I'm currently trying to broadcast my computer's audio output to a wireless microphone system receiver so that I can accompany my school's coming presentation with music. The frequency range is 480-598 MHz, and I can't find a device capable of emitting a signal that can be picked up by this system. Please, if you have any ideas on how I may do this, or have come across a product with said capabilities, please let me know. Thanks in advance!
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1$\begingroup$ Welcome to stackexchange! You should state your country, since 480-598MHz lies in the UHF broadcast band and is subject to licensing in many countries. It would also be useful to state your microphone system. $\endgroup$– Buck8peJan 7, 2022 at 9:28
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1$\begingroup$ In the US, the FCC allows unlicensed low power transmissions in certain broadcast bands under Part 15 rules. $\endgroup$– hotpaw2Jan 7, 2022 at 12:34
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3 Answers
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If you have an extra microphone, it may be as simple as placing it near the computer's speaker and adjusting the volume levels. This requires the mic and computer to be in a quiet area where it wont pick up outside noise. If the computer is in a noisy area, you could tap into the microphone circuit at the input and run a headphone cord direct between the two. You may need to use a transformer to get the impedances right. Check the wireless microphone system's receiver and amplifier for auxilliary inputs. You may not need wireless at all!
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An educational SDR kit, such as the ADI ADALM-Pluto or a Lime SDR Mini, can be used as a UHF exciter, with any modulation that your receiver requires generated by software synthesis (GNU radio , et. al.). I might use a Raspberry Pi to run the SDR modulator/synthesizer code.
If legal within your jurisdiction, you may need to use a suitable filter before any antenna, and way to estimate or measure the RF output power and purity, to make sure your RF emissions stay within regulations (FCC Part 15 in the US).
The harmonics of a toggling Raspberry Pi GPIO pin can also generate modulated UHF signals (see librpitx/RPiTx on GitHub), but a GPIO will definitely need filtering to produce a clean enough legal signal for any antenna.
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I have indeed done this simply by disassembling the wireless microphone and wiring in an auxiliary input jack in place of the mic element along with an attenuator so the AUX IN signal from the computer's earphone jack will not overload the transmitter inside the mic- as suggested above by R Pau.
It is also possible to signal-trace the (tiny) PC board inside the mic to find a point in the signal path where the signal level is close to that which your computer earphone jack furnishes so you don't need the attenuator, and then wire up the AUX IN to that point.
It is also possible to install a microswitch so you can turn off the AUX IN function and use the mic for its original purpose instead.
