[Amps] [TowerTalk] Are All Low-Pass Filters Alike? -

[Don Havlicek]

How does the amp produce trash that is not present at the input?
If your amp does this, it's a piece of trash and should be redesigned, 
not 'filtered'.
As for impedance matching 'at the harmonics' .. that's gobbledegook. A 
well-designed filter will attenuate as it is designed to attenuate IF it 
is inserted between a source and a load with correct impedance at the 
frequency IN USE.
Don N8DE

Jim Brown wrote:
> On Tue, 16 Aug 2005 16:10:22 -0400, Don Havlicek wrote:
> 
> 
>>Why don't hams place the LP filter between the Xcvr and the Amp?
> 
> 
> Yes. That allows a 100w filter to do the job. Doesn't protect 
> against trash from the amp, but it helps the receiver. And if you're 
> running barefoot, put it between the amp and the tuner. 
> 
> BUT -- the same cautions about impedance matching being necessary 
> still apply, and that's the fly in the ointment. Not only must you 
> be matched at the operating frequency for the filter specs to apply, 
> you must also be matched at the harmonics! The chances of that 
> occuring are slim to none unless you happen to be working into an 
> antenna that is resonant at the harmonics. We DO use some of those, 
> but it certainly isn't all that we use, and it would only apply to 
> single band filters. 
> 
> Jim Brown K9YC 
> 
> 
>