shared antenna ground / counterpoise?

[rjvalenta]

so i'm planning to put up 3 new antennas on my roof to go with the existing dual band and scanner.... lots of planning, getting up there requires scaffolding, i have to get it all done and tested in a day....

in a space around 30ft long and 20ft wide, i'll be putting the EFHW in the center of the roof on a roof peak mount, the CB antenna will be on the south end of the roof on the chimney, and the dual band antenna will be attached to a vent pipe about 10ft from the EFHW and lower on the roof.

my current dual band and my scanner antenna will be on the north end of the roof, roughly 15ft from the EFHW and the new dual band... but - all the coax comes in through a service cap on the north end of the roof.

i plan to run a ground wire the entire length of the roof and in with the feedlines. the ground rod will have to be at the south end of the house, it cannot be at the north end where the feedlines come in. but, this will allow me a common ground point for all the feedlines and the equipment inside.

when i looked online at EFHW installs, i saw a video where someone had a great low-noise antenna that ran a counterpoise/ground wire straight to ground

(check out the 2min mark or the attached pic where the ground/counterpoise is shown).

>> my questions <<

i plan on having all these antennas feed in and then putting in MFJ lightning protectors that connect to a shared ground bar that will then connect to the #4 stranded copper ground cable going across the entire roof, then to the ground rod. this way all antennas can bleed off any static from wind and RFI in the coax shield, and hopefully deal with any lightning.

would it be better to run grounds directly from the antenna to the exposed ground cable running the length of the roof, attaching at different points, or is it better to have them combine at a ground bar?

AND - given that the ground/counterpoise point on the EFHW are the same, will having the others attached make the other antennas part of the EFHW counterpoise?

thanks,

Richard
N0TZC

 

[prcguy]

I would not run a ground wire to the EFHW transformer and instead ground the coax near where it enters the building. Noise doesn't automatically go to ground, it doesn't know any better. The EFHW will benefit from a good ferrite common mode choke in the feedline before it hits the lightning protector.

I would also keep the ground wire running across the roof away from the EFHW. If it runs right under the antenna its about the same as lowering the antenna close to the ground and can degrade DX signals in favor of NVIS or signals coming in from very high angles.

 

[rjvalenta]

I would not run a ground wire to the EFHW transformer and instead ground the coax near where it enters the building. Noise doesn't automatically go to ground, it doesn't know any better. The EFHW will benefit from a good ferrite common mode choke in the feedline before it hits the lightning protector.

I would also keep the ground wire running across the roof away from the EFHW. If it runs right under the antenna its about the same as lowering the antenna close to the ground and can degrade DX signals in favor of NVIS or signals coming in from very high angles.

the roof is hard to explain... but it basically has a peak, then a second section under it that is nearly flat compared to the peaked part. the EFHW will sit on the west side of the peak mount, and the ground cable will run alone the base of the peak where it meets the nearly flat part on the east side... so... let's call that 6ft east and 6ft under where the EFHW balun will be.

but this is also why i was thinking it would be easy to run what would be a 10ft piece of extra cable from the balun to the ground line under it.

i do know myantennas and mfj both make chokes that could be put into the feedline, i will look into those.

is it bad to ground EFHW's or is it bad to combine the ground for EFHW's to other grounds?

 

[prcguy]

Just remember a long elevated ground wire under a wire antenna is a reflector and can alter the radiation pattern of the wire antenna. Grounding the EFHW at the transformer can do many different things. I have never experienced anything beneficial from grounding one. Some users have reported lower noise. And some have reported more noise because a ground that is common to other things like computers and switching power supplies in the house can be a source of noise and its not a good idea to bring that noise up to your antenna via a ground wire. You basically have to try it both ways and decide yourself.

 

[Lou-In-USA]

Technically, for lighting, you're supposed to have single-point grounding to your utility's ground rod, and make separate runs from each antenna. If that's impractical, your bus should be extra heavy-duty. If you decide to go with your own ground rod, then all your grounds need to go to it so you don't get ground currents on your coax and other equipment, since having multiple grounds in different locations on the land does create a ground-loop where current can flow and noise can be introduced.

Lastly, unless or until your coax goes underground and to your basement, you still need to choke your coax, even with some ferrites, before your receiver, and not just at the antenna, although that's very important too, especially if you're using a BalUn as you are, so your coax doesn't become another counterpoise.