Another caution: Magnetic "North" can vary substantially from the predicted
declination. I always calibrate my compass by sighting a physical object
and comparing the bearing to a map. I learned this while trying to aim a
microwave antenna on top of a ridge between Bethlehem and Harrisburg PA.
Mountain loaded with iron ore. My compass was about 30 degrees off! This
mountain is one of the few places on Earth where one's compass can be off
that much due to local conditions. --Mike, WV2ZOW
On Tue, Dec 1, 2015 at 9:01 AM, David Cole <dave@nk7z.net> wrote:
> If you are doing this by hand, as I do, then remember, to keep the map
> and your bearings, in either True, or Magnetic North, I always keep my
> maps in True North, and adjust my compass readings to True North, prior
> to plotting them.
>
> If you take a Google map, it will be True North, while your
> uncompensated compass, will be in Magnetic North. I use Google Earth
> images to draw my plots on.
>
> You need to convert both your map, and your readings to the same units,
> either True or Magnetic North, before you draw a bearing line on your
> True North oriented Google map. Here is how I get them to match the the
> easy no math way.
>
> I go here: http://www.acscdg.com/ and get a map of a long, straight,
> road that runs dead N, S, E, or W in my area, the actual bearing does
> not matter, it only matters that you know the bearing of the road
> exactly, and can read your compass to that same accuracy, hence why I
> use N, S, E, or W, they are easy to find on a compass, and almost every
> city has N/S/E/W roads.
>
> I pick a road that is long, and has a sidewalk, that way I can stand on
> the sidewalk, and sight down the sidewalk, not looking off to the side
> and sighting down the road from the sidewalk, thus introducing parallax
> issues. I then take my compass to that road, and sight down the
> sidewalk.
>
> I purchased an adjustable compass so I just adjust the compass to read
> the heading of the road, and my compass is now calibrated to True
> North.
>
> See: http://www.ngdc.noaa.gov/geomag/declination.shtml for why you need
> to do this...
>
> I then go home and take a bearing on something far away, from a known
> spot on my property, and write that bearing down. Then the next time I
> go out and start looking for RFI, I just sight on the object again, from
> the same spot, and adjust the compass if it has moved... I'm now all
> set to do True North bearing drawings...
>
>
> --
> Thanks and 73's,
> For equipment, and software setups and reviews see:
> www.nk7z.net
>
> For MixW support see;
> http://groups.yahoo.com/neo/groups/mixw/info
> For Dopplergram information see:
> http://groups.yahoo.com/neo/groups/dopplergram/info
> For MM-SSTV see:
> http://groups.yahoo.com/neo/groups/MM-SSTV/info
>
>
> On Tue, 2015-12-01 at 02:18 -0500, Roger (K8RI) wrote:
> > Select your area with as much resolution as possible.
> > Drive to a location, take a bearing. using the Google distance ruler,
> > draw a line through your point. Drive to another point and repeat. Two
> > bearings are often sufficient, but three leave a small diamond for the
> > region of error. Much easier to do than explain, although there is a
> > learning curve.
> >
> > It gets messy with RFI hunting when there are multiple sources, with
> > overlapping and similar patterns as in multiple networks or an area
> > where there are a mix og cable and outside antenna and the users just
> > wired the preamps and cable together. This sometimes can lead to a much
> > larger region of error.
> >
> > 73 es good luck
> >
> > Roger (K8RI)
> >
> >
> > On 11/30/2015 8:16 PM, Karin Johnson wrote:
> > > I'm planning on doing some RFI hunting and wanted to know if anyone
> > > knows how to plot compass vectors on Google Maps?
> > > I need to plot intersecting vectors from a direction finding loop to
> > > find the source of an RFI generator.
> > >
> > > Karin K3UU
> > > Palm Harbor, FL
> > >
> > > _______________________________________________
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> > >
> >
> >
> > ---
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> >
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