FM Transmitter/Receiver guitar pedal

[Axe4Eye]

I built one with a cheap radio and a toy mic from Walgreens.  The result was staticy pulsating and fuzzy.  Sounded great for my needs but I think that lots of people would like something like this for that "lo-fi" sound.  My problem is that it is cumbersome.  A new circuit would need to be designed for such a project but this sound in a pedal would be awesome...especially if you can tune in the transmitting freq and the receiving freq with knobs.  Anyone like this idea?

[darron]

hey there. i've had that idea before. i tuned in to an ipod (radio transmitted) and heard this really cool distorted guitar in the song, then realised that the frequency was off by 0.5 once i corrected it the cool guitar was just a standard distortion

would it really need to be transmitted and received through radio frequencies though? i mean, you'd send it off through a metal arial, pick it up with a metal arial, does it need the 'air coupling'?

if people know much about radio, then what's the key to the distortion when you are slightly out of tune of the frequency?

[johngreene]

hey there. i've had that idea before. i tuned in to an ipod (radio transmitted) and heard this really cool distorted guitar in the song, then realised that the frequency was off by 0.5 once i corrected it the cool guitar was just a standard distortion

would it really need to be transmitted and received through radio frequencies though? i mean, you'd send it off through a metal arial, pick it up with a metal arial, does it need the 'air coupling'?

if people know much about radio, then what's the key to the distortion when you are slightly out of tune of the frequency?

When you are slightly off frequency with (mono) FM it is a lot like adding a DC offset to the signal. Therefore it will clip either the positive half of the signal or the negative half depending on whether you are high or low in frequency. With an iPod transmitter it is a bit more complicated. The stereo encoding is going to cause all kinds of intermodulation distortion because of the 19 kHz subcarrier. The stereo information is modulated on this 19kHz subcarrier but the makers of the FM modulator chips discovered that the waveform is exactly the same, and decodes almost the same, if you just alternate (chop) the FM modulating signal between the left and right at a 19kHz rate. So depending on the mix between right and left, amount of carrier offset, etc. you will get a variety of different sounds. The 19 kHz chopping will create alias frequencies that end up in the channel giving a ring modulator effect if it is far enough away that the receiver cannot capture the pilot.

I designed a 'pedal' that has a guitar amp sim into a speaker sim into a stereo FM transmitter chip that will also mix in a stereo line input. It allows you to play along with CDs and transmit it to any FM receiver such as a car radio, home stereo, etc. Kind of fun at the beach.

--john

[Solidhex]

  I was thinking about making something like that as well. Haven't done it yet but was going to buy one of those $12 FM transmitter kits from Velleman, stick it in an enclosure and hook up a jack to the "mic" input on it. Would be a fun studio toy. I heard rumours that the guitarist from Sir Lord Baltimore had used some sort of early wireless PA system to record guitars on their first record.

--Brad

[km-r]

check out the V5 project here:
come.to/sm0vpo

[Andre]

What about this idea:

Those who have ever listened to a so called SSB (Single Side Band) shortwave amateur radio broadcast
may have noticed that by slightly turning the tuning knob of the receiver, you can change the pitch of
the received signal.

In theory and hopefully in practice, but not by me I'm afraid, it must be possible to create a pitch shifter
using this SSB technique.

Any HF specialist or radio amateur here ?

André

[Paul Perry (Frostwave)]

In theory and hopefully in practice, but not by me I'm afraid, it must be possible to create a pitch shifter
using this SSB technique.

Not by me either I'm afraid.
But, I believe that what would happen, using SSB techniques, is that you would get all the frequencies in the signal moved by an equal ammount of Hz.

Which unfortunately would trash your harmonic relationships.
Harland Bode made a frequency shifter of this kind - later marketed by Moog I think - back in the early e-music days.
It's like a ring modulator, but you manage to do some trigonemetric magic via a 90 deg audio passband filter to give you only one side to the harmonics.
See teh second patent in this list: http://www.till.com/articles/moog/patents.html

As for detuning FM signals, a lot depends on what kind of demodulator you have. I'm not up to speed on teh modern stereo chip ones, but the old ones used either a phase locked loop -which gives perfect results when detuned, until it is TOO far away, and trhen snaps off - or 'slope' detection, using the slope of the response of a tuned circuit. That really IS rough, but I can't imagine many receivers have used it for 20 years or more.

[Andre]

But, I believe that what would happen, using SSB techniques, is that you would get all the frequencies in the signal moved by an equal ammount of Hz.

Which unfortunately would trash your harmonic relationships.

I think you're right about that.
So, single note whammy effect only  or multiple note noisemaker 

André

[Roobin]

Anyone seen this: http://www.talkingelectronics.com/projects/BeetleMklll/BeetleMkIII.html

Ok so there's no receiver, but looks workable...

[Axe4Eye]

  Thank you so much for all of your help!  I am a noob so I dont understand everything completely.  So this project would pretty much allow for all manner of sounds such as pitch shifting, tremelo, phasing, fuzz, static/noise, lo fi and unusual distortions, all dependant primarily on the receiver used?