Re: [IRCA] Max. Groundwave Propagation Distance?

[Nick Hall-Patch <nhp@xxxxxxxx>]

At 01:52 AM 3/8/2008, you wrote:
>My best distance midday reception, was KORL-650-10KW-Honolulu, HI (2500
>miles over water) heard around 1970. KORL was mixing with KYAK-Anchorage
>(1800 miles also over water). That would be nil to impossible today with
>CISL there. No Sacramento CA on 650 then either. I also heard several
>Midwesterns (WMAQ,WGN, WBBM, WLS, WHO, etc) around 1 PM Pacific time
>back in the early 70s too. In those days I had a 600 foot longwire
>running  N/S.
>   In recent years around 2000 I logged
>around 2PM or so in mid winter, KATQ-Plentywood MT, KFTI-Wichita KS, an
>Houston TX.  So long haul  Midday Winter DX can be had. 


I guess the problem is determining what is ground wave and what is skywave especially during a winter day in the northern part of the USA, or any part of Canada.   If there's any amount of fading over less than a few minutes, it's generally thought that there's a skywave component.

There's several scientific publications that I've seen that address MF groundwave from a theoretical standpoint;one (NTIA Report 99-368: Medium Frequency Propagation Prediction Techniques and Antenna Modeling for Intelligent Transportation Systems (ITS) Broadcast Applications by Nicholas DeMinco,   available at http://www.its.bldrdoc.gov/pub/ntia-rpt/99-368/) says "At 0.5 MHz over average ground, the ground wave predominates over the sky wave from the transmitter site out to distances of about 150 km, where
the two signals are equal. The signals add as vectors, and destructive and constructive interference
can occur. At distances beyond 150 km the sky wave is the predominant signal. At a signal
frequency of 1.5 MHz, the distance where the two signals are equal reduces to 45 km, because of the
increased loss at the higher frequency."

Given the above figures, I'm not sure how I received CBK-540 here in Victoria at 2PM local on a mid-July afternoon (1PM sun time, given it was daylight saving time then); I wouldn't have expected much skywave then.  

The references in the above publication will give you a wealth of sources, some of them stiff with mathematics.

Other publications
http://www.its.bldrdoc.gov/pub/ntia-rpt/86-203/index.php

http://downloads.bbc.co.uk/rd/pubs/reports/1978-07.pdf

The FCC's AM groundwave field strength graphs:  http://www.fcc.gov/mb/audio/73184/index.html


Gordon Nelson's article, "Skywave or Groundwave Reception", National Radio Club reprint P9 (http://www.nrcdxas.org/) addressed the problem of identifying which is which for the DXer, and was an initial introduction to long haul groundwave propagation for me.

Hope this helps.

best wishes,

Nick



*****************************
Nick Hall-Patch
Victoria, BC
Canada 
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