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Message |
    
Cm3885
Advanced Member
Username: Cm3885
Post Number: 501
Registered: 12-2003
| | Posted on Thursday, July 08, 2004 - 1:44 am: | 
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I dont get the peaked radio part. I run my radios all peaked and most of the time my swrs are a 1.2-1.. Ive never had problems..
Sooooo i operate mostly on 27.285 mhz with RG 8 U coax so my proper lenth would be what???
Hope this is right..
27.285
divide 492 by 27.285 = 18.03
Multiply 18.03 by .66 velocity factor
and i get..11.8'
11.8' X 4 is 47.2' for my lenth to go from the antenna to my radio here in my room...
Dunno if i did this right. this stuff is kinda above my head...
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Geekster
Member
Username: Geekster
Post Number: 56
Registered: 6-2004
| | Posted on Thursday, July 08, 2004 - 8:45 am: |
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Great links!
I am reading up on the train waves, resonant, non-resonant feedlines at the moment. All feed-lines are resonant to an extent according to Terman's theories. If I stumble across anything interesting I will post it here and on my website.
I am in process of Power vs. Distance right now for ground wave...
Thanks for the links. |
Cm3885
Advanced Member
Username: Cm3885
Post Number: 504
Registered: 12-2003
| | Posted on Friday, July 09, 2004 - 2:55 am: |
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Ok..
Heres what i have in coax..
Cable experts RG 8U.. 95% shield..
Dont have a clue what the actual velocity factor is.. Im assuming its 78 or 80% since it is foam PE coax..
I talk normally on CH 28 27.285 and move away frm home channel a lot so what would i have to cut it to lenth??
I cut my coax on my beams at the folkes to 1/2 wave multiples and have had pretty good luck but thats been a while ago and i cant remember if i did it exactly what the figures came out to.. All i know is the moonrakers work great!! |
Tech808
Moderator
Username: Tech808
Post Number: 2895
Registered: 8-2002
| | Posted on Friday, July 09, 2004 - 8:41 am: |
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Somehow I must have must have missed something and been doing everything wrong for years.
I run the amount of coax I need with a little extra and adjust the antenna using my Palomar R-X Noise Bridge & SWR / Watt Meter for the lowest possible SWR I can get.
However i did give all of my Coax & Jumpers a Test last night to try and find the True Answers! 
However I did not let the radios know if they were stock or peaked / modified. (I kept this a Secret from them.)
I hooked 4 radios Peaked & Un-peaked from 4 watts to 200+ and used Stock Mics and Power Mics (Hand & Desk) and some with echo, up to my SWR / Watt Meter and then and asked them all the exact same questions.
The Questions I asked my Coax were:
#1 ~ Can you tell which radio is the 4 watt, 20 watt, 50 watt or the 200+ one?
#2 - Does your SWR Change with each radio?
#3 ~ Are you mad at me for not getting the calculator out and measuring you before I cut you?
#4 ~ Are you mad at me for just cutting your head & your feet off and soldering PL-259s on you and adjusting the SWR at the Antenna?
Sad to say I guess I have some VERY DUMB COAX as none of them answered any of the questions or noticed the difference between the different radios or the different lengths of coax running the the different antennas.
So my conclusion is they are either very happy and perform very well or they are afraid to not perform well as they know I will re-place them and whack them into Jumpers. 
NOTE!
All tests were performed under Highly Professional Conditoins with my coax cutters sitting in plain sight of all coax.
Lon
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Cm3885
Advanced Member
Username: Cm3885
Post Number: 505
Registered: 12-2003
| | Posted on Friday, July 09, 2004 - 12:34 pm: |
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LOL!!!!!!! :-D
Its good to know some on here still have a sense of humor.. That was funny Lon!!!
Like i said i have all my radios peaked and tuned some do 30 watts some do 220 watts but ive never had any ill effects from my coax.. Yeah i like to keep my SWRs well below a 1.5=1 and ill admit i do get fussy trying to get my SWRs below a 1.5. I prefer a 1.2-1 as i found my radios seem to work much better at this reading. Now my antennas coax up at the folkses are all cut to 1/2 wave multiples and they work fine but like i posted i dont belive they are cut to exact lenth. all i know is they work very well.. |
Skunkweed
Junior Member
Username: Skunkweed
Post Number: 13
Registered: 1-2004
| | Posted on Friday, July 09, 2004 - 5:06 pm: |
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... should be as long as you need. Mike |
Tech833
Moderator
Username: Tech833
Post Number: 762
Registered: 8-2002
| | Posted on Friday, July 09, 2004 - 5:29 pm: |
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I give up. This post shall serve as my official notice of giving up on this subject. |
Tech808
Moderator
Username: Tech808
Post Number: 2899
Registered: 8-2002
| | Posted on Friday, July 09, 2004 - 7:20 pm: |
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NOTE!
As this topic was getting way out of hand, I made the above post to lighten things up ONLY!
I have had to refuse & edit several posts because of differing points of view that got carried away and way off the topic.
I made the post above to hopefully give every one a laugh and to try and calm some of the members down.
It was not meant to be taken seriously by anyone or to deter from the topic that was posted.
Lon
Tech808
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Rover
Junior Member
Username: Rover
Post Number: 12
Registered: 2-2004
| | Posted on Friday, July 09, 2004 - 7:26 pm: |
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I don't mean to be critical at all, but I truly do NOT understand why people spend so much time worrying about coax length. I must say that in no other radio area is this subject taken so seriously than in CB radio.
