This RX-TX connection is a bit messed thing…
Generally say you are right. We “used to” use them like Rx to TX and TX to Rx BUT…
Take a look an the “nature” of device what you are connecting to.
Lets talk about the radio first.
Radio is to send any info from its input to other radio via air. Also it is to receive other radio’s signal and send out the info over its demodulator output to your endpoint device.
In our case the radio has two port pins RX and TX.
TX is “talk”, RX is “receive”. If you want to send a series of bytes over the radio to another one which port would you use like the input of radio (input this case is the series of bytes what you want to send over the air) RX? No. RX is for the received info, what radio received from the air from another radio) So on RX port you will get what somebody else sent to you. Shortly RX is the output of your radio.
If you want to send out that byte series, you want to “talk” over the air, so the input point of the radio is the TX pin. (the bytes put to TX pin will be send over the air by the radio.)
Well the radio “input” is TX and the radio output is RX (from this aspect.)
If you agree up to this time then let’s take a look on your endpoint device (e.g. RPI3)
It function is to process data comming/receives from other devices via its input pin. This pin is called RX, To this pin we should wire the point of radio which “received” the information (with other words for that pin where info is comming out from the radio) Which is that pin of radio? TX? Not. it is the RX pin of the radio.
So you can see in this special case (because the “nature” of the two devices you are wireing together are different) you must wire RPI3 RX pin to radio RX pin!
Let’s look the TX.
The other function of your RPI3 device is to generated any information (series of bytes) then send it to the radio which will send that information via air to another radio/user.
Whic pin is RPI3 where bytes commin out? RX? No. (Rx is an input not output in this case) Bytes comming out from RPI3 on pin TX. Because of this RPI3 TX pin should be wired to radio’s TX pin too. !!!
Think over it!
with simple words:
in case of serial communication between devices we must wire 1st dev input to 2nd device output and 1st device output to 2nd device input.
in our case:
TX = input
therefore should wire TX to TX and RX to RX even it sounds weird.
take a try. Nothing will go wrong in your devices.
If you have an oscolliscope you can easily check out what I said.
In fact more attention should take to the function of pins than as they are named.