No comment on how they work just a word of caution.
If you are using a Canon EOS camera the 12 volt trigger circuit in these will void the warranty and it could damage your camera. In an email exchange with Canon I was told that despite the manufacturers claims of no damage because of the low current level that the voltage can cause damage to the camera. After considerable thought I spent the money and bought Pocket Wizards and have never regretted the decision.
First a pair (transmitter and reciever) of Pocket Wizard Plus units are available for about $350.00 from B&H and many other dealers.
Pocket Wizards may be 20 times more expensive but how much would it cost to repair your camera if it was damaged by the yhdc-a triggers. If the manufacturer or the seller are not willing to guarantee in writing that these units will not damage your camera, and will not guarantee in writing that they will pay for the repairs if they do are you willing to take the chance based on an eBay vendors online words. Please do not trust me on this contact Canon yourself and ask the questions.
On another note while I have not tried the yhdc-a I did try a setup like these from a company called Morris Electronics on my trusty old A1. The units were unreliable and had a very limited range some times they would not even work across the 50-75 foot space of a church sanctuary. They were prone to going off at unpredictable times because they wanted to or perhaps from interference I never did figure out why and sometimes they would not fire even when the shutter was released. On the other hand my Pocket Wizard Plus units have never given me a moments trouble. They worked reliably for me at distances of several hundred feet and even from the inside of buildings to a camera set up outside of the building. And this brings out another aspect of radio triggers can the yhdc-a be used for anything other than triggering strobes. With adapters I have found dozens of uses for the Pocket Wizards both in and out of photography will the yhdc-a be as flexible.
Your money, your equipment and your decision but to me it would not be worth it based on my experiences.
And this brings out another aspect of radio triggers can the yhdc-a be used for anything other than triggering strobes. With adapters I have found dozens of uses for the Pocket Wizards both in and out of photography .
I don't really know. All of the readings were within .2 volts if I recall correctly. This could be variances in manufacture, age of the battery, or human error.
Also, most electronic components, like resistors and capacitors, have a tolerance of around 10%, thus a resistor marked 100 ohms may actually measure between 90 and 110 ohms. The voltages varied from 4.8 to 5.8 which doesn't seem unreasonable.
Even though all of the units we bought work on the same frequency, there were differences in packaging and the molding on the cases. Although they were all the same shape, the word "test" next to the test button was done differently. In some cases it was raised, in others there was a recessed oval around it. Cosmetic differences, but indicative that they same from different injection molds and perhaps have different innards. We didn't take them all apart to see.