Garmin 205

Thinking about buying a Garmin 205 just for the GPS to use on the Ski and the bike as they are currently ?130 from Wigle!
Any reasons why I shouldn't?

A garmin305 currently costs CDN$189.00- about106.00 GBP at GPS city in Calgary. The post works pretty well.
www.gpscity.ca/garmin-forerunner-305.html
The older models are getting hard to come by, it seems.

Jim

Cheers Jim, thats a good price! Have search a little harder see If I can match that in the UK for the 305

Andy

The 205 is great and does everything you need it to do if, like me, you aren't interested in heart rate.

Cheers Gary, yes I'm not intersted in HR from thsi and searching the net it looks like the 205 is a good lump cheaper in the UK so i will probably get one ordered while the stocks last.

just saw some new forerunner 301's on sale on ebay aus for $170

pretty good buy I reckon

I recently bought my first GPS, the new Garmin 310XT, and it is great. However, being new to using a GPS I wondered if any old-hands could tell me how reliable they are when it comes to recording one's maximum speed.
In a downwind race (Fish Hoek to Buffels in Cape Town) in a double ski on Saturday, my maximum speed was reading as 118kmph afterwards! Clearly this is impossible, so although the timer was definitely stopped, I don't know if the GPS somehow picked up on our return drive to Fish Hoek, or if this is an error that can occur due to loss of signal during the paddle, and then reading a fast "jump" when signal is picked-up again.
Other spikes from the paddle show 55kph & 53kph (again, I would think impossible), and then coming into the realms of possibility ... 24kph, 26kph, & 35kph (it definitely felt like we were flying at times but the latter might also be pushing it).
Has anyone else exprienced this; is it normal or do I have a faulty GPS device?

Are you sure you didn't have it on whilst driving? !!!

One feature to look at is the speed smoothing mode, on/off.

But I have never had this sort of issue unless it was from my stupidity to forget to turn the damn thing off when I finished!!!

Hmm... I just got a review unit of the 310XT, which I also used (for the first time) on Saturday.

The stats looked perfect for me - ave 13.4kph/max 20.1kph.

Yesterday's Reverse Millers also looks good ave 12.6/max 17.5. I stopped a couple of times to let the other guys catch up

Where did you mount the unit?

I used to see spikes like this on my old 301, but not so much since then.

Did you upload the data? Can you see where the spikes are and when they occurred?

Hey Rob

I was sitting in the back of a double ski and had it mounted on the footstrap, screen facing towards me. The boat wasn't draining too well so with the swell, I did end up having water sitting just over the top of the unit for some extended periods, but I wouldn't have thought this would have mattered ... would it? It still seemed to be reading whenever I glanced at it.

On the upload, the graph showed several other spikes but I don't see my 118km/h interval! The speed axis on the graph doesn't go anywhere near that level.

I've mailed Garmin support and they replied as follows:
"This would just indicate a speed spike, this is quite normal with gps and can be particularly common if you were in an area with poor satellite reception such as in a valley. To avoid this leave the watch with a clear veiw of the sky for a few minutes before moving off."

What I don't understand is that I've spoken to other guys (like Dale, or you for that matter) who paddle in the same locations & conditions and have never had this issue. We did paddle quite close to shore going past Smitswinkel on Saturday, so maybe it's possible there was interence from the peak, but that doesn't really explain the 82.7km/h maximum I got when paddling around Hout Bay harbour on Tusday night.

I have often seen absurd high velocities recorded on a 305, downloading data into sporttracks. This only happens when i use it in one location, travel to a different location, but fail to reset. The events are split on import and GPS was off. However the imported graph shows a line from the first location to the second with the distance between incorporated into the second event, and no added time. Had this happen with Garmin 60c also, in fact if don't reset it always happens with the 60c. I have done this at least twice after traveling 700 mile to paddle, resulting in very impressive speeds! Doubt this explains the smaller speed spike, which probably were result from lack of smoothing.

No problems with the 310 XT, but I did have the same on an old 201 a few times.


Or maybe the gym program was yielding massive gains???

nickpick wrote:

I was sitting in the back of a double ski and had it mounted on the footstrap, screen facing towards me. The boat wasn't draining too well so with the swell, I did end up having water sitting just over the top of the unit for some extended periods, but I wouldn't have thought this would have mattered ... would it? It still seemed to be reading whenever I glanced at it.

On the upload, the graph showed several other spikes but I don't see my 118km/h interval! The speed axis on the graph doesn't go anywhere near that level.

I've mailed Garmin support and they replied as follows:
"This would just indicate a speed spike, this is quite normal with gps and can be particularly common if you were in an area with poor satellite reception such as in a valley. To avoid this leave the watch with a clear veiw of the sky for a few minutes before moving off."

Water (especially salt water) is a notoriously bad medium for RF signals (GPS signal) to propagate through. In other words, the GPS signal, after losses from the signal being reflected from the water surface, will be further massively attenuated (reduced) on its journey from the water surface to the receiver under water. If your GPS was submerged, then it is highly likely that it lost lock on some or all satellites causing massive errors in your data. Much worse than being in a valley as Garmin suggests as a cause. When the unit re-acquires lock it does so from a HOT condition, so does this very quickly (typ. <1s) which may be why you never saw anything amiss on the display.

In order to avoid this, people using the GPS to record their data while swimming often keep the GPS under their swim cap. This also avoids the problem of the GPS picking up on you arm speed rather than your swim speed.

As far as the discrepancies go between what the unit reports and the uploaded data, this will have to do with the amount of smoothing that each applies to the raw data. I use SportTracks (far better than Training Center in my opinion) and in the program you can select how much smoothing to apply.

Thanks.
I may have had it on while driving back to the start, but I had certainly at least hit the Stop button, so I would have thought this would prevent it from clocking my driving speed as part of the Activity's maximum. Looking at some of the other replies, I will try and make a point of resetting and see if that helps.
I can't find a speed smoothing mode - either on the device or in the instructions.
Nick

Thanks for that.
From what you;ve explained, the submerging issue, even though it was only just submerged, sounds like it may have been a major factor (if not THE factor).
On a different paddle in awful weather 3 days later, I did also get another erroneous maximum speed of 82km/h and I don't think the unit ever got submerged during that paddle because it was within a protected harbour (there was wind chop but I don't think anything big enough to swamp the boat).
Anyway, I will see how it goes with all these point sin mind.

An interesting test would be to incrementally submerge the GPS and see what effect it has on how many satellites the Garmin is receiving data from and the stated accuracy. At least 4 satellites are needed for an accurate measurement, although the more the better. On my 305 this is done by selecting MODE->NAVIGATION->SATELLITE and then the UP/DWN buttons for different display formats. I think that on the 310 it is MODE->SELECT GPS SATELLITES and then UP/DWN.

But from what you say, that this happens in calm conditions as well, it might not be the cause of your problems. I do not know how Garmin handles the loss of adequate signal strength, they might autopause the recording of data for this time so that no funnies are recorded? I am not sure.

You could try a soft reset of the unit by pressing Lap and Mode together until screen goes blank. This does not erase any data or settings but should clear your satellite cache. This might fix your problem, but it is a bit of a Hail Mary. You should be sure to be in a nice open space when acquiring satellites for the first time after this and it might take a bit longer than usual.