Book - Man returns from Vietnam and opens portal to another world with his ham radio

Question

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.

Answer 1

Although some of the details are a bit off, this sounds like Conquistador by S.M. Stirling.

From the Wikipedia description:

John Rolfe VI is an infantry captain who comes back from World War II with a war wound and few prospects, but in 1946 a radio he is rewiring malfunctions and creates a gateway to a parallel universe. This universe is one in which Alexander the Great lived a full lifespan, creating an empire that stretched from Spain to India.

That's the same "rewiring a radio to create a portal" that you remember, except it wasn't Vietnam.

Deciding to take advantage of the untapped resources that await in this different California, Rolfe gathers members of his infantry company to help him explore and develop this new world. Over the next 60 years, he builds a new nation, which he calls the Commonwealth of New Virginia.

In 2009, two California fish and game officers, Tom Christiansen and Roy Tully, are trying to solve the mystery of how large numbers of pelts from endangered species are showing up. They finally deduce the secret of the gate to the parallel world, but before they can make the secret known to their superiors, they are kidnapped and permanently transported to New Virginia

It's not the FBI that's after them (or at least, that's not the focus, although they may be too it's been so long since I read it I can't remember), but fish and game officers.

Still, it sounds close enough to what you're asking about.