Squarewave driven Tx coil

[dfbowers]

A question for the experts:

I wanted to entertain a question about the advantages and disadvantages of a pure sinewave driven Tx as opposed to a plain old squarewave. I have seen post here in the past emphasizing the importance of using a pure sinewave. For the moment, let us forget about designs that use a squarewave for the purpose of multi frequency sampling and think only of the fundamental frequency.

First, let us state the obvious. A pure squarewave generates an infinite series of harmonics that can cause problems in other parts of a circuit. This could also mean that not all power will be delivered at the fundamental frequency. (1)

So, why do some designs use what approximates a squarewave for a Tx signal (or approximate a sinewave for that matter). Some of the Russian designs seem to be big on squarewaves, or squarewaves that have a tuning cap to make them to look more sinusoidal. My experience with a squarewave Tx starts and ends with the Volksturm SM, which by the way seems to go deeper than my other IB detectors. So, that is what spawned this thread. (I need to qualify that by saying that I have only tested in the all metal mode, which by default goes deeper anyway).

Would not the power delivered to a coil by a pure sinewave be only .707 times that of what a squarewave of the same amplitude and peak current would be or close to it? (1)

Also, IF squarewave are disruptive, then why use them as timing signals in sensitive circuits?

Don

[moodz]

A question for the experts:

I wanted to entertain a question about the advantages and disadvantages of a pure sinewave driven Tx as opposed to a plain old squarewave. I have seen post here in the past emphasizing the importance of using a pure sinewave. For the moment, let us forget about designs that use a squarewave for the purpose of multi frequency sampling and think only of the fundamental frequency.

First, let us state the obvious. A pure squarewave generates an infinite series of harmonics that can cause problems in other parts of a circuit. This could also mean that not all power will be delivered at the fundamental frequency. (1)

So, why do some designs use what approximates a squarewave for a Tx signal (or approximate a sinewave for that matter). Some of the Russian designs seem to be big on squarewaves, or squarewaves that have a tuning cap to make them to look more sinusoidal. My experience with a squarewave Tx starts and ends with the Volksturm SM, which by the way seems to go deeper than my other IB detectors. So, that is what spawned this thread. (I need to qualify that by saying that I have only tested in the all metal mode, which by default goes deeper anyway).

Would not the power delivered to a coil by a pure sinewave be only .707 times that of what a squarewave of the same amplitude and peak current would be or close to it? (1)

Also, IF squarewave are disruptive, then why use them as timing signals in sensitive circuits?

Don

Hi Don ... lots of questions there ..... a square wave can be broken down to a harmonic series of pure sine waves. Most of the power will be delivered in the first few harmonics. A square wave is used mainly because the sharp rise and fall times define the pulse edges much more accurately than the edges of a sine wave. If a circuit has to decide if a voltage is above or below 0 volts for instance the sharp rise time of a square wave makes this much easier. For measuring parameters like phase for instance this is handy in logic circuits where 1 is somewhere towards say 5 volts and 0 is somewhere towards 0 volts depending on the type of logic deployed. A sine wave would give pretty lousy response in a logic circuit due to the "slow" rise and fall times compared to a square wave.

Best regards ... Moodz.

[taliesin]

Hi Don ... lots of questions there ..... a square wave can be broken down to a harmonic series of pure sine waves. Most of the power will be delivered in the first few harmonics. A square wave is used mainly because the sharp rise and fall times define the pulse edges much more accurately than the edges of a sine wave. If a circuit has to decide if a voltage is above or below 0 volts for instance the sharp rise time of a square wave makes this much easier. For measuring parameters like phase for instance this is handy in logic circuits where 1 is somewhere towards say 5 volts and 0 is somewhere towards 0 volts depending on the type of logic deployed. A sine wave would give pretty lousy response in a logic circuit due to the "slow" rise and fall times compared to a square wave.

Best regards ... Moodz.

could a zero crossing comparator help with a sine wave signal ??

[moodz]

could a zero crossing comparator help with a sine wave signal ??

Yes a zero crossing comparator is typically used to "square up" a sine wave however on very low level noisy sine wave on recieve this would be very messy without some method of accurately extracting the sine wave amplitude and phase. The noise on the signal would make the zero crossing detect point jump all over the place.

Regards,

moodz.