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RG8X wattage????

nitroturbo4u

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Feb 17, 2013
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<More audio>Tested a very large amp on this.
50 foot section.Amp uses 3cx500 total of 4 tubes.
Now there is 2.8 ohms resistance in the coax.From center conductor to center.
Shield is Zero ohms from connector to connector.
Should i trash it??? Or cut it in half?????Got a 50% shot at it that way..^^ ab v c^^
 

I am not sure that I understand the problem but, I would cut off 9 feet of it, put PL-259's on it and test it into a 50 ohm dummy load; you should read 1.0 to 1 SWR on your meter. Test OK, then go to the other end of the coax run and repeat the procedure again. You will probably will find the problem at one end or another.

Both jumpers good, take your ohmmeter and check the remaining coax, there should be "zero" ohms from center conductor to other "CC" and "zero" ohms from shield on one end to other end; there should be "Infinite" ohms between center conductor and the shield.

BTW: The coax on your station that runs to your antenna and connects the different appliances on your station should be in 1/4, 1/2 or, whole wavelengths of your operating frequency, cutting the 50 foot run in half would not really serve your purpose after you found the problem.

Good luck, 73

ETA:
Coaxial Cable Power Ratings
Maximum input power rating - Watts at (MHz)​

RG/8x CABLE
1.0 MHz -- 4000w
10 MHZ -- 1500w
50 MHz -- 800w
100 MHz -- 550w
200 MHz -- 360
400 MHz -- 250w
900 MHz -- 200w
1000 MHz - 150w
3000 MHz -- 65w
5000 MHZ -- 50w

.
 
Last edited:
I am not sure that I understand the problem but, I would cut off 9 feet of it, put PL-259's on it and test it into a 50 ohm dummy load; you should read 1.0 to 1 SWR on your meter. Test OK, then go to the other end of the coax run and repeat the procedure again. You will probably will find the problem at one end or another.

Both jumpers good, take your ohmmeter and check the remaining coax, there should be "zero" ohms from center conductor to other "CC" and "zero" ohms from shield on one end to other end; there should be "Infinite" ohms between center conductor and the shield.

BTW: The coax on your station that runs to your antenna and connects the different appliances on your station should be in 1/4, 1/2 or, whole wavelengths of your operating frequency, cutting the 50 foot run in half would not really serve your purpose after you found the problem.

Good luck, 73


Absolutely no good reason in the world to do that. Using a 1/4 wavelength multiple simply inverts the impedance mismatch while 1/2 wave multiples simply repeats. You can't have two opposites being the best thing for something. The proper way is to match the antenna properly to the feedline and then run whatever length it takes to reach the gear allowing enough extra to go around any rotators or in the shack to move gear around.
 
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<More audio>Tested a very large amp on this.
50 foot section.Amp uses 3cx500 total of 4 tubes.
Now there is 2.8 ohms resistance in the coax.From center conductor to center.
Shield is Zero ohms from connector to connector.
Should i trash it??? Or cut it in half?????Got a 50% shot at it that way..^^ ab v c^^


Check those tube numbers again. AFAIK they never made a 3CX500. A 4CX250B, 4CX300, and 4CX350 yes but 3CX500 no. I can't find any data on them either and I doubt it was an amp with four 4CX5000's in it. :eek:

Bottom line is it was cheap RG8X. Throw it away or cut it up for jumpers and buy better cable suited for the power level being used.
 
Absolutely no good reason in the world to do that. Using a 1/4 wavelength multiple simply inverts the impedance mismatch while 1/2 wave multiples simply repeats. You can't have two opposites being the best thing for something. The proper way is to match the antenna properly to the feedline and then run whatever length it takes to reach the gear allowing enough extra to go around any rotators or in the shack to move gear around.

Whoa, at what point did the OP mention anything about an "Impedence Mismatch" and, why in the process of troubleshooting a bad piece of coax (not connected to anything) would a "Impedence Mismatch" be an issue with a DC operated VOM?

"QRN", perhaps you might now tell him HOW to properly match his coax to his antenna, that is, after he has found the bad jumper, here a better idea, let's tell him to go out and buy a MFJ-259b Antenna Analyzer then he can solve all his own problems.

.
 
I am not sure that I understand the problem but, I would cut off 9 feet of it, put PL-259's on it and test it into a 50 ohm dummy load; you should read 1.0 to 1 SWR on your meter. Test OK, then go to the other end of the coax run and repeat the procedure again. You will probably will find the problem at one end or another.

Correct

Both jumpers good, take your ohmmeter and check the remaining coax, there should be "zero" ohms from center conductor to other "CC" and "zero" ohms from shield on one end to other end; there should be "Infinite" ohms between center conductor and the shield.

Correct again.

BTW: The coax on your station that runs to your antenna and connects the different appliances on your station should be in 1/4, 1/2 or, whole wavelengths of your operating frequency, cutting the 50 foot run in half would not really serve your purpose after you found the problem.


