| Author |
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Alsworld
| | Posted on Wednesday, January 09, 2002 - 12:27 pm: | 
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Hello all, I'm very good at being long winded so I'll do my best to reverse that here. Back into radio after a long hiatus. Very much an amateur with limited experience but think I've got the basics. Years ago bought a used President Lincoln cb/10 meter and got some accessories with it. Now setting it up primitively before I start spending any real cash. I've got an older radio book that helps and confuses me but working through it. I run no additional power (amplifier) but am using it as a base station. First question is antenna. I've now got it hooked up to an old 102" whip screwed into a mirror mount leaning against the wall in my garage. The mirror mount has about 10ft of 10 gauge copper wire running directly to a grounding rod. Using RG-8U for coax. SWR's are ok with 1.4:1 at each end of the CB bands and lower in the middle. I would like to temporarily put this antenna outside and try to make it work. Like many, I've got to hide it. I don't have enough coax to put it up in the tree just yet but think I can elevate it above the roof for now. This would put the top of the whip at about 17 ft. At this point, I'm not trying for worldwide communication but to make do with what I have an learn, learn, learn then do it right. This basic (ugly) system currently receives fairly good right now but am I at least on track? I've read a lot here an know that no one likes the 102" as a base but for now it will be mine until I'm more experienced. I've got a million more questions but will shut up for now. Thanks |
Vernonott
| | Posted on Wednesday, January 09, 2002 - 8:35 pm: |
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You don't know if you don't ask.As long as you can hold your SWR down , you won't damage any equipment.You have to experiment sometimes with what you have and talk to whomever you can reach. |
lugnut
| | Posted on Thursday, January 10, 2002 - 1:53 am: |
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I'm confused!!! |
bruce
| | Posted on Thursday, January 10, 2002 - 7:57 am: |
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Ament and to double check SWR use a 6 foot jumper coax to change the feed line from your antenna by 6 foot going to the SWR bridge. By adding and removing this jumper you will not allow your meter to be tricked by coax lengh |
Alsworld
| | Posted on Thursday, January 10, 2002 - 11:41 am: |
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Sorry for the confusion. I'll try the jumper to verify swr's. Headed out tonight looking for antenna pole to get it up higher than my first post. I guess my question is, with the cheap aluminum mirror mount the antenna is attached to, by running some heavy gauge copper wire from it straight to a grounding rod, is that a sufficient or proper ground? I will ground the antenna pole to the rod also. If I can make this system work, putting up a true base antenna should be a breeze....I hope. Looking at the Maco 5/8 commercial. Lot's of lightning here come spring/summer. I've also got a question on how importmant is the length of coax in relation to wavelength? With a 10 meter wavelength being 35 ft, I currently have a section of 51 ft of coax. That's 1 1/2 even wavelength. Should I try to keep the coax these lengths or does it really matter? |
bruce
| | Posted on Thursday, January 10, 2002 - 7:36 pm: |
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no the lengh of the coax means nothing if it effects your antenna you need to decouple the ant with ferite beads or rap a loop of coax at the base of the antenna.I have heard for many years the stories of cutting coax to match a antenna but lissen your antenna is 52 ohms your coax is 52 ohms your radio output is 52 ohms IF TUNED CORRECTLY there will be only a minor change in swr with changes in coax lengh if there is a large one say at 20 foot 1.2:1 and 30 foot 4:1 you got something very wrong with your antenna. NOW AS YOU GO FROM CH 1 TO CH 40 the reading will change tune your ANTENNA NOT COAX for the channel you want to use. Coax is not the same as a wave in free air the factors in coax run from .66 to .80 so you got to TIMES by that. Ground everything to one point check with your building dept people to see what code they use in your county... if you get hit and your ant is grounded to that code it will give you a better case if you need to collect on your homeowners. The height above ground may effect the antenna somewhat but if you are decoupled after the first 36 foot it should not matter rememberanother safety factor never mount a ant highter than the distance to your power wires if it falls you dont need 7200 volts going through you do you?
bruce
radio-doctor@juno.com |
Marconi
| | Posted on Thursday, January 10, 2002 - 8:35 pm: |
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Alsworld, if you get the V-5/8 maybe tune it with a resonant 1/2 wave line of multiples thereof, or tune at the antenna with a very short piece of coax. I use a 5' non-reactive line as feed into a non-reactive 52 ohm dummy load. This will help you stay out of line trouble when tuning the match. I do not encourage your current setup.
After you get your antenna tuned as best you can, you can run any random length of coax, but the shorter the better.
