Topband: [Bulk] Re: [Bulk] Re: Skywave vs. Earth Conductivity

[Grant Saviers]

I finally got around to some modeling and rereading of N6LF's work on 
elevated radials to respond to Jim's post.

The comparison on 15m was being made between a crankIR on dry compacted 
sand about 70' from and 6' above high tide line.  Hence the assumption 
that this was "typical earth" conductivity.  It had one radial elevated 
60" and pointing towards NA, where the reporting stations were located.

The vertical on the beach had wet sand below it at all times, thus sea 
water conductivity is the assumption.

My NEC4 analysis of these two situations on 15m shows the crankIR had a 
gain peak of 1.9dbi at 15deg and the v-o-b a gain peak of 4.5dbi at 6deg 
and a broader low angle lobe.

Hence it is reasonable to me that 1 or 2 S units (or more) might be 
heard in signal strength difference over a 6000km path.

The crankIR is not disadvantaged as a single radial implementation to 
40m (with extensions which we take) since both the vertical and radial 
are not doubled back.  On 80m there is some small loss of gain with the 
folded element.  We followed the (correct) advice to aim the single 
radial in the favored QSO direction and elevate it as much as 
practical.  There is a terminal on the crankIR to add more radials, and 
more are certainly desirable on average or worse ground.

As a sanity check I referred to N6LF's work on elevated radials. Over 
average ground, he modeled a single 40m radial at 48" and reported a 
gain loss of 0.77db in the reverse direction of that radial vs 4 radials 
at the same height.  My model showed a "f/b" of 1.8db for the 15m single 
radial at 60" which is consistent with his advice about the height of 
elevated radials to be > 0.05 wl.

On two dxpeditions our teams have had good signal reports from two 
crankIRs.  However, putting a crankIR into/at the water isn't a good 
idea (or possible with the necessary guys).  So I've used a SS whip with 
2 radials for 20 - 10m if the high tide line is accessible. One radial 
models within 0.2db of two.

For a suitcase dxpedition there aren't many alternatives to a crankIR 
that fit in a suitcase and cover 80-10m.

My rule of thumb is get within 1/4wl of the salt water for best 
results.  Then v-o-b's rule.

Grant KZ1W

  2/13/2015 1:11 PM, Jim Brown wrote:
> On Fri,2/13/2015 12:29 PM, Grant Saviers wrote:
>> At TX5D (FO-A), I was able to instant A/B a 15m vertical (two 
>> elevated radials) at high tide line vs a crankIR tuned on 15m about 
>> 70' from high tide.  US stations (5k to 7k km)  reported 1 to 2 S 
>> unit improvements with the antenna nearer to the lagoon salt water. 
>> Received signals were at least that much improved. 
>
> What radial system did the Crank-IR have?  The version that they demo 
> has only one. That could account for at least part of the difference. 
> A greenhorn DX trip used one or more of these antennas, and they were 
> piss-weak.
>
> The nature of the earth under a vertical has a strong impact on its 
> EFFICIENCY -- that is, it burns some the TX power, so that fraction is 
> not radiated, thus never sees the earth in the FAR field, nor does it 
> excite skywave. It is this loss in the earth under the antenna that a 
> radial system reduces. While I'm sure that many of our readers are 
> aware of this, many may not be.
>
> 73, Jim K9YC
>
>
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