I was able to set the deviation on an FM transceiver using this method using a mobile phone, an SDR receiver, and an oscilloscope. It took a couple attempts because the makeshift signal generator did not keep a constant audio level as the frequency changed. Once I realized the problem, I changed my method a bit. Take the specified deviation in the service manual and divide by 2.405. Use a tone generator to produce tone at this frequency. Set the tone level to what is specified in the service manual by checking with an oscilloscope. Play tone into radio input while transmitting. Watch the waterfall on the SDR transceiver, and adjust the radio's deviation until the carrier frequency disappears. When I was finished, the resulting adjustment was within about 1.5% of what the radio arrived with.
Tnx Peter and congratulate you on doing this all in English so that you can reach a large audience.I'm wondering if you do this as a hobby or professionally. It does not matter, you are doing a great job!
I used to give analog and digital modulation lectures long time ago. I wish I had got an SA to show my students the modulations spectrum in the frequency domain. Thanks.
Great job Peter, I loved the way you tied things back to the mathematical fundamentals, it gives me a warm and fuzzy feeling ;o) Keep up the great work and thanks for sharing.
Very cool, Peter! Thanks for the thorough description. I've heard of the Bessel Null function in FM broadcasting, but it's neat to see what it means and how it's derived. You should do more theory discussions like this! :-)
Hi Peter, an informative presentation. I used my OWON XSZ1015P Spectrum Analyser and my Marconi 2031 Sig Gen to test it out at 28MHz with 5KHz deviation at -10dbm. I found 2 lower frequency nulls #1 at 581.4Hz, #2 at 909.4Hz and #3 at 2.083KHz all nulling down the fundamental to about -90dbm. The Spectrum Analyser in ''modulation mode'' showed a Peak deviation of 5.05KHz, 5.04KHz and 5.01KHz. All quite close results. Based on the modulation Index of 2.4048 for 1st Bessel null this calculates to an audio freq of 2.076KHz for 5.00 KHz deviation. So I am confused by the 1st 2 nulls as they should not be there. I think the best way is to to use the formula to calculate the audio freq based on Audio (KHz) = Deviation/2.4048 and trim it for a null on the SP. Cheers Mike
I need to see what the shape of the Modulating signal is on my Harmonica notes. looking at one note at a time. The vibrating free-reed is basically the carrier. So, I see on the spectrograph that the fundamental frequency is spread out wide. But it is a wide blurred line. I suspect that there is FM going on. Can you give me any tips.
Great video for introduction to FM and FM deviation. However the carrier null shown does not seem to be the first null (2.4). Audio frequency at start was very low which means very high m. As the fm is increased m decreases and the null shown is a higher order null. Deviation by calculation should be much higher than 5 KHz.
8:56 but this diegramm is a little bit confusing , I mean for FM because I usuelly can't see the modulation like that on my oecilloecope unless there is a really slow signal like 10 Hz or something so then I can see sinewave expanding on the screen...
Hi Peter, I am trying to fix my HP8590L spectrum analyzer and would like to seek your advice on some of the issues. 1. I tried to measure the signal path from the RF to the IF with a 500Mhz scope which I borrowed but I cannot see any sensible signal between the output and the input of the different stages. Of course at 2.4 Ghz I would expect issues with the scope shorting the signal due to capacitance but at 300 Mhz I expected it to work. When I disconnect the wires from the SA I see on the screen that the signals disappear hence there must be a signal inside the cable its just that my scope doesn’t seem to pick it up. Do you have a recommendation how I could check the signals, I do not have another spectrum analyser. I tried a small hand made coil (contact less) but didn’t help either. Is it impossible to measure in your opinion ? 2. I see a nice signal on the SA at a SPAN of 100khz and above. The moment I tur the nob below 100Khz the signal becomes useless. Can you recommend where to search ? www.eevblog.com/forum/repair/hp8590l-spectrum-analyzer-calibration-signal-issues/new/?topicseen#new Highly appreciated Bjoern
Good evening, thanks for the interesting video. I have a question: @minute 37'30" you said "...we have seen that our Bessel zero is @ 2.4". I searched backward but I didn't understand how you can say that. Please can you help me to understand? Thanks again. Andrea
Ein sehr guter Vortrag. Ich würde es für begrüßen, wenn Sie diesen Votrag für alle, die nicht englisch verstehen, eine deutsche Version zu veröffenlichen.
