35 - AM Modulators
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- Опубликовано: 12 сен 2024
- Nick M0NTV builds and tests a couple of simple AM Modulators.
Fesz AM Modulator video: • Electronics tutorial -...
My Schematic: drive.google.c...
Alan's video (W2AEW) on producing AM modulation with a double balanced diode ring mixer: • #345: Generating AM an...
My Schematic for DC Offset Injector: drive.google.c...
Many thanks too to Bill (N2CQR) & Pete (N6QW) for facilitating the transmission of the Soldersmoke podcast on 1MHz AM!!!
The first modulator is ok if you are only looking for low modulation levels. It`s very prone to distortion if you try to get near 100% but is an easy build for testing purposes. The diode ring modulator on the other hand is capable of broadcast quality modulation when properly adjusted. When used for AM you might not think that balance is too important as you are going to unbalance it anyway to generate the carrier, however this is not the case if you want the best performance. This is because if it is slightly unbalanced to begin with, when the audio signal goes near zero, the modulator will still be passing some RF and this will have the effect of not allowing the negative modulation to get near 100% carrier pinch off, (I limit my neg mod to 98% to avoid splatter). Don`t forget that this type of modulator will be followed with more than 30db of amplification, so any leakage can mean watts of carrier that cant be controlled with the audio signal. Balance can be achieved with using a ready made ring modulator (expensive) or for the rest of us, carefully selected 1n4148 diodes. I have used the ring modulator with great success for low power (10s of watts) but for higher power rig builds, I prefer high level modulation of either a class E, D or C transmitter using pulse width modulation. You can think of this as supplying a transmitter output stage from a switched mode PSU thats output voltage is controlled with the audio signal. The commercial medium wave transmitters used this scheme, achieving DC to RF conversion efficiency of over 90%. As you can probably tell, I am a big fan of AM, when properly done, it can sound fantastic! You will mostly find me on 1977 and 3615khz You have done a great demonstration as usual and a special thanks from the AM lads for encouraging interest in the subject.
Thank you so much for watching and for your helpful and detailed comments. I confess to being a 'Newbie' as far as AM is concerned but I'm having some fun learning more. I may have to pick your brains when it comes to demodulation. It's not so much the demodulation itself as the selectivity and frequency translation that precedes it - the whole no-no of inserting a locally generated carrier on top of an existing (out of phase) carrier etc. This is very much still a work in progress! Thanks again. 73 Nick
@@M0NTVHomebrewing You just reminded me of another technical can-of -worms, that is how would you demodulate double side band suppressed carrier? At first it seems simple, just re-insert the carrier and have an IF that is wide enough to accept both side bands. However, this will not work (sound nice), because the re-inserted carrier would have to EXACTLY (not nearly as in ssb) match the carrier frequency and PHASE. This is a work in progress for me as being able to lose the carrier and keep the side bands and audio quality, would be very nice. As for demodulation and IF architecture of a good AM receiver, this is fairly straight forward, depending how deep you want to go. I have cheated a little as I kept all those PYE taxi radios of the 80s (remember those?) They are a great source for crystal filters and IF coils. Happy to share any information I have, just email me if needed. address on the ABOUT tab on my RUclips info.
Thanks again Chris. That's the thing about going back over the basics isn't it - it turns out some of the things you thought you knew and were quite simple turn out to be not quite so simple as you once thought! It's all good fun. Thanks - I'll probably be in touch via email at some point. 73 Nick
I've used the PWM scheme you describe with great results in 50, 100 and 200 watt Class D AM Transmitter on 160, 80 and 40m. When you build such a transmitter you realise what a huge advance PWM technology is for AM. 73 to you both and keep experimenting.
Thanks very much Paul. It's a whole new world to me! 73, Nick
Hi Nick, great to have you back and hoping you had a speedy recovery? Clearly explained and loved the summary. 73 Bob
Thanks very much Bob. 73 Nick
Your videos always motivate me to turn the soldering iron on. Built a top band Poppet AM tx (early Sprat design) and still think that that 2km to a friend was good DX! Learnt so much from a simple project.
