Glenn, Jim's Great Circle Map (Pizza) has both rectangular and polar map projections menus. The rectangular map has the curved lines. The polar map has straight lines, but both are great circle bearings. I assume the map he is using in this exercise is the polar projection. The menu is slightly different than his freeware version. Perhaps he can clear this up. Come to think of it, polar projection may only give straight lines for one point of origin, and not all points on the map. 73, (Gil NN4CW Stacy, IRCA via DXLD)
I think that only an azimuthal equidistant projection (and therefore centered on only one location) would give straight lines to any reporter's location. Polar - per se - wouldn't do the trick. So maybe Jim took a reasonable guess as to that location, did an az equi and any resulting errors are minimal. Dunno. I'm just taking an educated guess (Chuck Hutton, ibid.) Glenn, There's a map (I can't recall the name) which is a projection of the earth from the standpoint of a globe where the bearings can be drawn as straight lines. The map is distorted as the map would be if it were a picture of the earth. This map is used by the military for DFing. I don't know if it's available for civilians or if it's unclassified (Chuck Bolland, FL, dxldyg via DX LISTENING DIGEST) I guess that`s the azimuthal equidistant projection as the previous Chuck just mentioned. But straight lines as Great Circles apply only to radiating from the central point of the map. Nothing classified about them; hams commonly have them custom-made to know where to point their beams (Glenn Hauser, DX LISTENING DIGEST) Gents: First, someone wrote to tell me the lines I drew on the 1610 map were not correct. The map, I replied, was really a great-circle projection and was correct. Ha! The joke was on me. The map was indeed correct; the LINES were off by varying amounts. It will take some work to correct the situation. End of confession! As of 10:30 this Saturday morning we have three pretty good bits of data on the 1020 signal location. Each of the data has been entered into the "system" and the results drawn without error (this time). To do this within a reasonable time frame required some manipulation on my part and I had to draw the lines by hand and scan the resultant. It is now posted here: http://tonnesoftware.com/1020.gif As can be seen, a couple of listeners with decent accuracy in getting the signal direction from points in central or eastern New York or Pennsylvania will nail it. Send your name, city/state, latitude, longitude and the apparent source azimuth and I'll add it to the list. So far the data seems pretty good (JimTonne, Dec 2, radio-insight.com DX board via DXLD) Have not yet seen Jim`s direct reply to me, held up in some digest, I suppose. Latest verson of above map shows the lines are still straight. I don`t see any way to change the projexion; the buttons on the edge don`t work (Glenn Hauser, DX LISTENING DIGEST) Here`s another pertinent post: We need to refine our direction finding capabilities. My I suggest that instead of using compass angles from your location use the deviation angle to a known station transmitter site instead. Transmitter site coordinates are very accurate. Get a null on a big power house and then retune and adjust antenna for a null on the unknown signal. Anyone with a Quantum loop or equivalent or a good quality portable radio can easily do this. For example the test tone on 1020, report your bearing relative to KDKA, KYW, WBAL or other easily heard powerhouse in the vicinity. From my location the signal from the tone tester on 1020 is about ten degrees south of bearing to KDKA. The station on 1610 was a few degrees south of bearing to WTAM on 1100. The map created by Jim Tonne looks good and is a great idea, lets give him more accurate information to use for a better fix on the tone testers. Anyone with ideas or suggestions to improve on this are welcome (Tom Jasinski, Shorewood, IL, Dec 2, IRCA via DXLD) > From: Glenn Hauser > Jim, > > Looking at your 1020 map as well as 1610 map, it seems that all the lines > are > straight. Since a bearing is really a great circle, shouldn`t they be > curved on > that map projection? Or is it possible for your base map to be based on > great > circles even tho we don`t really know the center, since that is what we are > trying to locate? As someone else mentioned a while ago, NOT using great > circles, but drawing straight lines on a flat map can cause large errors at > several hundred miles distance, defeating the purpose of this exercise. > > This is a separate issue, of course, from making correxions for magnetic > declination, which is also essential if using a compass. > > 73, Glenn Hauser ____________________________________________________________________________________ Do you Yahoo!? Everyone is raving about the all-new Yahoo! Mail beta. http://new.mail.yahoo.com _______________________________________________ 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]