It worked! I was able to get an estimate of the deviation variation of an old signal generator using my basic Siglent 100MHz oscilloscope. But not in real time (the scope only takes 1024 points, not enough frequency resolution) but saving the signal values (about 20000 points) and doing DFT via software and using Carlson bandwidth formula.
Great and many thx ! I didn't have a clue that the Bessel functions have something to do with the spectrum of a FM modulation, now you just proved it. I vote to have now some more expalantions (of the math side), could you give us a site or something to read more about this ? When I study for the HAREC license, these little formulas sound silly, I would be happy and remind easyier if I can unterstand the math under the formulas.
squelch is used in receivers not transmitters. The squelch basically mutes the receiver when the signal strength falls below a certain level. Once the signal strength is above a certain level the squelch "opens" and the receiver un-mutes. The squelch level threshold is usually controlled by the user depending if they want to hear strong signals or weak signals.
I think the bessel 0 point you have achieved here is not the first bessel 0 point (i.e modulating index =2.41) because if it was so then while you were increasing the frequency of the audio signal amplitude of the central tone should go from negative to zero as shown in the bessel graph. But in your case amplitude of central tone was coming from positive to zero while you were increasing the frequency so maybe it was any one of the next bessel 0 points.
Dear Sir , thanks a lot , please I have question : If I set the carrier ( from waveform generator ) to say 10 KHz , set the deviation ( FM modulation from the waveform generator ) to 1 KHz , so is it possible to view the analog FM signal on the Oscilloscope ? Thanks and best regards
FM deviation it's not easy to understand, but we appreciate a lot what you have done for your followers. It's not so clear 4 me, how it's possible see deviation without carrier signal. :(
I was able to set the deviation on an FM transceiver using this method using a mobile phone, an SDR receiver, and an oscilloscope. It took a couple attempts because the makeshift signal generator did not keep a constant audio level as the frequency changed. Once I realized the problem, I changed my method a bit.
Take the specified deviation in the service manual and divide by 2.405. Use a tone generator to produce tone at this frequency. Set the tone level to what is specified in the service manual by checking with an oscilloscope. Play tone into radio input while transmitting. Watch the waterfall on the SDR transceiver, and adjust the radio's deviation until the carrier frequency disappears.
When I was finished, the resulting adjustment was within about 1.5% of what the radio arrived with.
How great it is to attend one of professor Peter's lectures at TRX University without leaving home. Thanks Prof P !
LOL glad that you liked it Todd! Thanks for feed-back 73
Very interesting and thorough, as always. Thank you again for your video production here and for all the others.
You are a genius sir. So well explained. A pleasure to watch.
Excelente profesor. Saludos desde México!
I clear understand about FM deviation by your video ,so i'm very thank you for it.
Another great tutorial Peter. Well done!
Thank you Buddy! Take care my friend 73
Tnx Peter and congratulate you on doing this all in English so that you can reach a large audience.I'm wondering if you do this as a hobby or professionally. It does not matter, you are doing a great job!
Thank you so much!
Awesome - now I understand better. Thank you for taking the time to explain sir.
great presentation i have ever seen ... Now i have seen my entire theory in practical experience thanks a lot professor
Hi Peter, Thanks for taking the time to do a FM deviation tutorial, always enjoy your videos. 73
Thanks for watching Larry! 73
I used to give analog and digital modulation lectures long time ago. I wish I had got an SA to show my students the modulations spectrum in the frequency domain. Thanks.
Great job Peter, I loved the way you tied things back to the mathematical fundamentals, it gives me a warm and fuzzy feeling ;o) Keep up the great work and thanks for sharing.
