amps] low pass filter fail

["Carl" <km1h@jeremy.mv.com>]

> -----Original Message----- 
> From: Ian White
> Sent: Tuesday, April 29, 2014 3:14 AM
> To: 'Jim Thomson' ; amps@contesting.com ; 'Benedikt Sveinsson'
> Subject: RE: [Amps] low pass filter fail
>
> > ##  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.)
> 73 from Ian GM3SEK
>
>
> ##  whoa.  The amp generates harmonics.... it doesn’t amplify harmonics 
> from
> the driver.
>
> Jim  VE7RF
That only assumes the input is completely free of harmonics and spurs.
Im using stubs made from RG-213 to eliminate QRM to the FM band and the 
local police and FD site about 200' away on my 6M amp. At 1200W they barely 
show any heat.
On 2M the 28' boom stacked yagis seem to be good enough as filters since 
neither the military or hams on 432 have complained....432.6 or so is far 
enough away from the active part of that band anyway.
Due to the commercial site across the street and the UHF/FM/Govt/commercial 
site about 1.5 miles away on the next hill top I did have to build bandpass 
filters for 6 and 2M to keep all their crud out of my receivers and they do 
double duty on TX.
Years ago cavity filters were popular on 2M at the KW+ level. Construction 
is simple using copper pipe but getting the coupling stub loss very low and 
the tuning disc screw to make good contact requires some skill.
Carl
KM1H

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