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I was wondering if it is possible to measure the capacitance of a gamma rod using an L/C meter. I tried to measure one by clipping one of the alligator clips on the outer aluminum tube and the other one on the inner core of an insulated piece of RG213 which used inside the aluminum tube but the meter showed 0.

I doubled checked the meter by measuring couple of "normal" capacitors and it measured them without any difficulties

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    $\begingroup$ Aren't you supposed to remove the shield and insulation from the coax used for the inner part? Leaving it on is going to reduce the capacitance because you have a larger plate spacing. (Wouldn't think that would be enough to make it unmeasurably low, though.) $\endgroup$ – Kevin Reid AG6YO Jan 31 '15 at 15:38
  • $\begingroup$ Hi Kevin, thanks for your message, I have removed the outer PVC jacket and the braid from the cable, it is left only the PE insulation and the inner copper wire to act as dielectric and the other plate respectively $\endgroup$ – Electro Jo Feb 1 '15 at 10:15
  • $\begingroup$ Perhaps you could edit your question to clarify that. You said "an insulated piece" which I would assume meant all the original parts were present. $\endgroup$ – Kevin Reid AG6YO Feb 1 '15 at 16:17
  • $\begingroup$ I guess it is clear through these comments, also having the insulated part of the coax and the inner core of it is the standard process of creating a gamma rod, right? $\endgroup$ – Electro Jo Feb 2 '15 at 9:05
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Sure, if your L/C meter is designed to work at those capacitances. The capacitance of a gamma rod isn't much -- it's probably measured in pF. The lowest range of the inexpensive L/C meter I have from eBay is 200pF, which is fine for most of the capacitors in my parts drawer, but not so great for RF.

Also keep in mind: if you are making connections with long alligator clips, these are going to have inductance and capacitance in addition to the gamma rod. Depending on how well the clips chomp down they may add significant resistance, too. Unless you take some very special care to keep those leads short or compensate for them, you are going to introduce so much stray reactance with the leads that any measurement you obtain won't be of much use.

In practice, anything designed to measure the reactances typical at RF stops being called an "L/C meter" and starts being called an "antenna analyzer" or a "network analyzer". So, while it certainly is possible to measure the capacitance of a gamma match, it's probably not possible to do it with something marketed as an "L/C meter".

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  • $\begingroup$ Hi Phil,Many thanks for your answer, the L/C meter I am using is an LC200A, a meter of around 35$ from eBay, which supposedly measures capacitance from 0.01 pF - 10uF. $\endgroup$ – Electro Jo Feb 1 '15 at 10:20
  • $\begingroup$ @ElectroJo those specifications sound highly suspect. The leads of that device alone have a capacitance of more than 0.01pF. $\endgroup$ – Phil Frost - W8II Feb 1 '15 at 12:49
  • $\begingroup$ I know what you mean, I guess I have to find some kind of small variable capacitor and try different positions to check on its capacitance readings on the meter $\endgroup$ – Electro Jo Feb 1 '15 at 13:48

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