Clairtone Console Stereo Video #30 - FM Alignment Using an SDR Radio

As an experiment born out of frustration, I attempt to utilize my cheap RTL-SDR radio as a spectrum analyzer to assist with the alignment of the IF stages and the detector stage. And it seems to work out!

[Rebel]

That radio show sort of reminds me of an npr show called "Wait, Wait, Don't Tell Me", lol.

[randomsteve]

Let us recap this video...
After the manufacturer of the SDR dongle complained about not getting enough screen time for his toy, Jim set out to remove the last traces of factory alignment, until in a finale furioso he proudly presents a radio lacking separation, sensitivity and only barely manages stereo decoding with the signal generator blasting into it.
Good show...

[jcurnutte]

So peak the coils and set the stereo band pass for max and then check the dial and tweak the oscillator and antenna to get the dial on track and max the antenna (and the 67Khz trap is fixed and can’t be changed because it’s core is set to just spin around and not move in or out it’s there to keep the coil locked in)

[jcurnutte]

The IF is correct and that coil that puts AM in the signal because it needs it to allow the tuner slugs to be adjusted just like an AM radio which is needed to align the oscillator and antenna trimmers and that’s the issue and the stereo is already present in the tuner regardless of if you are tuned to a stereo or mono signal the coils are set to the main and stereo carriers and turning the slugs varies the frequency of the oscillator and antenna coils and because they are double coils wound to the correct difference frequency between the stereo channels there is really no decoder but a band pass for the right and left channels and if the band pass is off the signal will show up as a mono signal because the signals being transmitted by the radio station is coming through as a regular signal and that’s why when tuning you get multiple peaks because you are tuning in one or the other signal and that’s why you need to have the radio to peak in between the two signals so when you tune it the best signal is in between the two signal curves

[paul-c]

Why why why, did we buy all this expensive state of the art test equipment, when all we needed to do was buy a cheap & nasty SDR, buy 2 get 6 free toy.

[jcurnutte]

And let’s not forget the deviation and when that is factored in the IF is spot on at 10.785 MHz ( +_ 75 KHz) that means it can be 10.775 on the high end down to 10.625 on the low end)

[harrystevens]

Jim your far to eager to carry out a non-needed so called alignments, you screwdriver the hell out of every radio that ever arrives on your bench with dire results. Wish I could be more positive with my comments but hell your bad.

[jcurnutte]

And the IF frequency is wrong because at the factory they messed up the number of turns in the IF coils causing the IF to peak at the wrong frequency and it can’t be retuned to 10.7Mhz because they are wound to peak at a different frequency

[jcurnutte]

10.785Mhz is what the coils are wound to resonate at and can’t be changed unless they are replaced so chalk it up to factory error

[SIXSTRING]

The reason your scope is not reading the right voltage and not picking up things right in the time base is you have all the variable controls out and they are not at the setting they are supposed to be when off. No wonder you get inaccurate readings off that old Tek scope. Read the manuals on your equipment and it would get rid of half the 30+ videos of babbling guessing. Geez Louise

[jcurnutte]

And it doesn’t matter if you have the stereo signal coming out from the signal generator it’s coming from the tuner and without a way to turn it off you will get the double humps and the receiver is picking up both signals but it’s not passing it on to the amplifier because the circuit is very crude and is not capable of deciding a weak signal

[jcurnutte]

That’s where you should have stayed because you got it because that’s the way it came from the factory and the instructions are wrong and those wave forms are incorrect and the one thing that you never got to is the oscillator and antenna alignment and that’s where is messed up just leave everything else alone and do that part first