Thank you Michael! All the best 73
Great video, your a great teacher as always thank you very much for all information, Have a great day Peter
Thank you Dennis! 73
Very cool, Peter! Thanks for the thorough description. I've heard of the Bessel Null function in FM broadcasting, but it's neat to see what it means and how it's derived. You should do more theory discussions like this! :-)
Glad that you liked it Jason...Well some theory discussions are already here on my channel. Thanks for watching 73
Well done. Thanks for mentioning the original drum application
Hi Peter, an informative presentation. I used my OWON XSZ1015P Spectrum Analyser and my Marconi 2031 Sig Gen to test it out at 28MHz with 5KHz deviation at -10dbm. I found 2 lower frequency nulls #1 at 581.4Hz, #2 at 909.4Hz and #3 at 2.083KHz all nulling down the fundamental to about -90dbm. The Spectrum Analyser in ''modulation mode'' showed a Peak deviation of 5.05KHz, 5.04KHz and 5.01KHz. All quite close results. Based on the modulation Index of 2.4048 for 1st Bessel null this calculates to an audio freq of 2.076KHz for 5.00 KHz deviation. So I am confused by the 1st 2 nulls as they should not be there.
I think the best way is to to use the formula to calculate the audio freq based on Audio (KHz) = Deviation/2.4048 and trim it for a null on the SP. Cheers
Mike
Vielen Dank für das perfekte Video. Einfach und gut erklärt !
Freut mich das es gefällt. Danke fürs vorbeischauen...
I need to see what the shape of the Modulating signal is on my Harmonica notes. looking at one note at a time.
The vibrating free-reed is basically the carrier. So, I see on the spectrograph that the fundamental frequency is spread out wide.
But it is a wide blurred line. I suspect that there is FM going on.
Can you give me any tips.
Hello Peter, Good explanation. Have learned something again, thanks.
Thanks for feed-back Wob! 73
I understand so much more now. Thank you so much good sir
did you use a pure sinewave for the modulation?
So to sum up.. feed in 2khz and adjust deviation for the carrier or bazel null on the spectrum?
Great video for introduction to FM and FM deviation. However the carrier null shown does not seem to be the first null (2.4).
Audio frequency at start was very low which means very high m. As the fm is increased m decreases and the null shown is a higher order null. Deviation by calculation should be much higher than 5 KHz.
Don't the peaks technically go out to infinity but they are below the noise level?
Great educational video
Wonder how did you inject a 28 mhz carrier signal ,because your sig generator goes only to 25 mhz?you use another generator???? thanks ...Ruben
Hey dr op. Nice video!!! What is the m value of CB radios modulation? Is has to be smaller than 5?!
8:56 but this diegramm is a little bit confusing , I mean for FM because I usuelly can't see the modulation like that on my oecilloecope unless there is a really slow signal like 10 Hz or something so then I can see sinewave expanding on the screen...
Hi Peter, I am trying to fix my HP8590L spectrum analyzer and would like to seek your advice on some of the issues.
1. I tried to measure the signal path from the RF to the IF with a 500Mhz scope which I borrowed but I cannot see any sensible signal between the output and the input of the different stages.
Of course at 2.4 Ghz I would expect issues with the scope shorting the signal due to capacitance but at 300 Mhz I expected it to work. When I disconnect the wires from the SA I see on the screen that the signals disappear hence there must be a signal inside the cable its just that my scope doesn’t seem to pick it up.
Do you have a recommendation how I could check the signals, I do not have another spectrum analyser. I tried a small hand made coil (contact less) but didn’t help either.
Is it impossible to measure in your opinion ?
2. I see a nice signal on the SA at a SPAN of 100khz and above.
The moment I tur the nob below 100Khz the signal becomes useless.
Can you recommend where to search ?
www.eevblog.com/forum/repair/hp8590l-spectrum-analyzer-calibration-signal-issues/new/?topicseen#new
Highly appreciated
Bjoern
Thanks for your lesson Peter !
Glad that you liked it 73
Great explanation. Thanks
很专业 虽然现在我听不懂，也不明白，以后我会懂的 Very professional although I do not understand now, do not understand, I will understand in the future
Thanks for feed-back. Do you have just started your electronic studies?
Good evening,
thanks for the interesting video.
I have a question: @minute 37'30" you said "...we have seen that our Bessel zero is @ 2.4". I searched backward but I didn't understand how you can say that. Please can you help me to understand?
Thanks again.
