View Single Post
Old 01-24-2008, 08:47 PM   #174
Gnarly Adventurer
Joined: Nov 2007
Oddometer: 140
Originally Posted by TomW
Also, someone -- probably SPoTmaker -- said earlier that one drawback for remote antennas is feedline loss in the 0.4 watt UHF satellite uplink system. Losses in the feedline at this frequency (1.6 gHz) might negate any advantage of an external antenna. I'd like to see another unit come out that has some external jacks and more transmitter power (when connected to an external DC supply).
Yep, that was me.

We've had a nightmare on industrial products offering an external antenna option for the uplink. People solder up their own cable made out of about 50 feet of speaker wire, that gives them about 60 dB loss (when they had 15 dB of margin to play with in the first place) and then bitch about how bad our transmitter sucks. (I'm not even exaggerating! ) Hence, no external antenna jack!

For what it's worth, I'm of the opinion that the GPS receiver is usually working just fine, but the failure to post position messages is probably due to the uplink to the commercial satellite system not getting through. This is more noticeable in tracking mode since each message is only sent once.
I and all of us at Axonn concur. You hit the nail on the head. Our entire engineering staff is convinced that when the guy who wrote that review complained about the "lack of sensitivity of the GPS" what was really happening was that he was giving the unit no path to transmit. He was interpreting the lack of tracking points on the map at as lack of GPS reception. He was forgetting that the transmitter has to get through too.

Insider hint about belt clip use: (Take notes ).

I did some tests myself with the SPoT clipped on my belt at my side. I got almost no tracking points at all!!

Then, I realized what was wrong. My arm was blocking the antenna!

Solution, clipped it on in back, right above my butt crack. In the open, that gets me about 60% of my track points!

I walked around for the better part of a day in Lugano Switzerland with the SPoT clipped on my belt at the back. These are narrow streets lined by buildings that average 6 - 10 stories. Got about 40% of my track points under those conditions. I tried about 5 "check in" messages with it on my belt like this in Lugano and got all of them.

Later, I walked around for several hours in Milan Italy. Similar narrow streets but the buildings average around 12 stories. Same results. (About 40% track.)

Obviously, you don't get as good a results with the thing on your belt as you do with the SPoT logo facing the sky. The antenna aim is not optimal, and there's a body absorption issue.

I'll leave it to those people who've been reading all the SPoT related press releases to guess what I was doing in Lugano and Milan.
SpotMaker is offline   Reply With Quote