[600MRG] EIRP and such

[Edward R Cole]

Eric and all:

I can give evidence to the 80m dipole laying on 
ground working well.  On many checkpoint 
locations on the Iditarod Sled Dog race the hams 
were not always able to get dipoles very 
high.  At one checkpoint in the village of 
Kaltag, I used the clothesline poles as end 
supports for my dipole that was barely 6-foot 
above the snow and maybe 10-foot about solid 
ground.  The antenna tuned great and worked super 
well into Anchorage HQ for the race (about 400-miles).

This is all interior AK which has a lot of permafrost.

But on the Kenai Peninsula it is not common 
especially in well drained land where birch and 
white spruce grow.  My inverted-L manifests 
ground resistance effects being better in summer 
and worse in winter, enough that I have two taps 
separated by two turns of the loading coil for each season.

We still have poor alluvial gravel and sandy soil 
so I would guess resistance is quite low.  My 
guess we resemble most of the coastal areas from 
Alaska down to Oregon as far as soils, terrain, 
and climate (being coldest at our end).

73, Ed - KL7uW

At 10:47 AM 10/6/2015, kl7aj at acsalaska.net wrote:
>Just to add more input to the discussion....the 
>average ground conductivity in Alaska is a few 
>orders of magnitude worse than the worst soils 
>in the continental U.S. Â  The entire Interior 
>of Alaska lies on a huge glacial silt lens. Â 
>This can actually be a mixed blessing. Â Since 
>the ground conductivity is SO bad, you can lay 
>an 80 meter dipole right on the ground and it 
>works just fine....the "real" ground is down around 60 feet in most places.
>However, getting a real ground wave is a severe 
>challenge. Â I ws chief engineer at KJNP at 1170 
>KHz for 25 years, and we had a full half wave 
>antenna, AND twice the number of radials 
>required by the FCC to get anything like a 
>stable ground field. Â  I had at one time 
>calculated the miles of radial copper we had 
>laid down. Â For about half that time we had a 2 
>tower directional antenna.....I don't know HOW 
>we ever could have done this with 1/4 wave 
>'sticks" since the seasonal ground changes would 
>have been enormous. Â The 1/2 wave antennas we 
>had relied a lot less than most AM towers on the 
>ground system, but it ws far from independent of it!
>
>One thing that's notable here is that the 
>dielectric constant is just as important as the 
>resistivity when figuring out grounding systems. 
>Â In most "normal" places, the resistance dominates. :)
>
>Eric
>
>On Tue, 6 Oct 2015 11:24:55 -0700, Rudy Severns <n6lf at epud.net> wrote:
>I think you guys need to read my recently published QEX article (Jul/Aug,
>>Sept/Oct) on Rr and Rg at LF-MF versus HF. A copy of the prepublication
>>draft is on my web site: www.antennasbyn6lf.com
>><http://www.antennasbyn6lf.com> . When I get a final .pdf of the
>>published article I'll post it but the differences are small.
>>
>>
>>What I argue is that, because the soil characteristics are dominated by
>>conductivity and LF-MF, the Rr for small antennas at LF and MF is very close
>>to the value for ideal ground. The value for Rr is easily found using
>>either modeling or calculation. As I show, this is not true at HF but who
>>cares! We're not concerned with EIRP on 20m.
>>
>>
>>I argue that all you have to do is model/calculate Rr for ideal ground and
>>measure your antenna current. The radiated power Pr= Io2Rr. The EIRP for
>>the small antennas likely to be used by hams is simple Pr/3. For EIRP= 5W
>>we are allowed Pr=1.667W. You can also determine Pr from a measurement of
>>Ri and Pi: Pr= PiRr/(Rr+Ri). Besides the base 
>>article there are an extensive set of appendices with the
>>back-up for my argument.
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>
>
>
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73, Ed - KL7UW
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