External Antenna

[+hookedoncache]

I have another question that someone brought up.

 

External antenna. I have a 60CS and with all of the lost signals that I get I was thinking about this but from some of what I read I'll need a power source? I did see some that didn't require a power source but are they worth it?

 

What external antennas do you recommend?

 

Thanks,

 

Marshall

[Phoenix2001]

There is a "GPS Units and Software" forum that's a good place for hardware questions.

 

The 60CS has an MCX antenna connector. An external antenna plugged into it draws power from the 60CS and causes the 60CS to switch from the internal antenna to the external antenna. The newer Garmin receivers supply 2.5 volts via the antenna connection if they have an external antenna connection. Make sure you get an external antenna with the appropriate connector (MCX) and operating voltage range. Some antennas that are specified to work from 3 to 5 or more volts will work at 2.5V.

 

eBay can be a good source for external antennas. A Gilsson antenna from GPSgeeks is a common one purchased.

 

The early Garmin eTrex series (I don't know about the new color models) did NOT have an external antenna connector. You need to use a re-radiating antenna with them and the re-radiating antenna needs a power supply - it doesn't have a physical connection to the receiver's batteries.

 

The 60CS has a pretty good antenna. The external antenna may not make a big difference. If you are blocking signals often with your body, the external antenna will help if you mount it on top of a hat, etc. If vegetation is attenuating the signals, it might help enough. If buildings and mountains are blocking the signals no amplifier will work because there aren't any signals to amplify. Amplifying signals bounced off a wall, rocks, or refracted through leaves is also not good (multipath).

 

In other words an external antenna will help in some conditions but not always.

[Phoenix2001]

Another thing that might help is to use some satellite prediction software or just pay attention to the satellite patterns on your GPSR screen. If you are going into an area where the satellites are going to be blocked from the horizon to a fairly high elevation (angle), go there when you will have a good distribution of satellites high overhead. A straight line is a very poor pattern. The patterns repeat about 4 minutes earlier each day (sometimes a satellite will be down for a day for maintenance or other reason).

 

Sometimes there are few satellites overhead and many close to the horizon. This is not a good time to go into a wooded canyon. The distribution of satellites is not the same throughout the day.

[+Tread-n-Lightly]

I have the 60CS and can personally recommend the GILSSON antenna. I haven't used it enough to give in-depth details (battery usage, etc...), but I can tell you that it works great! It comes in 3, 6 or 9 foot lengths and it's really inexpensive.

I don't use it too often because the 60CS's antenna works fine (so far).

 

W5TTX

[+JohnnyVegas]

When you say loss of signals do you mean the you have lost the lock on the sattelites, or do you mean your are not tracking as many birds?

 

Before spending money on an antenna that may or may not help. I would recomend finding more caches with your GPS as it is. I know a few local cachers in my area that have numbers in the 1,000s and they do not bother with exteranal antennas.

[+hookedoncache]

Thanks everyone!

 

To answer the question:

When you say loss of signals do you mean the you have lost the lock on the satellites, or do you mean your are not tracking as many birds?

 

The GPSr is constantly loosing contact with enough satellites and will beep then request me to press enter to start it looking for satellites. This happens all the time while in a wooded area and once in the open.

 

Tread-n-Lightly - thanks for the recommendation

[+tirediron]

and causes the 60CS to switch from the internal antenna to the external antenna

I wasn't aware of this; I have checked the manuals for both the 76CS and the 60CS and find no mention of it. It was my understanding that even with an external AE plugged in, the unit still used input from it's built-in AE.

 

That aside, I have Glisson type external AE for my 76CS, and find that it provides a noticeable improvement in signal reception strength, as well as the number of held birds on certain occasions; typically, in dense cover or limited sky-exposure areas.

[Phoenix2001]

The GPSr is constantly loosing contact with enough satellites and will beep then request me to press enter to start it looking for satellites.  This happens all the time while in a wooded area and once in the open.

The receiver might not be operating "within spec" and should be sent to Garmin for repair. Try using it more in fairly clear areas. If you continue to have trouble note how often so you have some good statistics to give to Garmin's technical support.

[Phoenix2001]

and causes the 60CS to switch from the internal antenna to the external antenna

I wasn't aware of this; I have checked the manuals for both the 76CS and the 60CS and find no mention of it. It was my understanding that even with an external AE plugged in, the unit still used input from it's built-in AE.

