Twin Antennas

[dobbo049]

hey
im new here so ill introduce myself as Stuart, im a agricultural student so i use CBs alot in tractors n stuff
and im putting one in my truck but i want to use two CB antennas. onto a roof bar...

It will look a little somthing like this ......
(excuse the bad drawing i just did it quickly on paint)




I have 2 main Questions.....

Can wireing two Antennas through a T connector (FMF) be done this way or is there a different way of connecting i need to use?

Can sombody please recomend a mount that i can clamp to my roof bar, most clamps iv found are just for mirros and wont fit a roof bar well.

Help would be much apreciated
Thanks
Stuart

[Offplanet]

A "V Bolt Mirror Mount" from Thunderpole should fit around a roof rack bar.

A "Zetagi AX2 splitter" looks like what you need to connect two antennas - from Thunderpole again, and the description is as follows: "Dual Antenna Coupler allows you to connect two aerials to one transceiver".

Another option is to use a co-phasing harness.

Cheers.

[stampman]

look good but work crap you need at least 9ft between the antenna or you radiation pattern will be all over the place youd be better with a top range antenna mounted on the bar wit a mirror mount use longer bolts to fit it

[dobbo049]

look good but work crap you need at least 9ft between the antenna or you radiation pattern will be all over the place youd be better with a top range antenna mounted on the bar wit a mirror mount use longer bolts to fit it

ahh thats annoying, i need 2 really so that it will look good. as i have a britax flashing amber beacon in the middle, a CB areial either side would be perfect but to stick one in the middle rite behind the beacon would look abit crap compaired to two :S

[andy@thunderpole.co.uk]

It would work much better if you had two on there but just connected one antenna

Andy

[dobbo049]

what do you mean it would work better but only have one on? ..... surely if it works better then 2 is fine.

did you mean it would look better?

[andy@thunderpole.co.uk]

I meant it would work much better having one connected than two, if they are not configured correctly and at least 9 feet apart.

If you wanted two antennas to look good then the best way would be to do it like this...



Just make sure they are at least 2-3 feet apart to prevent reflection.

Andy

[dobbo049]

hmm yea, i spose thats what ill have to do.
Seems abit silly wasting an antenna though..... i spose it would save me £20+ on the connector and leads.

[robroy]

Co-Phasing Your Mobile Antennas ("Twin Truckers")

Co-Phasing antennas simply means taking two identical antennas, mounting them on the vehicle and feeding them in-phase. One of the biggest misconception of radio operators is what kind of effect this has on the radiation pattern. Most people think that after you Co-Phase two mobile antennas, your signal will be strongest in line with the vehicle body (meaning the signal is strongest down the road straight in front of you and straight behind you also. This is the theoretical effect that you would get from co-phasing two omnidirectional antennas. However, to realize this effect you need to satisfy a couple of requirements. For one, a good earth ground with long (over a wavelength or so) radial wires is required. Secondly, at CB frequencies the closest you would be able to place these antennas are about 18 feet apart. Since it is impossible to satisfy these requirements, the effect of co-phasing is seriously diminished. Unfortunately, even the "Radio Shack Antenna Book" states that co-phasing two mobile antennas will produce a two directional signal.

So then, is there any advantage to co-phasing two mobile antennas? Why yes, there is. Before we noted that the radiation pattern of a single antenna is "pulled" where there is the most metal vehicle body. You can see the pattern is not perfectly omnidirectional like we would expect it be. As we travel down the road, you will notice signal fade ("flutter" or "waver") from this uneven radiation pattern. Co-phasing two antennas will even out the pattern irregularities. Instead of making the pattern more two directional, it will make it more omnidirectional. Do not expect more "gain" from two antennas. Figure 3 shows how co-phased antennas clean up the radiation pattern. Read the section "Co-Phasing" for instructions on how to make a harness to feed your co-phased antennas. It best to get them as far apart as possible. The best way would be to mount one on the front bumper in the center and one on the back bumper in the center also. Most people think this looks silly (me included!) and mount one on each side of the vehicle