Patch Vs. Quad Helix Antennas

[+Sputnik 57]

Forum Lore: On balance, quad helix antennas outperform patch antennas. This sort of makes sense, since Garmin and Margellan put quad helix on their higher-end units. Is this real or just a marketing ploy?

 

Forum Lore: Quad helix antennas work better in tree cover, but patch antennas may actually work better in canyons, whether natural or concrete, since quad helix antennas use a wider angle "view" of the sky. Does anyone have some real world side-by-side comparisons to back this up?

 

Forum Lore: An external (patch) antenna will boost signal strength on a GPSr with a quad helix antenna. I know that when I plug my Gilsson external into my 60C, sat bars go up and EPE goes down, regardless of my location, although it is more noticable with a clear view of the sky. Does plugging in the external turn off the quad helix, or are they both contributing to reception?

 

Forum Lore: Patch antennas on the newer units (e.g., Legend C) are better than those on older Etrex units. Can anyone confirm that?

[+Renegade Knight]

..Forum Lore:  Quad helix antennas work better in tree cover, but patch antennas may actually work better in canyons, whether natural or concrete, since quad helix antennas use a wider angle "view" of the sky.  Does anyone have some real world side-by-side comparisons to back this up?...

eTrex Vista vs. GPS V in the canyon at Twin Falls and under tree cover in Sun Valley.

 

The difference is noticable, but not enough to stop you from buying the GPS you want based on other features. Especially in Idaho where you are about 50/50 on canyones, rock faces and forest. At least in Southern Idaho. Those northerners have more trees.

 

The newer generation of GPSs seem to have better reception than the old ones in general so it's going to be interesting to see how they stack up. New patch vs. Old Quad etc.

Edited March 7, 2005 by Renegade Knight

[+Jamie Z]

I tend to think that the biggest difference is not necessarily in antenna design, but in size.

 

Clearly the eTrex was designed to be small, so its antenna was made as a compromise. In my experience the eTrex does not get or maintain a lock as well as my Meridian does.

 

The Meridian is a much larger unit and has room for a bigger antenna.

 

But.. that's just forum lore. An EE with some background in antenna design might be able to better answer what the differences are.

 

Jamie

[+Poindexter]

Jamie Z is correct. Size matters. If I had my camera with me I'd show you a quad helix for a marine receiver that's bigger than my Garmin Map76S altogether. With the two types of antennas of the same "aperture", there is no user noticeable difference whether under tree cover or not. When an external antenna is used, the internal one is disabled. The current flow of the external antenna is used to determine when it's connected. With a patch antenna the unit must be held horizontally for best reception and I suspect that most people don't do this. With a quad helix antenna, you have more leeway with respect to orientation of the antenna. Holding a patch antenna at a 45° angle will cause much more signal degradation than doing the same with a quad helix.

[peter]

To address your 4 points in order:

 

1) I don't see there being any clear-cut superiority of one type over another. Both have pretty similar gain patterns, but there is a slight tendency for the patch to be better overhead and the helix better toward the horizon. As to the tendency toward helix in higher-end models, I don't see that either. Among Magellans there are helix antennas on such low-end models as the older 315/330 series and the SporTracks whereas patch antennas are used in the eXplorist 400/500/600 and I believe also in the RoadMates. Garmin also uses helix antennas in some of the lower end models like the Rino110 and a patch in models like the 26xx series, Quest, and iQue. I.e. both antenna types are found at various price levels. Frankly I've seen bigger differences in individual samples of the same model than between helix and patch antenna types overall.

 

2) The slightly greater sensitivity toward the horizon can be a detriment from the standpoint of multipath in canyon situations, but the effects seem to be pretty minor.

 

3) When an active antenna is plugged into a Garmin or Magellan, the unit senses the current draw and disables the internal antenna. That prevents any interference between signals from the two antennas. The external antennas generally give greater signal strength, but there's again a trade-off with possible multi-path problems. Makers of external antennas know that their products will be judged by how much the signal strength is increased over the regular antenna, so they're presumably inclined to err on the side of higher gain.

