so ive been sitting on doing the mars/cap mod on my FT-857D for a while now and finally just did it last weekend. took like 10 minutes, just the two diodes on the main board. figured id share some thoughts since i was going back and forth on it for months before pulling the trigger.

honestly the main reason i did it wasnt even for out of band TX, i wanted to be able to do some NVIS stuff on 60m with a bit more flexibility and also just wanted to unlock the TX on 6m down lower than the stock limits allow. the mod itself is pretty well documented over on mods.dk if anyone hasnt seen it, pretty hard to mess up if you have halfway decent soldering skills.

what i did notice after is the 10m and 6m performance seemed a little cleaner to me but that might be placebo honestly. anyone else done this and noticed any actual RF changes or is it purely just unlocking the freq range? also wondering if anyone has done any of the other mods, ive seen some stuff about improving the cooling on these since mine runs pretty warm doing any extended digital modes.

yeah did that mod years ago on mine, pretty standard stuff. the RF performance doesnt really change, its just removing the band lockout the factory puts in for type acceptance reasons. you're not touching anything in the signal chain so whatever you were getting before youll get after.

the cooling thing is a real issue though, especially if youre running WSPR or FT8 for any length of time. what i ended up doing was adding a small 40mm 12v fan blowing across the finals heatsink area and it made a noticeable difference, the rig stays way cooler now even at 50w digital. theres a thread somewhere on eham about tapping into the internal fan circuit to run an external one that kicks on with the stock fan but i just wired mine to a switched 12v line off the back. not pretty but it works. the 857 is a great little rig but yaesu definitely underspecced the thermal management on it for the duty cycles we actually run these days with digital modes being so popular.

i did the mod on mine too but honestly be careful if you ever need warranty work or send it in for repair, some service centers get weird about it even years after purchase. mine had a PA issue last year and the shop i used noticed it right away. they still fixed it but there was a whole conversation about it i didnt really want to have lol. just something to keep in mind. aside from that yeah its a simple mod and doesnt hurt anything.