Best portable base cb antenna

[CowboyCody]

I am in a interesting situation, I am currently living in a 5th wheel camper pretty much full time. Right now I am using a 1/4 wave groundplane that I built which is mounted on the top of my air conditioner. I want to move up to something that will perform a little better and get it away from the a/c so it will be quieter. I was thinking of just buying a imax2000 but I am concerned with having no groundplane it won't be that great at the low heights I'm planning on mounting it. I was thinking 2 sections of pipe would put me at 20 feet which will be higher than I am now. I also don't want a huge groundplane on top of my camper, it would stick out like a sore thumb and would be hard to take down when it is time to move. I know there is no perfect antenna, but what is my best option in my situation? I am leaning towards a vertical dipole for the simplicity of it, but I don't think it would be much better than what I have. I was looking at astroplane's and I considered building myself a loop out of PVC that I could take apart or lay on the floor of the camper while moving. Any opinions or ideas are appreciated !

 

[HomerBB]

A few years ago I traveled the country in a conversion bus. For its lack of physical intrusiveness, and ease of use, I carried an A99 around with me. I also had two 10' sections of fence top rail. This provided me with a very quick and easy means of putting the antenna in the air and breaking it down and storing for travel.

However, in my opinion if you are wanting something simple and easy, but less likely to bleed because it has no GP radials on it, I would suggest making yourself a dipole of this order:

Vertical Sleeve Dipole - How To

This is a center fed dipole, a full half wave antenna, that has the coax running up through the bottom tube which provides for easy vertical mounting. Read the thread at the link above to learn more.

 

[CowboyCody]

Thanks, that is a great idea! I wonder what the angle of radiation would be compared to a 1/4w groundplane at modest heights

 

[HomerBB]

I don't know. It is a little longer, and would be a little higher, so it may be slightly better.

 

[CowboyCody]

Yeah, it is hard to tell. The more I think about this design the more I like it, you are basically creating a sleeve balun with the lower element, so common mode should not be a problem, right?

 

[HomerBB]

It may would work that way except that this is a dipole. It has high voltage at the ends, or in this case top and bottom, so you should use a coax choke on it just beneath the coax exit from the bottom of the antenna.

 

[BOOTY MONSTER]

well , if you don't mind leaving the lower cone together and assuming you have room in the 5th wheel when you're rolling a vector 4000 could be a option . if you leave the lower 10 ft of vertical and 30 inch diameter cone together , you'll just have a few 10 ft'ish section for the remaining vertical .. all about the same length as the two pieces of fence rail your gonna use for mast .

sorry .... couldn't resist

 

[W5LZ]

I think that a typical half wave antenna will do at -least- as good as the 1/4 wave you're using now. Having it at the same height, or higher, would also be of benefit I think. End fed ot center fed isn't going to make a huge difference, the antenna is still a half wave and will behave as one. The biggest difference between the two methods of feeding one is the resulting input impedance. That can be handled in a number of ways, take your pick. I wouldn't worry a lot about 'take off angle', it just isn't as important as some people think. I also think that the 'practical' aspects will determine what will work the 'best' for you. Higher is better, but can you always get that higher mounting, are 'they' going to allow it? That sort of think.
Going from a 1/4 wave to a half wave will make a difference but that difference isn't going to be huge.
Have fun.
- 'Doc

 

[CowboyCody]

Thanks guys, I think I will try homers design mostly because it is cheap and stealthy compared to a ground plane antenna. If it dosent work out I guess I'm not out much and I can buy something. I'm thinking the extra height alone will make it worth the effort. I was doing some reading elsewhere last night and some were saying that with a vertical dipole it was beneficial to feed it off center some, so that the upper element is slightly longer by a few inches. Do you guys think there is anything to that ? I don't see how it would do much myself.

 

[CowboyCody]

Another thing I was thinking about, I have a piece of 3/8" aluminum rod from my groundplane, is there anything that says both sides of a dipole have to be the same diameter? If I use like 1 1/2" pipe for the lower, can I use the 3/8" rod for the upper? I know it's a dipole and it will work, I'm just trying to make sure it will work well.

 

[Needle Bender]

I've had the best performance from the Imax 2000 mounted on a 16', 4-section, military push-up mast I bought at a ham swap for $25 and which telescopes down to about 5'.
I've welded a side mount to the vehicle where it, or a screwdriver antenna, can mount.
When using the telescoping mast on that mount the antenna base is right at 18' above the ground.

I also purchased a Proton & an A99 to test against the Imax & each other.

I saw the weakest performance from the 17' 6" A99, better performance from the 19' Proton, but the best performer is the Imax 2000.

It's about 15-20 miles out where the Imax is still a viable performer but the 1/2 waves have died out, when parked & talking around mostly flat & level terrain.

 

[CowboyCody]

Thanks, I may just have to buy one so that I can compare it.

 

[CowboyCody]

I have been looking at the Siro Gain Master and reading all the good reports on it. Would this antenna be a good cantidate for this application or not? I am willing to spend the extra money if it will work better without the need for common mode chokes or radials.

 

[Robb]

The Sirio GainMaster isn't what comes to my mind when the word 'portable' is used in the same sentence.

However, a A99 or an Imax 2000 does come to mind when I think of the word 'portable'.

 

[gamegetter]

THIS

I think that a typical half wave antenna will do at -least- as good as the 1/4 wave you're using now. Having it at the same height, or higher, would also be of benefit I think. End fed ot center fed isn't going to make a huge difference, the antenna is still a half wave and will behave as one. The biggest difference between the two methods of feeding one is the resulting input impedance. That can be handled in a number of ways, take your pick. I wouldn't worry a lot about 'take off angle', it just isn't as important as some people think. I also think that the 'practical' aspects will determine what will work the 'best' for you. Higher is better, but can you always get that higher mounting, are 'they' going to allow it? That sort of think.
Going from a 1/4 wave to a half wave will make a difference but that difference isn't going to be huge.
Have fun.
- 'Doc

AND give this a try with your 1/4 wave:

http://www.bencher.com/pdfs/00361ZZV.pdf

at the very end of page 3 and into page 4 are some mobile home and rv install tips.

"Fortunately, the metal bodies of both MHz and RVs can be used as highly conducting ground planes for
vertical antennas in exactly the same way that automobile bodies, etc., provide the ground system for
shorter vertical antennas for mobile operation."