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AC8SW

Joined: Mon, Jul 28th 2014, 19:56 Roles: N/A Moderates: N/A

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Topic Created Posts Views Last Activity
External DC Source for Desktop Yaesu FT-60 Oct 14th 2014, 03:01 3 2,360 on 16/10/14
Gamma Match Question Oct 14th 2014, 01:45 3 1,825 on 31/10/14

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Gamma Match Question AC8SW on 31/10/14
After further consideration, I believe the far-end of the hollow gamma rod may be either electrically open or closed. The choice should have no impact on the gamma match performance.

Rationale: The inner surface of the hollow gamma rod and the conductor running along its axis form a coaxial structure often referred to as a “trombone capacitor”. But for RF signals, this structure is a coaxial transmission line with an open-circuit load. Because the line length is less than 1/4 wavelength (and neglecting any loss), the impedance at the input is entirely capacitive reactance. The reactance value is a function of the characteristic impedance of this line and its electrical length. Gamma match analysis can assume an equivalent capacitor having this reactance to be connected between the antenna feed line and the gamma match transmission line formed by the antenna driven element and the outer surface of the hollow gamma rod. (Please refer to the W3PG gamma match analysis article in the Jan 1969 issue of QST.)

The central point is that when the gamma rod inner surface and center conductor act as a transmission line, the RF signal is reflected back to the input at the open end of the conductor. Neglecting a small, local end-effect field, no electromagnetic field exists within the hollow gamma rod beyond the end of the center conductor. Consequently, the far end of the hollow gamma rod may be either electrically open or closed without affecting the gamma match performance.

73s

KD8ZIH
kd8zih@arrl.net
External DC Source for Desktop Yaesu FT-60 AC8SW on 16/10/14
Thank you for your response.
External DC Source for Desktop Yaesu FT-60 AC8SW on 14/10/14
Question, please. I'm a retired electrical engineer, new to amateur radio as of Aug 2014. I purchased a Yaesu FT-60 5W handheld that I'm using it as a desktop transceiver connected to a remote 4-element 2 meter yagi. I'm very disappointed that the unit did not come with a power brick for operating from 120 Vac. The FT-60 Operating Manual advises not to operate the unit, even in receive-only mode, using the 120 Vac input, 12 Vdc, 500 mAdc output power brick that feeds the Ni-MH battery charger. The only external DC source option offered by Yaesu appears to be a cigarette lighter adapter for mobile operation. Does anyone know of a suitable 120 Vac external DC source for the FT-60? Thanks.
Gamma Match Question AC8SW on 14/10/14
Question, please. For a gamma match that uses a coaxial capacitor formed by the interior surface of the hollow gamma rod and an insulated conductor running part way down the interior of the rod, should the far end of the hollow gamma rod (the end away from the coax cable connection) be electrically closed?

If the far end is electrically closed, it seems the RF current flowing radially through the coaxial capacitor will return on the interior surface to the open end (feedline end) of the gamma rod, then travel the entire length of the transmission line formed by the exterior surface of the rod and the antenna driven element before reaching the connection point between the two.

If both ends of the hollow gamma rod are open, it seems the capacitor current will flow out of both ends of the rod and travel to the element connection point by two parallel paths, only one of which is the intended gamma rod transmission line.

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