I have a Nikon d3000 - jjc wireless flash trigger kit & Sigma EF 500 flash. I have a hotshoe & tripod also. I can get it to work together only when I am less than a foot away. I have 2 sets of the jjc kits so it isnt a faulty transmotter or receiver. Any suggestions to get them to work correctly together so I can be atleast 5 feet from the flash, Thanks
Sadly, you are (probably — see end note) out of luck, at least unless you do so with hacking or spend some money on different gear. That's because the Sigma flashes are TTL-only, and cannot be triggered by shorting the center pin in the standard way. I know, that sounds so stupid that it's hard to believe, but there it is.
So, what can you do? Well, first, I found someone who did a DIY conversation so the Sigma EF-500 DG will trigger. Working inside a flash is very dangerous, though, because the capacitor can retain a deadly charge for a long time.
Second, if you have the Super version, you can trigger it as an optical slave with an on-camera flash (unfortunately for you again, not with the popup flash of the D3000 you own).
Or, third, if you get some of the more expensive triggers which use all of the pins and do Nikon's proprietary TTL protocol by radio, it should work.
Note: I have seen some people saying (including a note from people who should know) that the Super version of the flash can trigger in the standard way, but only when out into
SL (slave) mode and possibly also only when set to Channel0 (even though you won't be using that). If you have this model and can test, I will update my answer either way.
My first thought would be to search for other nearby devices that use the 2.4GHz band used by the JJC wireless flash triggers. Interference from other devices will increase the noise side of the Signal to Noise Ratio (SNR) to the point that the receiver can't detect a discreet signal from the transmitter unless it is very close to the receiver.
Most wireless radio devices today use digitally encrypted pulses to transmit signals for different "channels" on the same frequency, thus all 16 combinations of the typical set of four two-position dip switches are actually all on the same channel. It's just that if a transmitter broadcasts a binary "1001" and the receiver is set to respond to "1010" then it won't fire. But if your JJC triggers are an older design and use analog signals, then it might be that the transmitter and receiver are set to slightly different frequencies. Since almost all radio transmitters will 'bleed over' into adjacent frequencies at very close range, even if the two are tuned to slightly different frequencies, there is enough "bleed over" coming from the transmitter for the receiver to detect it when so close to the sending unit.
Beyond that, the obvious question is "What is the charge state of the batteries in the transmitter and receiver?