 

Trying to use two antennas at the same time would be something like my putting headphones on you and feeding one person talking into one ear and delayed by a fraction of a second into the other ear.

 

Better example....

The position that is calculated is where the signals "come together" i.e. at the antenna. If the external antenna is put 200 ft. away and the receiver tried to used both, it would be trying to calculate the position of both antennas at the same time.

 

When using a re-radiating antenna with a GPS receiver it's important to make sure the internal antenna can't receive the signals directly from the satellites and only from the re-radiating wire.

 

That aside, I have Glisson type external AE for my 76CS, and find that it provides a noticeable improvement in signal reception strength, as well as the number of held birds on certain occasions;  typically, in dense cover or limited sky-exposure areas.

 

I did mention that an amplified external antenna can help when vegetation attenuates the signals. My primary use is mapping trails. I use a GPSmap 76 in my hand with it's internal antenna and a GPS 76 in a belt holster connected to an external antenna on top of my hat. Sometimes one does better, sometimes the other.

Edited October 5, 2004 by Phoenix2001

[+briansnat]

Thanks everyone!

 

To answer the question:

When you say loss of signals do you mean the you have lost the lock on the satellites, or do you mean your are not tracking as many birds?

 

The GPSr is constantly loosing contact with enough satellites and will beep then request me to press enter to start it looking for satellites. This happens all the time while in a wooded area and once in the open.

 

Tread-n-Lightly - thanks for the recommendation

That doesn't sound right. I rarely have that problem with my eTrex and the 60C has a slightly better antenna. Is it new? Did you turn it on and leave it out with a full view of the sky for 15-20 minutes when you first got it?

 

Do you turn it on well before you enter the woods? You should let it find the sats under clear skies. That way it knows where they are and can find them easily under tree cover.

 

If yes, it might need to go back to the mfr. Your GPS should not be frequently losing signals. Once in a great while maybe.

Edited October 5, 2004 by briansnat

[Phoenix2001]

I've assumed you are using it correctly....

That model needs to be held vertically for best reception. It won't do well if you hold it horizontally, which you have to do for the magnetic compass to work well (If Garmin is still using the hardware that's in the 76S).

[+hookedoncache]

Phoenix2001 I have looked and looked but I can not find where it says to hold the unit vertically not horizontally when following either a map or pointer. I did see where the manual states to hold the unit level while using the compass and while calibrating the compass.

 

Maybe that is what I'm doing wrong!

 

As far as the first initialization I did that and it only took about 5 minutes. I believe that I will recalibrate the whole unit to be sure that all is as it should be...

[+tirediron]

and causes the 60CS to switch from the internal antenna to the external antenna

I wasn't aware of this; I have checked the manuals for both the 76CS and the 60CS and find no mention of it. It was my understanding that even with an external AE plugged in, the unit still used input from it's built-in AE.

 

Trying to use two antennas at the same time would be something like my putting headphones on you and feeding one person talking into one ear and delayed by a fraction of a second into the other ear.

 

Better example....

The position that is calculated is where the signals "come together" i.e. at the antenna. If the external antenna is put 200 ft. away and the receiver tried to used both, it would be trying to calculate the position of both antennas at the same time.

 

When using a re-radiating antenna with a GPS receiver it's important to make sure the internal antenna can't receive the signals directly from the satellites and only from the re-radiating wire.

 

That aside, I have Glisson type external AE for my 76CS, and find that it provides a noticeable improvement in signal reception strength, as well as the number of held birds on certain occasions;  typically, in dense cover or limited sky-exposure areas.

 

I did mention that an amplified external antenna can help when vegetation attenuates the signals. My primary use is mapping trails. I use a GPSmap 76 in my hand with it's internal antenna and a GPS 76 in a belt holster connected to an external antenna on top of my hat. Sometimes one does better, sometimes the other.

Do you have a reference for this? I am quite curious about this. All of the indications that I have seen when using my 76CS with the external AE indicate that it is still using the built-in as well. With repsect to your comment about being 200' away, I understand what you are saying, and I agree completely with the theory, but I don't think that the 9' of cable between my Glisson and my GPSr are going to make a difference (I tried to work the signal time delay equation on that, and didn't have enough zeros on my calculator!) You're right about the re-rad, totally different kettle of fish. Not trying to flame, just very curious about this....

