cobra 29 LTD and an 11 meter dipole

[deadhead]

howdy,

trying to setup my first CB base station so I figured I'd come straight to the experts. I have a cobra 29 LTD in my basement, and I ran coax up into my attic, and I strung a 11 meter half wave legth (18ft) dipole up in my attic. I honestly have no idea if this is a good setup or not. I'm still waiting on my SWR meter to show up at the front door, so I don't have one as of yet, but it should be here soon. I guess I have a couple of questions.Has anyone here used the same setup and have any gotchas I should be on the lookout for? Also, this is my first time at this, so even though I have a SWR meter on the way, I have absolutely no idea what I'm doing with it. I did power my radio up, and I noticed the red antenna light came on. I thought that was indicative of a short in the antenna, so I replaced the coax connectors, and can't find any opens or shorts, so is there another reason my red antenna light would be coming on? Any assistance would be greatly appriciated.

Thanks, Peace.

 

[towerdog]

I have used dipoles with CB. My advice, check SWR on ch.40, then on ch.1:
hopefully it will be higher on 40 than 1, then trim a little, but if its higher on 1 than 40 you might need re-cut the wire, you cut too short.
trim it equally on both ends, and trim a little bit at a time.
you might also want to think about making the bottom half of it by running coax into a pipe and screwing the shielding to pipe, coax balun or just have to coax feeding it 90 degrees off for about 1/4 wavelength. they work better when the coax does not radiate.

 

[W5LZ]

I don't have your exact set up but have used dipoles for some time. The biggest problem you may have is a difference in polarization, horizontal instead of vertical. Tuning the dipole is always to be expected, it's normal for any antenna.
One solution to that horizontal/vertical thing is to run one leg of that dipole vertically, the other horizontally. That's basically a one radial groundplane. Or, if you've got the room, just hang the thing by one end, let it hang vertically. Either will work.
It takes a while to learn how to use anything, so play with changing the antenna and reading the SWR meter. Lower readings are better than higher readings with SWR. But, danged near anything close to 1.5:1 is pretty good.
Have fun.
- 'Doc

 

[W5LZ]

I don't have your exact set up but have used dipoles for some time. The biggest problem you may have is a difference in polarization, horizontal instead of vertical. Tuning the dipole is always to be expected, it's normal for any antenna.
One solution to that horizontal/vertical thing is to run one leg of that dipole vertically, the other horizontally. That's basically a one radial groundplane. Or, if you've got the room, just hang the thing by one end, let it hang vertically. Either will work.
It takes a while to learn how to use anything, so play with changing the antenna and reading the SWR meter. Lower readings are better than higher readings with SWR. But, danged near anything close to 1.5:1 is pretty good.
Have fun.
- 'Doc

 

[Superidgit]

Hello there and welcome to boards, glad to have you.

Yup what you are doing has been done before. Is it the the greatest set up in the world? Probably not. Can you make this setup work? Absolutely!!

Here is a Link to a Dipole calculator KWARC Dipole Calculator
You make have already used one since you are pretty close in your length.

Good thing you are waiting for your SWR meter. You could possibly damage your radio buy transmitting with high SWR's. To check your SWR on your antenna, take your meter and place it inline between the antenna and the radio. Set your meter to calibrate. Key the mic ( do not speak into mic just deadkey). Then turn adjusting knob so that the meter is in the "cal" spot. switch meter to SWR and key mic again this should give you a pretty accurate reading. Here is a link that CBRadiomag guy did. ‪How to use a SWR meter - CBradiomagazine.com‬‏ - YouTube

Once you have your SWR readings you can begin adjusting the lenth of antenna. Some people cut , But I tend to fold when working with dipoles. Yes, this is gonna require running up and down the stairs a lot. But just simply fold the antenna wire back on itself a couple inches at a time. You do need to fold each end of your antenna as equally as possible. Use some tape or something to hold the fold in place while you run back down stairs to check SWR. I also think the Cobra 29 has the ability to check SWR's it may not be the most accurate check in the world but it will get you close enough that you can start talking.


Now your red light question, hmmmmm....

So you power on radio and the red antenna light comes on. Does this radio have Soundtracker (ST)? If so I am pretty sure that means you have that function enabled and is why you are seeing a red light. I just dont think the Cobra 29 came with an SWR warning light. I may be wrong and I am sure someone along the way will point that out to me. But if your radio has ST try turning it on and off and see if your red light goes on and off. If this isnt your problem you may have to provide a bit more details. Like does light go off if you unplug antenna, if you hook a different antenna up, yada yada and so on.

Just a couple of links that I think you might enjoy.

http://www.worldwidedx.com/cb-antennas/111992-very-good-swr-demo-link.html

http://www.worldwidedx.com/cb-antennas/71876-5-8-wave-dipole-citizens-band-radio-radio.html

I hope I helped. And once again Welcome to the boards happy to have ya.

 

[Superidgit]

Oh and BTW if you would please share with us what you learn.

Also if you can when routing and hanging your antenna try to avoid powerlines, appliances, or anything that might generate interference. Inside a home this can be kinda difficult. You may just have shrug and say, " Thats the best I can do." Which is fine. Who knows you may make some nice contacts if the radio gods allow it. I got to talk to someone in Virginia today on AM for a few minutes in my mobile.

