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Rechargeable batteries for your GPS

October 12, 2005 By Leave a Comment

For some time now, I’ve been wanting to research and blog about choosing recharegable batteries for your GPS receiver. This is one of the few topics I regret not covering in my book, GPS Mapping: Make Your Own Maps. I didn’t have to look far to research the subject. I turned to one of my favorite GPS/mapping software discussion boards and found this thread. The idea of being able to recharge batteries in only 15 minutes was quite enticing, so I went out and bought the suggested unit, a 15-minute charger from Energizer (Amazon link), which comes with 4 AA batteries. I got mine at Target, but as you can see from the link, Target is also selling them through Amazon.

I did a quick test with my GPS, a Garmin GPSMap 60CS (Amazon). Granted, it wasn’t the most scientific test, but I was pleased to get 20 hours out of two batteries, which is exactly what the unit is rated. I’m quite excited, since all four of my GPS receivers use AA batteries, as does my digital camera.


Filed Under: Accessories, Best of the boards, Hardware

Serial to USB converters and GPS receivers

October 9, 2005 By Leave a Comment

So you got a new laptop, which has no serial port, but your GPS came with a serial cable. What do you do? The answer lies in a serial to USB converter, but sometimes they don’t work at first. I’ve heard people say that some cheap models are problematic, and that you should buy a name brand. Generally speaking, I think this is good advice. But I’ve also heard of cheap brands working and name brands failing to. What is going on here? A thread on the Yahoo OziExplorer discussion board delved into the topic this past week. Here are a few key snippets from the discussion…

read more

Filed Under: Best of the boards, Hardware

GPS reception indoors

September 19, 2005 By Leave a Comment

In our second "best of the boards" post, we examine why you might be able to receive GPS signals indoors. Last time, we learned how water impacts reception, but what about the roof over your head? This question was posted on Geocaching.com’s foums, aka Groundspeak. Their GPS Units and Software forum   is an excellent resource for anyone interested in GPS and mapping software. Peter, a geocacher, provided the best answer…

They come through my roof (plywood and spanish tiles on top) just fine too, and they also make it through typical fiberglass boat construction. Most materials are not good absorbers of microwaves, but anything with a high water content (incl. people) or metal will block the signals.

As a general rule, anything that will heat up readily in a microwave oven will also absorb the GPS signals although the frequencies are a little different (1.5 GHz for GPS and a little over 2 GHz for ovens).

So as long as the wood and shingles on your roof are dry they’ll pass the signals ok, but of course insulation with a metal foil layer would block them.

The physical reason why things with water absorb the signals is that water molecules are highly polarized with the oxygen end having a negative charge and the end with the two hydrogens having a positive charge. When the GPS signals go through water the oscillating electrical field of the microwaves cause the water molecules to rotate back and forth and this absorbs energy from the signals.

Here is the full thread.


Filed Under: Best of the boards, Hardware

Does heavy cloud cover affect GPS reception?

September 10, 2005 By 15 Comments

Here, in our first best of the boards post, I’m quoting from alt.satellite.gps. The question that was asked  was, does heavy cloud cover affect GPS reception?

Dave Patton, Canadian Coordinator of the Degree Confluence Project had posted the best answer as of this morning…

The GPS signals will not be affected by clouds, rain, fog,
snow, etc., because of the combination of their passing
through water vapour, and the signal wavelength meaning
they "pass through" rain etc.

On the other hand, water will block/attenuate GPS signals.
For example, you can’t receive GPS signals underwater, although
having a GPS receiver antenna very close to the water surface
may allow some reception.

Most cloth that would be covering a GPS receiver’s antenna
will pass GPS signals(e.g. backpack, jacket, etc.), but cloth
with a metallic component will block/attenuate the signals.

Cloth that covers a GPS receiver’s antenna and gets wet
(e.g. from rain) can also block/attenuate the GPS signals.
In fact, you don’t even need the cloth – water on the case
that covers the GPS receiver antenna can block/attenuate
the GPS signals. That water could be drops, and/or a film
of water. I’ve seen that happen myself, when using my etrex
Venture in the rain – the signals were weak/blocked, but
a quick drying-off of the GPS case over the antenna brought
the reception back, which then degraded again as water
accumulated on the case. Similarly, GPS signal reception
is degraded in wet forest canopy conditions compared to
when the forest canopy is dry.


Filed Under: Best of the boards, FAQs, Hardware
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