Andrea
If you go back to minute 30:42, there's a graph of 'J' signals. 2.4 is the first zero crossing of J0 signal. I hope that makes sense
Ein sehr guter Vortrag. Ich würde es für begrüßen, wenn Sie diesen Votrag für alle, die nicht englisch verstehen, eine deutsche Version zu veröffenlichen.
Nice video, I think I will watch it again and I will add it to my "electronics education and stuff" list of saved videos. 73 Leo
Glad that the video is useful to you! Thanks for feed-back Leo 73
Thanks for the explanation. I will try to measure the deviation of my signal generator FM modulation option which is not documented.
Good luck
It worked! I was able to get an estimate of the deviation variation of an old signal generator using my basic Siglent 100MHz oscilloscope. But not in real time (the scope only takes 1024 points, not enough frequency resolution) but saving the signal values (about 20000 points) and doing DFT via software and using Carlson bandwidth formula.
Hello. Which rf generator do you use?
Terrific video! What software is that, it’s fantastic to have that on your pc
thank you a lot! this was very helpful
Great as usual!
Thanks Peter
Thank you Eduardo! 73
Why there are minus signs and why is start with minus sign in vertical -axis?
That was pretty interesting ... Thank you 👌
Great and many thx ! I didn't have a clue that the Bessel functions have something to do with the spectrum of a FM modulation, now you just proved it. I vote to have now some more expalantions (of the math side), could you give us a site or something to read more about this ? When I study for the HAREC license, these little formulas sound silly, I would be happy and remind easyier if I can unterstand the math under the formulas.
Glad that it was in any kind helpful for you! Thanks for watching 73
Can I ask you how does squelch work in FM transceivers? Is it signal strength based or something else? Thank you.
squelch is used in receivers not transmitters. The squelch basically mutes the receiver when the signal strength falls below a certain level. Once the signal strength is above a certain level the squelch "opens" and the receiver un-mutes. The squelch level threshold is usually controlled by the user depending if they want to hear strong signals or weak signals.
Thanks a lot Sir, it is very educative and answered lots of questions that I had in mind. Keep it up !
gld that my video was of any help...Thanks for feed-back 73
Beautiful equipment!
Thankyou so much.
splendid, magnificent, brilliant, dazzling, glittering, glowing, radiant, gorgeous, transcendent, impressive, imposing, spectacular, striking, stunning, glorious, superb, majestic, great, awe-inspiring, breathtaking, fine; informalsplendiferous; raresplendacious, magnolious
I think the bessel 0 point you have achieved here is not the first bessel 0 point (i.e modulating index =2.41) because if it was so then while you were increasing the frequency of the audio signal amplitude of the central tone should go from negative to zero as shown in the bessel graph. But in your case amplitude of central tone was coming from positive to zero while you were increasing the frequency so maybe it was any one of the next bessel 0 points.
Hi Peter,
what do you mean, could I also measure that with a CW receiver and narrow band filter of for example 180Hz?
73 Bernd
Hi Bernd, not entirely sure what you mean. Well you may see the vanishing centre frequency with varying the AF frequency. Just try it. 73
TNX for another great video !!! 73 N8AUM
Great Video , please could you kindly help to view FM signal and AM on Oscilloscope , so to check these signals in Time domain .
You will have trouble to see the FM deviation on the scope as the frequency delta is to small compared to the transmitter frequency.
Dear Sir , thanks a lot , please I have question :
If I set the carrier ( from waveform generator ) to say 10 KHz , set the deviation ( FM modulation from the waveform generator ) to 1 KHz , so is it possible to view the analog FM signal on the Oscilloscope ?
Thanks and best regards
What is the make and model spectrum analyzer, please?
The entire answer is here in my video ua-cam.com/video/9wYDpzf-sl8/v-deo.html
FM deviation it's not easy to understand, but we appreciate a lot what you have done for your followers.
It's not so clear 4 me, how it's possible see deviation without carrier signal. :(
Hi Alessandro well finally Bessel is the secret but to understand it more in depth we would need the to use the maths approach. Thanks for watching 73
I like your accent :)
thanks!
50kh dummy plug?
Junkbox