Posted by
n7ws on
May 12, 2010; 3:04pm
URL: http://elecraft.85.s1.nabble.com/Semi-OT-seeking-circuit-designs-for-2-meter-LPF-tp5041223p5041556.html
I don't believe that the FCC *requires a LPF*. They require a minimum amount of spurious suppression:
"The mean power of any spurious emission from a station transmitter or
external RF power amplifier transmitting on a frequency between 30-225
MHz must be at least 60 dB below the mean power of the fundamental."
They don't care how you achieve it.
This (former) EMEer used a loaded 1/4 wave cavity type BPF on the output of my 8877. I would forget trying to use an LPF. You don't need low insertion loss at DC, why try to achieve it?
--- On Wed, 5/12/10, Lew Phelps K6LMP <
[hidden email]> wrote:
From: Lew Phelps K6LMP <
[hidden email]>
Subject: [Elecraft] Semi-OT: seeking circuit designs for 2 meter LPF
To: "Elecraft" <
[hidden email]>
Date: Wednesday, May 12, 2010, 8:01 AM
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.htmlwhich 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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