so ive been sitting on doing the mars/cap mod on my 857D for like two years now because i kept reading conflicting stuff about whether it actually affects rx performance or messes with the filters or whatever. finally just did it last weekend, took maybe 20 minutes once i found the right diode pads on the board.

for anyone whos never done it, its a pretty simple solder bridge on D900 area of the main board, the service manual shows it clearly once you know what youre looking for. opened up the rig, did the mod, buttoned it back up, and the radio came right back to life no issues. TX now works down into the 1.8 area without the usual hard cutoff which is what i needed for some 60m stuff i've been experimenting with.

what i actually wanted to ask though is whether anyone has gone further and done any of the IF filter swaps on one of these. i know you can drop in a murata or similar ceramic filter to tighten up the SSB selectivity a bit. my stock radio sounds fine honestly but i do notice it gets a little muddy on crowded band conditions during contests and stuff. wondering if the filter swap is actually worth the hassle or if im just chasing marginal gains at this point.

did the same mod on mine probably 4 years ago, no regrets. the filter thing though, ive gone back and forth on this. i did put a 2.4kHz collins mechanical filter in an older 756 i had and the difference was actually pretty noticeable, like genuinely better adjacent channel rejection. but on the 857 the architecture is a bit different and from what ive read you dont get quite the same bang for your buck because of where in the IF chain the filtering happens. someone on eham went into a lot of detail about this maybe 2018 or so, might be worth digging up that thread if you can find it.

honestly for contest conditions i ended up just running the built in contour and notch more aggressively and that helped more than i expected. not the same as real filter selectivity but it gets you partway there without opening the rig back up.

the mars mod is so easy on those rigs, good call finally pulling the trigger. i always tell people just do it even if you never use the extended TX, it takes 20 mins and costs nothing.

cant really speak to the 857 filter situation specifically but i will say filter mods in general are kind of hit or miss depending on the rig. some radios the stock ceramic filter is already decent and swapping it gives you maybe 10% better performance and some rigs the stock filter is genuinely awful and the swap is transformative. youre probably better positioned than me to judge which category the 857 falls into since you've actually listened to the thing in anger on a crowded band.