This is the part I was talking about. You did not say anything about using such lengths for testing only. It reads as if you should only use such "tuned" lengths for normal usage which is what I was disagreeing with hence my post which I quoted below.


Absolutely no good reason in the world to do that. Using a 1/4 wavelength multiple simply inverts the impedance mismatch while 1/2 wave multiples simply repeats. You can't have two opposites being the best thing for something. The proper way is to match the antenna properly to the feedline and then run whatever length it takes to reach the gear allowing enough extra to go around any rotators or in the shack to move gear around.


Whoa, at what point did the OP mention anything about an "Impedence Mismatch" and, why in the process of troubleshooting a bad piece of coax (not connected to anything) would a "Impedence Mismatch" be an issue with a DC operated VOM?

He didn't. That was stated because of what you said about 1/4 or 1/2 wave etc lengths and I was stating what those lengths are used for.

"QRN", perhaps you might now tell him HOW to properly match his coax to his antenna, that is, after he has found the bad jumper, here a better idea, let's tell him to go out and buy a MFJ-259b Antenna Analyzer then he can solve all his own problems.

.

QRN?? WTF did that come from? Must be a glich in the forum software. That screen name has not been used in years and I do mean YEARS. Anyway to answer your question, sure it is a great idea to get an antenna analyzer if you can. I highly recommend it to anyone. It makes it real easy to see what the antenna is really doing and you can take it to the feedpoint MUCH easier than an SWR meter and controlling the TX from such a distance. Truly the BEST way to tune an antenna is right at the feedpoint if at all possible however if that is not possible the antenna should be fed with an even multiple of 1/2 wavelengths of cable as the impedance will be repeated at the far end of the transmission line.Maybe this is what you meant above although it did not seem like that when I read it. If so forgive me for not understanding what you meant.

FWIW when I tune my antennas I use a 1/2 wavelength of some cheap RG8X cable as the cable type does not matter. I had lots on hand so I used it. Once the antenna is properly tuned I install it at the final location if not already there and run a convenient length of appropriate coax cable beit Belden 8214, 9913 or LDF4 heliax with total disregard for whether it is any fraction of any wavelength. This is because most of my antennas are multiband and 1/2 wave on one band is only 1/4 wave long on another. I have 1/2 wave lengths made up for each band I operate on and this technique has yet to fail me. Hopefully this answers things and if I misunderstood your statements above forgive me. No harm no foul.
 
CK. so,you use an antenna tuner then for normal operations?

No just the abnormal operations. :laugh: Seriously, right now due a complete antenna and tower replacement project, all I have is an 80m doublet installed for all bands and fed thru a Yeasu FC-40 automatic antenna tuner mounted outside the house. From there is a 1:1 balun into 450 ohm ladder line to the antenna. this is the only time (other than mobile) that I use a tuner. All the antennas in the past and the ones I plan to install this summer are all either monoband VHF antennas or multiband HF antennas with enough bandwidth to cover the entire band. I only ever use an antenna tuner to either "touch up" the band edges on an 80m wire antenna or on something strung up temporarily like a random wire or an inverted L.

The antennas going up are a pair of 13B2's for 2m, a home made six element yagi for 6m, a Cushcraft A3WS for 12m and 17m and a Hygain Explorer-14 for 10m, 15m and 20m with the add-on kit for 40m which is the only band that may require a tuner to trim up the band edges due to the antenna having a narrower bandwidth. For 80m I will be using various half slopers arranged around the tower and switched via a remote antenna switch. These should not require a tuner as I do not generally operate all over the band and stay confined to about a 100-150 KHz segment. All the antennas are here waiting for decent weather and work schedule to go up.
 
QRN?? WTF did that come from? Must be a glich in the forum software. That screen name has not been used in years and I do mean YEARS

No Glitch in 'da software.......just tells you how long I've been around.



Surely you remember that.

We were both correct, my general comments were specifically about 50 ohm coax used in a single band application and, they were only my humble opinions garnered from 40 + years of RF experience BUT, a whole 'nother argument/opinion comes into play if you are talking about multi-band antennae or, balanced vs. unbalanced feedlines.

Catch you a little later

.
 
No Glitch in 'da software.......just tells you how long I've been around.



Surely you remember that.

We were both correct, my general comments were specifically about 50 ohm coax used in a single band application and, they were only my humble opinions garnered from 40 + years of RF experience BUT, a whole 'nother argument/opinion comes into play if you are talking about multi-band antennae or, balanced vs. unbalanced feedlines.

Catch you a little later

.


Yeah I have been around a while.Since waaaay back in the EZ-Board days. 40 years hey? I've only got about 36 years in but 22 of those were in commercial broadcasting so it just seems like it has been a lot longer. LOL. Did you edit out the Captain Kilowatt name and replace it with QRN or did it just appear that way when you quoted me? The reason I ask is that it has happened on other people's quoting of me in the past.

Nice amp BTW. LOL I don't remember it however I'll bet Doc does. :laugh:
 

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