16 - The Dark Art of the Band Pass Filter

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16 - The Dark Art of the Band Pass Filter

Рет қаралды 6,306

Күн бұрын

Nick (M0NTV) talks through the challenges of homebrewing a 17m Band Pass Filter - including designing and testing. IMPORTANT: My apologies that there is an error in the schematic. The top line should not short out both transformers! That never works too well! Only the grounds should be connected. The QRP Labs schematic is of course correct. Thanks to Tony Fishpool for alerting me to this.

Пікірлер: 35

@acestudioscouk-Ace-G0ACE 2 жыл бұрын

Great video, well explained as usual and I'm beginning to think I could actually manage some homebrew. Glad to see you settled in your new home and hope you have many happy years there.

@M0NTVHomebrewing 2 жыл бұрын

Thank you very much.

@boxingday11 2 жыл бұрын

Good to see you back 👍🇬🇧

@M0NTVHomebrewing 2 жыл бұрын

Thanks very much.

@tdumnxy 2 жыл бұрын

Very good video. I find all your videos helpful and clearly explained. Thanks.

@M0NTVHomebrewing 2 жыл бұрын

Thank you very much Stephen. Glad you enjoyed it. 73 :)

@w1rcp 3 ай бұрын

I've built two filters using Elsie, and holy crap my insertion loss is terrible. I keep fussing with them, and it gets better all the time, but I'm shooting for a 3-pole design that I haven't been able to achieve sub -3dB insertion loss yet. It's a dark art for sure! -W1RCP

@M0NTVHomebrewing 3 ай бұрын

Keep going! 73, Nick

@alanmacdonald65 2 жыл бұрын

Great video as always Nick! M0VLT

@M0NTVHomebrewing 2 жыл бұрын

Thanks mate :)

@TheTemporalAnomaly 2 жыл бұрын

I`m getting to be a regular here, I do like your work. Very well done. I have however spotted a mistake on the diagram (time 6:49), that will have newcomers chasing their tails if not corrected. The hot ends of L2 and L5 should not be connected as transformer action here is needed to match 50 ohms. Likewise L1 and L2 hot ends should not be connected either. Also I recommend low loss variable caps making up some of the capacitance in the tuned circuits to allow for fine adjustments. I have also been known to `cheat` with C2 using twisted teflon wire as a `gimmic capacitor.` Complements, Chris. UK.

@M0NTVHomebrewing 2 жыл бұрын

Thanks Chris, I realised this quite early on so there is a bit marked 'IMPORTANT' in the video description that highlights it. Thanks for watching. 73 Nick

@davidbrodie5044 2 жыл бұрын

I've been making filters recently, both using Hans kits and freestyle from his published data which have worked well - I do need to get mine boxed up like yours to stop stuff bypassing the filter by radiation/coupling. Thanks for the vid, very useful.

@M0NTVHomebrewing 2 жыл бұрын

Thanks very much David and well done on your own filter construction. 73

@kp4md 2 жыл бұрын

A curiously strong filter. Well done! de KP4MD

@M0NTVHomebrewing 2 жыл бұрын

Thank you!

@batica81 2 жыл бұрын

Great video! I want to build one of those and use it with my cheap sdr receiver that has no frontend filtering. Idea is that it will keep very strong local interference away and give me much better reception on a specific band. Do you think that may work?

@M0NTVHomebrewing 2 жыл бұрын

Hi Vojislav, thanks very much. Yes it should work very well for that. As long as your SDR input is expecting a 50 Ohm impedance - which is what my filter was designed for. You can of course design a filter to match different impedances if necessary. Happy homebrewing! 73 Nick (M0NTV)

@BShocked Жыл бұрын

Very useful! I found similar schematics online for band pass filters. I'm always confused about what rating components to use though. If I want to operate at 100w how do I know a component, part, or wire can handle that sort of power?

@M0NTVHomebrewing Жыл бұрын

Thanks. Check out my reply to radiotech76 below. Basically for 100W I would use a T68 toroid and high voltage caps (e.g. rated 400-500V) + the thickest wire you can get away with. You could probably get by with less but I'd rather build in a bit of headroom. Hope this helps. 73 Nick.

@paulchapman603 2 жыл бұрын

Why does the schematic appear to show primary and secondary of both transformers in parallel? Is it a mistake, or some standard I'm unfamiliar with?

@M0NTVHomebrewing 2 жыл бұрын

Hi Paul, yes that is a mistake on the schematic I'm afraid. It is documented in the video description. The transformers should be wired the conventional way and not with their signal lines shorted together! 73 Nick

@radiotec76 2 жыл бұрын

Nice presentation! I’m looking for bandpass filter circuits that can handle 100 watts full duty cycle. Should just a matter of using toroids, capacitors and wire sized to handle the increased voltage and current.

@M0NTVHomebrewing 2 жыл бұрын

Hi! Thanks for watching. It depends where in the signal chain your bandpass filters are going. Usually they won't need to take a lot of power - unlike the transmit low pass filters that will need, as you rightfully say, components that can handle the larger power. In my latest rig (which puts out just over 80W at full power) in the transmit low pass filter I used T68 toroids and mica capacitors (good for 500V). You'll also need to be mindful of shielding (I put mine in metal tins) and your coaxial connections - use good rf connectors and coax that will take the power. Thanks again. All the best.

@renuabel 2 жыл бұрын

Have you got the ferrite core part number, cannot find any...

@M0NTVHomebrewing 2 жыл бұрын

Hi Abel, the toroids are T37-6. (Note they are iron dust and not ferrite cores). Hope this helps. 73 Nick

@JimSky Жыл бұрын

The schematic is wrong. The transformers are drawn as parallel inductors. Thanks

@M0NTVHomebrewing Жыл бұрын

Hi Jim, the second sentence in the comments (marked 'IMPORTANT') makes this clear. Re-recording with a corrected schematic was not an option at the time. Well done for spotting it though! 73 Nick

@JimSky Жыл бұрын

@@M0NTVHomebrewing Thanks OM, I didn't see the correction. Enjoying your projects. 73

@M0NTVHomebrewing Жыл бұрын

No worries Jim. Thanks for watching. 73 Nick

@twobob 2 жыл бұрын

as a musician. such filers are obviously second nature. Might I ask is it possible to create a (or maybe a stack? of) low and high pass filter(s) and just have no losses on your wanted band?? Maybe I'm being stupid - in music I would do that???

@M0NTVHomebrewing 2 жыл бұрын

Hi! You can stack high and low pass filters but unless your wanted pass band is very wide indeed I don't know why you'd bother - that's precisely what a band pass filter is for. Also there is no such thing as a lossless filter in the real world. Every filter you insert will have some attenuation upon your signal. However, if you build your filter carefully then these losses will be acceptably low and you can compensate for this by adding gain (i.e. amplification) in other places. Hope this helps.

@twobob 2 жыл бұрын

@@M0NTVHomebrewing it makes perfect sense. Many thanks :)