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Old 08-10-2017, 09:51   #1
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LMR-400

Is it really worth it for a SSB?
I ask as my install manual for my 802, and the install manual put out by dockside radio call for plain ole RG58. I would have thought that the dockside radio book at least would have called out the low loss cable if it really made a measurable difference.
Coax run of approx 25 is expected.
Also does the ultra flexible version of LMR -400 have the same low loss or is the stiffer stuff better?

I have about 50 of RG 214 that I was going to use, but its just too easy to buy coax already made up if anyone wants it.
Pick up only at Brunswick Marina. Ill likely put it on the give away tanks tomorrow.
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Old 08-10-2017, 10:14   #2
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Re: LMR-400

It all depends upon frequency and line length. I would use 25 feet of rg-58au (this is tinned and stranded - important for anti-corrosion and flexing) At SSB (HF) frequencies, losses will be low. Especially since this probably leads to an antenna tuner which will keep the SWR to a minimum on the line.

If it were VHF (157 MHz) at 25 feet I might consider lower loss line - but probably not until a 50 foot run.


Note: In an hour I travel to a tower site which has 5 FM stations, 3 of which are combined into one antenna. Todays job is to track down a troublesome intermodulation product and design modifications to cure the interfering signal.
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Old 08-10-2017, 11:10   #3
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Re: LMR-400

I should also mention other important transmission line choices for marine use:

No water absorbing insulating dielectric. No aluminum, can't have dissimilar metals ... and good soldered connectors with good waterproofing.
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Old 08-10-2017, 11:25   #4
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Re: LMR-400

how about RG8U, direct burial.

i use both that and LMR400 in shack here to antennas

Other thing is to use coax seal tape for the connectors.
That stuff 'melts' into the previous wrap.
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Old 08-10-2017, 11:37   #5
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Re: LMR-400

For the typical short run for pleasure boat HF (transmitter to tuner) RG8X is more than adequate. Tinned 8X from Anchor is probably money well spent. Any thing beyond that is just "gilding the lily".

If you are going to get in the Pactor business include an in line choke in this feed, back beside the tuner. Also include a few ferrite cores on the tuner control cable. Double loop on the ferrite cores.
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Old 08-10-2017, 12:47   #6
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Re: LMR-400

Quote:
Originally Posted by a64pilot View Post
Is it really worth it for a SSB?
IMO no it is not worth it. We are talking about HF not VHF or microwave frequencies. Do they really recommend RG58 for the transmitter to tuner cable? I think that might be a misprint. Probably they mean RG8X or something similar.
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Old 08-10-2017, 13:02   #7
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Re: LMR-400

go all the way to the bottom and have a look at their kit.

Icom SSB Radio Kits & Components
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Old 08-10-2017, 14:40   #8
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Re: LMR-400

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IMO no it is not worth it. We are talking about HF not VHF or microwave frequencies. Do they really recommend RG58 for the transmitter to tuner cable? I think that might be a misprint. Probably they mean RG8X or something similar.


Im looking, and cannot find anything at all in Docksides install manual, just references coax.
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Old 08-10-2017, 14:42   #9
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Re: LMR-400

For Belden RG58au, loss at 10 MHz is rated at 1.3 dB per 100 feet. 25 feet would be 1/4 of that. That is so low as to be considered negligible ... http://www.belden.com/techdatas/english/8219.pdf
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Old 08-10-2017, 14:49   #10
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Re: LMR-400

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go all the way to the bottom and have a look at their kit.

Icom SSB Radio Kits & Components


OK, got it RG-8
I guess I read somewhere 50 ohm coax and my mind went to 58?
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Old 08-10-2017, 17:27   #11
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LMR-400

OK along similar lines, the RF output line from the tuner, gto15?
Anyway I know it should not be ran parallel to other wires, but I have no choice, so what is a realistic distance, I know the further the better, but can I get away with 6?
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Old 08-10-2017, 17:46   #12
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Re: LMR-400

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Originally Posted by a64pilot View Post
OK along similar lines, the RF output line from the tuner, gto15?
Anyway I know it should not be ran parallel to other wires, but I have no choice, so what is a realistic distance, I know the further the better, but can I get away with 6?

I'm not clear if you're referring to coaxial cable (hopefully not) or single conductor wire to the insulated backstay? I would hope single conductor wire - remember that all of it is antenna at this point and it radiates.

The tuner should be mounted as close to the connection to the insulated backstay as possible. Mine is two feet away. And six inches wire spacing should be a minimum.

If coaxial cable, wire spacing is a bit less critical, but length of coax to insulated backstay should be kept very short. If this is too long, you are decreasing the effectiveness of the tuner (because of added shunt capacitance of the cable)
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Old 08-10-2017, 17:55   #13
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Re: LMR-400

Don't think 6" would cause a problem. Just recently changed out my Stbd backstay that serves as my antenna. I did away with the lower insulator (after some testing) and it works just fine. Having said that, the entire lower end of the wire/ rigging is now hot when transmitting. I used a short length of pex tubing to cover the wire down to the stud. My antenna connection is now a small length of the copper foil (tinned) wrapped around the swaged stud with the GTO 15 soldered to the foil, taped over. Going to add a length of PVC pipe over the pex and a short length of hose over the turnbuckle. One less rigging part to fail. GTO 15 right through the rear apron to the tuner output just inside and below. MMSN Control told me the other night that I had the best signal of the night coming out of Florida . YMMV
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Old 09-10-2017, 05:37   #14
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Re: LMR-400

At right angles 6" is probably ok. If nearly parallel then you may have to clamp some Ferrites around those other wires (not the GTO) to avoid noise when transmitting.
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Old 09-10-2017, 06:04   #15
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Re: LMR-400

I haven't used my SSB even once over the past six years. Please let me know when you get yours hooked up so we can test them.
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