Ok I'm done teasing with photos. Here it is, the VAS/True RC Crosshair!
The Crosshair antenna is the newest FPV RX antenna. Developed as a joint effort between IBCrazy (Video Aerial Systems) and HugeOne (True RC), the Crosshair delivers a nearly perfect axial ratio in the front and boasts an 8.5dbic forward gain in a nice compact package or a full 10dbic in a larger panel. Unlike the helical, the Crosshair needs no tuning and is much more compact. The bandwidth is fairly large, but circularity drops off very fast as you get off of the center frequency and thus it must be made for a specific frequency for best results.
In comparison to the helical, the Crosshair gives three distinct advantages: it is compact in size, is 98% efficient, and does not require tuning. It isn’t perfect, though. While the circularity is great right out front, it loses its axial ratio to the peripherals (sides) faster than the helical antenna. Also, while the bandwidth is quite large, the circularity suffers greatly as you get away from the center frequency.
Extra care must be taken to ensure the antenna is made very precisely. Additionally, moisture detunes the antenna. Thus it was designed for ~70% humidity. Excessive moisture (or lack of it) will detune the antenna just a bit. It also is nearly impossible to make for 5.8GHz. Hugo and I are still working on that one, so stay tuned (excuse the bad pun).
I give this tutorial to all hobbyists who wish to try their hand at constructing one. However, I ask that you not produce these for commercial sale. Making one for a friend or something is certainly ok, though.
Copyright C. Alex Greve Feb 1, 2012
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