| Author |
Message |
    
Boxcar
| | Posted on Thursday, May 16, 2002 - 9:27 pm: | 
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Hey All. Got a quick one for you. I've heard cutting coax for base antenna's should be cut in 25 foot sections so I cut mine at 66 feet due to 3 jumpers that I have at 3 feet a piece. Is this a good length for a tower of 45-50 feet?? Haven't got it all hooked up as of yet but just curious as to if this will work fine. Thanks all!!!!! |
Tech181
| | Posted on Thursday, May 16, 2002 - 10:00 pm: |
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Boxcar,
Cut it for the length you need, it will work fine.
Steve
Tech181
Tech181@copperelectronics.com |
bruce
| | Posted on Thursday, May 16, 2002 - 11:48 pm: |
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ament no more coax cutting! |
bullet
| | Posted on Friday, May 17, 2002 - 11:14 am: |
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i cut it to go from point a to point b plus enuff for slack for rotation if its for beams and enuff for rain "drip" loops plus a bit if i want to move my desk from one side of the room to the other.... and thats it.
tech181,
i think a freq asked question section (FAQ) would be very usefull for alot of users that ask good questions but are ones that are asked often.
is this a possability on this forum?
later bullet |
RCI2990
| | Posted on Friday, May 17, 2002 - 4:07 pm: |
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id say cut it to go from PT A to PT B and thats it! But i have an ols avanti manual for my sigma 4 from the 1970s that says "If using solid dielectric coax, cut to multiples of 12 foot. If using foam type, cut to 14 foot multiples." When i put up my mooraker 4s and my sigma 4 i used this formula for figuring out my coax lenth and it works for me!  |
Scrapiron63
| | Posted on Friday, May 17, 2002 - 6:26 pm: |
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You would think those people that made the antennas knew something, huh. The old Avanti book with the PDL II's gave instructions to cut coax in 4 foot multiples. I've always been a point A to point B, except for jumpers, I use 3,6, or 9 feet. |
bruce
| | Posted on Friday, May 17, 2002 - 9:48 pm: |
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i tried something just for kicks i checked my VSWR on 28.5 it was 1.2:1 then added a 5 foot peace it went down to 1.1 : 1 ...well then i unhooked the antenna and put a mill spec 52 ohm load and rechecked both were 1.1 : 1 if your antenna is tuned corectly the coax lengh is not a factor all you are doing is moving the meter up or down the voltage wave. and remember your meter is reading VOLTAGE. |
bullet
| | Posted on Sunday, May 19, 2002 - 2:12 pm: |
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exactly! |
ss8541
| | Posted on Sunday, May 19, 2002 - 4:34 pm: |
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that is exactly right bruce.
to throw in a tad more, if your antenna is tuned correctly there will be no or very little standing/voltage waves present. this is where the term 'flatline' comes from. on a 'flatline' you can move your swr meter to any point on that line(or add more) and swr will stay the same or change slightly like in bruces example above. on a mismatched line, one coax length may 'show' a good match while another length gives the true bad match. now you see how adding coax just fools the meter.
well let me hush b4 bruce, bullet, and myself get stoned for 'preaching' antenna/coax theory. it seems that teaching coax theory is like a preacher having a sermon on sin. the congregation won't have it. or is that for meters??? oh well, i've caught he!! in the past for both. |
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