Marconi |
Alsworld
| | Posted on Friday, January 11, 2002 - 3:22 pm: |
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Thanks for all responses. I hate to show such ignorance but what is meant by "decoupling" the antenna? I have an idea but need to clarify as it will make Bruce's sentence make much more sense (to me). A lot of good points. Yep Marconi, only a temporary setup. Between Copper's forum and others I've found, one heck of a learning curve happening here. Thanks again. |
bruce
| | Posted on Friday, January 11, 2002 - 6:39 pm: |
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decoupiing the ant from the feed line ( coax) is done because if you dont and this is what the ground plane does keeps rf from going back down the coax if it does part of your power is being radiated form your coax's sheild ... not good.
the beads or looping the coax at the antenna form a choke the choke acts like a resistor and limits the RF from going past it... get any ARRL antenna book or handbook they explain this in detail
bruce
radio-doctor@juno.com |
Highlander
| | Posted on Friday, January 11, 2002 - 9:09 pm: |
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Bruce, how many turns and how big should the loops be(for 27mhz, rg-8) for the coaxial balun?
Is the radiating coax-shield problem the same thing as "common mode" rfi? |
bruce
| | Posted on Friday, January 11, 2002 - 10:45 pm: |
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highlander common mode??? well i havent heard that used but the sheld being a common ground makes sense to me. As for size i bet in on of the ARRL books some one a lot briter than me has a chart giving you just that info. Now i know over rg-8 the more beads you use the better but of course i bet after the first 10 your not going to gain much what i got there was a place that sold the beads in qst the name skips me but they were in calafornia i bought ones that went over rg-8 and put 6 or 7 for a 6 meter balum it worked real well all you had to do was heat shrink over them and you were done |
bruce
| | Posted on Friday, January 11, 2002 - 11:09 pm: |
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the place i got mine fron in 95 was amidon assoc in california last phone number 1-800-898-1883 it may be good still. |
Alsworld
| | Posted on Saturday, January 12, 2002 - 11:36 pm: |
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Well I guess I better end this thread with an update. Thanks for all the help. I tried my original setup with some pretty miserable and unacceptable swr's. I knew I'd have to work through it but determined I had a bad connector on some old coax. Headed up to the local Radio Shack for a new connector and grounding wire and lo and behold here sits a 1/2 wave 10 meter/CB base station antenna on clearance for $24 (reg $69.99). Well I haven't read anything good about Radio Shack antenna's and figure they aren't so good but a brand new 17ft'er for $24 was just too good to pass up. Sooo... I set about erecting this pole and tuned it. SWR's are better than I ever expected (yes even with a jumper). I put it on top of a 20 ft pole so it reaches about 37 ft, pretty close to one full wavelength. Grounded it well and I'll be damned if I didn't hear Tokyo Japan giving a hollar on 10 meter! I've heard the skip but never that far. Anyway, my setup is not so crude afterall even though I realize it's not the best antenna. I'll probably order a ground plane for it. I figure I'm just starting out with my first base station and I still need to learn so much more. I've spent more on pizza than this antenna so I don't feel so bad even if it turns out it sucks. I do have a problem with bleed over through the television, even with a low tvi filter installed inline but I'll save that for another thread. Got to work on the road for a week. I'll work that question on a new thread upon returning home.
Highlander - check out this site http://members.tripod.com/~cb_antennas/coax_basics.html Page 6 gives your answer but my printer did not catch it all but it answers your question. |
Warchild
| | Posted on Tuesday, February 05, 2002 - 4:36 pm: |
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can someone tell me the best way to ground my ant. i have it on 25ft masst on the sied of my house. and will it help me get out bater??? thanks . |
Tech181
| | Posted on Tuesday, February 05, 2002 - 8:25 pm: |
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Warchild,
Pound an eight foot solid copper rod (leave about 8" sticking up) into the earth. Be careful of foundation footers, septic/sewer lines, electrical lines, water lines, etc.
Attach one end of a 6 AWG copper cable securely to the copper rod and the other end to the mast or the clamp your antenna is held to the mast with.
Steve
Tech181
Tech181@copperelectronics.com |
BLACKSMITH663
| | Posted on Tuesday, April 29, 2003 - 1:49 pm: |
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hey guys,get back to basics.
elevate ant. to 36 ft. (first wavelenght)
attach ground cable (not coax) from base of ant. to ground rod, salt it down (keeps it wet)
do not rely on pole or coax to ground, INSTALL ONE!! tune ant. pot (inside radio) to max power while holding dead key (mike gain off) tech 181 is right on .... catch ya
26.9050mhz. or 27.2650mhz. THE BLACKSMITH 663 |
