[Elecraft] Duplicating the KPA100 LP filters

[Vic K2VCO]

Phil Kane wrote:
> On Sun, 18 Jun 2006 21:36:25 -0700, Vic K2VCO wrote:
> 
>> I'm thinking about duplicating the KPA100 LP filter section so I can use
>> this amp as an output stage for another rig.  

>   Why not use an outboard LP Filter like most of us have done
>   for decades?  I wouldn't connect ANYTHING to a HF antenna
>   without one.

Well, you need several selectable filters, because you need to reduce 
the low-order harmonics.  The usual lowpass TVI filter cuts off around 
30 MHz or even 50 MHz.  But you need to eliminate the 14 MHz (etc) 
harmonic that goes with your 7 MHz desired signal.  A tube rig doesn't 
have this problem because the tuned plate tank circuit has enough 
selectivity to reduce these enough.
-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco