so i've had my 857 for probably 6 years now and finally got around to doing the mars/cap mod to open up the TX a bit and while i was in there i figured id document some other stuff i've been doing to this radio over the past year or so because i havent seen a lot of people talk about the combination of mods together.

the extended RX mod is dead simple, just the two diodes on the main board, D4901 and D4902 if i remember right, pulling those gets you coverage down into the AM broadcast band and up past 500mhz on the high end. reception quality drops off at the extremes obviously but for scanning its totally fine. the mars mod is also just a diode but i always forget which one and have to look it up every time.

the thing i actually wanted to ask about is the DSP filter mod. ive been running the sherwood engineering narrow filter in the IF chain and the difference on crowded 40m SSB is actually pretty significant, like i can actually pull stations out that i was just getting walked over before. anyone else done this or messed with the internal filter options on the 857? curious if theres something better than what im running or if im already at the ceiling with this radio.

yeah the diode mods on those yaesu radios are pretty well documented, ive done similar on an older FT-897 and its basically the same board layout in a lot of areas. the extended rx is nice but like you said dont expect miracles on the high end.

on the DSP filter question — the sherwood mod is probably about as good as youre gonna get without going external. the 857's IF architecture isn't exactly what id call flexible, so you're kind of working within tight constraints. i know some guys have gone to running an outboard audio DSP like a timewave or even just a cheap SDR as a panadapter and monitoring both simultaneously, which sounds overkill but honestly if youre doing a lot of 40m contesting or just working crowded bands it makes a real difference for weak signal work. the radio itself is only gonna give you so much.

did you do anything to the PA section? thats the other area people mess with on these, some guys rebias the finals slightly for cleaner output at lower power levels but i never bothered on mine.

i ran an 857 as my main HF rig for like 4 years and honestly the filter situation was always my biggest complaint. ended up just living with it because the form factor was too convenient for my setup to switch. never tried the sherwood filter specifically but a buddy of mine swears by it for exactly what you're describing on 40.

one thing i did do was the ref oscillator upgrade, there's a TCXO option that tightens up the frequency stability noticeably, especially on digital modes where drift actually matters. probably not relevant if youre mostly doing phone but figured id mention it since youre already in there poking around anyway.