SmaTrig 2.1

Technical review of the Yongnuo RF603ii radio remote release

Image of Yongnuo RF603ii

In this short review I describe the Yongnuo RF603ii from the technical point of view focusing mainly on two topics difficult to test without specialised equipment: the trigger lag and the power consumption of the devices.

The Yongnuo RF603 ii radio remote release became quite popular under photographers recently. It offers all the amateur needs at a reasonable price. It has various connection options like the flash hot shoe, a 2.5mm jack connector and the PC sync plug. It uses standard AAA batteries in it's mk2 version. Something really great is the possibility to trigger Yongnuo's YN560-iii flash unit directly. None of the big camera manufacturers came up with this simple idea. They prefer to use their master-slave pre-flesh communication and hide this feature in less expensive camera models.
Each device can operate a sender or a receiver. This is practical, but leads also to non-intuitive handling. To trigger a camera over the jack cable both devices must be in receiver (or transmitter mode, TRX) mode, not sender/receiver. Once figured out, the function is very reliable.

Here is the summary starting with the pros:

  • Standard AAA battery used
  • Device can work as sender or receiver
  • Connections: hot shoe, 2.5 mm jack, PC sync
  • Some Yongnuo flashes can be triggered directly (e.g. YN560-iii)
  • Fixing screw for hot shoe
  • 16 channels to avoid interference with other devices
  • Decent build quality
  • Good value per money

Some cons surfaced during the measurements described further down. They are:

  • Trigger lag rather long and significantly varying, but OK for non-high-speed usage
  • Battery life in receiver mode could be longer

Trigger lag

After receiving my pair of the RF603s I was wondering how fast the communication between the sender and receiver happens. I wanted to figure out how big the delay between triggering the sender and releasing the camera or flash connected to the receiver is. Is this radio remote release useful for high-speed photography, for example in connection with the SmaTrig?

To clarify this question I have connected the sender to the SmaTrig running in interval mode (1 s interval) and the receiver to the oscilloscope. In the image below you see the result. It's an overlay of a series of multiple trigger events. The curve going down first is the sender trigger signal, the one going down later is the receiver response.

shutter lag of Yongnuo RF603ii

It's easy to interpret the image. The trigger lag varies randomly with each release quite significantly. It ranges between about 450 us and 580 us. For the non-engineers, this equals to 0.45-0.58 ms or 1/2222 - 1/1724 s.

This result is OK for "normal" flash photography with about 1/250 s shortest exposure time. For high speed photography the delay might be too long depending on the particular application. Drop photography should work fine, flying bullets will not be captured correctly. A little bit worrying is the significant variation of the delay of about 20%. This fact can make the results quite random.
Changing the channel did not have any influence on the timing.

Flash trigger lag and multiple receivers

The question now is, what happens when multiple receivers receive the same signal from one sender. Will they all have the same delay? Is the trigger lag random form shot to shot but equal for all receivers? Or is it random from shot to shot and for each receiver?
To figure this out I have wired up a simple setup using two receivers. One was the second RF603ii from the set driving a Speedlite 430EX, the other one was the Yongnuo YN560-III flash which has a built-in receiver compatible with the RF603ii. After each release both flashes fired on a fast photo diode connected to the oscilloscope. The scope was triggered with the sender release pulse.
An exemplary result of the test is shown in the image below.

Synchronous triggering of YN560-III flash and transmitter

The falling edge on the left is the sender trigger pulse. The two peaks on the right stand for the two light signals from both flash units set to 1/64 and 1/128 output power respectively.

Unfortunately the peaks were at a different location for each release and overlapped only randomly. It seams, the trigger lag measured for a single remote control above varies for each device. This is of course bad news for people doing high-speed photography. The time difference might result in ghost images when multiple flashes are connected remotely. For "static" imaging the 50-100 us flash-to-flash mismatch will not be visible. In case the flashes are running at a higher power the trigger lag variation will be anyway much shorter than the total flash duration. Measurements of the flash duration depending on the power setting can be found here.

Battery life

To calculate the battery life of the RF603ii I simply measured the battery current for both the sender and the transmitter mode. The results are listed below.

Function Battery currentBattery life (~1000 mAh)
Sender mode TX 3.2 mA 300 hours -> 12 days
Transmitter mode TRX18 mA 55 hours -> 2 days

The difference between the modes is significant. The explanation is simple: the sender wakes up just on demand, the receiver must be awake all time. A battery life of two days should be no limit for spontaneous shooting, but might be critical for long time installations like photo traps in nature observation. When the remotes are used randomly as sender or receiver the battery life should be equal for each device in the pair.

RF603ii disassembled

In the following you'll see how the RF603ii looks inside. Most components are mounted on the top side of the PCB (facing the top conver) which is accessible after desoldering the pins of the top hot shoe. This is not trivial with the two-sided PCB.

RF603ii disassembled RF603ii PCB view

The flash output seems to be triggered with the MAC97A6 logic level triac capable of switching up to 400 V. The MMBT8050 NPN transistors seem to switch the camera outputs.
During experiments I noticed the PC sync output doesn't trigger some camera models. The inner resistance of the triac is probably too high.

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