I started fooling with antennas when I was in high school (ham and hobby radio mostly). I didn't even use a CB until I was in college, and NO ONE under whose training I was EVER mentioned that their coax had to be a certain length. HONEST! Had this been the case, I am positive that someone would've mentioned it during those early years when CB radio was outside my interests or experience. During the time that I was learning about making HF radios work, I was getting excellent results with the old tube transmitters, dipoles, and mobile whips, and coax length never figured into the calculations!
We used ammeters to measure antenna current, and florescent tubes to see how well the antennas were working. One way we knew our antennas were set pretty close to frequency was that we could hold a floresc. bulb up to one antenna with NO signal transmitted, and key up on the same frequency from another nearby mobile. If the "passive" antenna struck, or lit up, we knew we were in the groove.
RF theory is the same from DC to Daylight. It applies to 100 KHZ to 1000 KHZ, etc.
Therefore, I will only say it one last time and, like Tech833, I will let the subject drop. Coax length does NOT matter except to keep it as short as possible. Tune the ANTENNA, keep the coax (if that is what you are using) SHORT as possible, and FORGET all the important-sounding formulas and gobbledegook. The Velocity Factor does NOT matter!!!!!!! For-Get-About-It. It sounds important, but the only thing it means is the speed at which a radio signal travels from point A to point B. Period. It does NOT affect the overall SWR, or the performance of the antenna.
Here's another point to ponder. 492/freq in mhz equals a wavelength in FREE SPACE. There is more resistance in wire, for example, so the actual divider should be 468/freq in mhz. For half-wave dipoles, then divide by 2. A Quarter wave is 234/freq in mhz. That 492 divider is actually useless for figuring wavelengths in solid mediums.
People are going to believe what they wanna, and that's fine. I must admit I do snicker a bit watching people tinkering and snipping coax to get that exact number of "SWRS" (how many "swr's" are there in one feedline ;)) But riddle me this: If I am operating on 3.915 MHZ in a mobile, according to this flawed formula (and it IS flawed, sorry but it IS), then I would have to have about 60 feet of coax in my car, right? That's what your coax length urban legend is saying, right? What am I going to do with 60 feet of coax in an S-10 pickup? Coil it up in the bed (another CB urban myth). HAH! That, makes a nice attenuating RF choke. Coiling up excess coax--another popular CB legend. So, seriously, tell me what one is to do with 60 feet of coax in a little pickup? If he has the ability to operate on thousands of frequencies, or bands, he'd have to have a specific length of coax for EACH band he operated. That would make the vehicle a coax nightmare!
Yet, thousands of commercial, amateur, and military stations operate multiple HF bands with ONE coax, none of which of them happen to be a particular length. Many of these electronic engineers NEVER heard of coax length. Mine happens to be about 10 feet long.
Believe what you like, and I make this long post with the utmost respect. Coax length equals that distance that is directly proportional to the distance between the radio and antenna feedpoint! NO more, no less. OTH, I am waiting to hear a logical explanation of the scenerio I outlined above (I have used this before, and NO Coax Length guru has EVER been able to explain why a station operating at 3.915 MHZ can do so with a random length of coax of about 10 feet or less in a pickup truck. LOL! (The reason is, he CAN'T!) Cuz it just ain't so!!!!!! There are some special situations, but let's deal with the simple question first, OK ;)
73
Rover |
Cm3885
Advanced Member
Username: Cm3885
Post Number: 506
Registered: 12-2003
| | Posted on Saturday, July 10, 2004 - 12:50 am: |
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Why did i use .66??? Maybe it was a typo. I dunno! I do make a mistake now and then.. Sorry bout that there guy! I looked on my cable and all it says is RG8U 95% and thats it.. |
Pig040
Intermediate Member
Username: Pig040
Post Number: 487
Registered: 7-2003
| | Posted on Saturday, July 10, 2004 - 10:25 am: |
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Hey Lon.
You should have told us it was a joke in the post, I spent half the night trying to get my coax to tell me if it felt good, or it felt like it needed a trim! The radios wouldnt talk either, I thought they were treating me like a red headed step child. I even tried to bribe them to talk with a plate of Oreos, still nothing!
Lol, Rich |
Tech808
Moderator
Username: Tech808
Post Number: 2904
Registered: 8-2002
| | Posted on Saturday, July 10, 2004 - 12:42 pm: |
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Sorry Rich but I might of had an advantage as the 1st Sargant was thinking of mean things to do to KB and I think our Coax was afraid to answer.
Lon |
Tech833
Moderator
Username: Tech833
Post Number: 766
Registered: 8-2002
| | Posted on Saturday, July 10, 2004 - 2:36 pm: |
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The meanest thing you could do to KB is pose as his doctor and tell him he won't see his next birthday unless he becomes a strict vegetarian. |
Rover
Junior Member
Username: Rover
Post Number: 13
Registered: 2-2004
| | Posted on Saturday, July 10, 2004 - 10:53 pm: |
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Dang it. I caught an error in my post. 492 is the HALF WAVE-length in free space; 468 is the divider for 1/2 wavelength thru a solid medium, and 1005/freq in MHZ = a full wavelength in free space. Sorry.
(Anyone wanna take a shot at my posts above? LOL!)
73
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Moonshadow
Junior Member
Username: Moonshadow
Post Number: 42
Registered: 7-2004
| | Posted on Friday, August 06, 2004 - 6:57 pm: |
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Wow, talking radios and coax??? I bet they listen as good as my cats do......lol!
Poor Shirley, I feel your pain, CM3885 talks to walls ;)! |
Keithinatlanta
Intermediate Member
Username: Keithinatlanta
Post Number: 340
Registered: 3-2003
| | Posted on Friday, August 06, 2004 - 7:49 pm: |
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Sorry folks, my foodservice calculator does not have that many numbers.
Keith in Atlanta |
