gchabs,
1) In general, yes the line isolator should be placed as close to the
antenna tuner as possible.....this reduces the possibility that any stray rf currents flowing on the outside of the coax could be radiated / cause RFI into other systems on-board....
And, this IS always what I recommend...
But, this is not a 100% absolute necessity in all cases....(there are some
SSB installs that
work fine, even without an isolator)....
2) So, what should you do???
Depends on where you are, how available coax/connectors are, and how much
money you wish to spend....
Your choices are:
a) Try it as-is, with just a short coax between the existing line isolator location and the radio....If it works well, for you....good....If not, move the isolator....
b) Move the isolator as close to the tuner as possible, using as short of run of coax as practical, and add new coax run to the radio....and you'll be fine.....
I recommend choice "b"....
3) Cable losses on HF, especially for these short lengths, are moot...
The issue are:
a) cable strength/longevity...
b) cable sheilding / % of sheilding....
In general, I prefer larger coax than RG-58, such as RG-213 / 214, as it will survive being pulled thru bilges, etc. better....even RG-8x is sometimes a better choice....
BUT, there are some pretty poor examples of RG-8x out there, and some very good RG-58 available....so, there is not one simple answer here...
Note that SGC supplies very good RG-58 coax, and shouldn't be an issue (meaning no need to change that...)
Again this depends on where you are, what is available to you in regards to coax/connectors, how your coax will be run/secured, and how much you wish to spend$$$....
My choice is RG-214 (double shielded) and will last longer than most will ever need (25+ years).....but it ain't
cheap....
So, assuming you have access to wide varieties of choices, go for all new coax for you new/modified install, and use RG-213 (or 214, if you wish to spend the $$).....
4) Adding mix 31 ferrites will do NO harm...but are gnerally not necessary on the coax if you have a line isolator....
So, I'd snap those ferrites on the other wires to/from the
M700...such as place a couple ferrites on the tuner control /
power wires (near the tuner), as well as on any wires/cables going into/out-of the
M700, such as
modem I/O connections, etc....heck, even on the 12vdc power wires....
5) Soldering of PL-259 connectors isn't rocket science, but since this is a critical piece of
gear, I'd NOT recommend that a "novice" attempt this....
Best
advice:
a) buy quality, pre-made
cables (DX Engineering, etc.)
b) pay a pro to make them up for you...
I hope this helps...
Fair winds...
John
s/v Annie Laurie