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I just built a L/C meter kit called the L/C Meter IIB from "Almost All Digital Electronics", http://www.aade.com. The kit cost $99.00 (US) and had a few features that would appeal to PI coil makers as well as matching critical capacitor values in the Hammerhead circuit. The above web site has a detailed comparison to other well-known LC meters. The assembley instructions are also located there.
The unit is self-calibrating and self-zeroing. When in the inductance mode it subtracts the residual inductance of the shorted test leads and when in the capacitance mode it subtracts the residual capacitance of the open test leads. This ensures that low value measurements are accurate...and they are! It comes with a component test fixture that allows surface mount and leaded L/C components to be easily tested.
The unit comes both assembled as well as in kit form. I chose the kit and it went together in about 2 hours with no problems. One unique feature is that two capacitors come in a separate envelope and they are selected to be a combined standard value when installed together to form the basis of measurement accuracy.
Here are some uses of this LC meter for PI coil makers and Hammerhead builders.
Measure the capacitance of coax wire, shield to center conductor. This is important when trying to make very fast coils with the lowest possible total capacitance. You may be surprised to see how much capacitance is in you coil coax lead to the control box. A good range will be between 16pf and 25 pf per foot.
Measure the capitance of the shield to the coil. Just clip one meter lead to one of the coil wires and the other meter lead to the shield and see how many 100 pfs your shield adds to the total capacitance as seen by the pulse circuit and is reflected in the value of the damping resistor. Remember higher values of damping resistor means you have less capacitance in the circuit and this means a potentially faster and more sensitive coil. So if you want to reduce the coil to shield capacitance this LC meter is just the thing to see effect of changing the spacing between the coil and shield, using different wire sizes, using thicker or thinner insulating coil wire, or using different types of wire insulation, kynar, teflon, vinal, etc. Remember, the fewer turns you have in the coil (with the desired inductance) will result in a lower shield to coil capacitance as each turn within the coil adds to the total measured capacitance. If you are planning to use a series current limiting resistor in your TX coil circuit, you can always a thinner wire and make a faster coil. 50 ft of Radio Shack Kynar wirewrap AWG 30, wound on a 10.375" diameter coil form with 18 turns will make a 380 uH coil as measured by this LC meter.
Coil inductance measurements can be found by using the on-line calculators such as:
http://my.athenet.net/~multiplx/cgi-bin/airind.main.cgi
This calculator will get you in the ball park but are not very accurate when winding a multi layer coil that you are going to tightly wrap with plastic spiralwrap to space the shield. Thinner wire, spaced more closely together, gets you higher inductances. This means that you get the desired inductance (say 300uH) with 17 turns of AWG 30 Kynar wirewrap vs. 21 turns of AWG 22 stranded hook up wire. The coil to shield capacitance of the AWG 22 stranded hook up wire will be higher than the thinner Kynar wire bundle. This meter is just the thing to see the results. Some of the results are counter intuitive!
My old workhorse LC meter is a tube-based Tektronix 130 LC meter that has a maximum inductance measurement of 300uH full scale. If I want to go higher I need to add a known inductor value in parallel with the unknown inductor and use the parallel inductor formula to calculate the value that is larger than 300 uH. This is not very convenient when winding coils in the 300uH to 500 uH range.
When I finished with the L/C meter IIB kit, I measured and adjustable inductor set to 300 uH. Then I measured the same inductor on my Tektronix 130 and it was exactly 300 uH. You can't beat that!!! Even though the web site and the meter specifications claim it is accurate, I had to see for myself. I'm convinced!
In the Hammerhead circuit, Carl mentioned that C17 and C18 are candidates for being matched to get the same response from both inputs of the integrator stage. This LC Meter IIB has a matching mode that will very accurately help you find matched capacitor pairs.
Considering the percision of this meter, it's ease of consuction, relatively low cost and value to PI experimentors, I wanted to share this with the Geotech Forum members.
bbsailor
The unit is self-calibrating and self-zeroing. When in the inductance mode it subtracts the residual inductance of the shorted test leads and when in the capacitance mode it subtracts the residual capacitance of the open test leads. This ensures that low value measurements are accurate...and they are! It comes with a component test fixture that allows surface mount and leaded L/C components to be easily tested.
The unit comes both assembled as well as in kit form. I chose the kit and it went together in about 2 hours with no problems. One unique feature is that two capacitors come in a separate envelope and they are selected to be a combined standard value when installed together to form the basis of measurement accuracy.
Here are some uses of this LC meter for PI coil makers and Hammerhead builders.
Measure the capacitance of coax wire, shield to center conductor. This is important when trying to make very fast coils with the lowest possible total capacitance. You may be surprised to see how much capacitance is in you coil coax lead to the control box. A good range will be between 16pf and 25 pf per foot.
Measure the capitance of the shield to the coil. Just clip one meter lead to one of the coil wires and the other meter lead to the shield and see how many 100 pfs your shield adds to the total capacitance as seen by the pulse circuit and is reflected in the value of the damping resistor. Remember higher values of damping resistor means you have less capacitance in the circuit and this means a potentially faster and more sensitive coil. So if you want to reduce the coil to shield capacitance this LC meter is just the thing to see effect of changing the spacing between the coil and shield, using different wire sizes, using thicker or thinner insulating coil wire, or using different types of wire insulation, kynar, teflon, vinal, etc. Remember, the fewer turns you have in the coil (with the desired inductance) will result in a lower shield to coil capacitance as each turn within the coil adds to the total measured capacitance. If you are planning to use a series current limiting resistor in your TX coil circuit, you can always a thinner wire and make a faster coil. 50 ft of Radio Shack Kynar wirewrap AWG 30, wound on a 10.375" diameter coil form with 18 turns will make a 380 uH coil as measured by this LC meter.
Coil inductance measurements can be found by using the on-line calculators such as:
http://my.athenet.net/~multiplx/cgi-bin/airind.main.cgi
This calculator will get you in the ball park but are not very accurate when winding a multi layer coil that you are going to tightly wrap with plastic spiralwrap to space the shield. Thinner wire, spaced more closely together, gets you higher inductances. This means that you get the desired inductance (say 300uH) with 17 turns of AWG 30 Kynar wirewrap vs. 21 turns of AWG 22 stranded hook up wire. The coil to shield capacitance of the AWG 22 stranded hook up wire will be higher than the thinner Kynar wire bundle. This meter is just the thing to see the results. Some of the results are counter intuitive!
My old workhorse LC meter is a tube-based Tektronix 130 LC meter that has a maximum inductance measurement of 300uH full scale. If I want to go higher I need to add a known inductor value in parallel with the unknown inductor and use the parallel inductor formula to calculate the value that is larger than 300 uH. This is not very convenient when winding coils in the 300uH to 500 uH range.
When I finished with the L/C meter IIB kit, I measured and adjustable inductor set to 300 uH. Then I measured the same inductor on my Tektronix 130 and it was exactly 300 uH. You can't beat that!!! Even though the web site and the meter specifications claim it is accurate, I had to see for myself. I'm convinced!
In the Hammerhead circuit, Carl mentioned that C17 and C18 are candidates for being matched to get the same response from both inputs of the integrator stage. This LC Meter IIB has a matching mode that will very accurately help you find matched capacitor pairs.
Considering the percision of this meter, it's ease of consuction, relatively low cost and value to PI experimentors, I wanted to share this with the Geotech Forum members.
bbsailor