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Why You Should (or Shouldn’t) Care about SiRF

Feb
21
2006

I’ve had many readers contact me with questions about SiRF, the SiRFstar chipsets, and especially the SiRFstarIII chipset. As more and more people look at chipsets when making a purchasing decision, more questions arise. This article isn’t meant to specifically address any of the direct questions asked, however it should provide an overview for everyone.

So let’s take a step back look at this from the perspective of a new GPS user since that is what most readers here are. Just like your computer has a central, core processor chip (like an Intel chip or a PowerPC chip, etc) GPS devices also have a core chip inside which receives the GPS signal and passes that information along to the GPS software. (I’m simplifying things a bit for this conversation.)

What many people might not know is that various GPS manufacturers don’t typically use a GPS chipset they have developed themselves. The GPS manufacturer will build the device and construct the software that you see running on the device, however the “heart” of the GPS receiver, the GPS chipset, most often comes from a different manufacturer.

Thus you can have GPS receivers from different companies that use the same underlying GPS chipset. Thus the strength of the reception from GPS receivers using the same chipset should be identical, as should the initial acquisition time. What might differ between the GPS receivers is the shape of the device, weight, screen size, and perhaps most importantly the software you interact with.

Lately a company called SiRF has been getting a lot of attention from GPS enthusiasts, specifically their SiRFstarIII chipset. This chipset is known for having fast acquisition times as well as being able to receive a GPS signal where other GPS chipsets might not have been able to acquire a solid signal, or “fix”.

So should you only consider a GPS receiver that is built using chipsets by SiRF or the SiRFstarIII chipset? No. While we agree the SiRFstarIII chipset is great I wouldn’t avoid a particular GPS receiver if it didn’t have a SiRF chipset. However if you are currently dissatisfied with the reception of your GPS receiver and it has an older chipset, SiRFstarIII might be something you want to consider in your next GPS.

In short, I wouldn’t avoid purchasing a GPS receiver that wasn’t SiRFstarIII equipped, however when I receive new GPS receivers for evaluation if it has a SiRFstarIII chipset I know the signal will be acquired quick and be strong.

12 Responses


  1. I have a Garmin etrx and I loose signal when hiking in the woods or when I hang unit around my neck. Would the Garmin gpsmap 76csx which advertizes coverage in dense foilage actualy work in the forest and hung in vertical position. It utilises the SIRF chip and uses a quad helix antena?

    Wolfgang Lugauer - September 23rd, 2006
  2. Woldgang – Yes, the Garmin 76CSx and the Garmin 60CSx both have the SiRFstarIII chipset which is a 20 channel receiver versus the 12 channel receiver in the regular eTrex. That should provide you with much better signal strength in trouble areas.

    GPS Review - September 23rd, 2006
  3. I live in NYC. I brought a IWAY350 on a trip to N.C. It worked good there but has soon has I came back to NYC. I could not get a signal to save my life. Even on elevated Hwy with clear views in long island. I was so fustrated that I return it. Which would work well in NYC & surrounding?

    John - November 16th, 2006
  4. John, look for a GPS with the SiRFStarIII chipset. You can start looking here if you don’t have a few in mind:
    http://www.gpsreview.net/automotive-select/

    Tim - November 21st, 2006
  5. I’m an electrical engineer that has been using GPS for many years. I have owned more units than I can count and have “grown up” with the technology. I do not work in GPS receiver or systems design, and I am not an expert in the field. I study the subject just enough to settle my curiosities and to make educated buying decisions. The key is not the chip manufacture or the number of channels (once you get to 12-channel receivers), it’s the number of correlators. GPS satellites transmit with very low power and they are very distant. In addition, they all transmit on the same frequency. The correlators find the very weak signal among the noise and confusion. As a result, the receiver technology, along with the map accuracy/currency, seems like a major purchasing decision to me. I don’t care how clever the style, packaging, or user interface is if the unit can’t get a fix when I need it and if the maps are not accurate. The key aspect of the SiRFStar III chipset is a design feature referred to as massively parallel correlators. This is what enables the receiver to have the ability to receive very weak signals. I would not buy a GPS navigator that doesn’t use this technology. In fact, I own 4 GPS receivers at any one time (two for cars and two for hiking) and I have revamped my entire set with units that utilize this technology. Anyone that has been frustrated by the lack of a fix when hiking in canyons, or hiking in deep cover, or driving in cities with tall buildings will appreciate this recent improvement in receiver technology. This technology also has the ability to improve a phenomenon called multi-path (where the receiver sees more than one signal because it is being bounced off objects or structures). This is counter intuitive to some, because the technology can make the problem worse due to it’s inherent design. The Motorola Instant GPS, the SiRFStar III, and Global Locate’s chips all have designs that incorporate massively parallel receivers. To my knowledge, Magellan has not incorporated this technology into their chips yet, Garmin is hit and miss so read the specs, and TomTom is pretty committed. I agree with the author in that I would not buy units that only use the SiRFStar III chips. Instead, I look at the receiver sensitivity. For example, the SiRFStar III advertises a sensitivity of -159 dBm. The Global Locate Hammerhead is -160 dBm. The Motorola Instant GPS was part of a SiRF acquisition of the Motorola GPS line. The SiRF Instant GSCi-5000 is -142 dBm. The larger (more negative) the number the better.

