[Elecraft] > Subject: Semi-OT: seeking circuit designs for 2 meter LPF

[elecraft at g4fre.com]

I have my K3 driving an I0JXX 500W solid state 144Mhz amplifier. With this i 
use an LPF from an old ARRL manual http://g4fre.com/2mlpf.pdf using doorstop 
capacitor which has 0.1dB insertion loss and works well 

Dave 

ww2r 

> 
> Message: 48
> Date: Wed, 12 May 2010 07:01:05 -0700
> From: Lew Phelps K6LMP <k6lmp at me.com>
> Subject: [Elecraft] Semi-OT:  seeking circuit designs for 2 meter LPF
> To: Elecraft <elecraft at mailman.qth.net>
> Message-ID: <59286ECA-CE4B-45F6-A458-80691EBF23AD at me.com>
> Content-Type: text/plain; charset=us-ascii 
> 
> I'm building a 300 watt external amplifier for use on 6 meters and 2 meters, a specialized "VHF Contesting" amp that I will use with my K3-10 (with internal 2 meter transverter).  
> 
> There's a good design for a kilowatt-capable 6 meter low pass filter in the ARRL Handbook (2007), but I haven't found a design for a 2 meter LPF filter that I really like.  The best I've found so far is at: 
> 
> http://rf-transmitter.blogspot.com/2008/09/200w-lowpass-filter-for-150-mhz-2-meter.html 
> 
> which seems fine except it's only rated for 200 watts. My amplifier (Communications Concepts AR313) is rated to deliver about 250 watts at 144 mHz when driven with 10 watts, and running off of 28vdc power supply.  Given that I will be transmitting on SSB at somewhat less than 50% duty cycle, a rated power capacity of 200 watts is probably sufficient, but I'd like to know what alternatives, if any, are available. Surely the EME crowd has good designs for legal limit LPF projects for 2 meters?  I haven't found any online. 
> 
> It should be noted that the amplifier itself (due to push pull design) suppresses even order harmonics very deeply, and at 144 mHz suppresses 3rd order harmonics -40dB or more, so it doesn't really need a low pass filter, except that (my understanding) the FCC require a LPF on any amplifier.   
> 
> Any thoughts appreciated on whether the cited 200 watt LPF will do even though it's slightly under-rated for power capacity, and also any pointers to other filters, would be appreciated. 
> 
> Thanks in advance.  Please reply off list unless you think the group as a whole would benefit from your reply. 
> 
> 
> Lew K6LMP 
> 
>