#590

[@MrBanzoid]

It's interesting to see theory visualised. It makes mixers a bit more real and understandable. It also shows that things are a lot more complicated in the real world where you have all these harmonics and spurious signals popping up! Cheers.

[@Manf-ft6zk]

Thank you for the demonstration. With a frequency modulation of the rf signal (in this case of about 2-5MHz) you can recognize the individual mixing products by their width. The second harmonic has twice the width and so on. With a ramp on the amplitude of the fm, you can distinguish between up or down conversion. It might be easier with a rather slow sawtooth as fm signal when you use it together with the averaging function of the display. This gives plenty of information on many of the mixing products, where they come from.

[@BruceNitroxpro]

Manf 1234 , Interesting observation.

[@subramanianr7206]

Very interesting to see how a mixture works and I do understand the limitation of the drive level (here -7dBm). A beautiful visual demonstration of the IMD products on the display. I remember you once said it is a 100 MHz spectrum analyser. Your 70 MHz Oscillator and the filter are really handy in the demonstration. Thanks again.

[@pbaemedan]

Great video, the spurious emissions are called intetmodulation products. They are formed by the non-linear response of the diodes. Thank you.

[@JohnTarbox]

Exactly. That is why the drive level for the LO is specified by the manufacturer, one wants to operate the diodes in their linear region as much as possible.

[@IMSAIGuy]

@@JohnTarbox That explains a lot for me, thanks

[@egbertgroot2737]

I thought mixing was only possible if the signals are fed thru a non-linear circuit ....

[@JohnTarbox]

@@egbertgroot2737 Clearly I over-simplified. Does this help: www.qsl.net/va3iul/RF%20Mixers/RF_Mixers.pdf In short, you are not wrong.

[@egbertgroot2737]

@@JohnTarbox That is a nice PDF with information. You made my day. Thx!

[@vidasvv]

TNX 4 the demo, always get a better understanding when you can actually "see" whats going on in the real world! 73 N8AUM

[@brucebennett4378]

I love you circuits is possible for you to make a video for a OP-AMP LOG Amplifier & how to plot the log input and outputs and get the out voltages Thanks

[@IMSAIGuy]

Thanks for the idea!

[@herbertsusmann986]

I believe you can drive the LO with a 50% duty cycle square wave with a +7dBm fundamental amplitude and then the diodes act like on/off switches and you get the RF signal inverted and then non-inverted according to the LO polarity at the moment. This effectively multiplies the RF signal by a square wave so you get LO +/- RF and also 3*LO +/- RF, 5*LO +/- RF, etc... The even LO harmonics will be there also but at much reduced amplitude because a 50% duty cycle square wave only has odd harmonics. If the RF signal is high enough amplitude so it generates harmonics of its own in the ferrite transformers then you get all those mixing products as well. Normally the RF amplitude is small so you don't tend to get those harmonics much.

[@yuriantunes2916]

Hello there, can you please tell me where do you find those nice casings you use on your circuits?

[@IMSAIGuy]

eBay seller had surplus. I don't think there are anymore

[@Tjm-eh6ej]

What oscillator do you use?

[@IMSAIGuy]

kzbin.info/www/bejne/qWOTenVvbMuSgLMsi=IX2iDkvkfu9ki2FB

[@JohnTarbox]

If you had two clean signal sources other than your 70 MHz oscillator, it would be interesting to use those two sources into the mixer with an output frequency of 70 MHz. Then you could feed the output of the mixer into the70 MHz filter and observe the output of the filter.

[@AECRADIO1]

SBL-1, TFM-2?

[@IMSAIGuy]

sbl-1x

[@mepacrina9291]

I expected to open the lid :) ... and see the magic ;)

[@IMSAIGuy]

most are hard to see, many are encapsulated. it is just a toroid and some diodes.

[@mepacrina9291]

@@IMSAIGuy yeap, I know, and some transmission lines (some with weird shape ;) ) , I do not resist to open the box to see mixers, mmic or YIG when repairing measurement instruments or scrapping obsolete equipment . (only few filters remain intact, I do not want to spend hours retuning :)) ). Thank you for answer, nice video.

[@egbertgroot2737]

Would have been interesting to see when RF freq in was higher than LO freq.....

[@JohnTarbox]

Another ham who with a KZbin channel who goes into the practical aspects of building a double-balanced mixer is Charlie Morris, ZL2CTM. Here is a link to his video on making a DBM: kzbin.info/www/bejne/rHLcfGauqLmieKc