GPS for range testing radio devices?

"Grant Edwards" <grante@visi.com> wrote in message 
news:13jk6iub42s7mca@corp.supernews.com...
> On 2007-11-13, Donald Harris <harrisdw1@verizon.net> wrote:
>
>>>> However, is there an off-the-shelf GPS receiver that will show these
>>>> sorts of distances *in feet*?
>
>> About any GPS has a serial output in NMEA 183 format at 4800
>> baud. Feed that serial stream to your link and receive it at
>> the other end. using another identical GPS unit to compare
>> with, you have DGPS!  Take the difference in position to get
>> range.  Quite accurate over the range you are talking about.
>
> Except that "taking the difference in position" isn't trivial.
> There might be a way to use maps.google.com or some other bit
> cartography package, but writing and debugging a program to
> compute line-of-site distances between two points on the
> surface of the geoid is icky.
>
> -- 
> Grant Edwards                   grante             Yow! Awright, which one 
> of
>                                  at               you hid my PENIS ENVY?
>                               visi.com

For the distances involved, you can consider the earth flat.  It will be 
close enough.

The calculations are quite easy.  One minute of latitude is one nautical 
mile (~6076 feet).
The longitude is the same except that must be multiplied by cosine of 
latitude.  Bring
both readings into a spreadsheet.  Let it do the calculating.  Dist = 
SQRT(X^2 + Y^2).

If you often do the range testing, set up a series of points at known 
distances.

Don

In article <1194971925.285906.240050@o80g2000hse.googlegroups.com>, 
zwsdotcom@gmail.com says...
> I often need to do range tests on short-range radio devices from 500
> to at most about 25,000 feet separation. A clear line of sight for
> laser rangefinding is not always possible. Measuring the range using a
> GPS is simple enough; just set a waypoint at the fixed end, tell the
> GPS "navigate to that waypoint" then walk away with the other end of
> the link.
> 
> However, is there an off-the-shelf GPS receiver that will show these
> sorts of distances *in feet*?
> 
> Most handheld devices show a limited number of digits onscreen, so the
> accuracy drops as you move away: it will quote the range in feet up to
> perhaps 500 feet, then switch to fractions of a mile.
> 
> While money isn't exactly an important factor, I'd like to keep it
> under US$1k.
> 
> Thanks for any advice.
> 
> 
Why not just record the transmitter position to as many digits
precision as the GPS will report, then record the receiver
position as you move away?  Plug the numbers into a couple of
equations and voila!

NS distance =  6000 * latitude difference in minutes.
EW distance =  cos(lat) * 6000 * longitude difference in minutes

range = sqrt(NS * NS  + EW *EW)

Range should be good to  +/25 feet out to 5 miles.

If you plan to move away from the transmitter along a known
path,  you could pre-compute  a few dozen ranges,  along
with coordinates, and simply move from one set of coordinates
to the next for the tests.


Mark Borgerson

Grant Edwards wrote:

> Except that "taking the difference in position" isn't trivial.
> There might be a way to use maps.google.com or some other bit
> cartography package, but writing and debugging a program to
> compute line-of-site distances between two points on the
> surface of the geoid is icky.
> 

To the accuracy he's talking about, at the distances he's talking about 
(5 miles), he can ignore the geoid and assume the world is spherical. I 
doubt if it matters whether he gets 25000 feet or 25010 feet.

Un bel giorno Donald Harris digit�:

> About any GPS has a serial output in NMEA 183 format at 4800 baud.
> Feed that serial stream to your link and receive it at the other end. using 
> another
> identical GPS unit to compare with, you have DGPS!  Take the difference in
> position to get range.  Quite accurate over the range you are talking about.

I wish it could be that simple! You can't assume that two identical modules
"drift" in the same way, so that you increase the precision just by
calculating the distance between the coordinates. In fact, identical
modules drift in completely different ways even if they are at one meter
from each other! If you use two modules in this way, you will get the exact
same precision that you would get by using only one module.

DGPS works in another, more indirect way. The GPS satellites send some
"correction parameters" that take account of several disturbances
(ionospheric delay, slight changes in the trajectory of satellites, etc).
However these parameters have some intrinsic precision limits, because you
can't predict in realtime which will be the exact status of the
disturbances at a given moment and at a given point on the Earth.
Therefore, with DGPS you need to know *for sure* the exact position of one
of your two modules (with a long term surveying or by using a more precise
instrument). In this way you can apply the reverse formulas and precisely
determine the correction parameters, so that you can send them to your
mobile station.

-- 
emboliaschizoide.splinder.com

Un bel giorno larwe digit�:

> The resolution here is tighter than I need. 25ft accuracy would be
> acceptable.

You can buy for 200 or 300$ a GPS-equipped palm device (for example I own
the Asus A636 which is quite good), then use some of the several low cost
(or free) GIS related programs designed for Windows Mobile.