 

4) The new eTrexC models do tend to show greater signal strengths. Not clear if that's because of a change in antenna design or just a decision to boost the amplifier gain. Garmin knows that the older eTrex models were criticized for low sensitivity, so that could encourage them to increase the gain (even if it might make them more susceptible to multi-path). They may also have developed better software algorithms to reduce multipath problems and can therefore run the amplifier a little hotter.

[+EScout]

Your GPSr is a radio receiver, consisting of 3 parts: the antenna, radio receiver and processor. As for the antenna, the quad helix has more gain at lower angles (lower on the horizon) , which is where you need more gain because satellites at lower angles are further away. Satellites at very high angles are closer and do not need as much gain.

As for the radio receiver, there is the sensitivity, noise floor, IMDs, adjacent channel selectivity, and so on. As for the processor, there is the speed and programing.

 

With a little experience with satellite communications in amateur radio, I would always choose a quad helix over a patch. (I would choose an Eggbeater II over a helix, but the Amsats move very quickly in their paths.) With over 2 years experience with a Legend and a Meridian, the Meridian has performed better in nearly every situation: Tree cover, under cover on a ferry boat, in canyons, near tall buildings. By better, I mean more satellites, stronger signals, more accurate position. Where they perform they same is in open clear areas. How much of this is due to differences in the receiver and processor, and how much the antenna?

[+NightPilot]

I think your experience is too small a sample to be used to prove anything. As Peter said, differences in samples of the same model can be greater than the difference between different models. The quality control people just check to make sure a unit meets the minimum specs, and they don't reject one which exceeds the specs. A sample of at least a few dozen, preferably several hundred, would be needed before drawing the conclusions you seem to be drawing.

[+Alan2]

I have a GPS that slips into my CF slot in my Pocket PC. It's one of those dual sensitivity models (sirf chip set) that uses a patch antenna, I believe (it's flat). In the high sensitive mode, I was pulling in 8-9 sats while sitting in a diner. The updates are slower however and not good for autorouting while driving (you'd be past the street at the update). But of course it works better in the woods. In the low mode it was about the same as my Vista. That's where I'd leave it while driving.

 

Anyone familiar with the technology?

[+EScout]

These units are stamped out by the thousands. There might be minor differences amoung the units, but I doubt it is very significant.

[+JohnnyVegas]

About two years I asked garmins tec support about a Qud vs a Patch antenna, they said the quad was a better antenna.

 

As far as Escouts explanation, it is not just his opinion, it is a very accurate discription of how radios work. The higher gain antenna is going to do a better job of pulling in a distant station.

[+GrnXnham]

Forum Lore: On balance, quad helix antennas outperform patch antennas. This sort of makes sense, since Garmin and Margellan put quad helix on their higher-end units. Is this real or just a marketing ploy?

 

Forum Lore: Quad helix antennas work better in tree cover, but patch antennas may actually work better in canyons, whether natural or concrete, since quad helix antennas use a wider angle "view" of the sky. Does anyone have some real world side-by-side comparisons to back this up?

 

Forum Lore: An external (patch) antenna will boost signal strength on a GPSr with a quad helix antenna. I know that when I plug my Gilsson external into my 60C, sat bars go up and EPE goes down, regardless of my location, although it is more noticable with a clear view of the sky. Does plugging in the external turn off the quad helix, or are they both contributing to reception?

 

Forum Lore: Patch antennas on the newer units (e.g., Legend C) are better than those on older Etrex units. Can anyone confirm that?

1) True. My quad helix outperforms my patch 2 out of three times.

 

2) True under tree cover. Can't verify the canyon thing.

 

3) not sure

 

4) not sure

[+GOT GPS?]

My Garmin III and IIIplus units didn't seem to do as well as my vista around the trees and buildings near my house. I have done some running in my neighborhood, and when I would be running past some buildings that were 15 feet tall, my Vista was always cutting out. My GPS V unit was much better, but now my GPS 60C seems even better.

 

The location of the Click Stick and your Thumb to the patch antenna seems to me to be a problem. For good reception in the Vista, I would keep my thumb off to the side and the vista chest level about a foot in front of me.

 

Edited in:

 

Note also that the eTrex models are more compact units than the others listed. As a result, they have slightly less antenna gain (on the order of perhaps 2db

less) than the physically larger models and thus will have slightly less sensitivity which may be important under forest canopy.

