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Author Topic: Coax???  (Read 1374 times)
NZ4Z
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« on: April 15, 2011, 06:57:47 AM »

I need to order some new coax....I have stayed cheap in the past.... RG213 ect. ...... I will be running 1K to Legal Limit..... Current run is less than 100 feet. With that in mind....what is the better coax for the money? TM LMR-400....Davis Bury Flex.....Belden 9913? ..... Those seem to be the better ones I know of....not asking you to choose between those 3..... If you have another suggestion, please let me know. This will be for a dipole for now....maybe a new vertical.

Thanks

73


Steve
NZ4Z
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WS4E
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« Reply #1 on: April 15, 2011, 07:50:21 AM »

Choosing between 'regular' rg8 size coax is not so much about power as it is about signal losses (db/100ft) and LMR400 is probably the best choice.

I would just go to http://www.jefatech.com/category/d100 and get some of their  Low Loss 400(LMR400-type) COAX and you will be ok.


« Last Edit: April 15, 2011, 07:52:31 AM by WS4E » Logged
W8JX
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« Reply #2 on: April 15, 2011, 08:37:18 AM »

The signal loss on 100 ft of 213 at HF is not a concern but many seem to think it is. The difference in loss between 213 and :MR-400 is less than 1/2 db at 30 mhz and less at lower frequencies. This is not a issue.
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KG6MZS
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« Reply #3 on: April 15, 2011, 09:04:04 AM »

The signal loss on 100 ft of 213 at HF is not a concern but many seem to think it is. The difference in loss between 213 and :MR-400 is less than 1/2 db at 30 mhz and less at lower frequencies. This is not a issue.

Unless, of course, you are matching a non-resonant multiband antenna.  But then you should probably be using a balanced feed line and forgetting the coax altogether.
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WB2WIK
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« Reply #4 on: April 15, 2011, 09:26:38 AM »

I'd stick with high quality RG-213/U for a variety of reasons.

For a 100' run on HF, no reason to use lower loss coax that isn't as rugged and won't take the abuse RG-213/U will.
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NZ4Z
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« Reply #5 on: April 15, 2011, 10:41:06 AM »

Crap.....just ordered LMR400..... I could have saved with the 213....and I never thought about a short run, the 213 being fine. Oh well.
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AC5UP
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« Reply #6 on: April 15, 2011, 10:45:08 AM »

If you ordered real LMR-400 made by Times Microwave you'll be working with an excellent quality line that is, IMHO, worth the price differential... I have some runs that have been baking in the sun for almost 20 years without any visible degradation. Even the print markings still look good.
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KG6MZS
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« Reply #7 on: April 15, 2011, 11:28:34 AM »

This will be for a dipole for now.

Steve; are you only using the dipole on the band that it is cut for?
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NZ4Z
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« Reply #8 on: April 15, 2011, 08:00:52 PM »

For now due to my location a 10-80 dipole is all i'm doing........the 3E SteppIR is on the ground Sad
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KG6MZS
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« Reply #9 on: April 15, 2011, 10:26:14 PM »

I think you would be surprised at how much better it would perform if you fed it with a balanced feedine.
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KI4VEO
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« Reply #10 on: April 16, 2011, 02:49:52 PM »

The only place I use coax is for rig interconnects.  Outside the shack window it strictly open wire feedline...the REAL open wire line.  No vinyl window line stuff...it gets iffy when wet or covered with ice.

My BIG delta loop (560 feet of wire @ 70'), 200 feet of 450 ohm line and a 4:1 balun = a strong signal.

Having a Malcomized FT-102 and a Heathkit SB-1000 doesn't hurt, either.

And the smaller birds seem to like the open wire line as a place to rest.
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N3JBH
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« Reply #11 on: April 16, 2011, 03:08:08 PM »

Davis Rf sells two grades of RG-213 i use there better grade. As far as i know only difference is the outer jacket material The better stuff is supposed to have better weather resistance. I never had a problem with it and had some buried for years. But if you plan to use a dipole cut for one frequency it probably be a losing proposition unless it is a related frequency like 40/15 etc.  Been there tried it and it is not good. Jeff 
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N1LO
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« Reply #12 on: April 16, 2011, 06:51:35 PM »

Yeah, sorry, but if you're using an 80m dipole with coax on 40-10, you're really messing up.
Multibanding through coax can have terrible losses, because the high SWR on the bands where the dipole is not resonant multiplies the losses many times.

Seems to me that running high power multiband through 100 ft of coax is just asking for an electrical blowout at a high voltage point.

Add extra dipoles to the feedpoint for the other bands that are most important to you, or convert to ladder line.

As already pointed out, you will be a-mazed at how much stronger signals will be on some of the upper bands with parallel line.

GL,

Mark
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