Thanks very much Graham. I know what you mean by learning from doing: I've learnt an awful lot by doing it wrong! It's a great feeling when you do get it right. 73 Nick
Glad to hear you are well again! 😃Thanks so much for this video, it filled in some knowledge gaps and like you, crystallised some previous knowledge. Seeing the effects on a spectrum analyser and oscilloscope was really useful.
On a different note, after a 35 year break from the hobby, I've had my licence reinstated and am now G0ACE. 😁
Thanks very much Ace! Many congrats on your reinstated license. That's great you could get the 'ACE' into the callsign. Have fun. 73 Nick
Classic stuff, and very nicely done.
No matter ho many times I see this demonstrated, it takes me right back to the time when I first started out in electronics and Amateur Radio. Proving that all those funny pictures in the books and magazines were correct. 🙂
Hope the recovery continues well, that's more important than Utube videos no matter how much we look forward to them.
Andy
Thanks very much indeed Andy. 73 Nick
Great video Nick, I really love to see the 'back to basics' type stuff - so good to see these things illustrated this way!
Sorry to hear you've been unwell, getting towards beer season!
73
M0VLT
Cheers Al! Yes Mate - absolutely! See you soon. 73 Nick
Lacking 'presence' and I can see a little energy in the skirts ;)
Good to see you back Nick, 73 M0UAW
Thanks! That made me chuckle!
Nice examples! I have a little AM modulator on my bench that is an SA612 that's unbalanced by a DC offset, and works similarly to your last one. So, it works with a Gilbert cell too.
Thanks. That's interesting to know. 73, Nick
Really well presented Nick. Good job.
Thanks so much Tony. Hope you're doing OK. 73 Nick
There's something fascinating about AM for me, I build a simple AM TX / RX for 50Mhz a while ago and loved it although my only contact was with my (licenced) XYL.
Sounds great David. 73 Nick
Great content Nick, glad to see you tackling AM. A 1496 Gilbert Cell mixer also makes a decent amplitude modulator too, if unbalanced. NE602 probably can do the same. Follow on question... what class of power amp should you use to bring your milliwatt AM up to a few watts for a workable AM transmitter 🤔? 73 Paul VK3HN.
Thanks Paul. Hope you're doing OK. I might have to pick your brains a bit more on this stuff but I will contact you by email. Thanks again. 73, Nick
Thank you for the videos. Well done. Could you demo a LTSpice model (such as this one) and cover some of the analysis that can be done for RF circuitry? I see you have tran and ac directives listed presumable for Time and Frequency domain simulation. I see lots of Ham Radio videos for modelling circuits in LTSpice and I find videos that cover it generally for electronics but can't seem to find one that covers specifically both for amateur radio circuitry modelling. Thank you again. Cheers Todd
Thanks Todd. That's a great idea for a video. I'll put it on the TODO list! 73, Nick
I was sick for a few weeks, and just napping most of the time. So I have no complaint about you. I hope you're feeling fine now. Your videos are missed.
Thanks very much John. Yes, I'm fine! Glad you enjoy the videos. Hope you are feeling better yourself now. 73 Nick
Thank you so much for sharing information!
You are welcome!
Very entertaining and informative. Thanks.
Thanks very much Trevor. Glad you enjoyed it. 73, Nick
Amazing, thanks sir !
Thanks very much. You're welcome! 73 Nick
Interesting topic, well presented. Thank you. 2E0FXZ
Thanks very much Stephen. 73 Nick
When you show the modulated 1KHz in the time domain, would it not be an idea to trig the oscilloscope on the 1KHz signal instead of the RF signal?
Hi Jespur, thanks for the suggestion. When I eventually revisit the AM stuff I'll bear it in mind. 73, Nick
@@M0NTVHomebrewing Adjusting the holdoff control also helps stabilize the display.