0
vidiot

Wintec WBT-201 @ 4Hz

Recommended Posts

Quote

Is the Wintec WBT-201 still the preferred "puck" logger or has something better come along?



I prefer to have a MTK II chipset based GPS receiver or logger. Qstarz 818X, BT-Q1000X or I-Blue 747 A+. They are more sensitive, faster to get fix, have longer battery life. Anyway most places and software can not handle logs more than 1Hz fix.

Share this post


Link to post
Share on other sites
Quote

Could you share anecdotal description of how you use this for jumping? What jump craft are you in? Do you have to hold the device up to the window to get a signal or can you just turn it on and forget it?



I turn the GPS device on before boarding, and tell the software in the mobile phone to start logging when the plane takes off, and then forget about it, no need to hold the device near window, but I need to be near the nose of the aircraft, so the wing or the wall is not blocking the signal. I'm jupmping from Islander usually.
lego

Share this post


Link to post
Share on other sites
Has anyone thought of threading a thin copper braid through a seam in their jumpsuit and soldering a connector on it to plug it into a larger GPS unit (like a Garmin Vista).
I'm thinking something along the seam in the sleeve with the connector right at the inside chest pocket. The long-wire antenna should provide better reception in general and solve the location problem of the GPS since the antenna is in you sleeve.

Share this post


Link to post
Share on other sites
I was also thinking the longer antenna would pick up the signal in thin-skinned aircraft better than the loaded antennas in the GPS housing. When they are short and wound they are less sensitive; hence the idea of adding the longwire antenna in a suit's seam.

Share this post


Link to post
Share on other sites
Quote

I was also thinking the longer antenna would pick up the signal in thin-skinned aircraft better than the loaded antennas in the GPS housing. When they are short and wound they are less sensitive; hence the idea of adding the longwire antenna in a suit's seam.


You rather get a GPS signal repeater if you jump that plane regularly. Oh and get a MTK2 chipset based GPS.
Those have 66 channels to track satellites and really high sensitivity.
They _can_ log your track by 5Hz without any hack.

Share this post


Link to post
Share on other sites
Quote

I was also thinking the longer antenna would pick up the signal in thin-skinned aircraft better than the loaded antennas in the GPS housing. When they are short and wound they are less sensitive; hence the idea of adding the longwire antenna in a suit's seam.



This sounds dodgy. Is it based on RF design experience, or just a common familiarity with antennas generally? GPS uses a right-hand circularly polarized signal. At the very least, the kind of antenna you're describing would not take advantage of this polarization. More likely, I think, the GPS won't pick up a signal at all when using such an antenna.

Why keep the GPS on while in the plane? I've been testing a new GPS, and have had no issue at all with turning the device on when the door opens. I get a lock within a couple of seconds in freefall.

Michael

Share this post


Link to post
Share on other sites
My experience is with HAM radio transceivers. I figured that since you can affix an external antenna to a car and plug a GPS into it (or sat radio for that fact) there could be a way to do this with an antenna for a hand-held GPS.
I admit you sound much more educated than I on the matter. I was just curious. Could you explain more?

Share this post


Link to post
Share on other sites
Quote

Could you explain more?



The signals used by GPS are right-hand circularly polarized. By using the right kind of antenna, GPS receivers can eliminate quite a lot of noise simply because it does not have this polarization.

The effect is similar to what you get with polarized lenses. Without them, any reflective surface produces a lot of glare. Polarized lenses reduce the glare by blocking light that does not have a particular polarization.

Typically, GPS receivers use ceramic patch antennas or, less often, helical antennas. Both are tuned to receive only right-hand circularly polarized signals. Functionally, the main difference between the two is that the ceramic patch antenna tends to reject signals which are not coming from "above". This can be a problem if the antenna is not oriented toward the sky. The upshot is that it eliminates many reflected signals, which make it harder for the GPS to get a lock.

You'd think a helical antenna, which is less directional, might be better in the skydiving environment. However, because it is less selective, it's also less sensitive. The best choice for wingsuits is a ceramic patch antenna properly oriented toward the sky.

There are GPS-specific external antennas. Usually, these consist of a ceramic patch antenna and an amplifier. The amplifier boosts the signal enough that it can survive the trip through a coax cable to the GPS receiver.

Why is all this necessary? GPS signals are about 20 dB below thermal noise when they arrive at your antenna. This means the noise is actually about 100 times stronger than the signal when it reaches the antenna. A GPS receiver is able to overcome this hurdle using some really clever signal processing, but a poor antenna makes its job much harder.

Not sure if this answers your question. Let me know if I missed anything.

Michael

Share this post


Link to post
Share on other sites
Quote

So when you say properly oriented, which way is that for one of these units? On the side of the helmet (say like a dytter) or flat on top?



I can't say for sure with the WBT-201, but the WBT-202 I have uses a ceramic patch antenna with the top on the same side as the buttons and lights. I imagine the 201 is the same. In this case, the best is to mount the unit on the back of your helmet with the buttons and such facing out (probably the way you'd naturally do it). This way, when you're flying, the antenna will be pointing up at the sky.

Michael

Share this post


Link to post
Share on other sites
Cheers. I've been wearing my 201 on my upper arm in a mp3 pouch with a clear plastic window (more so for base) and been getting some funky results, but I don't think it likes the short freefalls. Some of my canopy data has been pretty weird or patchy as well though.

Might try gaffer taping it to my helmet and seeing if that makes any difference.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account. It's free!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
0