| Author |
Message |
    
Climber
| | Posted on Wednesday, April 02, 2003 - 11:47 pm: | 
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Hello Tech,
Putting up a new Maco V 5/8th soon from Copper, for a 60-65ft run of coax, use what kind of cable?
Currently I have .405 diam Solid Core 95% shielded or 98%. Its about 7 years old in a dry climate with little to no freezing temp. Can I reuse this line or should I replace it with ?
Is RG-8x Belden Cable with Amphenol PL259, Stranded Copper Center Cond. 98% Silver Tinned Copper Shield and Flex Clear Jacket an option or waht is a reasonably priced alternative running barefoot mostly.
Climber |
Tech833
| | Posted on Thursday, April 03, 2003 - 1:44 am: |
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If your cable is undamaged, there is no need to replace it. Cable should last 20, 30 or more years. One station I maintain has coax cable 60 years old in service that still works perfectly.
If you see evidence of water intrusion, remove and discard the damaged portion of the cable and continue to use any lengths that are undamaged. |
Dx431
| | Posted on Thursday, April 03, 2003 - 1:59 am: |
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Climber, I use the mini 8 coax on everything,MR4,A99, scanner, etc... it works for me.
My .02 worth.....
431 |
Tech833
| | Posted on Thursday, April 03, 2003 - 11:12 am: |
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431,
Any 50 ohm coaxial cable will 'work'. The difference is determined by the level of performance you desire.
If mediocre performance is all you need, mini 8 (RG-8M) will suit your needs. If better performance is desired, RG-8, Belden 9913 or similar may interest you. For even higher performance, you would prefer LMR-400 or similar double shield cable. For the highest performance, then Heliax is a must. |
Barracuda
| | Posted on Thursday, April 03, 2003 - 1:59 pm: |
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Tech833,
When you talk of performance are you talking about power handling and loss or is there something more that you mean?
Thanks,
Barracuda |
Climber
| | Posted on Thursday, April 03, 2003 - 10:59 pm: |
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Tech 833,
Thank-you!
Climber |
Tech833
| | Posted on Friday, April 04, 2003 - 2:12 am: |
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I mean loss and RF resistive attenuation. I also mean noise in the receiver. |
Barracuda
| | Posted on Friday, April 04, 2003 - 3:19 am: |
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Tech833,
Thanks again for the reply. And pardon me for asking so many questions that may sound obvious to most of the readers of these forums, but I'm trying to learn.
Your responses are appreciated.
Thanks,
Barracuda |
Kiwikid
| | Posted on Friday, April 04, 2003 - 3:18 am: |
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Hello Team,
Hey Tech833 I hear where you are coming from and don't get me wrong but are these losses and attenuation factors not so critical on HF as they are on VHF/UHF and higher frequencies.On HF unless the feedline is very long over 100ft. the losses between useing different types of coax will not be so noticeable or am I hearing things wrong.
73 Kiwi Kid |
Tech833
| | Posted on Friday, April 04, 2003 - 11:09 am: |
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Barr,
If you didn't ask, nobody would learn. Thank YOU.
Kiwi,
It is true that the RF losses of various cable goes up with frequency. However, it is never 'negligible' to the operator wishing the highest level of performance for dollar. With CB limited in power, it is important to remove as much loss as possible both for transmitting and receiving modes. TVI can also be reduced with lower loss, and better shielded cable in some installations. Also, with as much noise as is already present in AM and SSB modes on 27 MHz., noise is another factor, which is normally not even a consideration at VHF and UHF.
For instance, if you have a 100 foot run of RG-8M and a 100 foot run of 1/2 inch Heliax, the power at the end of the cables from the same transmitter would be slightly different. Sure, that loss may be acceptable to some but not all. Then again, hooking the same antenna to both cables, the Heliax would pick up less noise along its length and also bring more of those precious microvolts from the antenna to the receiver than the mini 8. That means higher signal to noise ratio, which means that the Heliax equipped receiver would hear signals that the mini-8 equipped receiver would not. The 'noise' on the S-meter of the Heliax equipped receiver would be lower than the mini-8 receiver, and the signals would be stronger. That's the equivalent of 'pulling signals out of the noise'.
The HF frequency range is different, but still important, although in a different way. How's that? You may quote me, but nobody would understand that last line! |
Kiwikid
| | Posted on Friday, April 04, 2003 - 4:53 pm: |
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Hello Team
Thanks Tech for clarifying some of the mysteries of coax.Climber all the best with your new installation and hope the DX come your way.
73 Kiwi Kid |
Dennis
| | Posted on Friday, April 04, 2003 - 5:06 pm: |
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Just to throw a wrench into things, but for the lowest loss, should you not be looking at using 450 Ohm window (ladder) line or even 600 Ohm open (air dielectric) ladder line.
The calculated cable losses are:
Beldon 9258 (RG-8x), 100 Ft. @ 27MHz @ 1:1 SWR = 1.552 dB loss
Andrews LDF4-50A (0.5 in. hardline), 100 Ft. @ 27MHz @ 1:1 SWR = 0.339 dB loss
450 Ohm commercial windowed ladder line, 100 Ft. @ 27MHz @ 1:1 SWR = 0.147 dB loss
600 Ohm air dielectric ladder line, 100 Ft. @ 27MHz @ 1:1 SWR = 0.101 dB loss
Regards,
Dennis |
Tech833
| | Posted on Saturday, April 05, 2003 - 12:02 am: |
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Dennis,
That would be fine if you were using an antenna with a ladder line impedance feedpoint and a radio with a balanced 450 ohm output. However, you are using a radio with a 50 ohm unbalanced output and an antenna with 50 ohm unbalanced input. Therefore, you would need to transform the radio output and the antenna input in order to use the ladder line. The loss in the transformers would more than cancel any gain in using ladder line. Expect anywhere from 0.5 to 1.2 dB loss in each transformer. Add the two and you are talking about adding another 1 to 2.4 dB loss to the ladder line numbers. You might as well use RG-8M!
Consider this, 7/8 Heliax would have less loss than your ladder line by .003 dB all by itself, ignoring the transformer loss mentioned above. Heck, you could use 1 5/8 Heliax and get even less loss. Or, use 6 inch air dielectric Heliax and get even less loss. Etc, etc. 1/2 inch Heliax will give around 0.2 dB loss for 100 feet of cable at 27 MHz. That is most acceptable and much better than ladder line w/transformer loss.
In this case, Heliax is by far the most performance you can get. Unless you completely redesign the radio and antenna to accept the ladder line impedance. Of course, the ladder line installation would be a lot more critical than coax as well. Ladder line must be balanced to work properly at the lowest loss.
One last thing, Heliax and hard line are not the same thing. Heliax comes on a roll and is semi-flexible. Hard line comes in 10 feet sections and is not flexible without a torch and pipe bender. It is assembled with center conductor 'bullets' and either soldered together, clamped, or bolted depending on the size and installation. |
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