So what if you ran the coax threw a hole in the bottom of the mast then out the top 28 ft later in a loop into imax 2000.?
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Lmr 400 inside mast ?
- Thread starter Last man standing
- Start date
Here is some info on the idea you suggest.
However, this idea uses a 1/4 wave resonant element at the frequency of choice to run the coax thru. The idea also says to short the shield to the mast at the bottom of this balun tube. The balun part is at the top of the second column.
http://www.comsistel.com/HAM%20documents/Good%20Analysis%20of%20a%20Balun%20.pdf
Here is how I apply this idea to my Marconi 5x antenna. It is not a perfect application, because the coax at the top should be totally down inside the balun. It does work however.
If you use LMR 400 you may get better results making the balun tube about 1.5" inches in diameter. I also center the top and bottom of the coax to the center of the tube as best I can.
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Running coax inside of a mast won't affect the coax any, unless it is pushed against a sharp edge of the top or bottom of the mast which could cause it to wear through the shielding and affect the properties of the coax, this would require replacing the coax to fix, so make sure where the coax enters and exits the mast are secure, and checking those points every so often won't hurt.
I am curious about something. Why use such high quality, low loss feedline, which is very likely serious overkill for what you need, just to feed an antenna that is known to be among the more lossy antennas available?
I'm not saying don't do it, its your money after all, do what you want. I just don't get why you would spend so much for part of the antenna system (the feedline) just to go cheap elsewhere (the most important part, the antenna itself)...
The DB
I am curious about something. Why use such high quality, low loss feedline, which is very likely serious overkill for what you need, just to feed an antenna that is known to be among the more lossy antennas available?
I'm not saying don't do it, its your money after all, do what you want. I just don't get why you would spend so much for part of the antenna system (the feedline) just to go cheap elsewhere (the most important part, the antenna itself)...
The DB
"Why use such high quality, low loss feedline, which is very likely serious overkill for what you need..."
One reason is that people get obsessed with that 'loss' idea. In most cases, meaning if you did things at least close to right, those losses aren't going to be significant. There are always losses in any antenna system, you can't get away from that fact. You can certainly minimize those losses, but you can certainly carry that to extremes.
- 'Doc
One reason is that people get obsessed with that 'loss' idea. In most cases, meaning if you did things at least close to right, those losses aren't going to be significant. There are always losses in any antenna system, you can't get away from that fact. You can certainly minimize those losses, but you can certainly carry that to extremes.
- 'Doc
Hey doc, good job addressing half of it, but you missed the big picture of what I am curious about... It wasn't just the higher than necessary quality coax to minimize losses, but that in combination with an antenna that is known to be more lossy than most... Care to take a stab at the whole thing?
The DB
The DB
DB, you, CK, and C2, might be right...maybe LMS just wanted to know what could happen if he put his coax inside his mast. I didn't give any consideration to LMS telling us he had made a personal decision to buy and use LMR400 on his Imax. He is free to make the choices he wished, and I don't see the point for such arguments?
I took his post to suggest he might be considering some technical reasons for doing what he described, and I responded with my idea.
I know that Avanti also recommends an optional "coax thru the mast" procedure for both their Sigma4 and the Sigma 2, installations, and I would imagine there are others too. My experience with this idea comes with the use and/or modification of this idea using the Starduster, and that idea was based on the link I provided above.
DB, after all these varied responses to LMS's question, I wonder what LMS had on his mind in asking his question?
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perhaps it was in the thread title
Amen RS.
DB, you were not the only one that was talking about LMS's use of LMR400.
Think about that for a minute. It isn't the antenna it's self that's lossy, it's the matching network used to end-feed it. Any impedance matching network used to match an end fed 1/2 wave antenna isn't going to be 'super efficient'. But, that also certainly doesn't mean that that particular matching network is so terrible. The antenna typically gets a 'bad-rap' because too much is expected of it to start with. So why do they use that sort of matching system/network? Cuz' it's less expensive than others, is fairly simple, and is easy to adjust. Want a more efficient method of feeding the thing? Easy, feed it in the center... But you just made it more difficult to errect, not as simple mechanically. See where that's going?
'Doc
'Doc