Hi there,

when I had a satellite dish put up on the roof I had the guys also put
up a CB antenna (Hurricane 27).
It's connected to the same support as the dish via an L piece of tubing
in such a way that the base of the antenna is slightly off to the side
of the dish, a bit like this:

|
O '

The SWR is miserable (like 3 or 4 or something - it's been a while
since I played with this).


Now, I once read that incorrect grounding (i.e. none) would be one
possible explanation. These
electricians claim that they did ground the antenna. However, since I
get the occasional shock when fiddling with the satellite cables I
suspect that this may indeed be the problem ;-)


Question is, does this setup have any chance of working ok?


I also ummm, had them place the dish/antenna at the highest point on
the roof (about 10 m above
ground level). Any thoughts on lightning protection? I've been getting
conflicting advice.


Thanks,

colin

Hello, Colin

I'm not going to tackle the question of lightning protection - that job is
best left to professionals.

As far as the 'ground', bear in mind you are talking two different grounds
here - one, earth ground, is important for lightning protection. The other
ground, rf ground, is what radials (or a large metal body such as a vehicle)
supply. You need something hung out there that will act as a low impedance
ground for rf. Quarter wave (at 27 MHz) sections of wire can supply that
for you. Without those, your coax tries to supply that rf ground and will
end up radiating rf plus is likely not supplying a low impedance at the
antenna due to its' rf length.

You can try hanging three or four nine foot lengths of wire (say 14 gauge)
and connect one end to the grounded part of the antenna (where the outer
shell of the coax connects). Then check the SWR. Very likely it will be
considerably lower.

As far as a shock, I'm not sure but I believe that there is a dc voltage fed
through the center conductor of your satellite coax. This is to supply
power to the low noise pre-amp located at the dish itself. For some reason,
I think it may be around 18 volts (not enough to shock you), so there may be
more at work here than simply that dc supply.

I hope at least a bit of this helps

Best regards from Rochester, NY
Jim

"Colin Howarth" wrote in message
...
Hi there,

when I had a satellite dish put up on the roof I had the guys also put
up a CB antenna (Hurricane 27).
It's connected to the same support as the dish via an L piece of tubing
in such a way that the base of the antenna is slightly off to the side
of the dish, a bit like this:

|
O '

The SWR is miserable (like 3 or 4 or something - it's been a while
since I played with this).


Now, I once read that incorrect grounding (i.e. none) would be one
possible explanation. These
electricians claim that they did ground the antenna. However, since I
get the occasional shock when fiddling with the satellite cables I
suspect that this may indeed be the problem ;-)


Question is, does this setup have any chance of working ok?


I also ummm, had them place the dish/antenna at the highest point on
the roof (about 10 m above
ground level). Any thoughts on lightning protection? I've been getting
conflicting advice.


Thanks,

colin



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In , Colin Howarth
wrote:

Hi there,

when I had a satellite dish put up on the roof I had the guys also put
up a CB antenna (Hurricane 27).


Never heard of it and can't find a pic.


It's connected to the same support as the dish via an L piece of tubing
in such a way that the base of the antenna is slightly off to the side
of the dish, a bit like this:

|
O '

The SWR is miserable (like 3 or 4 or something - it's been a while
since I played with this).


Now, I once read that incorrect grounding (i.e. none) would be one
possible explanation. These
electricians claim that they did ground the antenna. However, since I
get the occasional shock when fiddling with the satellite cables I
suspect that this may indeed be the problem ;-)


There are three types of grounding: RF ground, line-power ground and lightning
ground. Your dish is probably grounded for lightning strikes, and the shock you
receive is the static from your body discharging to the grounded cable.

I don't know if your antenna uses a ground-plane or if it is a coaxial dipole. A
coaxial dipole needs no ground-plane, but if it is a ground-plane antenna it
might be lacking the ground plane (radial elements at the bottom). It's also
possible that you are getting reflections off the disk. Don't ignore the
possibility that it could also be disconnected, bad coax, untuned, etc.


Question is, does this setup have any chance of working ok?


As long as the dish doesn't cause a problem. That shouldn't happen if the whole
of the antenna is higher than the dish.


I also ummm, had them place the dish/antenna at the highest point on
the roof (about 10 m above
ground level). Any thoughts on lightning protection? I've been getting
conflicting advice.


It should have been grounded when it was installed. However, that doesn't mean
your CB antenna is properly grounded for lightning. It wouldn't hurt to sink a
ground rod at the point where the coax enters the house and connect it to the
shield of the coax. Use thick wire.





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