Sunday, March 18, 2012

SiRFstar III reception under dense canopy

UPDATE: Here’s my 2010 take on SiRFstar III, which is rarely available these days.

My wife and I went on our weekly mountain bike ride today, and of course we took our GPS receivers along for the ride!  I was kind of excited about it; we were going to ride a trail in dense redwoods that I had never been able to map due to poor satellite reception. But today I had my Garmin 60CSx along, which has the SiRFstar III chipset on board.

Now when I say dense, I do mean dense. Redwoods are actually a low biodiversity plant community; very little grows on the forest floor due to their dense shade. I’ve heard it said that native Americans here didn’t like the redwoods — that they are downright spooky. More likely it was just the lack of game and edible plants, but you get the idea.

Manly_gulchThe trail we rode, Manly Gulch, is as challenging as it sounds — narrow and technical, with steep dropoffs. The photo at left is of me coming around a tight curve between two redwoods. The trail section pictured is a narrow perched run set between a cut redwood stump on the upper side and a retaining wall on the lower side.

But to make a long story short, the 60CSx and SiRFstar III performed admirably, as can be seen in the map posted at right. I’ve seen my 60CSx get a lock inside, and I knew it had greatly improved reception over the 60CS, but it was still nice to see it all work so well where it counts.

About Rich Owings

Rich is the owner, editor and chief bottle-washer for GPS Tracklog. Connect with him on Twitter, Facebook or Google Plus.


  1. What sort of mount did you use for the 60CSx? I’ve been eyeing one to replace an ancient etrex, but the garmin bike mount looks like a loosey-goosey cradle instead of the clamped-on back the etrex series uses.

  2. Dan-
    I used a RAM mount. Their catalog is hard to navigate by the way. I got mine from GPS City, which makes it easier to figure out which one to order. Also, if you have 31.8 mm handlebars, RAM mounts are harder to deal with. I had to use the Garmin mount on my wife’s bike, and yes, it isn’t as solid as the RAM. More info here…

  3. Wow, they make a lot of mounts. It looks like for mountain biking, you have a choice between the huge motorcycle version, and the “light duty” bicycle mount. Which did you end up with? Does yours have that big pivot ball, or do they have a more direct mount of any sort? Extra pivot points seem like a bad idea on the bike.
    I may hold off a bit and see if there aren’t any sirf-based etrex announcements at that trade show this week before I pull the trigger.
    Thanks for your help!!

  4. I’ve been drooling over the 60csx since I first ran into it..
    Anyway, that tracklog would make an excellent addition to a new trails site I’m working on:
    It’s free, and will generate elevation profiles, topo maps, and a 3D trail view in Google Earth.

  5. Dan-
    It’s the light duty mount, which is rock solid IMHO. Measure those handlebars first though.

  6. Sam,
    Cool site! And you have a trail in my neighborhood — the Trestle Trail, which I have yet to ride. Hmm, that one goes on the list.
    Sure, you are welcome to the Manly Gulch track. It includes a nice single-track approach, but I missed the single-track exit and had to grind up the road. I’ll email the file to you separately.

  7. Yep, a the SiRFstar chip is definately helpful in the thick canopy of Manly Gulch. Here’s a link to the same ride recorded with a ForeTrex 201:
    The reception wasn’t too bad, I applied MB Gravity to clean up the elevation.

  8. Hey Mike, good to hear from you. You must have had good satellite coverage that day!

  9. Hi all,
    Thanks for the review. I’m buying one today to use while mountailn biking. I fear that it will get destroyed if I mount it on the handlebars (I tumble a lot). How will it do if I throw it in the top of my backpack?

  10. I’ve had good results in the outer mesh pocket of my CamelBak. It may do pretty well inside. Water (and any product containing water)and metal both block signals.

  11. Hi Rich,

    I have a question regarding the gpsmap 60csx: I read once somewhere in the internet than not all 60csx have SIRFstar III chipset… Do you know if this is factual? I have an older 60csx which reads SIRFstar when powered up and the retail box has the sirf logo. I recently saw in an outdoor sports store a brand new 60csx, but interesting enough, the retail box did not have the SIRFstar logo.


  12. Daniel Austin says:

    I am a little confused about antennae and sensitivity under foliage, and would be grateful if you could clarify a couple of points that don’t seem to be answered elsewhere. As a guidebook writer working in Africa, I use handheld GPS (generally on foot) both in urban and forest environments. I use GPS for various purposes, including producing maps for publication for which accuracy is obviously important.

    I started with the most basic Etrex, and soon upgraded to a GPSmap 60. I had expected the latter to be an improvement over the former with regard to its ability to get a signal under forest cover, but did not find it to be really significantly better. Walking along a forest trail, my GPSmap 60 rarely manages to be locked on for more than 10% of the time (which renders it useless for plotting trails or measuring trail lengths). Perhaps I am expecting too much and the types of forests I tend to visit are just too dense for GPS use? I don’t know. What can I try to improve the situation?

    Both under foliage and not, I can sometimes get somewhat improved reception by walking with the unit held above my head, since my body is not shielding it from any direction. But clearly this looks ridiculous and is tiring over any distance! I have heard about external antennae, such as the GA-25MCX, which only ever seem to be mentioned in connection with vehicular use. I wonder if fixing a low-profile antenna extension to the top of my backpack (or hat) could bring benefits? I’ve never heard it suggested but it seems logical.

    My GPSmap 60 has now been damaged and I am considering replacing it with a GPSmap 62. In terms of ability under foliage, could I expect the GPSmap 62 to perform better than or broadly similar to the GPSmap 60? Also, could you confirm if external antennae are compatible with the GPSmap 62 (some websites suggest they are, but Garmin’s own website only lists external antennae as accessories for the 62s and 62st, not 62).

    Many thanks!

    • The GPSMAP 60 and basic eTrex are older units without a high-sensitivity chipset/receiver. Newer models with this feature will dramatically improve your reception.

      An external antenna will likely also improve things but may not be necessary. You are correct that only the 62s and 62st support an external antenna, but not the 62.

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