Really cheap yagi antennas

[megabyte]

I just noticed that a quick search for "2.4 yagi" on eBay brings up numerous listings for 20dBi yogi antennas (pictured below), shipped from China to your door for about 10 bucks.

Aside from having to change the RP-SMA they sound almost too good to be true for the price (a grid with similar gain costs about 10 times as much), so I was just wondering if anyone has any experience with these antennas, or could suggest any drawbacks I may have overlooked?

[IBCrazy]

I see a few different models of these. Some of them are actually quite good. Others not so much. I found one that wasn't very good until you hooked up the poorly made adapter to it. The adapter worked as an impedance transformer and the antenna worked really well.

-Alex

[megabyte]

So I guess it's a bit hit and miss. I'll put off buying one of these until I have built up the knowledge and resources to be able to verify its performance.

Thanks Alex,

[IBCrazy]

If you were in the U.S. I would have be glad to test it for you.

[aaron_gx]

I bought the 13dbi 1.2ghz yagi for 20bux shipped off ebay. Construction is sturdy, cable looks good etc... Performs like I would expect it to, very narrow beamwidth, high gain. Excellent value, IMO.

[megabyte]

Fair enough, I think it's the 20dBi and 25dBi claims that I find most dubious about these eBay auctions.

I'm just wondering:
1. Are yagis good for gains above 20dBi? If so, why do long range FPVers seem to prefer to lug around a giant grid for the same gain?
2. I heard that grids are usually inefficient, does this mean that an 11 dollar 25dBi Yagi might outperform a 150 dollar grid of similar gain?

It's a catch 22 that the only way I can really test the performance of the cheap eBay yagis is to buy the expensive grid as well and do RSSI field tests, but I guess testing is half the fun of FPV.

[ajhaggerty]

Fair enough, I think it's the 20dBi and 25dBi claims that I find most dubious about these eBay auctions.

I'm just wondering:
1. Are yagis good for gains above 20dBi? If so, why do long range FPVers seem to prefer to lug around a giant grid for the same gain?
2. I heard that grids are usually inefficient, does this mean that an 11 dollar 25dBi Yagi might outperform a 150 dollar grid of similar gain?

It's a catch 22 that the only way I can really test the performance of the cheap eBay yagis is to buy the expensive grid as well and do RSSI field tests, but I guess testing is half the fun of FPV.

Great question. I seem to remember never hearing much about yagis above 18dbi or so. I feel like the antenna becomes less efficient with that many parasitic elements present.

[IBCrazy]

^It does... sort of. Yagis are incredibly efficient antennas in terms of air volume. However they lose a lot of their main lobe to the sidelobes hence making the main lobe excessively small. This is why I don't care for Yagi antennas for FPV.

-Alex