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-   -   Mag vs RF pickups (http://www.talkbass.com/forum/f38/mag-vs-rf-pickups-933860/)

dougazbass 11-18-2012 07:06 AM

Mag vs RF pickups
 
Why do guitar manufactureres use Magnetic pickups and not Radio Frequency pickups?

grisezd 11-18-2012 07:09 AM

Can you give me an example of an RF pickup? I'm not sure how that would work.

Magnetic is easy, well understood, inexpensive, sounds good, and is well accepted in the marketplace. Competing technologies have faced an uphill battle.

SGD Lutherie 11-18-2012 10:18 AM

Because the bass doesn't operate at radio frequencies?

What exactly is a radio frequency pickup?

The way magnetic pickups work is as variable reluctance transducers. The steel string disturb the magnetic field (and are actually magnetized) and produce current flowing in the pickup coil proportional to the movement of the strings.

fdeck 11-18-2012 10:22 AM

There are magnetic transducers that sense changes in inductance or reluctance by applying RF to a coil. That might be what the OP is talking about. A metal detector is an example. There are also some linear position sensors that operate on this principle.

My guess is simply that variable reluctance is the thing that works and requires no power source.

SGD Lutherie 11-18-2012 10:51 AM

I'm guessing that metal detectors don't have permanent magnets. The magnet in the pickup is the power source.

I suppose you could make it work, but it might induce noise into the system. Metal detectors were not designed to reproduce the sound of a string.

fdeck 11-18-2012 11:32 AM

Quote:

Originally Posted by SGD Lutherie (Post 13466488)
I'm guessing that metal detectors don't have permanent magnets. The magnet in the pickup is the power source.

I suppose you could make it work, but it might induce noise into the system. Metal detectors were not designed to reproduce the sound of a string.

That's definitely true on both counts. The conventional magnetic pup works.

line6man 11-18-2012 11:48 AM

Quote:

Originally Posted by SGD Lutherie (Post 13466346)
Because the bass doesn't operate at radio frequencies?

Most people associate RF with frequencies millions of times higher than the human hearing range, but the bass, and human hearing range is considered extremely low frequency through very low frequency in the spectrum, so the term can still be applied.

But I'm equally confused at what this is about. :confused:

SGD Lutherie 11-18-2012 11:53 AM

Quote:

Originally Posted by line6man (Post 13466673)
Most people associate RF with frequencies millions of times higher than the human hearing range, but the bass, and human hearing range is considered extremely low frequency through very low frequency in the spectrum, so the term can still be applied.

But I'm equally confused at what this is about. :confused:

Right, RF starts at about 3k.

line6man 11-18-2012 12:18 PM

Quote:

Originally Posted by SGD Lutherie (Post 13466688)
Right, RF starts at about 3k.

Goes lower than 3kHz. Lower frequencies may be used for submarine communications. http://en.wikipedia.org/wiki/Sanguine_%28transmitter%29

khutch 11-18-2012 12:24 PM

Quote:

Originally Posted by dougazbass (Post 13465705)
Why do guitar manufactureres use Magnetic pickups and not Radio Frequency pickups?

I don't believe the radio frequency pickup has been invented yet. Like many here I have trouble even imagining what an RF pickup would be and I am an RF engineer. Light wave pickups have been made but have not attracted much of a following.

Ken

SGD Lutherie 11-18-2012 12:29 PM

Quote:

Originally Posted by line6man (Post 13466787)
Goes lower than 3kHz. Lower frequencies may be used for submarine communications. http://en.wikipedia.org/wiki/Sanguine_%28transmitter%29

Not sure if you would consider that the radio frequency band though, since it's outside of the radio wave range. That's more like ultra sonics like what whales use.

The difinition for "radio frequency" is:

"a frequency or band of frequencies in the range 104 to 1011 or 1012 Hz, suitable for use in telecommunications."

