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Registered Member #190
Joined: Fri Feb 17 2006, 12:00AM
Location:
Posts: 1567
I just got a DJI phantom on Ebay. The drone already had an antenna upgrade by FPVLR with a stage 2 kit. The antenna is a left-handed helix at 5.8 ghz.
I know almost nothing about antenna engineering. First, how can I use my oscilloscope to determine the exact frequency of my transmitter so I can fabricate a bigger, exact matching antenna.
Second, how do I make a larger antenna that matches the frequency? Thanks.
Registered Member #2939
Joined: Fri Jun 25 2010, 04:25AM
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Posts: 615
When you say "bigger" what are you hoping to achieve? Physical size is more or less determined by frequency and forward gain. If you want an antenna with more gain, the trade-off is increased directionality. I get the impression this is going on a drone? Increasing directionality could become a drawback, as you would have to be more accurate pointing your antenna at a moving target.
As for finding your exact transmitter frequency : usually the antenna match will be broad enough that using the number off the side of the box is good enough, with little real gain to be had with precision tweaking.
Registered Member #509
Joined: Sat Feb 10 2007, 07:02AM
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Posts: 329
Unless your photo is mirrored(or its just an example), thats a RHCP helix in the foreground, the one in the background is a left hand "half sphere helix" from a quick web search, it looks like a 2.4 ghz one A quick browse and it looks like they suppress the back lobes a bit better compared to typical helical antennas, and can have a wider main beam, for the same gain.
If thats your base station, you'd want an omnidirectional antenna on your quadcopter.
As far as measuring your transmitter frequency, the cheapest way to measure a 5.8 ghz output would be a frequency counter, but that will only tell you the carrier, and not the bandwidth too. Documentation on your transmitter will be your best bet on figuring out the exact frequencies. But that being said, most air dielectric antennas will be pretty broadband, hence the success of hobbyist made antennas with just careful measurements.
If thats your base station, and it is indeed a 5.8 ghz RHCP and 2.4 GHz LHCP, then pick up or make a corresponding LHCP 2.4 ghz pinwheel/planar skew/whatever is trendy this week in FPV omni antenna, and a corresponding RHCP 5.8 GHz antenna too. For initial testing, you could use a quarter,half, 5/8 wavelength whip, but youre going to take a nominal 3db hit in your link budget (~half the range) But at least with a circular polarized ground station, at least you wont lose signal when the craft pitches or rolls.
There should be a special prize for the first one to build a flying tesla coil of at least 1kw, to 300 ft AGL.
How about using a CW SSTC as a power transmitter for wireless charging/flight time enhancement of a small drone? You'd have two challenges: 1) To couple the TC to an efficient radiator and 2) Make a light enough receiving coil and LC tank which can receive enough power to exceed what is required by the drone to keep the added weight of the receiver in the air.
A more practical approach might be remote charging of a drone via microwave transmitter. Probably would need 10G uWave to not interfere with the 2.4g controller.
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5.8 ghz antenna left-handed helix
