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  #1 (permalink)  
Old 01-23-2012, 4:24 AM
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Default Mobile CB antenna as a base antenna?

Can a stud mount mobile antenna be effectively used as a base antenna? I know a mag-mount can be used with good results on a metal roof, I've done that. But what about bolting a stud-mount antenna to a 30' tower?

I'm thinking something like the Wilson 2000 using a mirror-mount clamp. I really like Wilson antennas, and would like to have a do it all mobile/base solution. I dont know if this can be done without causing all kinds of SWR and grounding issues, but I'd like to know. I've seen those ground-plane radial kits for mobile antennas, dont know if that would be of any use here.

I want to do this so I can have a decent base antenna that can be easily transfered to the car for road trips, maybe once or twice a year. On the car I would use one of those Universal 3/8 x 24 Mag-Mounts for studded antennas.
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Old 01-23-2012, 6:09 AM
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Ok, I found this article: A Stealthy Homebrew Vertical Dipole Antenna Using Mobile CB Antennas

He uses two fiberglass whips on the same bracket, one hot, one cold. I'm learning antenna theory here, so correct me if I'm wrong but the "cold" antenna is basically the ground plane, right?

If this is a good setup, I wonder how well one of these would work with two 102" stainless whips, especially in comparison to 1/2 wave base antennas (considering the whole assembly would be roughly the same size).

I found some "No Ground Plane" setups for RV's and whatnot, and I guess that would get me a mobile antenna on my house, but then it would be a hassle to transfer to the car.

And maybe to help me understand and learn a bit more, where/what is the ground plane when you use a dedicated base antenna like an A99? Is it the tower? I know they have radial kits for those, but what is the ground plane if you dont use the radials?

EDIT: If building a dipole using a commercially available mobile antenna, couldn't you use an appropriate length of "all-thread" or some conduit as the ground plane? Versus buying two antennas and basically wasting one as a ground? Of course, I guess all of this is moot if the tower is a suitable ground.

What about grounding of the radio chassis? In the mobile environment, everything grounds to the car body. But if I'm using it as a base, my power supply is grounded to the building, my tower is grounded to its own earth ground, and the antenna can be grounded wherever I want I guess, depends on how I mount it.

Sorry for all these questions and off tangent ideas. My brain has really latched onto this antenna theory thing and I'm trying to learn so I can experiment without damaging any equipment.
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Last edited by Baskt_Case; 01-23-2012 at 6:54 AM..
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Old 01-23-2012, 6:51 AM
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Just get a Antron 99 for your base Antenna I got mine new for $69 .Then save some money and go get a Wilson for your car .The lil Wilson you can get for around $30 new .
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Old 01-24-2012, 3:00 AM
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Originally Posted by freqs View Post
Just get a Antron 99 for your base Antenna I got mine new for $69 .Then save some money and go get a Wilson for your car .The lil Wilson you can get for around $30 new .
Whats the fun in that?

I'm more brain-storming than anything. And, I really dont want something quite as large as an A99.
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Old 01-24-2012, 8:19 AM
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Quote:
Originally Posted by Baskt_Case View Post
Ok, I found this article: A Stealthy Homebrew Vertical Dipole Antenna Using Mobile CB Antennas
...

EDIT: If building a dipole using a commercially available mobile antenna, couldn't you use an appropriate length of "all-thread" or some conduit as the ground plane? Versus buying two antennas and basically wasting one as a ground? Of course, I guess all of this is moot if the tower is a suitable ground.
The lower antenna isn't wasted, it is an actively radiating element. A way of thinking about ground radials, if they are used instead of the lower leg, is as a mirror for the remaining active element. This gives the correct impedance matching, but doesn't actually put out any signal on its own. All else being equal, using another antenna for the lower leg should double radiated power.

That's a pretty neat design at the link you posted. Using those continuously loaded Firestiks let him shoehorn an 18' dipole into 8', that's some cool engineering. BTW, Firestik sells a pre-made 5' with ground radials (IBA-5) all ready to go for attics; you can find them for about $40. But that's not nearly as cool as that DIY dipole.
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Old 01-24-2012, 11:15 AM
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Quote:
Originally Posted by Baskt_Case View Post
Whats the fun in that?

