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Coax failure at >25kw

i talked with a friend. he said that there is a mismatch between the output of the amp and the match on the antenna. when the rf gets to the antenna it start traveling back down and looks for a place to go.'

he also said the coax specs are for 100% duty for commercial broadcast which is why more power can be run. the 218 is rated for 11000 rf volts which is higher then hardline which is 6000 i think. i am doing this from memory which is not great so dont quote me these are not exact! the heliax has much less loss over long runs so when you have to get 30 watts 300 feet you need the whole 30 watts to get there. 218 would never work in a long run

kd7ugy to answer your question. 12' in the mobile and 40' feet to the tower.thank you for the offer and the info. i am going to try a different match of some sort or a balun.
 
a BALUN with 25kw because of a mismatch at the the output of the amplifier or input of the antenna on the ONLY band the whole setup is tuned for?? take your ANALYZER, not your swr meter, get the antenna set properly, check your 218 & see where it stands-if it's still good. when all that is good, if you still have problems, you need to bring the amp back to the builder & have it brought somewhere nearer to 50 ohms.

if you were to ever see the RF burns these little babies to the left can do to the steel mounting plate & roof sheet metal during matching issues, i GUARANTEE you will not want to key up again risking those burns to human flesh.

please, no comments on general RF exposure. once the brain cells have been killed off by the 8-pill training amplifiers, further destruction has no additional affects. my kids turned out fine-they're into video games, cell phones & IM on the computer-they HATE listening to 'all that static & crap'.
 
davegrantsr said:
a BALUN with 25kw because of a mismatch at the the output of the amplifier or input of the antenna on the ONLY band the whole setup is tuned for?? take your ANALYZER, not your swr meter, get the antenna set properly, check your 218 & see where it stands-if it's still good. when all that is good, if you still have problems, you need to bring the amp back to the builder & have it brought somewhere nearer to 50 ohms.

if you were to ever see the RF burns these little babies to the left can do to the steel mounting plate & roof sheet metal during matching issues, i GUARANTEE you will not want to key up again risking those burns to human flesh.

please, no comments on general RF exposure. once the brain cells have been killed off by the 8-pill training amplifiers, further destruction has no additional affects. my kids turned out fine-they're into video games, cell phones & IM on the computer-they HATE listening to 'all that static & crap'.
Click to expand...


o0p guess i should have read the thread tittle LMAO 25kw holey frizzle shnizzle batman.
 
Switch Kit said:
For Christ sakes ! 25,000 watts on CB !! I know of some legal AM radio stations that don't run that much , but chances are the power source isn't sitting right in front of the radio DJ's. either , Maybe IM just missing something here ? Some of the more super stations out there run 50,000 watts. Go figure
Click to expand...

I think the bigger question is why does it take 3 tubes with 4k watts diss to get 25 grand.

A single 4CX5K will get you 22 grand.

The problem he has is the beam is not fed correctly. Get a choke of some type at the feedpoint to the beam, and your problems should go away.

Incidental radiation from the coax is a bitch, and it will kill you.


--Toll_Free
 
KD7UGY said:
Well how long is the run of coax in your mobile compared to the length of the coax going to the beam? If you keep the 218 short it'll handle a lot more power than a longer length will. What diameter is 218? Around .625"? You might want to look into some larger coax for the beam, maybe some LDF5 or 6. I've got some 7/16 DIN connectors for LDF6 if you need any.
Click to expand...


How about any LC connectors.

I can't get them from Andrews anymore. They claimed they stopped making them.

Have a dual 4CX15000 amp ready to go out the door, but no connectors. Haven't played with DIN enough to trust them at this power level.....


--Toll_Free
 
Sorry, I don't have any LC's. The LC's seem to be hard to come by for Heliax and expensive when you do find them. I've been using the DIN connectors for a while now with success but I'm not running that much power. The DIN's aren't quite as big as the LC's and won't handle as much power but I would think it would be close.
Now as for the coax radiating power you definitely need a balun on that antenna. Once you put a good balun on there your problems should go away.
 
Toll_Free said:
Switch Kit said:
For Christ sakes ! 25,000 watts on CB !! I know of some legal AM radio stations that don't run that much , but chances are the power source isn't sitting right in front of the radio DJ's. either , Maybe IM just missing something here ? Some of the more super stations out there run 50,000 watts. Go figure
Click to expand...

I think the bigger question is why does it take 3 tubes with 4k watts diss to get 25 grand.

A single 4CX5K will get you 22 grand.

The problem he has is the beam is not fed correctly. Get a choke of some type at the feedpoint to the beam, and your problems should go away.

Incidental radiation from the coax is a bitch, and it will kill you.


--Toll_Free
Click to expand...

I would like to know whos building this 22kw box so i know not to deal with them
 
the 'box' they are talking about, funbiz, is the one you opened this thread about. and, yes, i'd stay away, too.
 
Dave, the 22K box funbiz99 is asking about is Toll Free's single 4CX5000, not the three tube POS that opened this thread.

For my money, anything that Toll Free had to do with is going to be a winner!
 
yes master chief, the 22k box, yes, but, follow the post prior to his & i think funbiz is commenting on the part that says-'The problem he has is the beam is not fed correctly. Get a choke of some type at the feedpoint to the beam, and your problems should go away.' right before that he mentions the 4cx5000 & before that 'I think the bigger question is why does it take 3 tubes with 4k watts diss to get 25 grand'. i believe funbiz is confusing things since HE says-'I would like to know whos building this 22kw box so i know not to deal with them'. funbiz appears to be thinking that the 22k amp needs the choke, not the 25k POS he originally posted on. just wanna make sure we're all talking the same language here.

in hindsight, should funbiz be messing with tubes & high voltage? from a safety standpoint, i mean....
 

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