OWLRC recently came up with a compact and affordable SWR meter that can measures 5.8GHz antennas performance, well, roughly. It has a simple UI, a bright touchscreen and powers off a 3S LiPo battery.
Buy the OwlRC SWR Meter from: http://bit.ly/2kVBQYx
What can you use the OwlRC SWR Meter for?
It’s perhaps not the most precise tool, but it’s useful for various things:
- Troubleshooting defective antenna, adapters and extension pigtail etc
- If you build your own DIY antennas, you can use the SWR meter to optimize it for a specific frequency (assuming the meter is well calibrated)
- Finding the best frequency to use with the antenna
- Check for consistency and quality control of an antenna by going through multiple samples
So, What is SWR?
SWR stands for Standing Wave Ratio.
The standing wave ratio is normally measured by inserting a device in the feeder cable of the antenna. It’s determined by how much power is going out from the antenna (transmitted voltage) compared to the power coming back (reflected voltage).
Ideally a good antenna will transmit all of the power with nothing coming back. A SWR number of 1 is the best possible result, a higher SWR means more voltage is reflected back and therefore performance is worse.
Note that SWR value is only one aspect of FPV antenna performance, there are many other factors as discussed in our FPV antenna tutorial.
A Close Look at the OwlRC SWR Meter
The OwlRC SWR meter is built inside a compact wooden box. It can be powered directly from a 3S LiPo battery, which seems to be designed specifically for the FPV community as most of us should already own a 3S LiPo, right? :)
Mine comes with a SMA connector for plugging in the testing antenna. The OwlRC SWR meter is equipped with a color touch screen so there is no buttons on this device (except the power switch).
There are only two modes, operation should be simple enough for most people? :)
There is a paper manual explaining how to use this device, if that wasn’t enough, there is also simple instructions in the “help” page in the menu.
It uses the built-in video transmitter (VTX) to measure SWR of an antenna. The real-time graph shows SWR, Vfw (forwarded voltage) and Vrev (reversed voltage) for the selected VTX channel. You can cycle through all 8 channels by pressing the up down arrow on the screen.
The available VTX channels are a set of frequencies that don’t seem to below to any common 5.8GHz bands for FPV, but pretty close to Raceband.
5645, 5685, 5733, 5771, 5820, 5866, 5905, 5945
I will probably be using this mode most of the times.
It measures SWR in a wide frequency range from 5645MHz to 5945MHz. You can move the cursor in the graph to read SWR value using the touch screen.
Unfortunately, it doesn’t really go through every frequency in this range, but rather just the 8 channels available on the VTX.
There are two options you can select:
- If Auto is selected it will repeatedly measure SWR through the whole band
- If Track is selected it will scan all the channels once, and then move the cursor to the channel with the lowest SWR value
How to read SWR graphs?
Here are some measurement examples I got by testing a few different antennas.
First off, we have the Foxeer Cloverleaf antenna. These are very durable yet probably one of the cheapest antennas in the market. So it doesn’t surprise me that the SWR aren’t the best in this test. The SWR goes up with frequency, indicating that it would work better with lower frequency.
Next up we have the Realacc Pagoda antenna. Not bad at all for the price and it seems to work better at frequency higher than 5866MHz.
Here is the result for the Aomway Cloverleaf antenna. They are known to be the best performing antenna for the low price. It should perform the best below 5645MHz and the performance will quickly get worse as frequency goes up.
Finally we have the ImmersionRC Spironet, which I’ve been using since 2015. Not the most durable but they do have excellent performance. The graph confirms that as it shows the widest flat line in all the antennas tested.
As you can see, you can find out which frequency is best to use with your antenna with this SWR meter :)
It’s a hobbyist grade tool and it’s far from perfect, definitely not precise enough to be a tuning tool. But it’s good enough for troubleshooting damaged antennas, and tell apart a good antenna and a bad one.
It’s a Toy?!
Although according to OWLRC, each unit is calibrated as a whole with the built-in video transmitter, you should keep in mind that it is not a laboratory-grade equipment, nor can you expect it to be at this low price.
I wouldn’t rely on the raw measurements from this meter, but it can still tell you the relative consistency and performance of an antenna at a given frequency.
It’s funny that OwlRC actually emphasizes that this SWR meter is a TOY in the manual.
No Data Logging…
One downside with this tool is the lack of means to export data. Data logging has to be done manually by scrolling along the graph to view each measurement.
It has a VTX so check before powering on
Tests are done using an internal 200mW VTX, so make sure you don’t use this SWR meter while other pilots are flying!
Am I going to use this?
Yes. I think it would be useful to test consistency of an antenna, like getting multiple samples of the same antenna and see if the SWR all come back roughly the same. Also, when testing video transmitter or receivers, it’s important to find out if the antenna I am using are of the similar performance to ensure the test is a fair one.