The RadioPopper site lists just a few Nikon-compatible flashes that work with their RadioPopper JrX and the RPCube for remote manual control. These flashes include Nikon Flashes SB800 and SB600, and not the newer SB700, SB900 or SB910. There’s no specific mention, officially, about the SB-80DX or any third-party TTL-Capable Nikon-Compatible Flashes.
How could I be sure my Nikon or Nikon-Compatible Flash would work, before purchasing it? I thought, all I had to do was to contact RadioPopper about a list they surely would have. Right? Nope. I tried twice, and both times the tech reps said they had no list, but I could try my TTL-Capable Nikon-Compatible flash. If the JrX/RPCube could not work with my flash, then I could send it back to RadioPopper on their money-back, satisfaction guarantee.
But why not extend the list of “tested” flashes?
I have two non-Official (not in their manuals, nor on their website, nor from their tech reps) flashes that work with the JrX/RPCube combo. By work I mean having the full remote/Manual functionality of the Nikon SB800 that is advertised on RadioPopper.
My four TTL-Capable Nikon-Compatible Flashes, which all had standard Nikon 4-pin flash mating, are
Nikon SB-800
Nikon SB80-DX
Sunpak 444D with Nikon-Compatible Module NE-2D TTL-Capable
Vivitar 3700 with Nikon-Compatible Module DM/N2 TTL-Capable
I won’t be demonstrating how the flashes work with the RadioPopper JrX and RPCube combination. That is amply covered in RadioPopper’s own pdf documentation (http://www.radiopopper.com/the-jrx-system ).
Settings on the RadioPoppers
Settings on the JrX transmitter were
Settings on the receiver for Group 1 (same for Groups 2 & 3) were:
Nikon SB-800
You need to set the SB-800 in TTL mode. This means you need to press the SEL button for 2 seconds, until the icon menu of the SB-800 comes up. Then select the icon that has two squiggle arrows, representing the wireless options. Make sure this icon is selected OFF.
Then press the SEL button again for 2 seconds to get back to the main screen, where you will press the Mode button repeatedly until TTL comes up.
Once the SB-800 is setup for TTL mode, connect the flash unit to the RPCube, attach the 3.5mm connection wire to both the RPCube and JrX receiver, and start shooting!
Nikon SB80-DX
This unit works almost like the SB-800, once you get it into TTL mode. To do that, go to the back of the unit and press the MODE button repeatedly until you see the TTL indicator on the top of the LCD screen. 
Push Mode Button Repeatedly to Set TTL
You also need to make sure the Wireless is OFF. Holding the 4-way SEL button for 2 seconds, and then make sure the wireless option (the one with the squiggle arrow icon) is OFF. If this option is ON, you will not be able to use the MODE button to select TTL.
Press SEL until Squiggly Arrow (Wireless) is OFF
Once the SB80-DX is setup for TTL mode, connect the flash unit to the RPCube, attach the 3.5mm connection wire to both the RPCube and JrX receiver, and you’re in business.
Sunpak 444D with Nikon-Compatible Module NE-2D
This Sunpak has is TTL-compability with their Nikon-Compatible Module NE-2D. The main challenge is to figure which of the manual (gosh, this is an old flash!) sliders really work, and how to set them correctly.
Here’s the layout of the back of the Sunpak 444D in M (Manual Mode), with ¼ power setting:
You don’t want to set the 444D on Manual mode while using the JrX/RPCube combo. Read on.
Note the NE-2D module on the bottom, which mates to the Nikon shoe--it provided TTL for my trusty Nikon FE-2 and EM decades ago. This module is what makes the Sunpak 444D Nikon-Compatible. The 444D had other Nikon-Compatible Modules. Make sure yours is TTL-capable.
There are two horizontal and one vertical sliders. The top horizontal slider ISO/ASA merely provides information/graph. It does not change the electronics of the flash. The next two sliders, horizontal (on the left) and bottom (A/full) are what change the electronics of the 444D to TTL-capable.
The manual slider on the left provides the various MODEs for this flash. There were 5 modes: M for manual, A for three ranges of flash in red/yellow/green, and one for Blue. Here’s what the red range looks like:
Vertical Slider on A red
The last (bottom) mode is a mysterious Blue dot 
.
.
Move Vertical Slider Downward for BLUE Dot
& Move Bottom Horizontal Slider Left on A/Full
I long ago lost the 444D manual. However, I found by testing, that the Blue dot is TTL, only if you set the horizontal slider to the left, under A/full. In other words you need to push the horizontal slider all the way down until the blue dot appears, and push the bottom slider all the way to the left, under A/full. Only under these conditions will the Sunpak 444D work with the RadioPopper JrX/RPCube combo.
Once the SunPak 444D is setup for TTL mode, connect the flash unit to the RPCube, attach the 3.5mm connection wire to both the RPCube and JrX receiver, and again, you’re in business. Except for the noted problem below.
