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It wasn't the ferrites. I rewound them all on T50-6 and T37-6 cores. Lots of turns for these and I still had the problem. The only thing left was the ceramic caps. The 2200pf caps were nice quality 5% npo caps that I bought for another project. The caps in the shunt branches were from a cheap capacitor kit with 30 of each value and 15 values. Replacing the cheapos fixed it. It is kind of surprising how bad the spurs were. I had heard of things like this but never actually experienced it.

Tony

________________________________
From: [email protected] <[email protected]> on behalf of Tony_AD0VC <canthony15@...>
Sent: Wednesday, July 7, 2021 9:35 AM
To: [email protected] <[email protected]>
Subject: Re: [softrock40] homemade chebyshev 7th order BB band stop to begin soon

I remember now. Ferrites are usually fine for transformers but not for inductors. I knew this and it just dropped off the radar. Sometimes I really hate getting old.

Anyway, I can fix this today. I have some 33uh and 22uh inductors that I can parallel for the 13uh and I have some T37-2 that I can wind for the smaller ones.

Tony

________________________________
From: [email protected] <[email protected]> on behalf of Tony_AD0VC <canthony15@...>
Sent: Wednesday, July 7, 2021 8:35 AM
To: [email protected] <[email protected]>
Subject: Re: [softrock40] homemade chebyshev 7th order BB band stop to begin soon

Just a heads up. I have been using the filter I built and I have a problem. I am seeing lots of IMD images of BC stations on the NDB band when my filter is installed. I tried installing an inline attenuator ahead of the filter because I thought maybe the low passband impedance was messing with the active loop amplifier but the images remained. Without the filter, no images so it is not coming from the loop amp. Finally, an alarm went off in my head as my poor memory dragged up an old recollection. I am pretty sure it is caused by the ferrites I chose for the filter. I have seen this before. I will have to try and locate some Txx cores in my junk box that will work in order to prove this.

As far as enclosures, I bought this pack of 3 from a**zon:

Amazon.com: 3 pcs 1590A Small Enclosure Box incl. Step Drill, PCB, Aluminum Guitar Effect Pedal Case, unpainted: Home Improvement<>

It includes a step drill which works fantastically well for the BNCs. But your filter is probably a bit too big for these boxes.

Tony

________________________________
From: [email protected] <[email protected]> on behalf of JonI via groups.io <ji425bt@...>
Sent: Tuesday, July 6, 2021 4:51 AM
To: [email protected] <[email protected]>
Subject: Re: [softrock40] homemade chebyshev 7th order BB band stop to begin soon

Here, it looks like your message came through twice, Gary, once last
night and then once today. Sometimes it takes a while to show after you
send it.

Unfortunately, don't own the Nano, but Tiny sure came in handy
yesterday, so much so that I ran down the battery and had to recharge
it. I'm not sure whether it takes on noise/ spurs/ harmonics if powered
via its port and didn't want to take any chances so let it charge for an
hour or so.

Well, about the only thing remaining with the filter is suitable
containment that's cheap! I found that I don't like the circuit board
containment I was originally going to use. I had soldered on three
sides and left one side open to make the filter, but found that I had
trouble getting the soldering iron into certain spots so decided to
remove the opposite side. It sure was a bear! A "bud" box is too
expensive for me for now. Any cheap alternative ideas welcome. With
the filter of course, I would like to have it shielded as well as
possible into the container.

Thanks,

Jon


On 7/6/21 5:50 AM, Gary wrote:

Let's try this again. I sent this message at 7 p.m. last night and it
hasn't shown up by 6 a.m. today. Did I commit some high crime and
misdemeanor?

Something that might be of interest is that the Surrey Amateur Radio
Club, VE7SAR, < <>ve7sar.net > has a wonderful newsletter that
comes out bi-monthly. The newsletter is usually around 110 pages.
The last several issues have had articles titled, Measurements with
the NanoVNA". The Nov - Dec 2020 article deals specifically with
"Establishing the Characteristics of Unknown Toroids".

73,
Gary - W6GVS
Dowagiac, MI

At 11:18 AM 7/5/2021, you wrote:

Thanks! Those are some good instructions, something I was looking
for yesterday on how to align the sections. Any advice to keep the
toroid turns in place once aligned? I find they can move quite a bit
during installation. Was thinking hot glue, but might hurt the enamel.

Jon


On 7/5/21 11:04 AM, Nick wrote:

On 05/07/2021 14:12, JonI via groups.io wrote:

I did check the inductance of the toroids before installation using
a separate capacitor, dip meter, and frequency counter.
Unfortunately, my dip meter doesn't go low enough to check the
resonances you indicate.

You should be able to do this with your noise source and TinySA.

Make up a test jig with a piece of scrap PCB and two BNC connectors.

Remove the resonators one by one from the filter and align as follows.

For the series resonators L1/C1 etc connect the two BNC centers and
strap the series resonator from there to ground.

Noise generator on one side, TinySA on the other. You should see a
sharp dip at the resonant frequency of 919kHz.? Squeeze or stretch
the toroid's turns to get that frequency, then reinstall the
resonator in the filter.

For the parallel resonators L2/C2 etc connect the resonator between
the two BNC centers. You should see a sharp dip at the resonant
frequency of 941kHz. Squeeze or stretch the toroid's turns to get
that frequency, then reinstall the resonator in the filter.

HTH

Nick