GMVSAT DD Coil

[Rick S]

Carl, I have found out that the GM Rx coil peaks at 49.1 khz on the scope and the Tx coil 53khz. Question: The Rx coil does not have any components on it, like the Tx coil does. Would adding a capacitor in parallel effect the performance of the Rx coil or the Rx input to the control box? Also, what does the scope do when you are looking for the resonance bandwidth of the Tx coil? The peak for the resonance high end is what I have been looking for, but the low end (bandwidth) I am not sure what I am looking for. Any help on this matter would be appreicated. Also, you have mentioned in the past that you have made a wire wrapping machine of some sort. Do you have any plans or some instructions for this machine? Thanks Rick S

[Carl]

Re: GMVSAT DD Coil

Rick, if you're using a scope and a frequency generator, then when you sweep throught the resonant frequency you should see the waveform grow larger, peak, then get smaller. The peak is obviously the resonant frequency, the bandwidth is the point where the signal on each side of resonance dimishes by 30%. This is often called the "half-power" points. To see all this you may have to put a small series resistor between the generator and the coil, and look with the scope across the coil.

Yes, depending on how much capacitance you try to add, it will affect the RX coil. At worst it will shift its resonance off of the desired peak and hurt sensitivity. Of course, if your new coil isn't tuned to start with then you might have to add capacitance to get it to peak correctly. In that case it's a good thing.

Also yes, I have a "coil winder". I've photo'd it, now I need to write it up. I'll move it to the top of the priority list.

- Carl

[Rick S]

Re: GMVSAT DD Coil

Thankyou for the reply Carl. I am getting closer to giving the coil a try on the GMVSAT. Where is the best place to look for the signal from the Rx coil in the circuit itself? After the op amp? Since it is a moving coil to get a signal, how would I approach attaching to my scope to see what is happening without the coil moving or does this have anything to do with this? It seems alittle different from the PI I built(Goldpic)to balance the coil to the circuit. Thanks Rick S

[Rick S]

Re: GMVSAT DD Coil

I just put my second coil,Rx,on the scope and instead of peaking for the resonance it was the valley with the proper value. Does this mean that I am 180 degrees out because the valley was 49.9 khz( looking for 50 khz)? The coil is almost on the money. The resistance is only 0.16 ohms over the exact number and the inductance is 0.16 mh below exact number. Any help what to do to match the store bought coil to mine? Thanks, Rick S

[Carl]

Re: GMVSAT DD Coil

For coil alignment I would attach after the amplifier, that way you can adjust for a deeper null point. Also, the scope won't load the coil.

[Carl]

Re: GMVSAT DD Coil

What do you mean by "valley"... did the signal dip down around the 50kHz region, but was strong everywhere else?

[Rick S]

Re: GMVSAT DD Coil

It is the same way one finds the natural reasonant frequency peak on a scope, but the wave direction is going in the negitive direction instead of the positive. You still see a positive sine wave, but peak reduction is downward or negitive direction. It is not much in the negitive direction either. When 50khz is reached then the normal left and to the right reduction occurs. I hoped I explained it better. A drawing would be very helpful, but I haven't learn how to post a picture on the web to down load to this forum. Any help on the computer end would be nice. I could email you Carl with a picture and better numbers if you want. Thanks Rick S

[Carl]

Re: GMVSAT DD Coil

Hmmm, still not clear. A picture would help a lot. You don't need to post it on the web to use it on the forum, you can post directly to the forum. Click the "Browse..." button on Image Upload below and you will get a file selection dialog box to select a file on your hard drive. The file you select (must be JPG or GIF) will get uploaded when you preview your message.

- Carl

[Rick S]

Re: GMVSAT DD Coil




I hope this will help clarify the scope situation. The Rx on the White's and the ones I have built have the same chacteristics with the peak and resonance. I wonder if I have to do so adjustments on the scope. I have put a resister in series between the frequency generator and the coil. I hooked up one of my coil arrangement DD and the Rx coil with the high ohms and inductance. That was way to sensitive, so I had another Rx coil and tried a lower inductance and ohms. It is closer, but still not there. I have to get the coils with a closer match. Rick S

[Carl]

Re: GMVSAT DD Coil

So what it looks like is the signal is dipping slightly at resonance instead of peaking. Doesn't make sense, unless maybe you have a series capacitance on the coil. Try different values for the series resistor, see if what you have is too high or too low. Can't see why it would work for one coil and not the other.