to ground or not to ground??????

[icemanrrc]

I was thinking of grounding my IMAX. I am using LMR-400 coax. My antenna is chimney mounted. The coax runs approx 40 feet down to the ground. Should I buy one of those ground kits for the LMR-400 style coax or just leave it not grounded?
Here is one of the grounding kits I was referring to.
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[jegs]

Just use a lightning arrester and ground the arrester.

[lonesome 500]

i'd run a wire from the mast to ground......direct route

also to help balance inductance

[icemanrrc]

If I run a wire from mast to ground, that would be like 30 feet of copper wire. Wouldn't that radiate and cause some serious RFI?

[North Texas Mudduck]

if you had a setup done right and had a metal pole dont you think it would radiate also

[icemanrrc]

Not really sure. Would I?

[Circuit Breaker]

The device you're talking about would work just fine. Put one as close to the antenna as possible and another one just before the coax enters the house. Connect them to more than one ground rod. Nothing will prevent a lightning strike, but the goal here is to give it a much easier path to take than through your equipment. Regardless, your antenna will probably end up being ruined by the high voltage...but your radio equipment will (hopefully) escape undamaged.

[lonesome 500]

if you radiated anything.........you'd want it to ground.......and not inside on your coax

ground is what makes this end fed work

[Circuit Breaker]

if you radiated anything.........you'd want it to ground.......and not inside on your coax

ground is what makes this end fed work

First of all, I think you're getting ground plane and grounding confused. While an Imax is an end fed antenna, it is also a half wave and does not need a ground plane. Even if what you said were true, any radiated energy would not go to ground because you would need an RF ground...that is very difficult to achieve. That is one reason why a ground wire will radiate energy if it is any length that would make it resonant on CB frequencies. The grounding that the original poster is talking about is for lightning protection.

[lonesome 500]

dc and rf grounds work in concession with each other

no i'm not confused....a ground wire will keep the coax from radiating if the '''coax'' is the only ground which the ant is seeing

here is you something to try.....we've done it

hang the imax by a rope with only coax.....check inductance.......then run a wire to ground......re check......look at the differences

rf...and dc is both VOLTAGE.......they both have earth ground seeking principles

on the lightening issue....you want straight ...shortest....and most direct to earth ground

and the imax will need a plane.....if a situatin where inductance vs resistance values are not acceptable

[Circuit Breaker]

dc and rf grounds work in concession with each other

no i'm not confused....a ground wire will keep the coax from radiating if the '''coax'' is the only ground which the ant is seeing

No, you are a little confused. They do not work in concession with each other...not exactly anyway.

Any wire will have inductance and therefore, inductive reactance. The longer the wire, the higher the inductive reactance and the higher the opposition is to the flow of RF current. The fatter or larger the wire, the lower the opposition to the flow of RF current. The effect is similar to the DC resistance of a wire. The longer the wire, the higher the DC resistance will be. The fatter the wire the lower the DC resistance for the same length wire. There is an important 'however,' that we must consider. First, when RF is applied to the conductor, the RF travels only on the surface of the conductor. Surface area is the important factor here, not the diameter or thickness of the conductor. Another major difference between DC and RF current has to do with wavelength. The wavelength of DC current is infinitely long. This is not the case for RF. When the XL (inductive reactance) is measured along the length of a wire, the magnitude of XL (the opposition to RF current flow) varies from very low to very high values. It continues to alternate between low and high values in cycles that have a direct relationship between the length of wire and the frequency. DC resistance, on the other hand, has no cycle. It simply increases linearly with the length of the wire.

When measuring XL, its value is very high when the length of the wire is around one-quarter wavelength long. Increasing the length wire to one-half wavelength, returns XL to a low value.

The length of the wire does not have to be very long for this effect to be observed. For example, at 27 MHz an 8' ground wire (or any wire for that matter) is approximately one-quarter wavelength long. If this 8 foot long ground wire connects your CB radio to your ground system, the ground wire may actually prevent RF from traveling to ground.

here is you something to try.....we've done it

hang the imax by a rope with only coax.....check inductance.......then run a wire to ground......re check......look at the differences

rf...and dc is both VOLTAGE.......they both have earth ground seeking principles

Correct...and wrong. As outlined above, the wavelength of DC is infinitely long...RF is not. When the XL (inductive reactance) is measured along the length of a wire, the magnitude of XL (the opposition to RF current flow) varies from very low to very high values. It continues to alternate between low and high values in cycles that have a direct relationship between the length of wire and the frequency. DC resistance, on the other hand, has no cycle. It simply increases linearly with the length of the wire.

and the imax will need a plane.....if a situatin where inductance vs resistance values are not acceptable

The only thing adding a ground plane to an Imax will do is lower the angle of radiation. Nothing more.

[lonesome 500]

nope...not confused in the slightest.......been here...done this problem

first....mount you an imax at 15' and check it's inductance....then add nothing but ground plane rad......recheck with 259b......there is difference.....not just only angle of radiation


second...not typing a book but...if you are saying he needs no ground to keep coaxial cable from radiating.....the first time he puts the juice to it and....burns out either a cap ...transistor...ic...or grid.......maybe even an rf burn...you can tell him oops..

i've known what you've typed out for years....but you can ''get by'' in a 2 for the price of one deal...sure rf grounds are to be as short as possible on the tranceiver end....but he was referin to a chimney mounted ant

btw on the rfi issue....the ant does not create rfi

maybe i should have interpreted he was looking for ''lightning protection'' and not ''maximum'' ant preformance

[Circuit Breaker]

As I stated...you are correct and wrong at the same time when it comes to RF grounds and I outlined why.

And you don't need an RF ground to keep the coax from radiating. All he has to do is make an RF choke by coiling the coax at the antenna using 5 or 6 turns and then using a zip tie to keep it together. Usually, RF radiation on coax is a problem on non-resonant antennas. In this situation, the antenna in question IS resonant.

You are very correct about antennas not causing RFI...the antenna isn't the problem. Back in the 80s the Shakespere Big Stick was always referred to as the Bleed Stick...when it wasn't the antenna that caused the problem at all. For whatever reason, some people think that fiberglass antennas cause RFI.

[Texas Mobil 219]

Just ground the thing. You cant go wrong. Its either going to improve your recieve and transmit or it wont change nothing. Its your choice what you want to do.

Im a firm beleiver in grounds. Meaning I ground everything. I had my Amtron 99 mounted to a metal pole, planted in a salt bed. And i still ran an External ground wire of 6 ga welding lead. I had great reception and transmission. Flat SWRs. So in my opinion. Ground everything. You cant go wrong.

Have a great day and good luck

219 wave'n from Texas and still stuffed from Thanksgiving.