CQ250 bandpass filter

[M0YDH]

Hi
I'm making the 146.5MHz bandpass filter in CQ250 described by Shaun. Can anyone confirm the coil diameter? The type doesn't get any clearer when enlarged. I've guessed it's 3/8" diameter and wound 4 off 6.5 turns on a 9.5mm drill

The rush is on to get filters ready for CAT17 workshop day.

73
David M0YDH

[M0SKM]

From the original article 9.5mm internal or 3/8".

I built one in a diecast box and they work extremely well. A friend found the copper clad board design unstable due to flexing.

http://www.m0skm.com/index.php/2m-band- ... er-another

73
Steve

[g8vpg]

David,
I've just measured my prototype and it is 10mm inside diameter, so 9.5mm or 3/8inch is just right. We've built several down here in Bristol and they do work well.
73 Shaun G8VPG.

[M0YDH]

Thanks Steve and Shaun.
Pictured is progress to date. I'm stuck for what to do with the 0.5pF "capacitor" wire. It's not connected yet. Hopefully at Saturday's workshop session at CAT17 all will be put right.

73
David M0YDH

[M5TXJ]

Would a 0.5pF capacitor made from FR4 (approx 2.6pF/sq cm) be too lossy?

73 Dave.

[M0SKM]

My capacitor is a length of RG405 semi rigid.
At one end the inner only connected to the cap/coil junction; the other has the outer connected to cap/coil.

Steve

Edited as first post too early in the morning Oops.

[g8vpg]

I didn't use a capacitor. I drilled a 3mm hole in the partition and just put a length of wire through, protruding about 6mm into the second cavity. You can adjust the coupling by the length and position of this wire. You really need a spectrum analyser with tracking generator to set it up properly.
73 Shaun.

[G8GKQ]

Hi David

If you were to bring the filter to Finningley, we'll have a spectrum analyser and sweep generator suitable for setting it up there. Please bring the lids so that we can close it up when we get it right!

Dave, G8GKQ

[M5TXJ]

Steve M0SKM,

If your coax is shorted inner to outer, you haven't a capacitor, you've a direct connection.

73 Dave.

[M0YDH]

Thanks folks. I'll make some coax capacitor samples and see how they measure on the LCR meter.
CAT17 workshop day is very important to me as no working spectrum analyser is to hand. I'll have plenty for Dave to examine! E.g. the QRP-LABS low pass filters for 4m and 2m as well as the new M0HMO power meter that I built at GQRP club Buildathon on Saturday.