Timeline for What is a Gamma match in the context of the driven element of a Yagi antenna?
Current License: CC BY-SA 3.0
11 events
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| Jul 9, 2014 at 11:39 | comment | added | Phil Frost - W8II | Also wanted to mention, if you wanted a way to transform the feedpoint impedance up or down without the "unintended" side-effect of adding inductance, that's just an ordinary off-center fed dipole. | |
| Jul 7, 2014 at 12:45 | comment | added | Phil Frost - W8II | Another common matching method is the "hairpin" or "beta" match, which uses just shunt inductance (the capacitance being provided by a shortened element). everything2 even describes a hairpin match and a capacitorless gamma match on the same page. | |
| Jul 7, 2014 at 12:36 | comment | added | Phil Frost - W8II | If you do a Google image search for "yagi" you will see a few, although far more common is to use a folded dipole for the driven element, which is a balanced gamma match (T match) with the shorting bar / tap / whatever you want to call it adjusted for 0 inductance. If the stub is less than a quarter-wave long (as usual in a gamma match), then it does present an inductance, and you need a capacitance somewhere. It doesn't have to be a series capacitor though: it can also be a shortened antenna element. | |
| Jul 7, 2014 at 3:30 | comment | added | HarveyB | Re: capacitorless gamma matches. That actually makes a twisted kind of sense, although as I said, I've only seen one and I'm pretty sure it was a mistake in construction. Have you any examples of commercial antennae without capacitors? | |
| Jul 7, 2014 at 3:18 | comment | added | HarveyB | What you call a "shorting bar" is a movable tap on the antenna element. Yes, it does have inductance, but that is incidental and an unwanted side effect. The series capacitance is used to neutralize this inductance (producing a series tuned LC circuit of zero reactance). | |
| Jun 28, 2014 at 14:15 | comment | added | Phil Frost - W8II | Also, I think when you see antennas with capacitorless gamma matches, they are either not designed to be adjustable at all (instead, manufactured to pre-determined dimensions), or they provide a mechanism to adjust the element length, thereby changing the capacitance of the element itself (which will probably be a bit short to assure it is indeed capacitive) | |
| Jun 28, 2014 at 14:12 | comment | added | Phil Frost - W8II | But moving the shorting bar doesn't get you a transformer-like impedance transformation like moving the feedpoint of a series-fed dipole does. Rather, it changes the length of a shunt shorted stub, effectively an inductor. | |
| Jun 28, 2014 at 6:01 | history | edited | HarveyB | CC BY-SA 3.0 |
added 2 characters in body
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| Jun 28, 2014 at 5:58 | history | undeleted | HarveyB | ||
| Jun 28, 2014 at 5:55 | history | deleted | HarveyB | via Vote | |
| Jun 28, 2014 at 5:54 | history | answered | HarveyB | CC BY-SA 3.0 |