antenna advice

[Outtolima]

I have a RCI 2950 dx .I dont transmit in anything other than the cb bands but enjoy listening to all else (im unlicensed at this point).I had this radio mounted in a semi that had a flat top sleeper and used a single 6ft frances antenna with very good results.

I recently purchased a new truck with a condo style high roof bunk and am in the process of installing all my gear but am wondering if the single antenna configuration will work as well on the new truck as on the old due to the higher roof.The general opinion seems to be that a dual antenna system will be superior.The roof is made of some type of plastic but has a wire mesh that runs through it for structural integrity,

I would rather use a single antenna system as i also have a scanner antenna and cell antenna with sattelite radio soon to follow so real estate on the mirror brackets to mount another antenna will be very scarce.Mounting anything on the roof itself is out of the question.

Any tips or advice re cb ,scanner, cell antenna installation , coax lengths etc will be greatly apppreciated. Thanks in advance.

 

[Al42]

Using twin antennas on the mirrors - if they're set up properly* - will make them directional, front to back. You'll lose signal in all other directions, with the most loss left and right.

*"Properly" means exactly 108" between the centers of the antennas. Any other spacing will give you effects that you'll have to use a computer program to calculate, and that won't be good for communicating.

The limiting factor is the height between the roof and the lowest overpass you have to drive under. Anything lower than that will work well. Anything higher than that will result in a large antenna bill, as you replace the antenna after each encounter with a steel bridge.

Remember that the cable shield has to be electrically connected to that wire mesh so, if you can't do that, you may want to look at antennas made to mount on fiberglass bodies. (They're not structurally different - they're electrically 18 feet long [they're much shorter physically] and the resultant high impedance [typically around 5,000 ohms] is matched to the 50 ohm cable with a matching network of one kind or another.) The best antenna will always be a 108" whip, but real world compromises sometimes have to be made.

 

[MarkEagleUSA]

*"Properly" means exactly 108" between the centers of the antennas.

The best antenna will always be a 108" whip

I've always been led to believe the optimum CB length is 102" (or at least that's what everyone seems to sell). Does the 108" whip length take into account the spring that might be used on the mount?

 

[N_Jay]

I've always been led to believe the optimum CB length is 102" (or at least that's what everyone seems to sell). Does the 108" whip length take into account the spring that might be used on the mount?

YES!

 

[N_Jay]

Using twin antennas on the mirrors - if they're set up properly* - will make them directional, front to back. You'll lose signal in all other directions, with the most loss left and right.

*"Properly" means exactly 108" between the centers of the antennas. Any other spacing will give you effects that you'll have to use a computer program to calculate, and that won't be good for communicating.

Properly cophased antennas at separation of greater than 1/8 wave length and less than 3/8 wave length give predicatble gain perpendicular to the common axis, and loss along the axis.

The amount of gain or loss will vary with the separation of the antennas, but does not change in direction.

 

[Al42]

Properly cophased antennas at separation of greater than 1/8 wave length and less than 3/8 wave length give predicatble gain perpendicular to the common axis, and loss along the axis.

The amount of gain or loss will vary with the separation of the antennas, but does not change in direction.

I don't think you're taking the huge mass of close to 1/4 wavelength metal between them into account. That would tend to change things with changes in spacing. It forms a beam with 2 fed elements and a short, very thick, parasitic element with changing spacing. In the book it only changes gain, but on a real truck ...

 

[N_Jay]

I don't think you're taking the huge mass of close to 1/4 wavelength metal between them into account. That would tend to change things with changes in spacing. It forms a beam with 2 fed elements and a short, very thick, parasitic element with changing spacing. In the book it only changes gain, but on a real truck ...

The truck is a factor with any antenna.

Since it is fairly symetrical I think you can still count on th edirection of the gain (th elittle there is) being to the front and rear.

 

[CGAUX]

Hey Outtolima, I have a scanner exactly like the one pictured in your avtar. I have no idea what to do with mine. What do you use yours for. Where do you get crystals for it?

 

[Outtolima]

Hey Outtolima, I have a scanner exactly like the one pictured in your avtar. I have no idea what to do with mine. What do you use yours for. Where do you get crystals for it?

I found the image on an e'bay ad and it reminded me of a scanner my uncle had when i was a kid so i used it for my avatar.Sorry i couldnt be of more help Re crystals etc.

 

[Al42]

Hey Outtolima, I have a scanner exactly like the one pictured in your avtar. I have no idea what to do with mine. What do you use yours for. Where do you get crystals for it?

www.icmfg.com/
http://www.jancrystals.com/
http://www.bomarcrystal.com/

Maybe these should be in the wiki?