This opens TX from just above the AM broadcast band to~30 MHz.
Disclaimer: You break it, you broke it.
Now for the next question: What about opening up UHF/VHF?
(only known way to transmit out-of band VHF-UHF is convoluted, and involves going into the service menu each time you want to have a "tx session".)
Use the concept show here to pretty much TX anywhere:
DON'T BOOGER IT UP!
i redid the jumper on jp3 and it is working fine.i have done a lot of searching on this mod,i have seen the mars mod done by jumping #3 or#5.the board shown may be a japan or eu. version,it shows jumper #1 and #2 bridged. i have seen this as a way to open up uhf and vhf.do your own research on utube or or internet before trying this .as buttfuzz says "don't boger it up.".tons of info out there..also the pic. shown is backwards from what you will see from the front of the radio with the front cover removed .so #1 is on the left seen from the front. also the 991 and 991a may not be the same mod. update my 991a is one month old i did the jumer deal on jp #3 IT DID NOT WORK,i reversed it and all is good now.