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Old 3rd Apr 2020, 7:17 pm   #2
Join Date: Nov 2018
Location: Freckleton, Lancashire, UK.
Posts: 111
Default Re: 6 metre 4 pole filter

Just a couple of pointers.

Not wishing to appear to be bragging, but back in the 80's I built a dual band 4 / 6 mtr processor controlled all mode transceiver which was published in RadCom and won the VHF Cup for that year.

You might to take a look at how the rx and tx chains worked and how the filtering was done etc.

The PLL would be a lot simpler these days - in fact if I was to do it again I'd make it SDR based with a A/D and D/A as superhets are 'yesterdays technology'.

Looking at your filter / amplifier it appears you have four tuned circuits ahead of the FET which will likely incur significant loss and so degrade the FET noise figure - important if it's going to be a rx LNA !

Also FET's at 50MHz can be difficult to get stable especially with 'hi q' tuned circuits on inputs and outputs.

Again take a look at my design or have a good google for best practices.

The band pass filters I used employed a combination of inductive and capacitive coupling to create a nice shaped filter symetrical on both sides.

regards Tim
Building and tinkering for over 50 years, from 807's to digital amateur TV.
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