With the testing equipment we have for quality assurance on our ClearBoost, we're able to test the reflection parameters of antennas in any frequency up to 6GHz.
I'm going to start the testing with my favourite long range antenna for 5.8GHz, the Circular Wireless HELIAXIAL58. As a note, this antenna is several years old, but has always been kept in its retail box when not in use.
In these tests, we're not looking at the radiation pattern of the antenna at all. This can have a HUGE impact on real world performance, maybe we will build a test jig for this in the future. Primarily we're interested here in how well the antenna is matched to FPV frequencies, and how wide this tuned section is. There's no point having an antenna perfectly tuned for say 5760MHz but only having a 20MHz section usable. You can read more about VSWR here. We're also pretty interested in seeing what happens when a human body comes near by, such as happens when wearing goggles. The human body can be exceptionally good at detuning an antenna.
For all of these tests, I'll add markers 1 and 2 at 1.25:1 (1.235% loss), and markers 3 and 4 at 1.5:1 (4% loss). You can see the frequencies that these match at in the top right of the pictures. A VSWR of 1.25:1 is very good, even 1.5:1 is good, however most antenna manufacturers would consider this to be a poorly matched antenna.
We're not testing in an anechoic chamber, however other than that all antenna testing best practices are applied.
So how does the antenna look?
Antenna in free space. Marker two shows 1.47:1 as we can only test to 6GHz. Vertical divisions are actually 0.25, not 0.2 as displayed.
What does this curve mean? This antenna is quite simply amazing for FPV. Most 5.8GHz FPV transmitters work between 5.7GHz and 5.9GHz, so we want to be at 1.25:1 VSWR or lower in this band. Markers 3 and 4 are at 4.67GHz - 5.89Ghz, between these frequencies more than 99% of the signal makes it out of a transmitter, or into a receiver. The lowest VSWR on this antenna is 1.13:1 at 4.78GHz however at 5.7GHz its still 1.14:1 (just 0.428% loss) which is very nice.
In a slightly exagerated test for goggles, I held my hand parallel to the helix 1cm away, and the directly behind the reflector but not touching it. The results were basically the same, as seen below.
As we can see, the lowest points of the line did move.. just. This antenna shows virtually no change in tuning by placing my hand next to it. The next antenna I'll look at will be an ImmersionRC 5.8GHz antenna that comes with their receivers, like all dipoles you'll see an enormous difference in the tuned frequency. This antenna is a great choice for goggles or for a fixed ground station on a tripod/similar or sitting above an FPV case.
Also to note on the test setup, I am not using the antenna adapters which were included, these have long since been mixed with others or lost in dirt. I'm using one of our Straight SMA to SMA adapters which are rated to 12.4GHz, and therefore should not affect the antenna performance.
My rating: Supreme. This antenna may be matched by others, but really sets an amazing benchmark.
This is an expensive antenna, however you absolutely get what you pay for, and after several years it is still performing perfectly with no sign of corrosion.
Where can you buy one?
Do you have an antenna you would like to see tested?
Please Contact Us, if you're happy to pay postage to us - we will test it, and pay the return postage to you.