Another mailbox item (and problems with crystal oscillators)
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- čas přidán 10. 09. 2024
- Sometimes crystal oscillators don't start. Sometimes components that should work don't. Watch as I try some experiments with a 1 transistor CW transmitter that has problems starting.
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Hi Peter, hope you are doing well! You keep pumping out solid, entertaining videos that teach me things. Thank you for all the work you do! 73 from Tracy VE3TWM.
Thanks for taking the time to investigate this. Super interesting to watch and learn.
Good job Michaela for taking the time to learn how to design a PCB and get it fabricated and assembled at the Factory. It's incredible how cheap an electronic device can be made this way. I did my first JLCPCB this year and it was a very worthwhile project! Once you know how it is quite tempting to lay out a PCB for a circuit you want to try. But I've learned that for all but the simplest circuits, it's best to prototype them ugly style or on a simple hand drawn and etched board first. Once you have it working, then run up a JLCPCB! Good luck with your projects!
Very cool, hope to see more designs down the road! I would like to make my own as well one day
I think it was very nice of Mr VK4XSS to send this and share this resource. For such a small and simple circuit, SMD is perhaps overkill - but a nice challenge to go so tiny (a challenge that will need more work to have it realised). Great that you tried to get it to do its RF wobble thing....."the neater it looks the less likely it will work"....PURE GOLD! Thanks for the educational content on your channel.....I always learn something here, in this case "crystals are not all created equal" and "messy and bigger is often better". The home-brew tips you provide, ideas and sheer enthusiasm you exhibit is inspiring. Oh and Mr XSS thanks for the PCB resource!
Mrs ;)
I might try doing another production run with through hole footprints for the crystal and incorporate the changes that Todd suggested below.
@@michaelawheeler64 oooops ….. Mrs! My apologies ….. the name should have given it away!!!! The transmitter was too cute…. If it gets past prototype …. Sign me up!!! 73
I think this device was designed to be a key holder. Not too big. The idea was very clever.
Great video man. Thanks.
so interesting and so well explained - thanks ever so much for your interesting content.
a cristal also it can be used as a vedio emplifiler
So L1 lit up? Some one either doesn’t know or, more to the point, doesn’t care, about current handling capacity.
I believe this is the same circuit from your breadboard/cutting board project? I had to change out the 22uh inductor for a 100uh one and got it to work. However, with 12v it fried the BD139 with in the 3rd CQ. I'm not sure how you have such good luck with them not getting EXTREMELY hot. Inquiring minds want to know. WV3V- Jason
Two things to do: 1. Put a resistor (10 - 100 ohm) in series with the key to limit current as mentioned by Todd. 2. Put a heat sink on the BD139 tab. I needed neither but YMMV.
Professional engineers conduct design reviews and prototype tests behind closed doors, but if you're an amateur I guess you do them in front of an international audience. I'm sure VK3FUR won't be embarrassed , and neither should VK3YE if it's pointed out that his original chopping-board design provided for no current limiting in either the collector or emitter circuits. Putting as little as 10 ohms before the RFC on the Vcc line alone might have prevented failure of the SMD choke, and some degeneration in the emitter circuit would have further limited the current and stabilized the whole oscillator. In fact, unless the power supply was current-limited, prolonged key-down would surely smoke the transistor as thoroughly as that surface-mount device was. So running a BD139 full-bore as an oscillator wasn't necessarily a better idea than using a light-duty SMD choke on an unnecessarily-small PCB layout.
“Everything should be made as simple as possible, but no simpler.” Albert Einstein, 1950.
But if you put that resistor in VCC…… that would be a bit biased, don’t you think? 🤔 😎😝….nerd electronics joke!
I often wonder when I see simple transmitters with low pass filters directly on the output - are the filters designed assuming 50 Ohms in and out, disregarding the actual output impedance of the transmitter? Without matching, there's going to be quite a bit of reflected power, maybe that adversely affects the circuit?
There is a certain 'sweet spot' around 2w where the final stage's output impedance is around 50 ohm with 12 volts. That makes things easy. You can also get around the problem with higher power stages (say ~5w) with a 4:1 transformer which is based on the PA impedance being 12.5 ohm. You are right, you do need to think about this if there is a significant mismatch and you are aiming for maximum efficiency. There are some online articles that explain this more thoroughly.
@@vk3ye - Thanks so much for your reply, Peter! The reason I ask is I’ve even seen many designs that omit matching, even 50 or 100mW VHF TXs running from a 9v battery, (eg Fredbox, Sixbox, etc.?) which must make them seriously inefficient with the PA’s high output impedance, but of course at those power levels it’s likely just ignored. I’m curious if a high amount of reflected power in the circuit you demonstrate in your video would be enough to stop oscillations with a marginal or smaller crystal.
Thanks for the marvellous videos, Peter!
I've had a run of 100 done with them before too
✋73's🎙 KD9OAM🎧📻📡