I'm more brain-storming than anything. And, I really dont want something quite as large as an A99.
Because it's simpler and Antron 99 has been around for years and is very good. BUT if you think you can design a better antenna go for it [personally I think your foolish]
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Old 01-24-2012, 5:54 PM
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As for that lower 'leg' of a vertical dipole not radiating, it certainly does (just like those radials on a groundplane antenna radiate).
- 'Doc

Last edited by LtDoc; 01-24-2012 at 6:01 PM..
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Old 01-25-2012, 3:11 AM
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Originally Posted by PrimeNumber View Post
That's a pretty neat design at the link you posted. Using those continuously loaded Firestiks let him shoehorn an 18' dipole into 8', that's some cool engineering. BTW, Firestik sells a pre-made 5' with ground radials (IBA-5) all ready to go for attics; you can find them for about $40. But that's not nearly as cool as that DIY dipole.
Well, come to find out, there are readily available mounts just like his. AKA the HamStick dipole. Guess he gets the satisfaction of building it himself though.
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Last edited by Baskt_Case; 01-25-2012 at 3:13 AM..
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Old 01-26-2012, 12:06 AM
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Conduit or all thread would work just fine. It needs to be 1/4 wavelength long (roughly somewhere around 102 to 108 inches long) You need to make sure you have a good electrical connection, don't rely on just metal touching metal, especially with galvanized conduit or rod. You can make pretty nice antennas out of copper pipe, it's relatively cheap, easy to work with, light, and you can solder it easily. In fact, you could make the whole thing out of copper pipe and have a pretty good dipole.

Nothing at all wrong with making your own antennas. Anyone can buy one, stick it up in the air, but you will learn a lot more, as well as have the satisfaction of knowing you made it yourself. I started off long ago, in my teens, with CB. I made a few of my own antennas, bought a cheap HF tuner and tried tuning up random wires, etc.

If you mount on a tower, put it on top. If you can't, you need to mount it in such a way as to get it as far away from the tower as you can. Ideally you want to be at least 1/4 wavelength alway from the tower or it's going to be directional away from the tower leg.

If you have a high enough mounting point, you can try making a simple wire antenna. You can play around and learn a lot at the same time. If you have fun with it, you can move on into amateur radio and have access to more modes and frequencies.
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Old 02-04-2015, 7:27 PM
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Default Cool Dipole

This setup apparently works pretty well, so let me pose a question about using a pair of 102' stainless steel whips. Will this same setup work with 2 102' whips?? A single 102' is really pretty darn good as well as I can recall. I used one in the early 60's, until the fiberglass ones came out. I am thinking about trying the 102' like he did with the fiberglass ones. The big question is will it work, and if not why? DonS
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Old 02-04-2015, 11:13 PM
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A 102" whip is quarter wave for CB, so it will need a ground plane or some sort of counterpoise to tune up right.

You can try two whips using one of these brackets, it'll create a simple dipole antenna:
Dipole Mount

Actually, you could build one easier using some copper wire, but if you have the whips laying around, it's worth a shot.
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Old 02-05-2015, 8:26 AM
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Yes the grounded or lower leg of a vertical dipole radiates the same as the hot side and equal RF currents flow in both elements. A 1/4 wave vertical with a single ground radial is simply an inverted V dipole and the single radial radiates.

However, multiple equal length ground radials heading in opposite directions like most CB ground plane antennas have DO NOT RADIATE. There is equal but opposite RF currents flowing in the radials, which cancels radiation leaving only the vertical element as the radiator.

This is why a 1/4 ground plane puts out slightly less singal than a 1/2 wave vertical center fed dipole or end fed 1/2 wave like an Antron 99 or similar, half the antenna is not radiating in the ground plane.
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As for that lower 'leg' of a vertical dipole not radiating, it certainly does (just like those radials on a groundplane antenna radiate).
- 'Doc
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Old 02-05-2015, 8:32 AM
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If you are proposing making a dipole with two 102" SS whips then yes, it makes a 1/2 wave dipole. The impedance will be higher than 50 ohms and will not match very well to 50 ohm coax, Usually lengthening the elements slightly will lower the resonant frequency but bring the match in a little better.
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Originally Posted by dswaff View Post
This setup apparently works pretty well, so let me pose a question about using a pair of 102' stainless steel whips. Will this same setup work with 2 102' whips?? A single 102' is really pretty darn good as well as I can recall. I used one in the early 60's, until the fiberglass ones came out. I am thinking about trying the 102' like he did with the fiberglass ones. The big question is will it work, and if not why? DonS
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Old 02-05-2015, 9:28 AM
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Also with a vertical dipole the coax should leave the antenna at a 90 degree angle for at least a 1/4 wavelength for best results.
BB
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Old 02-05-2015, 10:13 AM
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Anyone can go out and buy an antenna put it up and use it. That's not a big deal, but to experiment and home make one that is effective, that gives one self pride. Remember what all those folks said of Tesla and his ac electricity, it will not work. This country is powered by AC current and much of the world. Imagination, trial and error will get results, good bad or indifferent
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Old 02-07-2015, 6:25 PM
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I just had a flash back...

