Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

donate to eham
   Home   Help Search  
Pages: Prev 1 2 3 [4]   Go Down
  Print  
Author Topic: RG-8X Power Handling Capacity?  (Read 36703 times)
KK5DR
Member

Posts: 631


WWW

Ignore
« Reply #45 on: January 29, 2015, 06:39:18 PM »

I will never use RG8X, for any reason! It is the worst coax there is.
I use regular RG58 for low power jumpers, and RG213 for everything else.
Logged
W8JI
Member

Posts: 9748


WWW

Ignore
« Reply #46 on: January 29, 2015, 08:31:53 PM »

I use RG8X jumpers all the time, especially on my test bench where cables have to be flexible. So does Ameritron and others.

That cable just gets warm on ten meters at 2kW carrier, even testing amp after amp. I run 1500 watts on six meters CW through RG8X jumpers, and while it get a little too warm to make me comfortable telling others it is OK, it never gets so warm as to be an issue with failures. I would not, however, use a long run on six or ten because of cable loss.

With low duty cycle, it is generally good at 10 kW peaks or more. I routinely high-pot RG8X cables to 6-8 kV, and the normal breakdown is across the air gap in a UHF fitting, NOT through the dielectric. This means it is heat limited. Heat limited means it is duty cycle limited by I^2 R losses, so it is a skin effect and current limit based on duty cycle and ambient air.

I fully expect the person who said he saw RG8X being used at 2.5 kW carrier with 100% AM to be telling a plausible truth, based on how the cables I have seen test. RG8X will easily handle 2-3 kW with fairly high duty at lower HF, and it does not punch through at several kV, so it should easily handle 10 kW PEP on 75 meters.

RG8X is speced at 2 dB loss per hundred feet on 30 MHz. That is 47% loss in 100 feet. At 2000 watts that is 738 watts of heat in 100 feet. That is 7.38 watts per foot. With a 50% duty that is 3.7 watts per foot heat. That is warm when spread over a foot in open air, but it is not melting on 30 MHz.

On lower HF the loss is around 0.3 dB/100ft. That's 7% per hundred feet. That's 1.75 watts per foot on lower HF at 2.5 kW. Hardly an issue at all at 2.5 kW carrier. 1.75 watts a foot is nothing.
Logged
W3RSW
Member

Posts: 606




Ignore
« Reply #47 on: January 30, 2015, 06:27:07 AM »

Well, in the 3rsw book of "inverse time exponent," that 1.75 watts/ft. Is not spread evenly.
Every full wave length you have one concentrated hot spot localized on top of the coax and another concentrated spot on the bottom of the coax.  Grin

These hot spots travel along the coax at f/c * k ( velocity factor) in phase with themselves, hence subjecting the coax to accelerated but distributed wear.

Now the diameter of the coax has an inordinately ameliorating effect on this degradation, inverse square relation to the diameter. That's why RG8 is four times better able to withstand HV then RG 58.  Simple static breakdown of materials in the linear dimension of dimensionless time is only part of the story.  My book tells all.
You all get the drift.

Sorry, I couldn't resist.  Procrastinating about plowing the darn road off my hill again.

 Dragging up November necro posts got me going in the first place after the original subject was beaten to death ...and me even answering can't be any better in the second place.
« Last Edit: January 30, 2015, 06:34:24 AM by W3RSW » Logged

Rick, W3RSW
KM1H
Member

Posts: 5109




Ignore
« Reply #48 on: January 31, 2015, 03:46:10 PM »

Ive been using RG6 from HF to 6M for 1200W amps for decades, feeding LPF's, power meters and antenna switches. Then it is RG-11 foam to the hardline.

RG8X is no different if it is a good brand and not the cheap ham crap; I ran a good brand about 100' (hamfest purchase from estate, never used) to a temporary 80M sloper that wound up being used for 13 years at 1500W on AM plus the usual 1200W on SSB/CW. VSWR up around 3885 was about 5:1. I think it was Belden but not sure.

RG-58 is CB cable and RG-8/213 is too damn rigid to be useful around the benches.

Test equipment uses HP branded cable, RG-55, and Digital Equipment 50 Ohm Belden Ethernet cable that is foam with a foil and braid....no detectable leakage; a 1000' reel was $15 at a junk dealer ages ago. Ive also run 1500W+ thru it on the amp bench in a pinch with no problem.

Carl
Logged
KM1H
Member

Posts: 5109




Ignore
« Reply #49 on: January 31, 2015, 04:00:33 PM »

Quote
Sorry, I couldn't resist.  Procrastinating about plowing the darn road off my hill again.

As another hilltopper I can relate very well; I get substantially more snow than the flatlanders and swamp dwellers below me.

It took 2 days to do my property after the 41-42" from Monday/Tuesday, my fault for not getting my a** out of bed during the night a few times and waiting until there was already 30+" inches to shove around in gale force winds. My poor 78 F-250 wasnt up to it and I had to keep taking little bites and getting the plow and frame hung up. What a PITA. If I had any sense I would have bought chains ages ago....been up here since 89.

More gale force winds today left a good 12" blown back over on the driveway, parking areas and paths. Its all light fluff as we havent seen any melting temps; teens and single digits ahead for another week at least.  Where is that idiot Al Gore when you need him?

Another 12-18" predicted for Monday.

Carl
Logged
W1QJ
Member

Posts: 2948




Ignore
« Reply #50 on: January 31, 2015, 05:10:08 PM »

Quote
Sorry, I couldn't resist.  Procrastinating about plowing the darn road off my hill again.

.  Where is that idiot Al Gore when you need him?



Carl

Carl, just so I can understand for sure the humor.   Am I to assume you mean Al Gore is "full of hot air" so as to melt all that snow of yours?
Logged
KM1H
Member

Posts: 5109




Ignore
« Reply #51 on: January 31, 2015, 06:45:13 PM »

Well I guess superheated excrement releases a lot of hot air Lou.

Carl
Logged
W1QJ
Member

Posts: 2948




Ignore
« Reply #52 on: January 31, 2015, 10:51:59 PM »

Well I guess superheated excrement releases a lot of hot air Lou.

Carl
chortle
Logged
Pages: Prev 1 2 3 [4]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!