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Author Topic: The Best Coax To Use  (Read 3274 times)
KM6NFF
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Posts: 116




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« on: October 29, 2017, 11:32:08 AM »

I'm going to be setting up my first base station and would like to know the best coax to use. I probably will be using a vertical antenna along side my 2 story home and a Icom 7300 with no added power. I would like to know the best coax with the least amount of loss. I'll be running about 50 feet. I don't mind spending a little extra for better performance. Any help would be appreciated.
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WB6BYU
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« Reply #1 on: October 29, 2017, 11:43:22 AM »

In 50' of coax at HF to a matched load you can use just about any type of coax without
noticing the losses.  While you certainly can use one of the larger cables such as
RG-213, LMR-400, Belden 9913, or 1" hardline, something lighter and more flexible such
as a good quality RG-8X will be quite adequate.  Even RG-58 isn't that bad.

If you are using something like a 43' vertical with an un-un at the base and tuned by
a tuner in the shack, then the coax will be operating at a higher SWR, and using a larger
size might make more of a difference.  But I wouldn't see any need to use anything
larger than RG-213 for such a short run, unless the SWR is very high (in which
case you need to fix your antenna.)
« Last Edit: October 29, 2017, 11:46:33 AM by WB6BYU » Logged
KM6NFF
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Posts: 116




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« Reply #2 on: October 29, 2017, 11:55:16 AM »

In 50' of coax at HF to a matched load you can use just about any type of coax without
noticing the losses.  While you certainly can use one of the larger cables such as
RG-213, LMR-400, Belden 9913, or 1" hardline, something lighter and more flexible such
as a good quality RG-8X will be quite adequate.  Even RG-58 isn't that bad.

If you are using something like a 43' vertical with an un-un at the base and tuned by
a tuner in the shack, then the coax will be operating at a higher SWR, and using a larger
size might make more of a difference.  But I wouldn't see any need to use anything
larger than RG-213 for such a short run, unless the SWR is very high (in which
case you need to fix your antenna.)

I'm looking at the Comet 250B vertical. The side of my home will be somewhat in play. I have limited space and this is really the only area I can use. I have to keep a low profile so I'll be using a 10' mast with this antenna. Any help via the better coax I thought would help but since I'm running a short distance maybe it really doesn't matter.
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K1ZJH
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Posts: 3303




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« Reply #3 on: October 29, 2017, 11:56:45 AM »

LMR-400 fitted with the proper connectors installed correctly.

Pete
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KM6NFF
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Posts: 116




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« Reply #4 on: October 29, 2017, 12:01:11 PM »

LMR-400 fitted with the proper connectors installed correctly.

Pete

Thanks Pete. Is one brand any better then the other?
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HAMSTUDY
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Posts: 419




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« Reply #5 on: October 29, 2017, 12:42:46 PM »

+1 on LMR-400

For a brand take a look at Times Microwave.
https://www.timesmicrowave.com/documents/resources/LMR-400.pdf

You might like the UltraFlex version of LMR-400. 
https://www.timesmicrowave.com/documents/resources/LMR-400-UF.pdf

If you need a supplier for Times Microwave that offers a good selection of high quality connectors (including N connectors) along with the cable, take a look at Tessco Technologies.  If you want they will build the cable with the connectors you select.
https://www.tessco.com/
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KD0ZV
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« Reply #6 on: October 29, 2017, 01:01:07 PM »

I agree with BYU. 50' is going to be pretty forgiving on HF so no need to break the bank.

As an example with a 3:1 mismatch on 10 meters ordinary RG-213 is going to only have a loss of .76db which is the combined conductor and mismatch loss.

Times LMR-400 has a total loss of .56 db.

So both are extremely low. The lower bands of course are going to have even less loss.

I have not been around the CHA-250B but you might want to check out the reviews on this site. 3.7/5 stars is not stellar.

73,
kd0zv




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KC4ZGP
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Posts: 1637




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« Reply #7 on: October 29, 2017, 01:03:16 PM »

I use Belden RG-213 and RG-11 foam. I've not heard of other brands less or beter.

It's like which radio is better, Alinco, Yaseu or Kenwood.

Kraus

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KM6NFF
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Posts: 116




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« Reply #8 on: October 29, 2017, 01:31:17 PM »

+1 on LMR-400

For a brand take a look at Times Microwave.
https://www.timesmicrowave.com/documents/resources/LMR-400.pdf

You might like the UltraFlex version of LMR-400. 
https://www.timesmicrowave.com/documents/resources/LMR-400-UF.pdf

If you need a supplier for Times Microwave that offers a good selection of high quality connectors (including N connectors) along with the cable, take a look at Tessco Technologies.  If you want they will build the cable with the connectors you select.

https://www.tessco.com/

I'll take a look,thanks
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KM6NFF
Member

Posts: 116




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« Reply #9 on: October 29, 2017, 01:33:39 PM »

I agree with BYU. 50' is going to be pretty forgiving on HF so no need to break the bank.

As an example with a 3:1 mismatch on 10 meters ordinary RG-213 is going to only have a loss of .76db which is the combined conductor and mismatch loss.

Times LMR-400 has a total loss of .56 db.

