[Lf] re LF aerials]

[Andre' Kesteloot]

les at highnoonfilm.com wrote:

> I did an article in the Lowdown (publication of the LWCA) on this subject
> about ten years ago. I was fortunate at the time to be working as a
> communications officer onboard a nuclear submarine that was
> undergoing overhaul in Kittery, Maine.
>
> At the time, I was operating a one watt lowfer beacon on 184khz
> about 14 miles away. Since I had access to lots of LF test
> equipment onboard (calibrated F/S meters, antenna current
> meters, etc.) I decided to test a number of ground systems.
>
> The basic rules of thumb appear to be the same for LF
> as they are elsewhere with short verticals. On LF
> it is easy to get misleading readings, esp. if you're metering
> in the near field. (We lowfers found this out the hard way)
>
> To lower ground losses, the best bets are:
>
> 1. Get as much metal as possible at the base of the antenna.
> Meaning if you only have 400m of copper wire, you're better
> off putting down 32 short radials than one or two long ones.
>
> 2. "The Law of Diminishing Returns". We've also found
> out through hard experience a simple rule. In order to
> see an increase in antenna current, you have to double
> the number of radials. For instance, put down 2 radials
> vs a ground rod...you'll see an improvement. To see any
> more improvement, you have to put down 4, then 8,
> 16, then 32, then....
>
> Soil conditions do make a difference. But not as great as
> some of the effects you seem to be observing.
>
> I think that the amateur allocation in Europe is a significant
> change in LF in one area. Most of the installations are
> of the "backyard" variety, where as here in the states,
> LF activity is mainly limited to those who have
> some real estate to work with.
>
> You must consider the fact that any nearby objects,
> (trees, homes, gardens, etc.) have a VERY significant
> effect on the total system losses. You can easily couple
> 90% of  your signal into these objects. These objects
> will also affect any and all measurements that you make
> in the near field.
>
> Putting up bigger tophats, may also mean that those wires
> are brought closer to nearby objects, thus changing the
> system losses.
>
> In short, there are no "rules" and John is very right
> to caution against making blanket statements. It
> flies in the face of logic and experience to suggest
> that a single ground rod would outperform a large
> radial system. I would suggest looking hard for
> other ex plantations to your situation (such as
> coupling to nearby objects)
>
> Backyard systems are rarely going to approach
> the performance of commercial antennas mounted
> in the clear with good radials. So, another factor
> is to be realistic about what you can expect from
> your own situation.
>
> Les Rayburn, N1LF
> XMGR (186.404khz)