If we are going to be reviewing antennas from a electrical standpoint, we need a reference antenna, so I'm going to review the stock ImmersionRC dipole antenna. Hopefully we'll get to the BOSCAM/other chinese stock antennas soon. If you are looking at an antenna upgrade, this might just be what you are upgrading from if you use FatShark or ImmersionRC equipment.
Firstly, I tested 3 of these, all brand new and from either a transmitter or a receiver. The results vary considerably. Your antenna may be vastly different to these results. These were all tested one after another, and repeatable if I connect the antenna again.
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 from a radiated power standpoint, however most antenna manufacturers would consider this to be a poorly matched antenna.
So how do the antennas look?
Antenna A, 1.25:1 VSWR bandwidth 5.83GHz to 5.9GHz. Lowest VSWR 1.17:1 at 5.87GHz.
Antenna B, 1.25:1 VSWR bandwidth 5.83GHz to 5.89Ghz. Lowest VSWR 1.20:1 at 5.86GHz.
The two of these are pretty similar. Their bandwidth for 1.25:1 VSWR is almost identical with one antenna being slightly better than the other. I had a third antenna so I decided to test it too.
Antenna C, All points worse than 1.25:1 VSWR. Best VSWR 1.33:1.
So this antenna resulted in me switching between about 5 different antennas to see what happened to my calibration. Turns out, the other antennas are completely repeatable, and so is this one. It's just completely different. Did ImmersionRC switch suppliers? Its possible based on this plot.
A & B are tuned too high. At 5740MHz, ImmersionRC Channel 1 has a VSWR of 1.83 (9% loss of signal) - that is not insignificant amounts of reflection, which means a hot transmitter. CH1, 2 and 3 are not worth using with those two antennas. CH7 and 8 are relatively good.
Antenna C has a rather flat response through the whole ImmersionRC channel range. The best case on this is 2% signal loss, and thats not bad.
So how do these respond when we stick a head or hand near it, as would happen when using Goggles?
Suprisingly the antenna actually performs a better from a technical standpoint, however the frequency it's tuned to shifts upwards somewhat, which makes it worse for FPV use.
Holding my hand near the "odd" antenna makes it even more odd.
All I can say to this is "huh".
If I expand the frequency range for Antenna C, things become a little clearer.
I think what has happened here is that they have switched antenna manufacturers. From a 5.8GHz or 5.9GHz specific antenna to a 5GHz WiFi antenna which gives a much wider response. I'm fairly sure that Antenna C is newer stock than A & B. This is a pretty good move on ImmersionRC's behalf, its VSWR isn't as good at the point it is tuned, however it is superior in that the bandwidth is much wider, which means across all their channels it performs much better. It would be interesting to see some more ImmersionRC antennas and what they do.
My rating: Weird. Depending on when your antenna was manufactured, it may be less than average quality for FPV, or it may be a bit better than average.
This is just a stock antenna, if stock antennas were amazing there would not be such a large market for upgrades. We've found in flight that these are pretty terrible however from a tuning standpoint they are not too bad, but that could vary depending on what came in your box.
Where can you buy one?
I don't believe these are available individually.
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.