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Extending the range of my off-camera flash radio trigger

I have a radio trigger for off-camera flash, and would like to extend its range. It's the CowboyStudio NPT-04, which is dirt cheap and works very well, but the range is only about 25 feet.

I found a blog post showing a mod to a similar 433 MHz device:

formatting link

He added a 1/2 wavelength antenna, but it was wound into a coil. Apparently the mod was very successful. I don't understand why the coil works.

Mine is a little different. It appears that part of the antenna is formed of circuit board traces, and then there's a 1.5" length of wire soldered to that.

I've posted photographs of this in:

alt.binaries.schematics.electronic

with Subjects beginning "CowboyStudio". But note that I screwed up the post the first time, so download the articles with the usual yEnc format.

The device broadcasts at 433 MHz, and I can't make sense of the measurements I found - shown in the pictures.

Item A in the pictures appears to be a capacitor (no continuity with my meter).

Item B is just a plated-through hole with nothing but solder.

Item C appears to just be a jumper (near zero ohms).

Then as you'll see in the bottom pic, the C-to-D trace is duplicated on the bottom of the board. I assume that's significant.

Then at D the wire is soldered.

So I was thinking of replacing the wire with a coil like the other guy used. I could just try different lengths, but I'd like to understand what's going on - what ought to work.

Also, I wonder what complications might be introduced if I do succeed in extending the range. Will the transmitter use more power from the battery, or would the extended range be "free"? Might there be impedance mismatches that would tend to overload the output transistor and burn it out?

Well, this isn't really important, but if anyone would like to look at it and offer comments, I would appreciate it. As must be obvious, RF is not my strong point, particularly antennas.

Reply to
Peabody
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Because the total length of aerial wire, including what is on the pcb is an exact fractional multiple of the wavelength, in this case 1/2. Normally one would get by with 1/4 wavelength... To get the correct length, you will need to know the transmitter frequency... The length is only approximate as there are other complex factors that are involved. Clearly in this case, the original aerial is way off being a fractional length, but adequate for most people to be fit for purpose.What use is a flash at 300 feet ? Battery consumption will go up, but by a fraction of the overall current as most will be taken by the actual flash device.

Reply to
TTman

Thanks very much for your reply.

Yes, but I would have expected that it would be the length of the coil, after it's wound, that acted as the antenna, not the length of the wire that made up the coil. Actually, I just wouldn't have expected the coil to work well at all as an antenna.

The frequency is 433 MHz for his trigger and mine, which would be a 1/2 wavelength of 13.64 inches. He took a length of wire 12.39 inches long and wound it into a coil and soldered it to the end of the antenna trace on the board.

In my case it's more complicated because the trace goes

1.25", then goes back the same distance in the opposite direction, and that leg is duplicated on the bottom of the board, then the external wire is attached.

See the pics, but in a non-proportional font it would look like this:

1.25" |---------------------------------------
Reply to
Peabody

Try this at your own risk:

  1. Disconnect the Start point from the 1.25" trace at the top.
  2. Connect a 6" or so wire to the Start point.

If you must cut a trace, try to do it such that you can recover from modification.

John S

Reply to
John S

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