I have an external ATU made by LDG, The Z-100Plus Autotuner, connected to the rig with a short section of 50ohm cable (500mm long). I use this as the internal ATU inside the FT-450D will not tune my end fed dipole on any band.
Following on from a query by a local ham I need to explain I have been experimenting using the internal ATU within the Yaesu FT-450D at the same time as the external ATU and am having good results. I have the Yaesu internal ATU set to be in circuit both on transmit and receive (out of the box as a default the FT-450D is set to be in circuit just on transmit).
It must be stressed that I don't tune both ATU's at the same time.
The way I do it is tune up on the desired band and frequency using low power through the Z-100 Plus. This gets the load presented by the antenna to the rig within range. Then I press and hold the tune button on the rig and let it do its stuff too. A further tune on the Z-100 retains exactly the same settings. In other words the external ATU is still tuned so doesn't go through its tuning cycle again.
When I take the internal ATU out of circuit while receiving a fairly stable signal I do see the S meter drop 1 or two points. I have also switched it into circuit and found that I get a noticeable improvement in reception on very weak signals.
My belief is that both ATU's compliment each other and the only thing in the manual says "
Yaesu recommend keeping the ATU in circuit all the time". My view it that the internal ATU just sees a load to match to the power amplifier and doesn't know or care that there is another ATU between it and the antenna.
I am aware that there is debate whether both ATU's should be used and certain manufacturers rig operating manuals say not to do it. I only present the results that I am seeing and that is part of what amateur radio is about - experimentation. I take no responsibility for what you do in your own shack.