Re: RF power chain mods and improvements..

Jerry Gaffke
 

This post says the uBitx is using either the 45m15a (2 pole) or 45m15b (4 pole) for the 45mhz filter.
   https://groups.io/g/BITX20/message/33203
This post says it's the 2 pole 45m15a from WTL
  https://groups.io/g/BITX20/message/33260

I can't find a WTL data sheet, but here's one from Fox, their 45m15a is toward the bottom of page 2:
    https://www.mouser.com/ds/2/160/filters-15543.pdf
It's +/- 7khz on the 3dB bandwidth, +/- 28 khz for an 18 dB stopband
So we're going from roughly 3dB to 18 db while transitioning across 28-7.5=20.5 khz.
If that were linear (it's not), a 2khz chunk of that skirt would have a variance of (18dB-3dB)*2khz/20.5khz = 1.46dB
Might be less, if the attenuation we need is on a part of the skirt where it's changing a bit more slowly. 

My hearing is shot from chainsaws and tractors and such.  
But audio sounded about the same to me most anywhere on the skirt

I'll try to take some measurements later today.

Jerry



On Thu, May 24, 2018 at 07:55 am, Jerry Gaffke wrote:
I haven't measure the filter bandpass.
But just listening to it, it sounded ok to my ears, even when going way down the skirt.
And as I recall, I had to crank it over more than 2k khz before it seemed to be attenuating noticeably.
Busy now, but will take another look at that today.
Do you have a datasheet for the filter being used that you can point me to?

Jerry

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