Question. there are a number of RF Extenders around for both Pronto and Marantz and they are listed as being US or EU versions but I would like to know if they really are physically different or is it just a marketing jargon.

There is the Phillips RFX-6000 (US) and LI900 (EU)
or the Phillips RFX-6500 (US) and LI910 (EU)
Marantz love to confuse everyone by only have one model for both markets
RX-77 both (US) and (EU) version (2nd question how can you tell which it is?)
RX-7001 both (US) and (EU) version (2nd question how can you tell which it is?)

I have a EU remote but can get a US extender much cheaper, I question if the Extender can except both RF frequencies (433Mhz and 418Mhz) since Receiving a Frequency is not the same as sending one when it comes to FCC rules.

No, the extender and remote MUST be paired at either 418MHz or 433MHz.

Perhaps sending and receiving are different per FCC rules; I'd like an example of how you mean that they are different. There are obvious things, such as sending is a much higher power situation than receiving; and the mixing frequency of a superhet design receiver might accidentally radiate and must be controlled while transmitting designs have no such other frequency to deal with.

But when it comes to any kind of simplex (one-way) communication, the receiving frequency must be the same as the transmitting frequency. Otherwise the receiver will not receive anything. Thus 433 MHz and 418 MHz units must be paired with units of the same frequency. An EU unit should not have the same transmitting frequency as a US unit, so must have a receiver to match.

Ernie,

Isn't your 2nd bloated paragraph exactly what I said?

Yup. But...

It specifically answers this, and

it specifically answers this after the first paragraph said that the FCC rule thing isn't an issue. I've been taught to know more than the bare bones of how to solve a problem, and that has served me well. So, yeah, I write more than the simplest facts.

For a cheap and functional alternative look at the powermid IR transmitter/receiver. I have a UK RU950 and the RF receiver/IR transmitter part work perfectly with RF from my pronto. Obviously you use the ability to address several different one individually and you loose the facility of having multiple IR emitter wands but if all the equipment you want to control is in one location it works. I picked up just the part I needed (not the full pair just the receiver) on Ebay for a tenner.

Also if you have any RF equipment using the right frequency it MAY be possible to learn the codes using the Powermid (possibly with a following wind and a lot of luck)