What can interfere with GPS signal?
Receivers mounted on the roof.

Receivers on the dashboard.

Receivers in the house.

Etc., etc., etc...

I recently bought a USB GPS BU-353, and I find that sitting it on my desk in my home office, it will not "see" the satellites. If I place it on the window sill, it will not see the satellites. If I stick it through a crack under the window (and place it outside), it sees the satellites just fine.

I have used the receiver in my truck, on the dash board, and it picks up the signal just fine.

What materials we commonly encounter in various locations that will diminish or block reception of GPS signals? If the receiver is inside an enclosure, what materials should be used or avoided that affect reception?


Bill Lee
Marvin Hlavac
Hi Bill,

GPS signals are quite weak, and they can be blocked quite effectively by the roof and walls of a building. The main thing is that it works in your truck.

Generally speaking, metal is a very good material that blocks RF signals. You may use a plastic enclosure, if you want to, for your BU-353. But even a thin aluminum foil placed over it would prevent it completely from working.

The BU-353 is weatherproof, so you may not need to place it in any enclosure. Many of us have used this unit on the roof of our vehicles 24/7/365, in all weather conditions with no issues for years.

Other than the physical materials that block RF signals, there are other environmental factors to keep in mind.

Driving among tall skyscrapers may not allow for good reception. The weak GPS signals don't reach your antenna directly, but they may bounce off of the buildings first. That may degrade the reception.

Even just driving under a tree cover, especially when the leaves are wet, may have adverse effect on the GPS signals received by a GPS receiver.

GPS receivers may be affected by interference from electronic devices, if placed too close. This is quite often the case with the USG GPS sticks. People like to stick them directly into USB ports of their laptops, because that's how these units are advertised in many cases. However, the RF interference coming from many (most?) computers is just way too strong, and it often prevents such a GPS receiver from working. If the included USB extension cable is used, these receivers work just fine.

Some cars have tinted windows with metallic content that blocks GPS signals. Users of such cars may find a small area without tint right behind the rear view mirror. If that doesn't work, a unit such as your BU-353, or a GM-2, or some other unit that has a magnetic base, can be placed on the outside of the vehicle for better reception.

Occasionally some users of USB GPS receivers find that if a very long USB extension cable is used, their USB GPS receiver no longer works. USB GPS receivers are sensitive to the voltage they receive via USB. If the voltage is bellow certain level, they fail to work properly. If a long USB extension is required, a powered USB hub may help.
Ken in Regina
Hi Bill,

Marvin covered the bases nicely. I just wanted to comment on your experience in the house. Many folks automatically think that placing the receiver near a window will help it get better reception. That's not always the case. Marvin mentioned that the tinting in some auto windshields may contain metallic material that effectively blocks any radio signals. That is also increasingly true of window materials in our homes, especially if we have a newer home or have upgraded our windows in the past few years.

I installed new energy efficient windows in our home about fifteen years ago. If I put the receiver close to a window it will not function. But if I move it to somewhere closer to the centre of the house I can get a few satellites. I have a bungalow with a fairly shallow slope on the roof so there is not much material to block the signals. Of course it doesn't work right now, with a couple feet of snow piled on the roof.

I have an interesting test for the relative sensitivity of a new receiver. My home office is in the basement. I have a lot of metal ductwork running directly above it. Some receivers don't have a prayer of getting a signal down here. But a few will actually get a satellite fix down here. For instance, I just turned my eTrex Legend HCx handheld on a couple of minutes ago and it already has four satellites and a 3D lock. My BU-353 takes longer but it will eventually see enough signals to get a fix.

Anybody have an estimate if fiberglass would block the GPS signals to an appreciable degree?

