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" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; "Mailing list for the International Radio Club of America" <[email protected]> Sent: Monday, March 10, 2008 8:03 AM Subject: Re: [IRCA] Max. Groundwave Propagation Distance?--Thanks! --- "Jeff T. Casey" <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]> FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15' AM: Hammarlund HQ-150 & 4' FET air core loop ____________________________________________________________________________________ Looking for last minute shopping deals? Find them fast with Yahoo! Search. http://tools.search.yahoo.com/newsearch/category.php?category=shopping _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected] _______________________________________________ IRCA mailing list [email protected] http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: [email protected]
