Re: [IRCA] Max. Groundwave Propagation Distance?--Thanks!

[<huelbe_garcia@xxxxxxxxxxxx>]

Hi Jeff, Russ:

The Australian Authority for Civil Aviation has published an intersting 
document named "Operational Notes on Non-Directional Beacons" here:
http://www.casa.gov.au/pilots/download/NDB.pdf

At certain point, they say:
""The useful range of an NDB is influenced by the type of terrain over which 
the radio wave travels. It is greatest over the sea and least over sandy or 
mountainous country, and an NDB with a daylight range of 600 miles over the 
sea may only have a range of little more than 100 miles over unfavourable 
types of land. Therefore, when an NDB is located on the coastline, its range 
in different directions can be expected to vary considerably.""

Another document compiled by PY3JJ using data available from the old 
Brazilian Telecom Operator (Embratel), lists the "terrestrian ranges" for 
several MF/HF frequencies:

1700KHz - 160km
2000KHz - 144km
4000KHz - 88km
6000KHz - 80km
9500KHz - 64km
11900KHz - 56km
15100KHz - 56km
17800KHz - 40km
21550KHz - 32km
28000KHz - 16km

I think this is the "assured range".

Huelbe
Brazil

----- Original Message ----- 
From: "Russ Edmunds" <wb2bjh@xxxxxxxxx>
To: <ne2j@xxxxxxxx>; "Mailing list for the International Radio Club of 
America" <irca@xxxxxxxxxxxxxxxx>
Sent: Monday, March 10, 2008 8:03 AM
Subject: Re: [IRCA] Max. Groundwave Propagation Distance?--Thanks!



--- "Jeff T. Casey" <ne2j@xxxxxxxx> wrote:


> However, since surface conductivity (and resistance) presumably do
> not change significantly over time (except when it rains or floods?),
> it would seem that a signal arriving only via groundwave should come
> in either 24/7 or never (assuming no changes at the transmitter
> site).  So, I would think that a signal that is heard at noon on some
> days but not others must be arriving via skywave
>  only, but maybe I'm neglecting some important factor.
>
>


There can be a significant difference in ground conductivity in a given
area between when the ground is dry and hard, and when it is very wet
an flooded although maximum effect occurs when the gound is staurated.
A similar effect occurs when the ground is snow-covered.

When a signal isn't rock-steady at the same time day to day that is
usually indicative of skywave involvement unless we're speaking of a
water path or mostly water path.

Russ Edmunds
Blue Bell, PA ( 360' ASL )
[15 mi NNW of Philadelphia]
40:08:45N; 75:16:04W, Grid FN20id
<wb2bjh@xxxxxxxxx>
FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'
AM: Hammarlund HQ-150 & 4' FET air core loop


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