Problems using SA612a for AM Modulation - Page 1
Forum section: electronics / beginners

author: SRU
author_rank: Newbie
timestamp: December 19, 2024, 08:22:21 pm
content: Hello,Can someone confirm that my SA612a is genuine?I simulated my small schematic using LTSpice with expected results, but building the circuit twice using different chips from the same delivery, i get an additive mixing instead of the expected / simulated multiplicative mixing.Does anybody have an idea what i need to do wrong to get this failing result ?Thank you very much for your efforts!greetings, SRU

author: radiolistener
author_rank: Super Contributor
timestamp: December 19, 2024, 10:08:54 pm
content: Quote from: SRU on December 19, 2024, 08:22:21 pmwhat is wrong with your results? Can you show example?

author: iMo
author_rank: Super Contributor
timestamp: December 19, 2024, 11:00:53 pm
content: I would remove the C3..

author: SRU
author_rank: Newbie
timestamp: December 20, 2024, 05:50:26 am
content: Quote from: radiolistener on December 19, 2024, 10:08:54 pmThat is what the 5 attachments are for. Are these not viewable for everybody?Anyhow, add.jpg shows the false signal, out1.png shows the signal i am after.Quote from: iMo on December 19, 2024, 11:00:53 pmThanks IMo, will try (even if that is an example from the datasheet for external oszillators)Greetings, SRU

author: iMo
author_rank: Super Contributor
timestamp: December 20, 2024, 07:43:12 am
content: Quote from: SRU on December 20, 2024, 05:50:26 amCould you point me to that datasheet?? I've never seen such an example..

author: radiolistener
author_rank: Super Contributor
timestamp: December 20, 2024, 10:57:55 am
content: Quote from: SRU on December 20, 2024, 05:50:26 amCan you provide more details on how you get that screenshot? Which time/div scale? What is sync source and trigger type?Did you tried to take picture at slower time scale? (higher time/div setting)It will be nice to see how looks modulation signal at exactly the same oscilloscope settings.

author: CaptDon
author_rank: Super Contributor
timestamp: December 20, 2024, 02:07:51 pm
content: Digital storage scope? They alias like this. I had a horrible time to get the correct waveform displayed even though the output was actually working correctly. Some scopes will at slow sweep speeds drastically reduce the sample rate and you get the weird waveform. see if you can slow the horizontal sweep to correctly display 2 waves of the audio frequency (at 1 KHz it would be 2ms total or .2ms/div) and then if the scope allows it crank up the sample rate. It took me some fiddling to get musical AM modulation of a 1MHz carrier looking proper on my Tek TDS644B and it still looked much more natural when I switched to an old purely analog scope Tek SC504. Maybe your circuit is broken or maybe the scope needs more fiddling? Do you have an old analog scope?

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 20, 2024, 02:23:34 pm
content: Quote from: CaptDon on December 20, 2024, 02:07:51 pmI'd bet that the picture posted is from an 'old' analog scope.

author: jwet
author_rank: Frequent Contributor
timestamp: December 20, 2024, 02:55:25 pm
content: C6 at the input pins 1&2 should be removed. This is a differential type input and this cap is shorting the two together.

author: CaptDon
author_rank: Super Contributor
timestamp: December 20, 2024, 03:38:09 pm
content: I believe you are correct stating the picture is from an old analog scope. Looking closely at the picture I can see this is an old analog C.R.T. display and no digitizing.

author: SRU
author_rank: Newbie
timestamp: December 20, 2024, 04:11:33 pm
content: Quote from: PA0PBZ on December 20, 2024, 02:23:34 pmYou are completely right: Hameg 203 full analog... Not that there is not a siglent 1202 available, but it rests for 5 years in a box and i would need to retrain how to use it. The hameg however, produces stable signals instantly.

author: SRU
author_rank: Newbie
timestamp: December 20, 2024, 08:00:34 pm
content: Quote from: radiolistener on December 20, 2024, 10:57:55 amPlease find attached the screenshot done with the siglent. Well, the upper right corner 711.148 kHz confuses me; carrier is 7010kHz.C3 and C6 have been removed.

author: SRU
author_rank: Newbie
timestamp: December 22, 2024, 04:37:39 pm
content: Hi,I was able to solve it by using a crystal.Thanks all for the help!Greetings, SRU

author: radiolistener
author_rank: Super Contributor
timestamp: December 23, 2024, 12:15:18 pm
content: Quote from: SRU on December 22, 2024, 04:37:39 pmsomething still going wrong - waveform is asymmetric and has some spikes.AM 80% modulation should looks like this:

author: SRU
author_rank: Newbie
timestamp: December 28, 2024, 08:18:24 pm
content: You are absolutely right.But i have my proof of concept, and i can tell that the chips are working.I have seen that all too, but that is fine tuning which i will fix by myself.Thanks again for your help!(must i close this thread somehow? Was not able to find a matching button...)Greetings, SRU