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I have a low power wireless microphone (10 - 50 mW) with a large receiver designed to connect to a mixer/sound system. The mic transmits in the UHF band between 530 and 860 depending on the band (see frequency chart). I want to build a battery powered receiver that would pick up the mic and output the audio to a standard pair of headphones. What parts do I need? How do I "build" it?

I have no experience in building electronics, but I would still like an answer even if I won't have the technical skill to follow it.

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  • $\begingroup$ Are you wanting to build something to pick up any of the frequencies within 530–860 MHz, or one of them? $\endgroup$ – natevw - AF7TB Nov 13 '17 at 22:12
  • $\begingroup$ @natevw-AF7TB A small range of them. The mic transmitter operates several small ranges (about 20 MHz wide each) between 530 and 860 depending on what mode you select. For example, if you select "Band A" it operates between 530.025 and 559. My receiver would need to pick up that. $\endgroup$ – just.another.programmer Nov 13 '17 at 22:56
  • $\begingroup$ Do you actually want to build one or maybe buy one if the price is right. Here is one SDR receiver covering your bands of interest in UHF and available for $49: radioddity.com/… $\endgroup$ – K7PEH Nov 13 '17 at 23:02
  • $\begingroup$ If you want to build, the slide presentation linked on this comment gives a nice outline of SDR transceivers/receivers that could provide an initial guide to building upon current open software GNU SDR or other boards available: seapac.org/seminars/2017/SEA-PAC2017-uhf-sdr-transceiver.pdf $\endgroup$ – K7PEH Nov 13 '17 at 23:06
  • $\begingroup$ @K7PEH I would be happy to buy one! Would it be as simple as buying the SDR you linked and plugging in a headset, or would I need additional hardware and software as well? $\endgroup$ – just.another.programmer Nov 13 '17 at 23:32
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Sounds like you are wanting to build a DIY FM receiver that can be tuned over a broad portion of the UHF band.

[I'll leave aside any legal implications — but make sure that your goal is permitted in the jurisdiction you wish to accomplish it! Some countries are fairly lax, others are much more strict, regarding who may listen in on radio signals.]

For a small taste of what an analog UHF receiver for FM signals might involve, you could start by looking at this Simple FM radio receiver circuit, or browse through other FM radio receiver designs. Note however, that these designs are for typical (usually ITU region 2) FM broadcast bands, i.e. VHF frequencies in the range of 88–108 MHz.

So at minimum you will need to adjust the tuning portions of the circuit for your desired bands. You may find some of the components used for those broadcast-band circuits do not perform well at 860 MHz, and need to be replaced with something better. You will also have to worry more about your PCB layout to avoid stray capacitance and unwanted inductance from interfering with its operation.

This may/may not be for the faint of heart.

That said, I have a couple yellowed and fading amateur radio books that include DIY circuits — even tube circuits! — for the even higher frequency 23cm band. So I don't want to discourage you, even if there's no go-to "Instructable" for your band of interest.

Now, if you are looking for something a bit more plug-and-play, and have an Android phone/tablet, then why not pick up an RTL-SDR device and a USB OTG cable?

RTL-SDR dongles were originally meant as DVB-T tuners, and can usually be found for between $10–30 USD. They can be used more generically with a wider variety of software that has sprang up, and can usually tune over the full VHF and well into the UHF range, e.g. 25–1750MHz.

I personally like NooElec'sNESDR SMArt unit, which is also available in a kit with some starter antennas. (They graciously loaned me a bunch for an SDR talk I gave, so I do have a conflict of interest.) The RTL-SDR blog's kits are also an easy recommend too. You can find even cheaper devices on eBay or AliExpress (try searching for RTL2832U) if you want to try one on an even smaller investment.

Once you have the cheap tuner dongle (and a small antenna), plug it into your phone with the OTG adapter, and use an app like SDR Touch or RF Analyzer to locate the signal and demodulate the audio into your headphones.

There's even more desktop software options available if you get hooked on SDR (like most do :-) but it sounds like your initial goal is something portable.

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