#1647

[@erikburman530]

Sometimes it's a comfort to simply tune into your channel and escape from all the crap happening in the world right now.

[@TonyBarr99]

This was an awesome video. I learned so much about FM & bandwidth. Thank you.

[@catalinalb1722]

Oh.... that reminds me of the wireless headphones I had back in the day, they were running on Infra-red! Quite funny!

[@KG4JYS]

You already blew it. "Don't turn it on, take it apart," meaning disassemble it before testing it.

[@leonerduk]

Honestly surprised how simple that transmitter is. Just three transistors and no chip at all, that I could see.

[@IMSAIGuy]

yup, that's all you need

[@jspencerg]

Finger waving investigation. 😂

[@rfburns5601]

For any FM transmit frequency and a given deviation ( say 100.1 MHz with 75 KHz deviation ) there is a certain audio modulation frequency that will cause the carrier to drop to zero at 100% modulation. When transmitter maintenance is performed, the engineer will modulate the transmitter with this frequency increasing the modulation until the carrier nulls on the spectrum analyzer display, then he will adjust the modulation monitor calibration to read 100%. A bessel function can be used to calculate the modulating frequency. I've tried reading several articles on this, but they don't make any sense to me. So if I want to null the carrier of a 100.1 MHz transmitter with 75 KHz deviation, how do I calculate this? Can you splain it to me?

[@robinbrowne5419]

rfburns - It's F***ing Magic.

[@rfburns5601]

@@robinbrowne5419 Fornicating Modulation!

[@IMSAIGuy]

that is a lot of math. I would do it in matlab

[@rfburns5601]

@@IMSAIGuy I have discovered that it is not that hard. I was under the misunderstanding that the modulation frequency to null the carrier was dependent on the carrier frequency. It is not. It depends on the modulation index. There are multiple indices that will cause the carrier to null. The first index is at 2.4048. So if you want to set the deviation on your Kenwood, presuming you wanted 4500 Hz deviation, you could play 1871 Hz (4500Hz/2.4048) into the mic, and adjust the deviation til the carrier nulls.

[@clems6989]

So was it designed as mono ? I thought that was the issue....

[@paulperano9236]

... and now you're going to fix it ? ☺

[@TonyBarr99]

What is the "auto-scan" all about?

[@ProdigalPorcupine]

It's because the transmitter is a free-running oscillator and will drift a lot in frequency. The receiver locks in on it and follows the drift. I've seen the same trick on ultra cheap Chinese wireless microphones.

[@nickcaruso]

no static at all

[@joseppuig925]

This Silan chip is a knockoff of the Philips TDA7088T which was a success in making it possible to market lots of cheap auto-scan fm radios in the late 90's to early 00's. Successive improvements in technology led to DSP all-in-one receiver chips that also tune with buttons but with better specs and even in stereo; but they were developed by chinese chipmakers by themselves (well, maybe inspired by Silicon Labs DSP advances).

[@mr1enrollment]

gutless wonder xmitr