Have fun and expirement.

 

[n0zna]

You need to check the swr,it is very important.

Dipoles are great antennas for dx.Not for local.The better antenna would be a half square antenna,antenna is horizantal and vertical.Its easy to make.9 ft horz,and 9ft vert.and then trim to best swr.I use one on 10-11-12 mtrs...73s de JW

 

[W5LZ]

Those 'half-square's and others like them (eg:'bobtailed curtain'), are vertically polarized 1/4 wave arrays. They have physical parts that are horizontal, but the radiation is vertical. They are also directional. They are not just for distant, or DX use, but can be used for 'local' stuff too since most 'local' stuff is also vertically polarized. And like any directional antenna, you will have people who hear you well and some who don't hear you well.
I think you will also find that where you feed the thing -can- make a huge difference in input impedance and the -type- of feed line used. Coax isn't suitable for all applications of those array type antennas without some 'help' from a matching device of some kind.
I don't know about yours, but my attic doesn't have the height/space to put one made for 11 meters (maybe for 2 meters though).
- 'Doc

 

[deadhead]

Since I'm just now getting started, and haven't even recieved my swr meter yet, let me go ahead and ask the question, now that y'all have me thinkin'... I want a good omni directional antenna that I can get good distance out of. What are my best choices? From what I'm reading so far, my dipole may not be the best for what I want. What do most folks use for base station setups?

 

[pro151]

You said the red antenna warning light came on when you powered the radio up. Did you mean when you keyed the mic or with the radio in the receive mode?

I don't recall ever seeing the antenna warning light come on in receive, only in transmit

 

[deadhead]

yes, sorry, I should've been more descriptive. The red antenna light only comes on when I key the Mike for transmit. I was under the impression that this meant there was a problem with the antenna, so I've gone back through my dipole, and replaced the connectors. I also tried it with another car antenna, and without an antenna plugged in at all, and I still get the red antenna light when I key the mike, so now I'm not really sure why it comes on at all? I've watched videos of folks using the same CB radio I'm using, and I do not see the antenna light coming on, so that confuses me even more. What I don't want to do is ignore the light if it is truly indicative of an issue that needs my attention. I'm also looking at other antennas for my base... would a IMAX-2000 be a step in the right direction? or would a ground plane antenna make more sense for a base station??

 

[Superidgit]

yes, sorry, I should've been more descriptive. The red antenna light only comes on when I key the Mike for transmit. I was under the impression that this meant there was a problem with the antenna, so I've gone back through my dipole, and replaced the connectors. I also tried it with another car antenna, and without an antenna plugged in at all, and I still get the red antenna light when I key the mike, so now I'm not really sure why it comes on at all? I've watched videos of folks using the same CB radio I'm using, and I do not see the antenna light coming on, so that confuses me even more. What I don't want to do is ignore the light if it is truly indicative of an issue that needs my attention. I'm also looking at other antennas for my base... would a IMAX-2000 be a step in the right direction? or would a ground plane antenna make more sense for a base station??

Howdy,

So your TX/RX light goes from green to red when you key your mic? I am pretty sure that means the radio has switched from Recieve mode to transmit mode. I do not think its indicating and problem with your antenna or radio.

As far as your antenna goes. The Imax is a pretty good antenna, however, I have heard reports that the Imax is prone to create interference with other electronic devices. That being said the higher you can get the IMAX the less likely you will have interference.

Your choice of antenna will be based on what you can afford and what you have room for. Here is a great link for some great antenna threads that ASW was kind enough to put together for us. http://www.worldwidedx.com/cb-antennas/113870-index-popular-citizens-band-radio-antenna-threads.html Robb put together a series of threads about chosing an antenna that is really good and informative.

Also in the Home brew section of the board BootyMonster and HomerBB have a couple great home brew projects they put together. HomerBB even buit a ground plane using Aluminum tape.

 

[deadhead]

Thanks for the info, and yes, my TX/RX light goes from green to red when I key my mic, but the antenna light under the tx/rx light also goes red when I key my mic. I should be able to get pretty high with my antennas, nothing really stopping me as far as I know. Is there a legal limit to how high a guy can put an antenna up??

 

[AudioShockwav]

The antenna warning light "should" come on at a swr reading of 3 or above...if anyone has been in the radio doing tuning, this may be adjusted wrong ( there is a VR ( vr 6 I think)that controls when it lights) Exactly what model of radio is it?
Sound tracker, or night watch sound tracker or the WX ST model or a classic....
I think 60 feet i can not remember any more, is the limit.

You really need to wait until you have the swr meter before you can move ahead.

73
Jeff

 

[Superidgit]

Thanks for the info, and yes, my TX/RX light goes from green to red when I key my mic, but the antenna light under the tx/rx light also goes red when I key my mic. I should be able to get pretty high with my antennas, nothing really stopping me as far as I know. Is there a legal limit to how high a guy can put an antenna up??

There me be some laws in your area that say how high you can go. You will have to check with your local government to find out.


Ok Ant light coming on.... Grrrr..


Is your radio grounded well? Also there is a pot that controls this light in the radio. But wait till you get your SWR meter before you go adjusting anything. I believe that light comes on when the radio senses a SWR of 1.5 or higher.
I think once you get the SWR down your light will go away.