 

This quote is from:

http://www.gpsinformation.org/joe/gpsantennaspecs.htm

Edited March 8, 2005 by GOT GPS?

[+JohnnyVegas]

 

Forum Lore: Patch antennas on the newer units (e.g., Legend C) are better than those on older Etrex units. Can anyone confirm that?

I would say this is not true, For an antenna to work properly it is made to be the same wave length as the signal it is receiving, A patch antenna is a piece of metal that is stamped out so that the area of the antenna is electrically the same size as the wave length of the signal from the GPS. This cannot really be changed without having and adverse effect on the GPS receiver.

[+AtoZ]

Shees this doen't see to be any better then the lore the OP posted. Alls I know is a patch likes to be held parallel to the earth while a quad liels to be held perpedicular. The quad is more suceptable to reflecive sign as it has a lower angle of aquisition then the patch there for the patch is better in thes sutuations but then again the patch has a narrower are of focus so it may not pick up a signal if the sataeliites oare lower to the horizion.

For general geocaching either one is just a useful.

cheers

[+Poindexter]

I would say this is not true, For an antenna to work properly it is made to be the same wave length as the signal it is receiving, A patch antenna is a piece of metal that is stamped out so that the area of the antenna is electrically the same size as the wave length of the signal from the GPS. This cannot really be changed without having and adverse effect on the GPS receiver.

While antenna size is a function of the frequency used, it does not restrict it to "a wavelength" in size. There are many ways to make an antenna "resonant". This is done by varying the physical size as well as the electrical size with other components. I'll have to bring my camera in tomorrow and show you guys a pic of a quad-helix gps antenna that is as big as your whole receiver. Making an antenna of multiple 1/2 wavelengths (the basic starting point in antenna design) in size is the most common way of increasing an antenna's gain.

[+Poindexter]

Here's the pic of a quad-helix antenna for a Northstar Marine GPSr. These antenna's typically come with 30' of cable and a larger antenna (high gain) is required to overcome the losses in the cable run.

 

[peter]

These antenna's typically come with 30' of cable and a larger antenna (high gain) is required to overcome the losses in the cable run.

That's why most of our external antennas are the "active" type with an amplifier located right at antenna location. The amplification compensates for the signal losses in cable.

[+Poindexter]

The antenna shown is an active type. It is a few years old. All the marine antenna's Iv'e seen in the last couple years are of the patch type. Some passive (can be used with up to 25' coax) but most are of the active type.

[+Right Wing Wacko]

These antenna's typically come with 30' of cable and a larger antenna (high gain) is required to overcome the losses in the cable run.

That's why most of our external antennas are the "active" type with an amplifier located right at antenna location. The amplification compensates for the signal losses in cable.

One thing that always bothers me about external antenna's:

 

Since GPS works by measuring how long it takes for the Radio Waves to reach the receiver from the sattelite at the speed of light, does not adding 25 feet of Cable and therefore the added time it takes the signal to reach the receiver from the antenna guarantee an automatic 25 foot error? Especially if the antenna is sitting on the floor all coiled up! The signal still has to travel the full 25 feet of cable even though the actual distance may be only a two or three feet.

[Hoary]

One thing that always bothers me about external antenna's:

Since GPS works by measuring how long it takes for the Radio Waves to reach the receiver from the sattelite at the speed of light, does not adding 25 feet of Cable and therefore the added time it takes the signal to reach the receiver from the antenna guarantee an automatic 25 foot error?  Especially if the antenna is sitting on the floor all coiled up!  The signal still has to travel the full 25 feet of cable even though the actual distance may be only a two or three feet.

Satellites that make up the GPS space segment are orbiting the earth about 12,000 miles above you. Compare that to 25 feet and you can figure out error which that cable can cause.

Edited March 10, 2005 by Hoary

[+Couparangus]

does not adding 25 feet of Cable and therefore the added time it takes the signal to reach the receiver from the antenna guarantee an automatic 25 foot error?

 

In actuality the error will be -38ft. This because the velocity-factor of most coaxial cables is 66%. Radio waves travel faster through air than they do through a conductor.

