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Old 26-07-2012, 11:43   #1
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Location of line isolator - to move or not to move

Well, I have now moved my SGC 230 tuner closer to where the antenna leaves the boat, which is now going to be approximately 8-9 feet from my Icom 700 Pro SSb. The prior owner of the radio and tuner put a line isolator on the cable that comes from the tuner. The isolator is 5-6 feet from the tuner and is right next to the radio. The tuner cable is RG-58 with PL-259 connectors connecting the isolator and making the conection to the back of the radio. That cable also has four additional wires - two for power to the tuner - built into the cable. I have been advised to place the isolator closer to the tuner than to the radio in order to cut down on RFI. My questions to the group are;

1) Should I move the location of the isolator so it is within a foot of the tuner, or is the location fine where it is;
2) If I do change the location of the isolator closer to the tuner, should I use more RG-58 cable to make the connection the rest of the way from the isolator to the radio, or should I get a different type of cable?
3) I have bought a bunch of type 31 ferrites, should I use them on the cable from the tuner to the radio, even though the isolator is on that cable as well?
4) I know there is a debate about crimping vs. soldering connectors, but as an admitted novice to this endeavor, soldering does not look too difficult. I have watched enough videos on You Tube to convince myself that I can do it. Am I deluding myself?
Finally, should I just forget the whole thing, leave the isolator where it is, get a short piece of already made up RG 58 cable and make the rest of the connection to the radio?
Again, as always, thanks for the help. gchabs
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Old 27-07-2012, 12:43   #2
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Re: Location of line isolator - to move or not to move

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, 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...

s/v Annie Laurie
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Old 01-08-2012, 09:27   #3
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Re: Location of line isolator - to move or not to move

John: Thanks for the input. From my research, soldering a new PL-259 onto the cable is not exactly rocket science, but as you note, not for the novice either. I am a novice. So, I shall try to get someone in the Richmond, VA area to assist. In the alternative, I will contact SGC to see if they will shorten the cable from the tuner and put on a PL-259, so that I can then locate the line isolator closer to the tuner. I will then supplement the cable run to the radio with already made up RG-213 cable. Once again, thanks for the advice. gchabs.
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