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Re: [Amps] low pass filter fail

To: "Jim Thomson" <>, <>
Subject: Re: [Amps] low pass filter fail
From: "Carl" <>
Date: Tue, 29 Apr 2014 08:48:40 -0400
List-post: <">>

-----Original Message----- From: Ian White
Sent: Tuesday, April 29, 2014 3:14 AM
To: 'Jim Thomson' ; ; '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.


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