O.k., the reason for asking:

I have a big RV. It is quite common for me to drive it where an occasional limb contacts the roof, scraping along as I pass by. (I REALLY need to get out and trim the trees by the driveway! ) I would like to put the receiver on the roof fo the RV but I am fearful of it getting snagged by a passing branch. I have in mind making a small enclosure that could be securely attached up top to protect the receiver. Since I am reasonably competent working with fiberglass, if it wouldn't seriously degrade the reception, I could easily go that route.

Thanks for all of the comments and conversation. I am in a big learning curve right now.


Bill Lee
BellLee, I have a Bluetooth and the GM-2. I use the GM-2 as a back up. In my RV I put the Bluetooth in the cabinet right about the drivers seat. I pick up eleven satellites with 5 being above the 50% line. The Bluetooth battery holder is broke so sometimes I will loose my signal. This is when I will switch over to the GM-2 and I will place it up on the dash. Signal strength is no problem.

I like the Bluetooth so much better than the USB connection. That way I can move my Laptop around with out worring about damaging the GPS receiver. I am hopping to get the Bluetooth GPS receiver that Marvin is showing on the home page for XMas. This one is set up for Bluetooth or USB.

Good explanation... Worthy of Sticky status... Go ahead, reward yourself...
Marvin Hlavac
t1dunn, I can tolerate the maximum of 4 sticky threads, and there already were four of them in this forum section. But your suggestion makes sense, as Bill started a good topic which resulted in a number of replies potentially helpful to others.

I've created a new sticky thread ( http://www.laptopgpsworld.com/4119-laptop-gps-hardware-faqs-tips-tricks ) which lists all the 4 previous threads that were pined to the top of the index of this section, and I added this one, too. This way we can list more threads there without pushing new topics further down on the forum page.
Ken in Regina
Marvin, you are a mind reader .. a master of ESP!! You read my mind perfectly. Good move.

Cool, Marvin...
<edit>Broken image link removed</edit>

This thing will definitely interfere with GPS signals.

--- CHAS
Marvin Hlavac
Yes, a GPS Jammer! A tool one would use to make sure s/he is not being tracked!
Looks good for stealing rental cars.
Ken in Regina
I'm reviewing this thread due to a reference to it from another discussion. I just noticed that nobody ever answered Bill Lee's question about fibreglass. So for completeness for others who check here for information here's the answer.

Fibreglass will not block radio signals so an enclosure such as Bill was considering will be fine.

As an example, radomes, those ball shaped things that house radar installations like you see at airports and air bases, are made of fibreglass and house the radar facilities for air traffic control.

Any non-metallic materials should work. This would include fibreglass, plastcs and wood. The only issue with wood is if you use thick wood the internal moisture content of the wood can have an effect.

So if moisture in a piece of wood can be an issue, a human body it's also a problem? I would like to confirm this because in order to retrieve some gps routes with my cell phone I have to decide between carrying my cell phone attached to my arm, or attached to my bike.
Ken in Regina
Originally Posted by lermadae
So if moisture in a piece of wood can be an issue, a human body it's also a problem? I would like to confirm this because in order to retrieve some gps routes with my cell phone I have to decide between carrying my cell phone attached to my arm, or attached to my bike.
Welcome, lermadae.

As you guessed, your body being basically a giant bag of water makes an excellent shield from any sort of radio signals. Mounting the GPS device on top of your head or away from your body are the ideal solutions.

I mount my eTrex on the handlebars of my mountain bike and my Montana on the handlebars of my motorcycles. If I was using my smartphone for navigation I would find a sturdy bar mount for it. The closer it is to your body, the larger the "shadow" you'll get from your body.

There are other considerations. For instance if you mostly travel in open spaces where the device can see lots of satellites on the clear side (that should be a good 180 in an arm mount) it's not as critical where the device is, relative to your body. But if you're traveling in the concrete valleys of a downtown area or in very mountainous terrain and/or with a lot of vegetation surrounding you, you will want to give the device every advantage you can.

Hope that helps. ... Do you need to see the route or do you just want to hear the audible directions? That will also affect your possible mounting choices.

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