Semi-OT: seeking circuit designs for 2 meter LPF

Posted by K6LMP on May 12, 2010; 2:01pm
URL: http://elecraft.85.s1.nabble.com/Semi-OT-seeking-circuit-designs-for-2-meter-LPF-tp5041223.html

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
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