| Author |
Message |
    
Dx431
| | Posted on Tuesday, April 30, 2002 - 11:22 am: | 
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Here's something I thought was interesting......check out the link below.
http://www.qsl.net/w8cwe/coaxleng.html
DX431
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bruce
| | Posted on Wednesday, May 01, 2002 - 7:44 am: |
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HOW MANY TIMES HAVE YOU SEE ME POST THAT ??? COAX DOES NOT TUNE YOUR ANTENNA |
Taz
| | Posted on Wednesday, May 01, 2002 - 1:48 pm: |
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haha. lol |
Znut
| | Posted on Wednesday, May 01, 2002 - 6:16 pm: |
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We could drag this debate into how antenna height affects performance.
I don't worry about coax length in either case, unless I have a reason to think I should have an unacceptable SWR and my meter says its OK. Some antennas read as DC short, some as open. This can make a resonant length of coax "act" like a 50 ohm load. Hence, you will see a decent SWR @ the meter. Usually a coincidence for me.
Still, I would like to hear what more folks think about antenna height. It might be appropriate to start another thread but I'll get the ball rolling here.
Am I correct to consider antenna height only in terms of maximum obtainable with most antennas? I mean my antron 99 has a groundplane, why should I worry about the mast being resonant? The only time I would think about that is if I was working a low enough freq that I could not decouple the antenna at the base of it or have a groundplane. Otherwise I would get it as high as possible. More food for thought folks?!?!?!
Znut |
Znut
| | Posted on Wednesday, May 01, 2002 - 6:19 pm: |
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Here's my summary:
Coax; as short as possible.
Antenna; as high as possible.
(9 times out of 10 in both cases)
Znut |
blacksheep
| | Posted on Wednesday, May 01, 2002 - 7:26 pm: |
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easy bruce,no need to yell. |
bruce
| | Posted on Wednesday, May 01, 2002 - 9:07 pm: |
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znut, blacksheep your both correct ! |
ss8541
| | Posted on Wednesday, May 01, 2002 - 11:16 pm: |
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if the outerbraid is radiating, coax length does make a difference since now the coax is part of the antenna system. a balun will fix this if that is the case. |
Bill Maverick
| | Posted on Thursday, May 02, 2002 - 1:07 pm: |
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Could anyone get his formula to work? I have trouble with the example. |
Colt
| | Posted on Thursday, May 02, 2002 - 5:04 pm: |
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What I'd like to know is simply this. If I use only the SWR meter that is built into my radio and have only the coax that came with the antenna (mobile) between the radio and the antenna, eliminating all jumpers, meters, amplifiers and such from the equation and get the SWR below a 2 anywhere on the band that I talk, shouldn't my finals be safe? I'm not worried about getting the most true SWR reading I can get and squeezing that extra 1/4 of the width of an S-meter needle on the recieveing end of my xmit. I just want to have excellent quality of operation and no worries about overheating my finals.
Right now my Wilson 500 has an SWR of about 1.6 at 26.800Mhz and at 27.600 Mhz, with mostly a zero across the CB band using the meter built into my radio (President Lincoln). This is about all the range I want so far as where I can operate.
I know these readings are probably not the "true" readings that could be obtained under perfect conditions using a high quality SWR meter. But, generally, can't I count on this being "good enough"? |
Znut
| | Posted on Thursday, May 02, 2002 - 6:15 pm: |
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I haven't even tried the formula on a coax. Coax is simply the means to feed the signal from my rig to my antenna. Not to tune. Shorter is better.
Znut |
bruce
| | Posted on Thursday, May 02, 2002 - 6:25 pm: |
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what formula ? |
Sofkow
| | Posted on Thursday, May 02, 2002 - 8:59 pm: |
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Anyway you look at it, the shortest distance between point A and point B is a straight line. Not a looped or curled one. Anyone that says there is ABSOLUTELY no difference between the stregnth of an energy flow at 50 ft. versus 100ft. is dead wrong... |
bullet
| | Posted on Thursday, May 02, 2002 - 11:10 pm: |
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you know there are things like this coax length that should be put in a FAQ section so its not asked every month or so. |
bruce
| | Posted on Friday, May 03, 2002 - 4:54 am: |
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Here are coax lenghts if you have too cut it
again decoupled coax will not tune your antena
Rg-58, Rg-8 ( foam ) 1/4 wave in inches
L= (5540/f)*(.8)
for NON FOAM
L= (5540/f)*(.66) |
bruce
| | Posted on Friday, May 03, 2002 - 5:14 am: |
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OOPS that formula was for 1/2 wave.... hey its 5am |
Ohiobiker
| | Posted on Friday, May 03, 2002 - 6:59 am: |
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I have heard all I want to heart about coax length....I am going to Radio Shack and buying that little antenna that screws in the back of all my radios. Then I will not lay awake all night with nightmates of having the wrong length of coax. I guess I will look very weird (at 6'1 280lbs) up on my tower trying to hold my coffee, Microphone and my FT101-Z. While trying to log my contacts durring a pile-up. Bruce if your willing to help me while I work the DX, I could come over and climb your tower with you also if your going to go the way of the little screw in antenna along with me?...Just ribbing you guys...Have a nice Day~~~OHIOBIKER~~~ |
Colt
| | Posted on Friday, May 03, 2002 - 2:40 pm: |
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Well, anybody gonna answer my question?! |
bruce
| | Posted on Friday, May 03, 2002 - 6:38 pm: |
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ohiobiker im wondering what you put in that coffie and if i could have you send me some |
bruce
| | Posted on Friday, May 03, 2002 - 8:49 pm: |
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Sorry i got carried away colt yes your radio should be safe one way you can check is to monitor the current on transmitt if it is about the same accross the range of frequencys your useing chances are your finals arnt getting creamed even if they are disipating more as the vswr goes up most like the 2sc1969 are tough little buggers. Also check you case around them at lowest vswr and higest vswr and see if you can detect a change in heat if not they are happy and you should be safe .... does that help?
bruce |
Colt
| | Posted on Saturday, May 04, 2002 - 12:37 am: |
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Thanks, Bruce! It's nice to have someone at least take the time to acknowledge. Reminds me of how things are on the air sometimes these days. Everyone is so busy hearing their own heads rattle they don't even notice someone looking for a break.
The feeling the back heat sink sounds easy enough, but how do you monitor the current? |
bruce
| | Posted on Saturday, May 04, 2002 - 6:23 pm: |
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hook a amp meter up and it should work |
bruce
| | Posted on Saturday, May 04, 2002 - 10:21 pm: |
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colt if you need any help e-mail me |
antenna man
| | Posted on Sunday, May 05, 2002 - 2:06 pm: |
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Geezz! Another lenthy coax lenth discussion. Just get enough of the damn stuff to go between the radio/amp/meter and the antenna, get a good SWR and talk on the S.O.B!! Its not worth the hassle to go through the forumulas and textbooks to find out how much coax to go beteen a run of 50' or less. Its just CB!!! JMHO thats all guys!!! ;-) |
SNOOPY
| | Posted on Monday, May 06, 2002 - 9:59 am: |
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MY WIFE SAID LENGTH DOESN'T MATTER? |
RCI2990
| | Posted on Tuesday, May 07, 2002 - 11:21 pm: |
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..but its how you use it riiiiight??? ;-) |
THEOTHERGUY
| | Posted on Wednesday, May 08, 2002 - 9:42 am: |
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SHE TOLD ME THE SAME THING? |
