CW Rig. Part 1 - Homebrew CW Crystal Filter

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Overview video looking at the design of a superhet CW crystal filter. The idea was to use a cheap NanoVNA from AliExpress and the 'Crystal Ladder Filters for All' paper from Jack Hardcastle G3JIR
Apologies that it is just an overview, but a detailed video would have taken well over a hour or so.
It was based on the following source/reference material:
Crystal Ladder Filters for All
www.arrl.org/f...
Test Jig
qrp-popcorn.blo...
NanoVNA Control software by Rune Broberg
mihtjel.github...
Crystal Ladder Filter Program by Horst Steder DJ6EV
www.arrl.org/qe...

Опубликовано:

12 сен 2024

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Комментарии : 37

@nt1u 4 года назад

Thanks Charlie! Learn something new in every one of your videos. Appreciate the effort.

@CharlieMorrisZL2CTM 3 года назад

Glad to hear it Dave. If I can do it them anyone can.

@Paul_VK3HN 4 года назад

The 5% tolerance on those ceramic caps will account for plus or minus 50pF so I wouldn't bother with the 8pF. If you have a LC meter you trust, you are probably better to parallel small C to get close to a desired value as measured. Great narration Charlie!

@CharlieMorrisZL2CTM 4 года назад

Agreed and thanks Paul.

@mikemo1964 4 года назад

Nice work Charlie. Thanks for sharing.

@CharlieMorrisZL2CTM 4 года назад

My pleasure Mike. It was a too hard to cover everything, but hopefully you you got the gist.

@raafatalheety826 4 года назад

Nice video de Yi1hxh rafat 73 from baghdad

@CharlieMorrisZL2CTM 4 года назад

Thanks Rafat. 73s Charlie.

@scharkalvin 4 года назад

I've got one of those nano VNA units, and have been wondering how to use them to measure SWR and band pass filters.

@CharlieMorrisZL2CTM 4 года назад

They seem to work really well. I was using it to tune the antenna too. Just very the tuner until the Smiths Chart has it on the 50 ohm, zero reactance point. The PC software makes it nice and easy too.

@JimAndyAllyn 4 года назад

Check out the NanoVNA users group at groups.io/g/nanovna-users. There's a lot of good information in the wiki and files, and even more in the messages, but the messages can be a little harder to sift through to find the information you want. Have a look at the wiki and files first.

@drewf64 4 года назад

Thanks Charlie. Quick question: You use HC-49/U crystals rather than the more widely available HC-49/S. I'm sure there must be a good reason but I can't seem to find any info on the difference. Is it something to do with Q value?

@CharlieMorrisZL2CTM 4 года назад

I haven't, but I think the BITX does. I thought I read somewhere that they are not as good, but you do see them being used. I'd give it a go. I suspect the ones I have are not that flash, but hey, you get what you pay for!

@Paul_VK3HN 4 года назад

@@CharlieMorrisZL2CTM I'm no expert on this but from reading and my limited experience the quality of the crystal is more significant than the case style. I would avoid really cheap crystals, mthe quality of tbe resultant homebrew filter and my time are the important currency! Life's too short for junk crystals!

@CharlieMorrisZL2CTM 4 года назад

@@Paul_VK3HN No I agree. My take away is that the crystal were certainly not of high quality. That aside, the aim was to apply the process, which was enjoyable.

@geraldmoritz8523 4 года назад

Hello Charlie, I am also reading on Filters and Crystals for many weeks now. I do not understand your calculation on the impedance. Every filter I saw until now had an impedance greater 50 Ohm. Is 15 Ohm an average of the motional resistance Rm ? 15dB loss within the filter seems quite high for me ! Tnx de Gerald, OE3GOD (btw: thank you for each of your videos and calculations and your explanations !!)

@CharlieMorrisZL2CTM 4 года назад

Hi Gerald. I agree that the IO impedance is looks quite low, but I just took the value off the filter design software. I could certainly be misinterpreting that. Same with the overall loss, but again that seems to be in line with the original paper. The plan now is to build the receiver and see how it performs.

@BalticLab 4 года назад

Great Video, Charlie!

@CharlieMorrisZL2CTM 4 года назад

Thanks. I had way too much to talk about in not enough time. Oh well.

@BalticLab 4 года назад

@@CharlieMorrisZL2CTM In the electronics world it appears to be okay to have longer videos with rants and tangents without hurting viewer retention too much. EEVBlog being the prime example. But I appreciate that you try to keep your videos very short, structured and to the point.

@CharlieMorrisZL2CTM 4 года назад

@@BalticLab Thanks. I've had a comment that they are sometimes too long. As you know, I just hit record and start talking, and they finish when I start rambling! So long as people get the idea what I did then everything is fine. It's just a video log.

@nodzie1 2 года назад

Hi Charlie - I tried giving this a go but for some reason, I don't get the nice bell curve, I get a curve with a second peak or hump on the side of it, so approx -35db at 8997.8KHz and then -16db at 8998.2KHz. Could that be because the crystals are not close enough matched or the capacitors are not close enough to those calculated? Cheers, Chris VK3TUB

@FlexxVision 4 года назад

So nice the working modules, after/while do soldering an open flame from upside beware the board to curving on quench. What does an CW Filter exactly , i now an Bandpass filter , or netfilter with Pi-Cascades. From Mixer comes an Width band signal, and from this u extract only an +/- 300Hz like a strip of base signal width ?

@CharlieMorrisZL2CTM 4 года назад

Hi Karsten. For a single conversion superhet, the CW filter will sit between the first mixer and and the product detector. Just like its wider SSB filter cousin, it will only pass the desired signal (it is in effect a bandpass filter). The bandwidth is very narrow as the CW signals are much closer together than SSB. If it is too wide then you will have several stations coming through the AF amp. I didn't want it too narrow as tuning becomes much harder. Does that answer your question?

@FlexxVision 4 года назад

@@CharlieMorrisZL2CTM thx Charlie , i can imagine it.. in early times i have often create "gegentackt" oscilators , modulated with an capacity diode. Today i use only microcontroller's or SDR -radio boards (like ic-7300 or lime sdr) so i have a plug and play electronics world , from there i understod really only the basics . (working on I/Q Datastreaming) Thx for respons and i watch here to learn more.

@CharlieMorrisZL2CTM 4 года назад

@@FlexxVision SDR it lots of fun too. You can certainly do a lot in software.

@shizzle2817 4 года назад

Great video! Will a link to the spreadsheet be available as well?

@CharlieMorrisZL2CTM 4 года назад

I don't have a server sorry, and I haven't work out a way to leave it on the blog..

@qvatch 4 года назад

@@CharlieMorrisZL2CTM you can share a google sheets document as a view only link, which would let us make a personal copy to play with. Barring that, if you go to view>show formulas you could more easily share the methods of the sheet.

@shizzle2817 4 года назад

@@CharlieMorrisZL2CTM If you click "Share" in the top right corner of the GSheet, you'll get a dialog box, click "get shareable link." If you set the permissions to view only, folks can make a copy without editing your version.

@CharlieMorrisZL2CTM 4 года назад

Try this: drive.google.com/open?id=1z_6atlpIE2s3-KpkpvEUKJXDYJ4D5IQLUwoAj1T77Ec

@shizzle2817 4 года назад

@@CharlieMorrisZL2CTM Thanks!