There is a YouTube or three that show how to make home made antennas. If you have a mast to use, don't forget the ground plane radials. I like the fella that used a 102 whip and some radials. Truck stops and the internet both have blocks with stud mounts on the top and four around the sides. I've seen 6 radial blocks to mount screw in antennas to. These are made for trucks and motor homes with fiberglass roofs to boost the signal. It would work well as a ground plane at the top of your mast too: give it some distance with a horizontal plane, however small.

I will tell ya, I found the end cost on a home made antenna almost the same as a real base antenna on ebay. Might want to consider the total cost of a piece-together vs. a store bought.

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Old 01-31-2018, 9:33 PM
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Default Thank you

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Originally Posted by WA0CBW View Post
Also with a vertical dipole the coax should leave the antenna at a 90 degree angle for at least a 1/4 wavelength for best results.
BB
This is what I've been wondering. I've been debating on what antenna to get. I live in an apartment, so little choices. My landlord is letting put an antenna in the attic, so now I've been going crazy trying to decide the best option. I have limited funds (I have kids and a wife, enough said), so I was contemplating on getting either the FireStik IBA-5 or a firestick dipole, and in this thread I read that a ground plane will not put out as good as a dipole, but I kept thinking, what about the coax, that has to play into this some how... I was going to run it straight down, figuring that would be best, but now thanks to you, I'll run it straight from the antenna to the other side of the attic, then let it drop down, thank you for posting that.

I'm also putting a 1/2 wave horizontal dipole made of 16 gauge wire for skip, but I wanted something vertical for local, I hope this works....
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Old 02-03-2018, 9:24 PM
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Hi Bryan,
How's the antenna doing?
Drop me a pm after you make a few more posts.
If I can answer any questions.
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Old 02-05-2018, 7:23 PM
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Originally Posted by KC5AKB View Post
Hi Bryan,
How's the antenna doing?
Drop me a pm after you make a few more posts.
If I can answer any questions.
I have the regular dipole up, 1/2 wave horizontal, and it seems to get out. So far I've only talked to one person about 2 miles away and he said I sounded good. Also, he was on the end side, not the direction I'm broadcasting. My dipole is east west and he's east, so I'm somewhat encouraged.

I don't have a good SWR, it was 3:1 on ch 40, same on ch. 1, and about 2:5 on ch. 19. That was with 100' of coax. I can't go below 70', that's where it comes out of the wall. I used the full 100' because that was the length I bought and it came with connectors on both ends, so I thought I would just run it and use it.

Last night I did some calculating on signal velocity and wavelengths and came up with 15.29' as lengths I should use ( 492 x vf frequency), my nearest length over 70' was 75.95' so I cut it there (I read many posts saying length isn't important, and just as many saying it is) .SWR stayed at 3:1 on 40 but dropped to 2:1 on ch 1. I wish it would have gone the other way as everyone I know is on the higher channels. After that I read later in the same post that you should just go by 11' lengths, but it's too late as I'm already under 77'...

Reading other stuff on the web, someone put together a page on making a choke/balun by winding the coax around a piece of PVC, I'm going to try that and see if I can get the SWR down. Optimum Coax Coiled Turns Choke Baluns for Antennas

I'm hoping that adding that balum and adding a ground at the antenna end, I can get the SWR down...

The firestick dipole:
I still haven't put this one up yet, I was waiting on one part. After reading on this post that I want the coax leaving the dipole at 90 degrees, I ordered a 90 degree connector, and it just came here yesterday, Sunday. I'm planning on going to the attic tomorrow and installing it.

I was worried about all of this being a waste of time and money, then I thought, if all this fails, an antenna tuner and small boot will fix it all, but I'd rather not have to go that route.
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Old 02-06-2018, 3:16 PM
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This is all you need. I have this setup in my attic and it works great.
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