Noted Problems
The Nikons worked as advertised by RadioPopper. The SunPak took a bit of "fiddling" before working. By that I mean I had to adjust and readjust the mating of the SunPak before the JrX transmitter was able to make the unit flash. The JrX receiver seemed to obtain the transmitter’s signal (noted by the single blink of the green LED when the transmitter button was pressed). But the flash did not work until I manually re-seated the flash.
Vivitar 3700 with Nikon-Compatible Module DM/N2
There was nothing I could do to make the Vivitar work with the JrX. Groups 1 and 3 did not work at all. Group 2 did work, but did not respond to different powers on the JrX transmitter. I even tested that the flash worked with my Nikon D200--it did, even after 28 years!
Below is what the unit looked at, with TTL capability enabled (the Module DM/N2 made the Vivitar Nikon Compatible. I used the 3700 as my first TTL (on camera) Flash with my Nikon FE-2.
Testing of Each Unit with JrX and RPCube
I tested each unit by making sure each flash worked with the transmitter unit on my Nikon D200 DSLR. I set up each flash off-camera on a Manfrotto light stand, set from Max to 0. Increments of change were not the RadioPopper JrX power increments, because they were hard to consistently figure out from the analog dial. To provide consistent dial positions, I set the dial to the 0 position, then used it like a clock face, with the next increment being at the 3 o’clock position, the 12 o’clock, 9 o’clock and finally the max position of the JrX receiver. By dialing in these increments, I had repeatable positions, in increasing power.
I measured the light output with a Minolta IV-F flash meter using the flat diffuser at ISO-200. All flashes were set to 28mm angle. I used 28mm, because of the limitation of Sunpak’s fixed 28mm flash angle. The Nikons could be set to 28mm for flash.
I was after the ability for the flash to give “about” consistent reductions of power. All flashes registered 0 at the RadioPopper transmitter at OFF. All flashes registered about f16.6 at maximum. The table below provides my readings for different transmitter positions for the three flashes. Results across flashes did vary, partly because each flash had a slightly different maximum powers and different responses to the RPCube. I am fine with the differences, as I use a flash meter to start my ballpark estimates of exposure, tweaking in analog for effect. The main finding is that each flash works with the RPCube, but in slightly different power configurations from each other.
I also tested the units with different Groups, coming up with about the same results.
Summary
I’m satisfied all three units work with the RadioPopper JrX. My primary units are the Nikon flashes, with the SunPak as a reserve. I now know how well and accurately each unit works, and the “gotchas” with the SunPak. And I no longer worry about my Vivitar 3700. After 35 years it's headed into my Junque pile.
Next Steps
Should you have different TTL-Capable Nikon-Compatible Flashes that work with RadioPopper JrX/RPCube combos, please contact me, so I can collect a list of flashes (and how they need to be set) for other Nikon and Nikon-compatible RadioPopper users.
Wei Chong
Wei.PhotoArts@gmail.com
Vivitar 3700 Settings for Nikon TTL
Testing of Each Unit with JrX and RPCube
I tested each unit by making sure each flash worked with the transmitter unit on my Nikon D200 DSLR. I set up each flash off-camera on a Manfrotto light stand, set from Max to 0. Increments of change were not the RadioPopper JrX power increments, because they were hard to consistently figure out from the analog dial. To provide consistent dial positions, I set the dial to the 0 position, then used it like a clock face, with the next increment being at the 3 o’clock position, the 12 o’clock, 9 o’clock and finally the max position of the JrX receiver. By dialing in these increments, I had repeatable positions, in increasing power.
I measured the light output with a Minolta IV-F flash meter using the flat diffuser at ISO-200. All flashes were set to 28mm angle. I used 28mm, because of the limitation of Sunpak’s fixed 28mm flash angle. The Nikons could be set to 28mm for flash.
I was after the ability for the flash to give “about” consistent reductions of power. All flashes registered 0 at the RadioPopper transmitter at OFF. All flashes registered about f16.6 at maximum. The table below provides my readings for different transmitter positions for the three flashes. Results across flashes did vary, partly because each flash had a slightly different maximum powers and different responses to the RPCube. I am fine with the differences, as I use a flash meter to start my ballpark estimates of exposure, tweaking in analog for effect. The main finding is that each flash works with the RPCube, but in slightly different power configurations from each other.
Note the absence of the Vivitar 3700, which did not work with the RadioPopper JrX.
I also tested the units with different Groups, coming up with about the same results.
Summary
I’m satisfied all three units work with the RadioPopper JrX. My primary units are the Nikon flashes, with the SunPak as a reserve. I now know how well and accurately each unit works, and the “gotchas” with the SunPak. And I no longer worry about my Vivitar 3700. After 35 years it's headed into my Junque pile.
Next Steps
Should you have different TTL-Capable Nikon-Compatible Flashes that work with RadioPopper JrX/RPCube combos, please contact me, so I can collect a list of flashes (and how they need to be set) for other Nikon and Nikon-compatible RadioPopper users.
Wei Chong
Wei.PhotoArts@gmail.com