[Phoenix2001]

Phoenix2001  I have looked and looked but I can not find where it says to hold the unit vertically not horizontally when following either a map or pointer.  I did see where the manual states to hold the unit level while using the compass and while calibrating the compass.

Ahhhh, you didn't know you were supposed to read a GPS 76 manual?!?!?

 

Garmin manuals have plenty of room for improvement. It looks like they didn't say anything about how to hold the receiver in the 60C, 60CS, 76C, and 76CS manuals.

 

My Venture manual on one page says, "Hold the unit.... with the antenna pointing up." It doesn't say which direction is "pointing up". In this case the eTrex series have patch antennas that should be horizontal which is the same plane as the screen. In other words the eTrex models should be held horizontal (then the antenna is pointing up) but are also not that sensitive to orientation. I can turn the Venture upside down and have it still work.

 

The 76 series (76, map76, and 76S) have quadrifilar helix (sometimes referred to as quad-helix or just helix) antennas, as do the 60 series and 76C and 76CS. These antennas are sensitive to orientation. If you read a GPSmap 76 manual it will tell you to hold it in front of you "with the top of the unit pointed toward the sky." This puts the screen in a vertical direction - not the way you would usually put a map.

[+JohnnyVegas]

The GPSr is constantly loosing contact with enough satellites and will beep then request me to press enter to start it looking for satellites.  This happens all the time while in a wooded area and once in the open.

The receiver might not be operating "within spec" and should be sent to Garmin for repair. Try using it more in fairly clear areas. If you continue to have trouble note how often so you have some good statistics to give to Garmin's technical support.

I must agree. while I use Magellan now, I started out with the Yellow e-trex and a freind of mine use the legend, both of which have patch antennas and we never had that type of a problem and we both used the in some heavy tree cover. the signals would get week but we very rarely lost a signal.

[Phoenix2001]

Do you have a reference for this?

In terms of specifications from Garmin - no.

One indication that only one antenna is used is if I plug an external antenna into the GPSmap 76 and then block the external antenna - all the signal bars go to zero until I either remove my hand or disconnect the external antenna. I don't have a passive antenna to do more tests.

 

Check the following message in sci.geo.satellite-nav or do a google search in that group for "external antenna current" or some such. This was with a 12XL but I doubt they changed much.

 

<http://groups.google.com/groups?selm=5doj82%24qpi%40harpo.cs.ubc.ca&output=gplain>

 

I am quite curious about this.  All of the indications that I have seen when using my 76CS with the external AE indicate that it is still using the built-in as well. 

Would you share what these are?

 

With repsect to your comment about being 200' away, I understand what you are saying, and I agree completely with the theory, but I don't think that the 9' of cable between my Glisson and my GPSr are going to make a difference (I tried to work the signal time delay equation on that, and didn't have enough zeros on my calculator!)  You're right about the re-rad, totally different kettle of fish. 

 

Yes, 9' wouldn't make much of a difference. I think the error in the system is larger. The thing is, if I'm designing a system to use two antennas - what is the goal. I don't necessarily know whether the antennas are close together or far apart. I could compute the location of one and then the other and compare. Then what?

 

Note that combining the signals from the two antennas is not necessarily easy. The best solution might require two signal processing units and then compare the output from one with the output from the other. And perhaps in essence end up with an average of the location of antenna A and antenna B. Instead of the extra expense of making a "dual antenna" receiver why not just put the single antenna receiver at location A and mark then at location B and mark and average?

 

In other words I see engineering challenges, more costs, maybe not much in the way of benefits so I wouldn't expect it to work that way.

 

Not trying to flame, just very curious about this....

 

Not taken that way and I don't mean too either. I read to learn and help if/when I can and it's OK with me to disagree.

 

Thanks,

Dan

[+tirediron]

With apologies to the OP, I have started this thread in the GPS Units and Software forum, where parts of it would be more appropriate.

[+hookedoncache]

Well Phoenix2001 I guess that I didn't see that one coming. Who would have guessed that when you buy a 60CS that we should be reading the 76CS manual! Is there any other reading that I should do to understand how to use this unit? LOL