[R-390] Filter testing

[Bob Camp]

Hi

If the skirts have a problem, there's nothing you can do about it. Testing the insertion loss and then the first 20 db or so of the roll off will tell you everything you need to know.

Bob

On Apr 4, 2013, at 4:42 PM, quartz55 <quartz55 at hughes.net> wrote:

> So it was too cold to work outside today and the Dr. gave me a good report on my yearly physical this morning despite being 70 later this year, so back to the filter test set to try to get more range on my setup. I made an LC impedance matching circuit from the ARRL Handbook, 150pf in series and 780uH to ground should match 50 to 100K ohms, and I put that in a box with the filter matching capacitors.  Fed that straight to the filter being careful not to exceed 1V rms.  It gave me a bit more range, 50db max with the current setup with things attached to an aluminum ground plane and things grounded to the plane as in the picture.  I still get the same measurements on the nose but now I'm down to 50db on the skirts.  Only way I can figure to get more range now is to amplify the output of the filter, trying not to introduce more blowby. I may have to go to a piece of copper clad with ground points soldered to the plane and attached to the filter input, the filter body, and shorte
> n up the output leads considerably going into some sort of FET amp.  Since I've only got 1V going in, 22 db filter loss gets me to the -10 db scale and the bottom scale is -50, that really only gives me a 50db range accounting for the 10db on the scale.
> 
> Maybe I should just not worry about the ultimate filter rejection if I'm getting 50db now?  I'm not sure the circutry in the R390A is any better?
> 
> http://i251.photobucket.com/albums/gg287/DogTi/filtertestset1_zps45ebf3c3.jpg
> 
> http://i251.photobucket.com/albums/gg287/DogTi/filtertestset1pic_zps12505b88.jpg
> 
> Comments welcome.  That's the 4K filter I repaired with the new magnetorestrictive wire.  I've got an FA filter I'm going to install in the 2K R390A filter tube that reads good at 2.1KHz.  I'll get some pictures of that when I get to that one.
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