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Old 23rd July 2009, 09:19 PM   #1
methc is offline methc  Guyana
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Default Wireless Guitar Transmitter/Receiver

Hi Guys,

I did a search before posting, found a few threads but none of them had a solution so far.

I'm in search for a wireless guitar transmitter for my guitar. I play for my Church and also practice at home. Needless to say the guitar leads are annoying when they get tangled and could be VERY annoying when you move and they make feedback noise over your speakers! Especially in a concert or such!

Anyways, does anyone have a schematic?


Thanks

Meth
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Old 24th July 2009, 06:32 AM   #2
Enzo is offline Enzo  United States
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Unless you are just itching hard to build a project, you can buy perfectly functional wireless systems for under $100. You won't have to worry about making and tuning radio transmit and receive circuitry, not to mention tuned circuit stuff.
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Old 24th July 2009, 02:01 PM   #3
methc is offline methc  Guyana
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Hey Enzo:

I'm looking to build, for the fun of it. Besides, I have used products ranging in the line of 70-100usd and they either don't last very long or are built poorly (high hissing sounds, poor receiver to transmitter distance, etc).

Any ideas?
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Old 24th July 2009, 02:38 PM   #4
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The first consideration is what frequency segment you could practically put to use. Uh - say somewhere between 100Mhz and 2 Ghz. outside this range things become very tough. Also I hope you will stick to the frequency segments that are leagal for this kind of application. UHF (Ultra-High Frequency) band has some spots that can be operated in licence free. You could start with a kit--- but RF is a complex dicipline in it's self, and will require a pretty stiff learning curve. Mabe buy an existing product and reverse engineer it? My concern is that the regulatory agencies are in place for a good reason, and a mistake in designing a transmitter can result in legal and ethical problems.
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Old 24th July 2009, 03:00 PM   #5
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Hi methc,
I hate to tell you this, but you will be lucky if you can the performance of even a low-quality VHF transmitter with a DIY kit, or even an adapted design. I work in RF and can safely say that it's a domain that is totally unlike audio. Oscillators and tuned circuits are temperamental, and and getting them to work properly is not an easy thing for a novice.

Unless, you're not a novice in the RF field... I do agree this would be a fun project, I've even contemplated making one myself. As I recall, there was a article in ELECTRONICS NOW magazine in the nineties that had a VHF transmitter project.

If you are going to do this I suggest you use the unused exptremities of the FM band. An FM modulator is not that much harder to design than an AM transmitter. Mind you, with AM, you're pretty sure you won't bother anyone! And don'T think that because it's AM it woud sound like AM... you would full control on the frequency span since you wouldn't have to design-in a narrow audio filter. In any case, I don't really recommend using AM, it's prone to too much interference.
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Old 24th July 2009, 03:20 PM   #6
methc is offline methc  Guyana
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I found this FM Transmitter while googling. Works between 80 -110MHz FM.



I'm aware of the legal issues surrounding using certain frequencies on the airwaves and I'm obviously working around them to be on the safe side. Thanks for the tip tho, was all good...

Can you guys take a look at the schematic, let me know what you think.

Does anyone have a good receiver schematic that will tune to the 80-110MHz FM range?

See you guys around.

Thanks.

Meth
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Old 24th July 2009, 03:24 PM   #7
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Any regular FM radio will pick up this band.

Therein lies the rub. Anyone with a radio can tune to your guitar (nothing else) and you will be susceptible to interference. In some cities there may be a station on your channel.

Also, I'm pretty sure you need a license for this band.
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Old 24th July 2009, 03:55 PM   #8
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The schematic you found is for a LC tuned local oscilator witch has the draw back of being not frequency stable enough. You are going to have to find a design that uses a crystal as the local oscilator. It's leagal to transmit in the FM band without a licence but the power is restricted to such a low level that the range is typicaly limited to somthing like a couple of feet. This restriction is the effective radiated power, so there is no better antena or higher power that can be employed. Also the interfearance issue is a tough one. Try searching some similar products and see what frequencies they use. Also look up ISM band witch is the industrial sientific medical band. Look at how other people have delt with this question.
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Old 27th July 2009, 07:12 AM   #9
akis is offline akis  United Kingdom
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A simple FM transmitter at 70-120MHz is dead easy to build. Quality is perfect with FM modulation, sound will be very clear. There are some slightly more advanced tranmitters employing two transistors at the output stage for more power, but I doubt you'd need that in a church hall.

A simple transmitter, like the one you have shown above (I remember from memory those days we used the 2n2219/2n2222A not the BC54x series) that one will drift as others have said, it will drift with temperature, baterry power, and so on. Even if you wax the coil it will still drift. So the receiver at the other end will need to be constantly adjusted.

So you are looking for a schematic employing a crystal or PLL or something to make sure the frequency stays put.

A well designed transmistter using 2-3 transistors would last at least 6-9 hours using a 9V PP3 battery, no need for the bulky AAs.

At the other end you will need a receiver. Unlike the transmitter you are in luck, because space is not at a premium backstage, so you could use an ordinary radio, something with PLL and a digital display maybe.

Here is the trick. You open up the radio, find it's tuning circuitry and adjust it so it can receive 10%-15% off one side of the 88MHz-108MHz FM band! eg you tweak it so that it covers 80MHz-100MHz. I have done this many times, there is usually a set of variable caps you can mess with, dead easy to spot, mostly driven straight off the tuning knob (or via a belt/cable).

By tuning down to say 86MHz, you are ensuring that nothing else can interfere with you since commercial FM stations start, at best, at 88MHz. Or you can go the other way, eg 110MHz, 2MHz off the top 108MHz.

It could be said that you'd be breaking regulations by transmitting into bands you should not but I have two things to say. First your transmitter is so powerless that it would hardly make it backstage, let alone outside of the premises. Secondly many, hundreds or thousands of amateur hobbyists build radio transmitters, and while experimenting, and sometimes while not, they mistakenly transmit all over the place, what with harmonics, bad tuning pots etc. So they all do it, one way or the other. Finally as you are so close to the 88-108 range, it should not matter, eg 87MHz should be fine.

Of course someone is going to jump up and inform me that 87MHz is the frequency allocated for monitoring equipment at cardiac departments in hospitals or the well publisized frequency for remotely manipulating the control rods in your local nuclear power generator... Whatever :-)
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Old 27th July 2009, 03:45 PM   #10
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Quote:
Originally posted by akis
It could be said that you'd be breaking regulations by transmitting into bands you should not but I have two things to say. First your transmitter is so powerless that it would hardly make it backstage, let alone outside of the premises. Secondly many, hundreds or thousands of amateur hobbyists build radio transmitters, and while experimenting, and sometimes while not, they mistakenly transmit all over the place, what with harmonics, bad tuning pots etc. So they all do it, one way or the other. Finally as you are so close to the 88-108 range, it should not matter, eg 87MHz should be fine.
And if you are caught, they confiscate ALL your equipment, guitar, ampliifer, everything associated with the illegal transmitter.

Just buy a proper legal guitar transmitter, it will work a million times better and sound decent as well.
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