The ImmersionRC RF PowerMeter V2 allows you to quickly check if your VTX and radio transmitter are performing optimally. It can measure how much power your transmitter is actually putting out.
Further Reading: My VTX Recommendations
Where to Buy?
The package comes with a linear polarized (whip) antenna, and a female SMA to female SMA adapter. The connector on the power meter is a male SMA.
Why You Might Want an RF Power Meter V2
It’s useful to have a RF power meter if you race and fly with others, it’s even essential if you take part in racing events.
Some poor quality or defective VTX might be labeled 200mW, but it can be transmitting at much higher power. Everyone at the race will be scratching their heads wondering why they have terrible signal. You will be able to spot the issue more easily with a RF powermeter.
It’s especially a handy tool for race events, where each quad on the starting line can be checked for actual RF output power. The ones transmitting more than you want can be picked out immediately, preventing issues during the race with channels being stomped on by the higher power VTX.
If you only fly alone then verifying VTX power is of less importance. Though it can still be useful to check the performance of your FPV gear, or finding the best performing channel on your VTX.
ImmersionRC RF PowerMeter V2 Features
- Affordable and portable compared to equipment in the field
- Helps you find out about VTX output power
- Measures frequency from 35MHz all the way up to 6GHz
- You can use it to locate a crashed RC model with a powered VTX in tall grass. You just need to attach a directional antenna on it and it essentially turns into a quad finder. You get a stronger signal as you point it closer to the direction of the quad, allowing you to quickly locate its direction
- Removeable Li-Ion 10440 600mAh battery, one full charge should last 8 hours
- USB port for battery charging and firmware updating
There is the power button next to the mono colour LCD screen, and a multi-directional joystick. The Micro USB port is located on the right-hand side of the device.
Menu and Operation
The ImmersionRC Power Meter V2 only has four screens and four settings, making it super simple and easy to use.
Mode 1 – VTX Power Testing
By connecting a VTX directly to the power meter, you can check the output power of the VTX.
Every VTX has a power output which varies from channel to channel. Let’s say you have a 25mW VTX, it might read closer to 40 mW at 5645MHz, but only 18mW at 5875MHz. A power meter helps you find the best frequency for either accuracy (closest to the target output) or efficiency (highest output power verse current draw).
Also VTX can wear out over time, this testing device can tell you the performance/condition of your VTX.
You can test VTX output using an antenna as well, by simply placing it close to the transmitting antenna. However I found this way of measuring unreliable and inconsistent. The value can fluctuate a lot with a tiny bit of movement, and the result is often under-estimated compared to measurement from direct connection.
Update: as pointed out by Mr Joe Scully in the comment, with antenna to antenna measurement, you need to calibrate the power meter for the attached antenna by adding attenuation. According to him 8.5db to 9db is a good range to get started.
Mode 2 – Power Scope Mode
The PowerScope mode shows an oscilloscope-like display of measured power over time: a duty cycle and packet intervals. Resolution settings are 10ms, 20ms, 40ms, 80ms and 160ms.
This is great for testing radio transmitter, but not that useful for video transmitters which emit a fairly constant power level.
Mode 3 – Sniffer Display Mode
You can check a VTX against a benchmark to see if the transmitting power is too high or too low. For example, this feature can be useful for the race director in a racing event to walk down the starting line, and make sure all the quads are transmitting on the same power level.
However it’s not super precise. The measurement varies depending on where the sniffer antenna is placed relative to the transmitter antenna. But with a bit of practice it can be a very useful tool for races.
Update: Mr Joe Scully commented below with a video how you can make sure of this mode more effectively.
Is Attenuator Required?
In the older version, you had to get a separate and expensive attenuator for the power meter. Fortunately in the power meter V2, there is a built-in 30dB attenuator!
However, according to the datasheet, the absolute power limit you can plug into the meter is 1.3W (1300mW), anything higher might cause damage. For anything higher than 500mW, you shouldn’t have it connected for longer than 30 seconds to avoid overheat and damage (e.g. losing accuracy more quickly over time).
You are recommended to use an external attenuator if you want to test anything more powerful than 500mW for a longer period of time. I was suggested by Sander from ImmersionRC to use a 2W 10dB 18GHz attenuator, for example: https://amzn.to/2KLVbGs.
My plan is to test VTX with no more than 1500mW, so that should be good enough.
Note that when you make such measurements it is good practice to calibrate out the attenuator and any extra adapter you use. According to Sander:
Best way to do that is to use a lower power VTX on the same band and channel as the higher power VTX you plan to test and measure it without the attenuator, note down the exact output after it has settled (higher temperature might cause output to drop). Now attach the attenuator and hook up the same, lower power, Vtx and measure the output again and adjust the attenuator value in the menu (Attn option) to best match the value you measured without the attenuator. Now you can go ahead and measure the higher power Vtx and get an accurate reading, as you’ll have calibrated out the attenuator’s tolerance, which can be as high as several dB.
Power Meter V1 vs. V2
If you already have the V1, should you upgrade to the V2?
For racers, definitely yes. It’s more portable with the built-in attenuator, and it’s also more accurate. If you only use it on the bench for testing, V1 should be good enough IMO.
How reliable/accurate is it?
Unfoturnately I don’t have the right equipment to compare to. But according to ImmersionRC, these are individually calibrated in factory to within 0.5dB against a NIST certified laboratory grade instrument.
I guess the answer really depends on what you compare to, and what sort of level of accuracy you are looking for. But if race events are using these as the standard, then there isn’t really much to worry about.
As for consistency, it’s really good! I repeatedly tested the same VTX multiple times and every time I get the same measurement.
Can I use it for Digital FPV System?
Unfortunately no, the ImmersionRC Power Meter is almost useless for measuring output power of digital video transmitters such as DJI Air Unit, Caddx Vista, HDZero VTX’s etc. This is because the way power modulation works for digital RF compared to analog RF. To properly measure digital RF power you need lab grade gear which typically costs thousands of dollars.