Rick's scope drawings

[Reg]

Rick,
I posted a response on the previous page regarding your scope drawings. This is basically a repeat. What you see is not distortion. The 4053 is an analog switch used to sample the receive signal. The differences you see are the differences caused by phase difference in sampling times. My guess you are off by about 30 degrees or so.

You mentioned you have a capacitor across the receive windings. If you do, try removing it. Most manufacturers do not tune the receive, just the xmit. Look at the signal and see if it is closer or more like 180 degrees out.

Do you have a dual trace scope?

[Reg]

Re: Rick's scope drawings

Rick,
I should add more. The waveform you see is only part of a sinewave. VLF's take the receive signal and sample it using a 4053, a 4066 or a 4016 cmos switch. If a sample is taken at the proper time in the sinewave, the phaseshift and/or amplitude change caused by ground mineralization that would otherwise cause an audio change are basically balanced out and the ground signls seem to disappear. On the patents this technique is referred to as synchronous demodulation. In other words, the sinewave changes, but the sampled average appears to remain the same.

Reg

[Reg]

Re: Rick's scope drawings

Rick,
I should add more about your signals. The waveform you see is only part of a sinewave (about half). VLF manufacturers take the receive signal and sample it, normally using a 4053, a 4066 or a 4016 cmos switch. If a sample is taken at the proper time in the sinewave, the phaseshift and/or amplitude change caused by ground mineralization that would otherwise cause an audio change are basically balanced out and the ground signls seem to disappear. On the patents and in books this technique is referred to as synchronous demodulation.

In other words, the sinewave changes, but the sampled average remains the same at ground balance.

Reg

[Reg]

Re: Rick's scope drawings

First, sorry about the above duplication, computer screwed up and didn't think it got posted.

Rick, take a look at patent 4,249,128, figure 3. It shows a graphic representation of the gated signal. Looks like yours only 180 degrees out of phase. The pic in the patent is an example of taking a sample of the sine wave. The sum of the signal above and below the x axis is zero, therefore no signal out.

Reg

[Rick S]

Re: Rick's scope drawings

Reg,
25Mhz dual trace scope. Alot of info to digest. Rick S