My FT1000MP left my shack about a year ago and is now in service with another local amateur. One of the issues that I had with it when I owned it was the purity of the transverter output. As I was asked about the issue again the other day, here is what I found.
I used the FT1000MP on 14MHz to drive my JavornikII 2m transverter, however the comments here apply equally if you are transverting from 28MHz.
The transverter output has some rather undesireable spurii either side of the main carrier. The offset from the main carrier varies as the VFO is tuned across the band so they cannot be filtered out. At worst they are only 45dB down on the main carrier. If you are running 400W into a decent antenna system these spurii are going to cause problems for other local stations.
Reducing the drive level cleans up the output and the spurii dissapear into the noise. This may not be an option in all cases as the transverter output level is already very low.
The best option for me was to run the rig at about 25W into a power attenuator. This provided a cleaner signal at a level sufficiently high to drive my transverter. I am sure the IMD performance was worse though.
A long time after I moved over to a K3 I received a mail form a well known UK amateur who had spent some time looking into the problem. Unfortunately I don’t have his permission to post his email here but he pointed me at this article by Tom W8JI. If you have ever carried out a factory reset on your FT-1000MP the chances are that the IF TX gains are all set to default.