    Brian - December 24th, 2006
  6. Correction on my previous post. I was cruising the Magellan web site and found that Magellan has also started using the SiRFStar III chips. I would have expected them to incorporate this technology into their own chips, but I guess it makes more business sense to buy them. Anyway, this is a great example of competition raising the quality of our product choices.

    Brian - December 24th, 2006
  7. I am looking for a gps hand held unit that will work in the jungles of Venezuela. We may need to use the unit to track the position of a downed aircraft. What would be better, using a gps with SiRF technology or using a gps with an amplified external antenna?

    Thanks,
    Michael

    Michael Duehrssen - December 30th, 2006
  8. It isn’t good enough that it is SiRF technology, it has to be one of the newer products. Look for SiRF Star III. If I were taking the trip I would come with both a SiRF Star III or other equivalent (see my previous post) and an external antenna. I usually hike with a Garmin 60CSx and an external amplified antenna on the top of my backpack.

    Brian - December 31st, 2006
  9. I have used a number of hand held GPS receivers over the years. Mostly the Garmin eTrex and GPS 60CSx models, the latter having a SiRF receiver (which type exactly, I’m not exactly sure). The difference in receiver sensitivity is astounding. In general, once the Garmin 60CSx has acquired it’s initial fix after powering on, as long as it has even a small view of the sky it will maintain its lock on the as least some satellites and give a position. I’ve used it in different terrain from dense jungle, city CBDs, inside a bag inside a vehicle and still receives a signal. Once you’ll use a SiRF GPS you’ll probably never use one with it again (unless another company comes up with a more sensitive GPS receiver chip).

    foo - August 18th, 2007
  10. I am in the military looking for general use GPS device. I currently have a Magellan eXplorist 210. It can’t figure out where it is if there is even 20% cloud cover. It is useless. I’m looking to replace it. I’m looking at the Garmin line, specifically the GPSMap 60CSx and the three eTrex HCx models.

    The detailed specs for the GPSMAP 60CSx available on the Garmin web site (https://buy.garmin.com/shop/store/assets/pdfs/specs/gpsmap60cx_60csx_spec.pdf) say that the chip used in the device is a 12 channel SiRFStar III, not a 20 channel chip. Garmin is more secretive about what chip is used in the eTrex models.

    What I’d really like is a device that uses a 20 channel SiRFSTAR III chip, supports MGRS and is able to go > 20 hours on fresh batteries.

    Smittie

    Smittie - April 3rd, 2008
  11. The SiRFstarIII can track up to 20 satellites at a time, it is a 20 channel chip. However sometimes manufacturers still list it as a 12, or 14, or 16 channel receiver. (I’ve seen them list it in all forms.) Why? It is pretty much impossible the way the satellites orbit to be able to see more than a dozen from any one point on earth at a time. Therefore some manufacturers have chosen from time to time to call it a 12 channel receiver because (in their words to me) it will never really be able to track more than 12 at a time.

    Tim - April 3rd, 2008
  12. I have two GPS/DVD/TV/Bluetooth/Radio/SD/Ipod/etc car entertainments from China. I have installed both by myself, and the first one has the GPS antenna inside the top acrylic front bumper and the second one over the roof covered with a plastic box.

    The first one works with almost no problems except going to downtown (Washington DC) after 3:00 pm when for some unknown reason the signal gets distorted, and I can’t use it at all. After that, the signal is clear everywhere at anytime (except under tunnels and similar).

    The second one -which was much cheaper- is mostly “fighting” to find the GPS signal, and even when I have tried changing ports, nothing helps much. This second GPS system is “weaker”, it works but not all the time but mostly early in the mornings and at evenings. Still, I don’t know why.

    The voice of the device in the second vehicle reminds me in several occasions that the signal is weak, and I can see that it is “connected” to the satellites but the images are frozen and “recalculates” the route very often.

    This article has helped me a lot for my next shopping, because I will ask for the famous SiRFstarIII or a similar technology installed in such kind of device.

    Thanks.

    Gino - May 22nd, 2009



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