If I remember correctly, a guy comes home from Vietnam and starts playing with his ham radio and somehow creates a portal to another Earth. Then I remember a jump in time. Now, it's our time and there are "families" living over there. Not regular families, but crime families and others that have formed their own "families". I think they needed the crime families to help fence gold, etc. So they had to let them in and it gave the crime families a place to go if the law got to be too much for them.
I think the FBI is looking into them for questionable things. Also I think I remember that, since they don’t know how or why the ham radio does what it does, they never mess with it, but for some reason it gets turned off.
Thanks for any help I believe I read these some time in the 90's to early 2000's but I frequent used book stores so no telling their age. This was a paperback I believe since that it what I read 99% of the time.