So both are extremely low. The lower bands of course are going to have even less loss.

I have not been around the CHA-250B but you might want to check out the reviews on this site. 3.7/5 stars is not stellar.

73,
kd0zv


If you have any other idea's for a straight up vertical that might be better please let me know. I'm open to any suggestions. Thanks


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WB6BYU
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Posts: 17053




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« Reply #10 on: October 29, 2017, 01:35:00 PM »

Quote from: KM6NFF

I'm looking at the Comet 250B vertical... Any help via the better coax I thought would help but since I'm running a short distance maybe it really doesn't matter.



The losses in that antenna are higher than any reasonable coax will contribute.

Notice the ridges on that black plastic lump at the base of the antenna?  Those are heat sink
fins to help dissipate the heat that builds up in the lossy transformer when you transmit.

G8JNJ has an analysis of several antennas of this type on his web site.

The transformer is intentionally designed to be lossy to improve the SWR.  (The very
similar Diamond BB7V uses resistors in the base matching unit for the same purpose.)
It's not too bad on 17m (only 2 dB down from a quarter wave vertical, when both have a good
ground radial system), only down 4 dB on 20m and 6dB on 15m and 12m.  (Note that a loss of
6 dB means 3/4 of your transmitter power is dissipated as heat rather than being radiated.)
Even on 40m, where it is down 10 dB (not unsurprising due to the short length), you'd have
10 watts radiated with 100W input, which is still more than I do when I run QRP at 5 watts to
a good antenna, and I can still make plenty of contacts.  So it isn't that the antenna won't work,
but it won't work well compared to some other options.  And minimizing coax losses won't
come anywhere close to making a difference in performance.

How much loss is the coax going to have, anyway?  Not that much.

Looking at various coax loss tables, common types of RG-8X have around 1.5 dB of loss per 100'
at 30 MHz, and less than that on the lower frequency bands.  RG-213 might be around 1 dB, and
low-loss types like LMR-400 are around 0.8 dB.  (There is a fair bit of variation among specific
types within each group.) But that's for 100' on 10m:  the losses are half that for a 50' piece,
so the difference between 8X and LMR-400 is about 0.4 dB on 10m.  That's not much, considering
that 1dB is considered the level where the human ear can detect a difference in signal strength.
And on the lower bands the difference will be even less, quickly getting to the point of being
insignificant in normal ham operation.

So then it comes down to a question of price:  LMR-400 runs about $1 a foot or so, depending on
where you get it (and there are other similar foam cables that would work as well.)  RG-8X seems
to run around half that coast, maybe as low as 40 cents/foot.  If you don't mind paying an extra
$30 for no significant difference in performance, that's up to you.

If you want to maximize performance, I'd put the money into a better antenna instead.
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KM1H
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Posts: 2479




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« Reply #11 on: October 29, 2017, 01:42:15 PM »

Quote
I'll take a look,thanks

Just dont buy anything from Tessco, there are plenty of good cable sellers who wont rip you off.
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HAMSTUDY
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Posts: 419




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« Reply #12 on: October 29, 2017, 02:35:02 PM »

Might depend somewhat on your future plans.  If this is the only antenna you think you will have and you want to save on the budget, then RG8X might be the way to go.  On the other hand sometimes it makes sense to spend a few $ more for something if it will reasonably enhance quality and/or performance, especially if you might reuse it in another installation down the road that could benefit from the quality or performance.  For a difference of $30 if something saves you time in future research, buying, shipping, etc. it might be worth considering.

I might not have these numbers right but last time I looked I thought the specs said...

100' (so it would be half this for 50') at 150 MHz (I don't have the specs for 20 meters, 40 meters, etc) is:
RG8X 4.5 dB
LMR400UF 1.8 dB
LMR400 1.5 dB

If those are correct it would be 2.25 dB vs .75 dB for 50' at 150 MHz (and likely less of a difference below 50 MHz).  Or perhaps at some time in the future you might use the coax for VHF (or UHF), just something to consider.  At 450 MHz, for UHF, RG8X is 4.1 dB at 50' vs LMR400 is 1.35 dB at 50'.  You might never use it for VHF/UHF or you might not care about the difference at VHF/UHF.  And you might prefer the fact that RG8X is only 6.15mm vs the 10.29mm of LMR400 and LMR400UF.  Just sharing some specs and considerations, that's all.

It comes down to how much you need or want to pay for each dB.  For 50' of RG8X or LMR400 it might not be a big deal either way in terms of $ or performance.  My guess is that a year from now it will be hard to notice where the $30 went, or alternatively the 1.5 dB at 150 MHz.

As for Tessco, I had a very good experience but YMMV.

I agree that the emphasis should be on finding the best antenna that fits your space and budget - but if you work hard to squeeze every dB out of the antenna it might be worth gaining a dB wherever else you can find it/afford it/justify it.

73
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N2SR
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Posts: 635




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« Reply #13 on: October 29, 2017, 02:40:44 PM »

waveguide
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If no one is doing it that way, there is a probably a very good reason.
KD0ZV
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Posts: 38




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« Reply #14 on: October 29, 2017, 02:55:31 PM »

waveguide

LOL
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