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DJ, let me save you the time here. Don't bother trying to do this with under 70 inches of separation, a kilowatt of power, and no ground plane under the antenna. Complete waste of time in terms of performance! The antennas are so close their patterns will overlap rather then creating two individual patterns that combine. Mirror mounts are the worst for any type of high power because it places the antenna in a location with no ground plane underneath. You'll go nuts trying to get the VSWR right and when you do, it will be nothing but RF problems because of the poor ground. You'll likely get RF burns off the mic, radio, or amp.

It has already been mentioned here but I'll say it again. Put one antenna in the center of the cab and it will beat anything you can do on the mirrors. I know you can't put the same length antenna in this location but even a shorter one will beat what you're trying to do. The difference is one you can notice. Even a Wilson 1000 mag mount is a better choice here. Lose the magnet and drill a hole if you want the best ground.

Furthermore, the co-phase harness discussion here has almost completely overlooked the velocity factor of the coax used. You do not use two 75 ohm 1/4 wave lines. The length of the coax needs to be an ELECTRICAL 1/4 wave not a PHYSICAL 1/4 wave. The velocity factor of coax will make the length shorter then you expect and must be calculated using the given VF of the coax used.

<blockquote data-quote="Shockwave" data-source="post: 158532" data-attributes="member: 10882">DJ, let me save you the time here. Don&#039;t bother trying to do this with under 70 inches of separation, a kilowatt of power, and no ground plane under the antenna. Complete waste of time in terms of performance! The antennas are so close their patterns will overlap rather then creating two individual patterns that combine. Mirror mounts are the worst for any type of high power because it places the antenna in a location with no ground plane underneath. You&#039;ll go nuts trying to get the VSWR right and when you do, it will be nothing but RF problems because of the poor ground. You&#039;ll likely get RF burns off the mic, radio, or amp. It has already been mentioned here but I&#039;ll say it again. Put one antenna in the center of the cab and it will beat anything you can do on the mirrors. I know you can&#039;t put the same length antenna in this location but even a shorter one will beat what you&#039;re trying to do. The difference is one you can notice. Even a Wilson 1000 mag mount is a better choice here. Lose the magnet and drill a hole if you want the best ground.Furthermore, the co-phase harness discussion here has almost completely overlooked the velocity factor of the coax used. You do not use two 75 ohm 1/4 wave lines. The length of the coax needs to be an ELECTRICAL 1/4 wave not a PHYSICAL 1/4 wave. The velocity factor of coax will make the length shorter then you expect and must be calculated using the given VF of the coax used.</blockquote>

[QUOTE="Shockwave, post: 158532, member: 10882"] DJ, let me save you the time here. Don't bother trying to do this with under 70 inches of separation, a kilowatt of power, and no ground plane under the antenna. Complete waste of time in terms of performance! The antennas are so close their patterns will overlap rather then creating two individual patterns that combine. Mirror mounts are the worst for any type of high power because it places the antenna in a location with no ground plane underneath. You'll go nuts trying to get the VSWR right and when you do, it will be nothing but RF problems because of the poor ground. You'll likely get RF burns off the mic, radio, or amp. It has already been mentioned here but I'll say it again. Put one antenna in the center of the cab and it will beat anything you can do on the mirrors. I know you can't put the same length antenna in this location but even a shorter one will beat what you're trying to do. The difference is one you can notice. Even a Wilson 1000 mag mount is a better choice here. Lose the magnet and drill a hole if you want the best ground. Furthermore, the co-phase harness discussion here has almost completely overlooked the velocity factor of the coax used. You do not use two 75 ohm 1/4 wave lines. The length of the coax needs to be an ELECTRICAL 1/4 wave not a PHYSICAL 1/4 wave. The velocity factor of coax will make the length shorter then you expect and must be calculated using the given VF of the coax used. [/QUOTE]

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