 

C-A

[+Poindexter]

Position is determined by the time it takes for the signals to go from the satellites to the antenna. It takes at least 4 signals to get an ACCURATE fix. The time it takes for the signals from each satellite to travel from the antenna to the receiver is the same and therefore the x,y fix will be the location of the antenna without any additional error due to cable length. The elevation result will have some error due to cable length but the error depends on the angle of the sat's used for the fix and isn't just simply the length of the cable or length times velocity factor of the cable.

[+GOT GPS?]

The Antenna is the point of reference, so no matter where the antenna is, all the timing signals all feed through it at the same time, so it would be like the GPSr's position is at the antenna, no matter the length of the cable. The only difference would be if you had a 1000 feet of cable between the GPS and the super amplified antenna, that is like a delay loop on a radio station, in that every thing is delayed. What does occur over time with that long antenna wire is that the GPS's internal clock will be slightly behind that of another GPS sitting next to the first GPS, but with an internal antenna. Now if you could have a Remote antenna that can transmitt it's received signals from a Kite up in the sky, down to your GPS at the ground, you could in effect see how high your kite is flying, while holding your GPS at ground level.

 

Now heres an interesting problem:

If you had 2 indentical GPS units 3 feet apart in a car with their external antennas mounted on the roof of the car, and one GPS has a 3 foot cable, and the other GPS has a 1 millon foot long cable, and you are driving exactly 60mph down the hwy. How far behind will the map on GPS with the long cable be behind the other GPSr's map??

 

--------

 

Those big antennas arent quite a point source of signal. I would think that a big antenna could fuzz up your accuracy somewhat say on a trimbal GPS??

[+MrMac204]

wouldn't it be cool if the external antennae had a blue tooth thing?? I recently got one with my cell phone to my ear piece- works like a charm no cables to hassle with!

 

 

Mac.

[stevesisti]

Here's the pic of a quad-helix antenna for a Northstar Marine GPSr. These antenna's typically come with 30' of cable and a larger antenna (high gain) is required to overcome the losses in the cable run.

 

Watson and Crick would recognize it in a heartbeat !

[+Nurse Dave]

wouldn't it be cool if the external antennae had a blue tooth thing?? I recently got one with my cell phone to my ear piece- works like a charm no cables to hassle with!

 

 

Mac.

They do. We just need Garmin and Magellan to talk with it.

[+NightPilot]

You can buy reradiating antennas that retransmit on the GPS frequency, and no cable is required. You can put your GPS anywhere you want inside the car, and get a signal. These take some power, though, and plug into the cigarette lighter. I use a reradiator from PC-Mobile with my Legend that has no external antenna connector, but it's lower-power, so I need to keep the antenna loop over the internal GPS antenna with a rubber band. Works great, and 3 AA batteries last for a month or so. I've accidentally left it on for about 3 days, and the battery level was about the same as when I turned it on, using NiMH rechargeables.

[+Right Wing Wacko]

wouldn't it be cool if the external antennae had a blue tooth thing?? I recently got one with my cell phone to my ear piece- works like a charm no cables to hassle with!

 

 

Mac.

You could always get a Garmin GPS 10!

[Phoenix2001]

Getting the pseudo range to the satellites involves more than just the antenna. There's also the RF circuitry and the DSP processing. I don't know the particulars of the Magellan/Lowrance/Garmin designs but consider the article referenced below. It mentions that the "typical GPS receiver" has 32 correlators. For comparison, the system being discussed can get a lock inside a car trunk and uses 16,000 correlators and has a significantly longer dwell time than the "typical GPS receiver". I suspect the primary difference in performance between Garmin and Magellan is in the DSP architecture and not in the antenna.

Note that reflected (multipath) signals are relied upon for reception in the difficult areas.

 

http://www.globallocate.com/GlobalLocateIndoorGPS.pdf

 

If you record tracks at a fixed location, the Venture tends to make rectangular type patterns unlike a 12XL or 76 series, suggesting that the DSP is different in the non-color eTrex series than in other Garmin models. See:

 

http://searching_ut.home.sprynet.com/stati...y_tracklogs.htm

 

For some measurements comparing a Venture, 12XL, GPS 76, and GPSmap 76 and internal/external antennas see:

 

http://www.gpsmap.net/WaldoTestIntroduction.html