What distance for tower side mount for 2m vertical?

[Freqdomain]

I'm going to order a side mount for my TV tower, for a 2m/70cm vertical. (Diamond X30a). What is the best distance to mount from the tower, and what is the minimum distance?

I figure I will mount it so that the tower stands between the antenna and the direction that I don't care about. So for example, I don't care about W and NW, but I do have repeaters of interest to the S, SE, and E. NE and N would be nice but not as important because they are further away. The height above ground will be about 12 feet (just above roof gutter level, because that's all I'm willing to climb.)

So if the rule of thumb is 1/2 wave, then it's about 1 meter for the 2m band. But does it really need to be a half-wave? Would 28" be workable?

 

[buddrousa]

Side mounting any antenna will affect the antenna not following recommendations will affect the antenna more.

 

[prcguy]

I'm going to order a side mount for my TV tower, for a 2m/70cm vertical. (Diamond X30a). What is the best distance to mount from the tower, and what is the minimum distance?

I figure I will mount it so that the tower stands between the antenna and the direction that I don't care about. So for example, I don't care about W and NW, but I do have repeaters of interest to the S, SE, and E. NE and N would be nice but not as important because they are further away. The height above ground will be about 12 feet (just above roof gutter level, because that's all I'm willing to climb.)

So if the rule of thumb is 1/2 wave, then it's about 1 meter for the 2m band. But does it really need to be a half-wave? Would 28" be workable?

The rule is not a half wave and that would give you a clover leaf pattern with four gain lobes and four nulls. I would try for at least a full wavelength which will give an eight petal clover leaf pattern.

 

[Freqdomain]

The rule is not a half wave and that would give you a clover leaf pattern with four gain lobes and four nulls. I would try for at least a full wavelength which will give an eight petal clover leaf pattern.

Thank you for the helpful answer!

 

[Freqdomain]

The rule is not a half wave and that would give you a clover leaf pattern with four gain lobes and four nulls. I would try for at least a full wavelength which will give an eight petal clover leaf pattern.

Quick followup question:
Do the lobes begin inline with the sidearm? In other words, if a line drawn from the vertical antenna through the tower points North, is there a lobe that "faces" South?

 

[buddrousa]

What antenna are you using most antennas have a spec sheet that comes with them that shows the pattern depending on the mounting position. I always used Station Masters or DB420s or DB224s.

 

[prcguy]

Quick followup question:
Do the lobes begin inline with the sidearm? In other words, if a line drawn from the vertical antenna through the tower points North, is there a lobe that "faces" South?

At close spacing from the mast up to a little more than 1/4 wavelength it will be like a 2 element beam in the direction towards the antenna. So if the antenna is on the south side of the tower the lobe will point south. For antenna spacing more than 1/4 wavelength the pattern gets very complex with more lobes as you get further out from the mast.

 

[Freqdomain]

Okay, thank you both! I appreciate your help