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Author Topic: RG-58 coax for Base Antenna  (Read 8281 times)
KT4DLB
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Posts: 72




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« on: February 19, 2013, 01:46:09 PM »

I'm a newbie ham and was wondering about this, can I run RG-58 coax to an Diamond X-50 antenna or do I need to run RG-8 coax?

Lamar
KK4NZO
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WB2WIK
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Posts: 20543




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« Reply #1 on: February 19, 2013, 02:23:02 PM »

You can do what you want, but RG58 coax is extremely lossy on 70cm (440 MHz) and unless your run is very, very short (like less than ten feet), you'd lose an awful lot of signal in the coax.

For any more realistic cable length (20 feet or more) I'd go with at least RG-213/U or something better than that, like LMR400.
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W8JX
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« Reply #2 on: February 19, 2013, 02:52:06 PM »

You can do what you want, but RG58 coax is extremely lossy on 70cm (440 MHz) and unless your run is very, very short (like less than ten feet), you'd lose an awful lot of signal in the coax.

For any more realistic cable length (20 feet or more) I'd go with at least RG-213/U or something better than that, like LMR400.

Some seem to worry a lot about line loss but it is not as big a deal as some make it to be. I would not generally recommend RG 58 for VHF though it is fine for up to 50 feet fir 2m and up to 25 feet for 440 if you have some. 3db, give or take, is not a deal maker or breaker here that some claim it to be and a smaller line is easier to route.  A good compromise here is RG 8x. On a 50 ft run, LMR 400 looses a little over 1 db less than 8x on 2m and a little over 2 db less on 440 on same run so which is no big deal.  If you run much over 50ft though I would suggest at least 213 though. 
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KA4POL
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« Reply #3 on: February 19, 2013, 10:13:23 PM »

You did not mention the planned cable length. Basically in those cases you search the web for cable specifications and calculate from that what actually your losses will be using a certain cable. Next thing to keep in mind is are you doing FM or SSB, i.e. repeaters or DX. For DX it may be more interesting to count each single dB particularly in RX.
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AE5QB
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« Reply #4 on: February 20, 2013, 03:47:57 AM »

Several considerations as has already been mentioned.  If it were me and it was to be a permanent install I would opt for the good stuff.  LMR400 is good stuff but very stiff.  There are several good alternatives that are more flexible.  I use ABR Industries 400UF cable most of the time and am not having any issues.  As has been said, if the install is temporary or to be used primarily for local repeater use, then 8X should be adequate.  You can try what you have and if it doesn't work well for you, try something else.  This is not a one shot opportunity.
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K1CJS
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« Reply #5 on: February 20, 2013, 08:06:33 AM »

If it were a choice between 58 and 8X, the choice would be 8X, hands down.  All 58 is good for (and it depends on the type of RG58 it is) is short runs inside cars and such, although I've seen 58 used for HF antennas for short runs.  (I wouldn't do it!)  There are some RG58 cable that is only shielded by loosely wound braid that isn't good for anything but weak rope.  Rat Shack seems to have this type cable in abundance.
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AA4PB
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« Reply #6 on: February 20, 2013, 08:21:50 AM »

It all depends what you are doing. If I were putting up a 75M dipole and only going to run 100W then I'd use a good quality RG58. A 100-foot run on RG58 only has 0.76dB of matched loss on 75M.

On the other hand, 100 feet of RG58 at 440mHz has 10.67dB of loss. For 100W in you'd only get 8.5W delivered to the antenna.  Angry
« Last Edit: February 20, 2013, 08:26:35 AM by AA4PB » Logged
WB5ITT
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Posts: 100




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« Reply #7 on: February 22, 2013, 03:09:06 PM »

Depends on the length of the cable, etc. IF you want best performance for an antenna 10-20ft or higher, go with lowest loss cable...I have seen some commercial installs done with RG58 and shook my head on them.....that is poor engineering (and considering who did it, I was not surprised)..
Try to pickup some 1/2 Heliax (or even 7/8 if you can) since loss at UHF on it beats anything else (LMR is a cheap version but you can find used Heliax for the same price as LMR in a lot of cases and the Heliax is better in the long run...pun intended! Smiley
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K1CJS
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« Reply #8 on: February 23, 2013, 08:19:10 AM »

...If I were putting up a 75M dipole and only going to run 100W then I'd use a good quality RG58. A 100-foot run on RG58 only has 0.76dB of matched loss on 75M....

It isn't only the loss factor that should be thought of is longer runs.  The thinness of 58 is also problematic, since it tends to be more easily blown around and damaged when compared to even 8X.  The better and more robust the cable and the conductors in it, the longer it tends to last without damage or failure.  All too many people tend to forget that, and as a result have more problems with their systems then those who take everything into consideration when assembling their stations.
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AA4PB
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« Reply #9 on: February 23, 2013, 10:01:20 AM »

I've never had RG58 damaged by the wind, but I suppose it all depends on the particular installation. RG-213 is also much heavier and could cause stress on the connections when hanging from a dipole. Again, it all depends on the particular installation parameters.


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WB6BYU
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« Reply #10 on: February 25, 2013, 02:46:25 PM »

Quote from: K1CJS

There are some RG58 cable that is only shielded by loosely wound braid that isn't good for anything but weak rope.  Rat Shack seems to have this type cable in abundance.



That wasn't unique to their RG-58:  the RG-8x and RG-8 cables have
been known to suffer from insufficient braid on occasion as well.
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K1CJS
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« Reply #11 on: February 26, 2013, 05:25:01 AM »

Quote from: K1CJS
There are some RG58 cable that is only shielded by loosely wound braid that isn't good for anything but weak rope.  Rat Shack seems to have this type cable in abundance.

That wasn't unique to their RG-58:  the RG-8x and RG-8 cables have
been known to suffer from insufficient braid on occasion as well.

I guess I'm lucky that I've never come across some of that.  

The damage to the RG58 that I mentioned was at the connector ends.  For some reason (probably the smoothness of the sleeves that are used to 'adapt' the UHF connectors, the RG58 cable tends to sometimes be pulled right out of the PL259.  I've never had that happen to RG8 or RG8X.  Could also be the center conductor of the RG58 is at fault.  Stranded or solid, an 18 gauge wire isn't all that strong.  Ah, well, it's academic. A 1/4 inch rope isn't as strong as a 1/2 inch rope made out of the same material either.  73!
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AA4PB
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« Reply #12 on: February 26, 2013, 05:41:36 AM »

I think most connector mfgs would tell you that you should design the system so that you don't have excessive stress (pull) on the connectors.  Shocked
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K1CJS
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Posts: 5871




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« Reply #13 on: February 27, 2013, 05:30:00 AM »

That isn't really what I meant.  Anyone with half a brain would know to provide strain relief.  (Or should, anyway.  These days, though...)  The small amount of wire--braided shield or center conductor that RG58 has compared to RG8 or RG8X just doesn't lend itself to being as strong as the braid or center conductor (center especially) of RG8 or RG8X, and the stiffening by soldering at the connector doesn't help either.

In any event, to each their own. My thought is that 58 just doesn't have the durability for all that much and should not be used where there is even a chance of too much flexing--and failure. 
« Last Edit: February 27, 2013, 05:35:31 AM by K1CJS » Logged
KS4VT
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Posts: 141




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« Reply #14 on: February 27, 2013, 04:17:19 PM »

Even though the connectors are a bit pricey, I like to use 1/4 in. superflex.  It is thin, easy to manage, and has very reasonable losses.
I'm even utilizing it for my wifi router to increase the signal strength around the house by using an external antenna.
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