P.S. If you don't like M$, probably you will find an equivalent or better
alternative with PalmOS or Linux or whathever, by spending twice the time
and the money. But you will remain pure! <g> ;-)

-- 
emboliaschizoide.splinder.com

On Nov 14, 3:24 am, Mark Borgerson <mborger...@comcast.net> wrote:

> Why not just record the transmitter position to as many digits
> precision as the GPS will report, then record the receiver

Because this has to be a turnkey "it's working at 2000 feet" solution,
something handheld and standalone and capable of being used by a
technician. They explicitly do not want to carry a laptop around.

On 2007-11-14, Donald Harris <harrisdw1@verizon.net> wrote:

>>> About any GPS has a serial output in NMEA 183 format at 4800
>>> baud. Feed that serial stream to your link and receive it at
>>> the other end. using another identical GPS unit to compare
>>> with, you have DGPS!  Take the difference in position to get
>>> range.  Quite accurate over the range you are talking about.
>>
>> Except that "taking the difference in position" isn't trivial.
>> There might be a way to use maps.google.com or some other bit
>> cartography package, but writing and debugging a program to
>> compute line-of-site distances between two points on the
>> surface of the geoid is icky.

> For the distances involved, you can consider the earth flat.
> It will be close enough.

Could be.  Somebody provided a link to a page that does
calculations for both a spherical model and for
what's-his-name's geoid.  Before going with the spherical
assumption, the OP could verify the accuracy of the spherical
model at the location in question.

-- 
Grant Edwards                   grante             Yow! I once decorated my
                                  at               apartment entirely in ten
                               visi.com            foot salad forks!!

"dalai lamah" <antonio12358@hotmail.com> wrote in message 
news:1unei4gn3c4zj.1qxh33s1p4c3h.dlg@40tude.net...
> Un bel giorno Donald Harris digit&#4294967295;:
>
>> About any GPS has a serial output in NMEA 183 format at 4800 baud.
>> Feed that serial stream to your link and receive it at the other end. 
>> using
>> another
>> identical GPS unit to compare with, you have DGPS!  Take the difference 
>> in
>> position to get range.  Quite accurate over the range you are talking 
>> about.
>
> I wish it could be that simple! You can't assume that two identical 
> modules
> "drift" in the same way, so that you increase the precision just by
> calculating the distance between the coordinates. In fact, identical
> modules drift in completely different ways even if they are at one meter
> from each other! If you use two modules in this way, you will get the 
> exact
> same precision that you would get by using only one module.
>
> DGPS works in another, more indirect way. The GPS satellites send some
> "correction parameters" that take account of several disturbances
> (ionospheric delay, slight changes in the trajectory of satellites, etc).
> However these parameters have some intrinsic precision limits, because you
> can't predict in realtime which will be the exact status of the
> disturbances at a given moment and at a given point on the Earth.
> Therefore, with DGPS you need to know *for sure* the exact position of one
> of your two modules (with a long term surveying or by using a more precise
> instrument). In this way you can apply the reverse formulas and precisely
> determine the correction parameters, so that you can send them to your
> mobile station.
>
> -- 
> emboliaschizoide.splinder.com

Quite true, but the interfaces are the same!

Don 

larwe <zwsdotcom@gmail.com> wrote:

>On Nov 14, 3:24 am, Mark Borgerson <mborger...@comcast.net> wrote:
>
>> Why not just record the transmitter position to as many digits
>> precision as the GPS will report, then record the receiver
>
>Because this has to be a turnkey "it's working at 2000 feet" solution,
>something handheld and standalone and capable of being used by a
>technician. They explicitly do not want to carry a laptop around.

Strangely I was doing some similar range testing with someone last week.
They had a handheld GPS, think it was a Garmin Etrek or some similar name. 

He just marked the transmitter as a waypoint and drove away getting a
continuous reading of bearing and distance (in meters) to the transmitter
waypoint. 

I thought this is one of the most basic features of hand held GPS units. 

-- 

On 2007-11-14, nospam <nospam@please.invalid> wrote:

>>Because this has to be a turnkey "it's working at 2000 feet" solution,
>>something handheld and standalone and capable of being used by a
>>technician. They explicitly do not want to carry a laptop around.
>
> Strangely I was doing some similar range testing with someone last week.
> They had a handheld GPS, think it was a Garmin Etrek or some similar name. 
>
> He just marked the transmitter as a waypoint and drove away getting a
> continuous reading of bearing and distance (in meters) to the transmitter
> waypoint. 
>
> I thought this is one of the most basic features of hand held GPS units. 

Yes, the OP pointed out that you can do that.  The problem
described by the OP is that when range increases to a certain
point, the units of the displayed distance switches fro feet
(or meters) to miles (or km) with too few decimal places
displayed for the resolution required by the OP.

-- 
Grant Edwards                   grante             Yow! Make me look like
                                  at               LINDA RONSTADT again!!
                               visi.com