To cophase or not to cophase

[Sergeant Bilko]

I'm planning to install a Breedlove quick disconnected 102" whip, tuned for 10 meter band voice commo on the back of my road tractor, high at the roof line. My concerns are for adequate ground plane, omnidirectional radiation and db loss at the connection points.

Im pondering the idea of minimizing the effects of uneven ground plane at this mounting location by using 2 cophased 102s spaced at 1/8 wave to preserve omnidirectional radiation. This of course would also increase db loss at 2 Breedlove quick disconnects. Thoughts?

 

[kopcicle]

Heat a #2 phillips till red hot and jam it up your nose. It will actually hurt less.
Your other choice is to use a single whip an optimize the installation.

 

[Sergeant Bilko]

Your reply is a little vague but I think what you're saying is, I'll achieve a sufficient ground plane and optimal radiation by mounting a single 102" whip on the back of the steel portion of the truck's cab, centered at the highest point, which is about 8-9 feet above the truck's frame. There will be a large metal body ground plane to the front and 8-9 feet of air space to the rear before encountering the steel frame. The base of the whip will be at about 12 feet from the ground.

 

[Captain Kilowatt]

Phasing antennas (no such thing as co-phasing which is an erroneous CB term) is not as simple as cutting a cable to the theoretical right length and being good to go. Often you end up with more losses than gains when doing something without the proper gear to make sure things are done right. Unless the phase angle is dead on gains and patterns will suffer. When using i/8 wavelength spacing you may as well go with a single well mounted antenna and save a lot of headaches or false assumptions.

 

[Sergeant Bilko]

Thank you for the reply. Yes, my only motivation for phasing 2 antennas is to reduce the dependence on a ground plane, given the limitations of my installation option at such a height and drastic change in metal surface from the 0 degree to 180 degree position, I'm trying to avoid a poor ohm value when analyzing. If in your experience, a 2" ground plane spacing to the front coupled with a 9' ground plane to the frame at the rear, 13 feet above the earth surface, would provide acceptable numbers, it would be less cumbersome then tweaking 2 antennas for sure. Bear in mind, my primary concern is quality operation, not simplicity of installation.

 

[FL Native]

you are way over thinking this...… just mount it and make sure mount to cab has good connection and cab to frame.

 

[Robb]

I'm planning to install a Breedlove quick disconnected 102" whip, tuned for 10 meter band voice commo on the back of my road tractor, high at the roof line. My concerns are for adequate ground plane, omnidirectional radiation and db loss at the connection points.

Im pondering the idea of minimizing the effects of uneven ground plane at this mounting location by using 2 cophased 102s spaced at 1/8 wave to preserve omnidirectional radiation. This of course would also increase db loss at 2 Breedlove quick disconnects. Thoughts?

Emphasis mine.
Sooo; you are going to mount two 9 ft whips on the top of a diesel tractor?
Is that correct?
Aren't you concerned for clearances above ground?

 

[Tallman]

There will be a large metal body ground plane to the front and 8-9 feet of air space to the rear before encountering the steel frame. The base of the whip will be at about 12 feet from the ground.

Be prepared to be thumping the crap out the over passes. A lot of over passes are 13'9" so you will be breaking a lot of antennas.

 

[Tallman]

Emphasis mine.
Sooo; you are going to mount two 9 ft whips on the top of a diesel tractor?
Aren't you concerned for clearances above ground?

you beat me to it.

 

[Sergeant Bilko]

I think you may have missed the part where I'm using Breedlove quick disconnects because, well, obviously.

 

[Robb]

I think you may have missed the part where I'm using Breedlove quick disconnects because, well, obviously.

I think you missed the part that it won't matter.
Going under an overpass that has 19 ft of clearance and you are 21 feet means you can't stop for every overpass that doesn't fit. Must truckers use 5 ft firesticks mirror-mounted - and - might run two. Usually not.
Driving long?

 

[Tallman]

I think you missed the part that it won't matter.
Going under an overpass that has 19 ft of clearance and you are 21 feet means you can't stop for every overpass that doesn't fit. Must truckers use 5 ft firesticks mirror-mounted and - might run two. Usually not. Driving long?

I doubt he is a driver and maybe not even a CB'er.

 

[Tallman]

Im pondering the idea of minimizing the effects of uneven ground plane at this mounting location by using 2 cophased 102s spaced at 1/8 wave to preserve omnidirectional radiation. This of course would also increase db loss at 2 Breedlove quick disconnects. Thoughts?

What you are trying to do will never be omni directional due to the metal mass and distribution of the ground plane. You will transmit to the rear of the truck when dragging a trailer.

 

[Sergeant Bilko]

I doubt he is a driver and maybe not even a CB'er.

Ok, perhaps this might not be the right forum to find an Elmer but, let me break this down Barney Style for those of you who have confused this thread with Twitter:

I have cophased 11 meter band top loaded antennas for use while underway. Once parked for the night, I can climb the ladder and quick connect the 10 meter band whip(s), switch over the coax, and do some SSB for an hour before turning in for the night. Yes, this requires me to get out of my seat and venture outside for a few minutes but, exercise is good for the body, which is why I chose flatbed over dry van.

Anyone else confused? Anyone have any helpful antenna theory centered comments about the subject at hand?

 

[Tallman]

Ok, perhaps this might not be the right forum to find an Elmer but, let me break this down Barney Style for those of you who have confused this thread with Twitter:

I have cophased 11 meter band top loaded antennas for use while underway. Once parked for the night, I can climb the ladder and quick connect the 10 meter band whip(s), switch over the coax, and do some SSB for an hour before turning in for the night. Yes, this requires me to get out of my seat and venture outside for a few minutes but, exercise is good for the body, which is why I chose flatbed over dry van.

Anyone else confused? Anyone have any helpful antenna theory centered comments about the subject at hand?

If you did not get an answer you expected it is because you were somewhat nebulous on your operational conditions. If you are going to be doing this from a stationary situation you do have possibilities opening up for you. An end fed long wire with balun would do you pretty good and all you would have to take it down would is roll up the long wire and take down a short pole and store it.