Differences in sound of the same pickup wound to the same DCR with different wire AWG

[alexirae]

I'm fine with that

[big_teee]

This thread can be moved there if the folks here think it appropriate.

Steve Ahola
Super moderator

I'll just move it back.
Theory and hypotheticals belong here in the main area.
T

[Steve A.]

I'll just move it back.
Theory and hypotheticals belong here in the main area.
T

Say no more.

[Joe Gwinn]

Sorry to dig up this older thread, but since this post, I continue to come across contradictory information, saying that impedance is at a minimum at resonance:

http://hyperphysics.phy-astr.gsu.edu...ic/serres.html


Q and Bandwidth of a Resonant Circuit : Resonance - Electronics Textbook


Intuitively, I'm thinking the reason you have louder signal at resonance is because the pickup is doing the least to resist the flow of current at that frequency. Am I misunderstanding?

A pickup acts as a parallel resonant circuit, not series. The inductance of the coil is in parallel with the coil self-capacitance plus the guitar cable capacitance. In a parallel LCR circuit, impedance is highest at resonance.

[Joe Gwinn]

Still, it does happen occasionally.

I used to organize folk music concerts and dances at a hall that was built in 1929, had funky electrical wiring, and was less than half a mile from a commercial AM radio station. We provided the PA systems (different configurations for different events- usually all mic'd vocals and acoustic instruments). Occasionally, if you put your head right next to the main speakers, you could just barely hear the radio station. Until we held that concert with that duo from Hawaii with those electric slack-key guitars. That night, the station came in loud and clear.

At another location, a lodge built by the WPA at a campsite just below Camp David, our PA picked up a conversation in some Slavic language. It was during a break, and IIRC all the channel inputs were muted.
So I doubt that any amount of instrument shielding would have prevented the unintentional eavesdropping.

My girlfriend's Blackberry used to sporadically emit Morse code-like signals that were picked up by every device in the house- including the toaster.

Actual Question:
Am I correct in intuiting that lower frequency rf is more likely to cause problems than higher frequencies
(e.g. AM in the 535-1605 KHz band vs. cell phones at 800MHz and higher)?

Not really. The big issue is that the AM station is 10,000 to 50,000 watts, while cell phones are a few watts.

[Mike Sulzer]

Not really. The big issue is that the AM station is 10,000 to 50,000 watts, while cell phones are a few watts.

Not the big issue.

The electric field strength varies as the square root of the power, and thus it falls off as 1 over distance (ignoring some details if you are in the near field or in an unattenuated ground wave). This is 100 times, sqrt(10,000 watts divided by 1 watt). The cell phone could easily be within 1 meter of the equipment. Except in unusual circumstances, the equipment will be more than 100 meters from the AM transmission, usually much more. So the field strength from the AM station will generally be weaker, not stronger, although there can be exceptions.

A common method of rf interference pickup is current produced along the shields of connecting cables. At cell phone frequencies, the phase of the wave varies multiple times along the length of the guitar cable. This reduces the effectiveness of pickup compared to the long wave of the AM station. Also, shunt capacitances are far more effective at 1 GHZ rather than 1 MHz.

[John Kolbeck]

At cell phone frequencies, the phase of the wave varies multiple times along the length of the guitar cable. This reduces the effectiveness of pickup compared to the long wave of the AM station.

I'd like to read more about this, is there a common name for this effect?

[Mike Sulzer]

I'd like to read more about this, is there a common name for this effect?

You can find material about rf pickup on the web. But I think what you really want is an education in electrical engineering and physics.

[Joe Gwinn]

Not the big issue.

The electric field strength varies as the square root of the power, and thus it falls off as 1 over distance (ignoring some details if you are in the near field or in an unattenuated ground wave). This is 100 times, sqrt(10,000 watts divided by 1 watt). The cell phone could easily be within 1 meter of the equipment. Except in unusual circumstances, the equipment will be more than 100 meters from the AM transmission, usually much more. So the field strength from the AM station will generally be weaker, not stronger, although there can be exceptions.

A common method of rf interference pickup is current produced along the shields of connecting cables. At cell phone frequencies, the phase of the wave varies multiple times along the length of the guitar cable. This reduces the effectiveness of pickup compared to the long wave of the AM station. Also, shunt capacitances are far more effective at 1 GHZ rather than 1 MHz.

All true, but so what. If you are a mile from a AM station, everything is a rectifier. Iv'e seen in in ordinary telephone wires, where someone made a splice by twisting the bare copper wires together. Local disk jockey came in loud and clear. Soldering the twisted wires silenced the disk jockey.

[Joe Gwinn]

Dup -deleted.

[Joe Gwinn]

I'd like to read more about this, is there a common name for this effect?

It's called an antenna. Or a transmission line. Best place to start is the ARRL Handbook: http://www.amazon.com/ARRL-Handbook-...=arrl+handbook

AM Broadcast frequencies are around 1 MHz. At that frequency, the wavelength is (3*10^8)/(1*10^6)= 300 meters. So this isn't going to be a problem in most guitars.

[Mike Sulzer]

All true, but so what. If you are a mile from a AM station, everything is a rectifier. Iv'e seen in in ordinary telephone wires, where someone made a splice by twisting the bare copper wires together. Local disk jockey came in loud and clear. Soldering the twisted wires silenced the disk jockey.

The effective area of wire antennas goes as wavelength squared. There is one million times more power available to simple antennas at 1 MHz than 1 GHz given the same field strength.