Wikipedia list it as:

"Radio frequency (RF) is a rate of oscillation in the range of about 3 kHz to 300 GHz, which corresponds to the frequency of radio waves, and the alternating currents which carry radio signals. RF usually refers to electrical rather than mechanical oscillations, although mechanical RF systems "

The article on "Radio Waves" states:

"Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers."

SGD Lutherie 11-18-2012 12:37 PM

Quote:

Originally Posted by khutch (Post 13466806)
Light wave pickups have been made but have not attracted much of a following.

Yeah, they have been around a long time too... since the 70s with the Hoag Light Guitar.

http://www.opticalguitars.com/1977_musician_guide.htm

http://www.opticalguitars.com

khutch 11-18-2012 04:01 PM

I don't think there is really any hard lower limit to the radio frequency spectrum, other than DC. If you can make an antenna large enough then very low frequencies will propagate as electromagnetic waves and any EM wave with a wavelength longer than infrared is a radio wave. As far as I know EM waves have been generated down to at least 7 Hz. Of course for a radio frequency pickup to be properly called such the distance from the pickup to the strings would have to be on the order of 10 or so wavelengths and that rather severely constrains the lower frequency limit on an object the size of a bass guitar. That would imply a frequency well over a GHz. Anything else, even though it may use radio frequency circuits, would just be a near field proximity detector.

Like a Theremin.

Would you want a pickup that acted like a Theremin as you moved you hands around? Perhaps this is why the RF pickup has not been invented yet.

Ken

walterw 11-18-2012 04:54 PM

Quote:

Originally Posted by khutch (Post 13467471)
Anything else, even though it may use radio frequency circuits, would just be a near field proximity detector.

Like a Theremin.

Would you want a pickup that acted like a Theremin as you moved you hands around?

yes!

it would make everyone around angry as soon as i plugged it in; i could market it as the "Troll Pickup"!

dougazbass 11-18-2012 08:18 PM

http://www.motionsensors.com/speed-s...standard.shtml

We use them to detect rotor blades. I'll look for more info. They do not have as much magnetic attraction on the blades.

dougazbass 11-18-2012 08:25 PM

http://www.azom.com/article.aspx?ArticleID=1717

Heres more...

Angel LaHash 11-19-2012 02:34 AM

Theremin

I did think i seen some effect you attach, but i think its more using the oscillation side of it
[url="http://www.ebay.co.uk/itm/MINI-XLPC-THEREMIN-SCI-FI-SYNTH-/380515280580?pt=LH_DefaultDomain_0&hash=item58987a 66c4"]http://www.ebay.co.uk/itm/MINI-XLPC-...87a66c4[/url]
I like the theremin and been trying to find time to build one.. sadly if i have the time i have no money, plus the last one blew up one of the chips was in the wrong way around on the dam circuit drawings
so was last time breaking it down in to parts, been so long i cant remember were i put them all

SGD Lutherie 11-19-2012 05:37 AM

Quote:

Originally Posted by dougazbass (Post 13468342)
http://www.motionsensors.com/speed-s...standard.shtml

We use them to detect rotor blades. I'll look for more info. They do not have as much magnetic attraction on the blades.

Interesting. I have some proximity sensors here. I see this is similar to those but using a different approach.

khutch 11-19-2012 09:17 AM

Those are basically proximity sensors. They are designed to give square wave outputs so that a digital device can measure speed by counting the pulses per second. I think you would have to convert them to analog operation somehow to make a useable guitar pickup and other than freedom from power line hum I am not sure what the advantage would be over the pickup technologies we already have.

Ken

SGD Lutherie 11-19-2012 10:17 AM

Quote:

Originally Posted by khutch (Post 13469891)
Those are basically proximity sensors. They are designed to give square wave outputs so that a digital device can measure speed by counting the pulses per second. I think you would have to convert them to analog operation somehow to make a useable guitar pickup and other than freedom from power line hum I am not sure what the advantage would be over the pickup technologies we already have.

Ken

My thoughts exactly.


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