My apologies if this thread is in he wrong area, but I couldnt find a non hd radio section....
Anyway, I have 2 seemingly similar transmitters that are powered by the iPhone. He only outside difference is that the + and - buttons are in different places... Anyway I have soldered an external antenna to both and they now both have increased range, but one has 10 to 12 meters less range then the other. Upon further investigation the lesser range unit seems to have what looks like a slightly smaller capacitor (2/3rds he size). Could this be he reason in the dramatic drop in transmission range/strength? If so, is there way I can get the extra 10 meteres with the lesser unit?
How far are you trying to go? These units are usually only meant to transmit a few feet, and tampering with them voids the FCC Part 15 Certification, so any interference caused would come back on you (not the manufacturer).
If you are trying to cover a larger area (I think that about 100 yards is the limit), you'd need to buy a small, Part-15 accepted transmitter, from somebody like Ramsey Electronics.