Does the negative length of a dipole matter?

[WRVV250]

Howdy y’all,

I made a high mount for my midland 6dB gain antenna for the back of my Jeep to get rid of this weird garble that happens while driving. I thought it was rf from the engine (part of it was) but now I think it’s picket fencing but it’s particularly prominent with weaker signals so I’m not sure, but that’s not my question right now. Take a look at the picture attached please. 
The all thread rod is grounded so I suppose it acts as a vertical dipole now. Does the length of said all thread rod matter? Either way, is my current setup going to hurt me at all? Thanks in advance, I appreciate you!

[SteveShannon]

20 minutes ago, WRVV250 said:

Howdy y’all,

I made a high mount for my midland 6dB gain antenna for the back of my Jeep to get rid of this weird garble that happens while driving. I thought it was rf from the engine (part of it was) but now I think it’s picket fencing but it’s particularly prominent with weaker signals so I’m not sure, but that’s not my question right now. Take a look at the picture attached please. 
The all thread rod is grounded so I suppose it acts as a vertical dipole now. Does the length of said all thread rod matter? Either way, is my current setup going to hurt me at all? Thanks in advance, I appreciate you!

If the all-thread were 1/4 wave and not connected to the vehicle it would be a true dipole. In a true dipole both halves are balanced radiating elements. 
But since it is connected to the car chassis (ground) it’s just a quarter wave vertical with a vertically extended ground plane. I don’t expect it to hurt but experience will tell you. 
Having part of the ground plane be a vertical element may be beneficial, but I have no idea how much. Certainly getting the antenna higher up will help. 

[WRUE951]

i had that garble effect when i had antenna mounted on a rear tire mount in my jeep.  Moved it to the front right cowel and worked awesome..  

[WRVV250]

18 hours ago, Sshannon said:

If the all-thread were 1/4 wave and not connected to the vehicle it would be a true dipole. In a true dipole both halves are balanced radiating elements. 
But since it is connected to the car chassis (ground) it’s just a quarter wave vertical with a vertically extended ground plane. I don’t expect it to hurt but experience will tell you. 
Having part of the ground plane be a vertical element may be beneficial, but I have no idea how much. Certainly getting the antenna higher up will help. 

Thank you for the input!

[WRVV250]

14 hours ago, WRUE951 said:

i had that garble effect when i had antenna mounted on a rear tire mount in my jeep.  Moved it to the front right cowel and worked awesome..  

I have had the garble either way, can’t seem to solve it by positioning. 

[SteveShannon]

1 hour ago, WRVV250 said:

I have had the garble either way, can’t seem to solve it by positioning. 

The extra length of the section of all-thread makes for an antenna that is even more susceptible to buffeting by air currents. Any distortion due to Doppler or picket fencing will be more noticeable on weaker signals.  You might try a higher gain antenna, such as a no ground plane roof mount antenna mounted without the all-thread.  

[WRVV250]

1 hour ago, Sshannon said:

The extra length of the section of all-thread makes for an antenna that is even more susceptible to buffeting by air currents. Any distortion due to Doppler or picket fencing will be more noticeable on weaker signals.  You might try a higher gain antenna, such as a no ground plane roof mount antenna mounted without the all-thread.  

That would be a good idea. What if I make it to where the all thread is not grounded whatsoever/totally isolated?

[KAF6045]

2 hours ago, WRVV250 said:

That would be a good idea. What if I make it to where the all thread is not grounded whatsoever/totally isolated?

"Picket fencing" is sort of a doppler effect from the antenna moving around (unless one is driving past a really tall metallic picket fence  ) -- nothing that can really be adjusted by the grounding status.

You placed the antenna on top of a tall thin stick -- both the stick and the antenna are going to flex under wind and motion. The suggested roof mount takes out the tall stick.