CQ250 bandpass filter

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g0mjw
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Re: CQ250 bandpass filter

Post by g0mjw » Mon Sep 04, 2017 12:58 pm

Wouldn't a slot be a more controllable method? That or a coupling probe. I suppose it doesn't matter as long as you have the means to adjust the coupling, but it might be more repeatable.

Mike

https://www.wirelessdesignmag.com/artic ... ter-design

M0YDH
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Re: CQ250 bandpass filter

Post by M0YDH » Mon Sep 04, 2017 7:01 pm

My Atlas LCD meter is not coping sub 2pF! It's very out of calibration. 25mm lengths of coax inner to outer are coming out -6 to -8pF. RG316 and RG402. I'm making the lid and hoping for CAT17 magic.....

g0mjw
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Re: CQ250 bandpass filter

Post by g0mjw » Mon Sep 04, 2017 8:10 pm

M0YDH wrote:My Atlas LCD meter is not coping sub 2pF! It's very out of calibration. 25mm lengths of coax inner to outer are coming out -6 to -8pF. RG316 and RG402. I'm making the lid and hoping for CAT17 magic.....
As long as you know the capacitance per metre you can at least make an estimate - cut it long in case you need to shorten it. Lengthening it, once cut is hard. UT141 for example is about 29pF per foot which is about 1pF per cm.

Mike

M0YDH
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Re: CQ250 bandpass filter

Post by M0YDH » Thu Sep 07, 2017 7:30 pm

I made the lid and sides - the coupling can wait till CAT17 workshop session. Then I made a 432MHz comb line filter per the W1GHZ recipe on the club wiki. It looks like a piece of witch craft :D
I hope the club wizards can get it tuned on Saturday......
See you
David M0YDH
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G4FRE
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Re: CQ250 bandpass filter

Post by G4FRE » Thu Sep 07, 2017 10:03 pm

i built the w1ghz 432 filter a while ago and it tuned up "as advertised"

dave
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M5TXJ
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Re: CQ250 bandpass filter

Post by M5TXJ » Fri Sep 15, 2017 9:58 pm

Can anyone recommend a UK supplier for the UT-141 hardline to construct one of these filters?

73 Dave

G4KLB
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Re: CQ250 bandpass filter

Post by G4KLB » Fri Sep 15, 2017 10:34 pm


g0mjw
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Re: CQ250 bandpass filter

Post by g0mjw » Sat Sep 16, 2017 7:47 am

Buying it new tends to be expensive. There is usually a lot of it available used at rallies.

Mike

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M5TXJ
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Re: CQ250 bandpass filter

Post by M5TXJ » Sat Sep 16, 2017 12:34 pm

Thanks for the info, unfortunately working 3 weekends out of 4 limit the number of rallies I can get to, I think the next chance will be the Red Rose Winter rally.

73 Dave.

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