so ive been sitting on doing the mars/cap mod on my FT-857D for like two years now and finally just pulled the trigger last weekend. for anyone who doesnt know its basically just removing a diode on the main board that opens up the TX range below and above the ham bands. pretty simple once you get the bottom cover off, though the solder points are tiny and my eyes arent what they used to be.

anyway the reason i finally did it was i wanted to be able to use the radio on some of the GMRS freqs when im out with the family and also for some MARS nets i got invited to join. the mod itself took maybe 20 minutes, had to use my magnifying headset and a fine tip iron.

performance wise honestly i cant tell any difference on the ham bands which is what i expected, the mod doesnt change anything about how the radio performs it just unlocks the range. transmit audio still sounds the same on 40m, havent noticed any change in recieve either. i think some people expect the mod to somehow improve things and it just doesnt do that, its purely a restriction removal.

curious if anyone has done anything else to the 857D that actually improved performance - like the internal sound card mods or the noise floor stuff ive seen mentioned on eham. i feel like there must be more i can do to squeeze more out of this radio before i consider upgrading to something newer.

yeah the mars mod is pretty much the standard first thing people do, you're right that it doesnt change performance at all. if you want actual improvments on the 857 look into the Collins filter option - you can drop in a narrower SSB filter and it makes a noticeable difference on crowded bands. i did mine with a 1.8khz filter and 40m pile-ups got a lot more manageable. the install isnt bad but you have to order the right filter module and double check the slot because there are a couple versions of the board floating around depending on manufacture date.

also some guys do an external audio mod where they tap off before the internal speaker amp and feed it into a better audio chain but i never bothered with that personally.

I did the diode mod on mine about 3 years ago for basically the same reason, MARS stuff. One thing I'd add - if you're going outside the ham bands for any kind of legit use make sure your power levels are appropriate and you're not accidentally splattering into adjacent channels, the 857 isn't always the cleanest thing at full power on non-ham freqs in my experience. I keep it at 25-30 watts when I'm on the MARS freqs just to be safe. Haven't done any other mods to mine but I'm curious about that filter upgrade the other guy mentioned, never really looked into the slot filter situation on this radio.