Patch Antenna or Quad Helix?

[htabdj]

Hi all, I am about to purchase my first GPS. Without getting into technicalities of different models etc. I want to know if there is noticable differences in performance between Patch and Quadrifalar antennaes.

 

I have heard someone say in the past that Patch antennas are actually better than Quad in certain situations.

 

Is there any truth in this?

 

Thanks,

[+weakfish]

Quad-helix should be less sensitive to the orientation of the antenna...

 

In theory, a patch completely perpendicular to the transmitter will collect more signal.

 

Since you need signals from multiple transmitters, ideally spaced as far apart as possible, the edge goes to quad-helix.

[+hurley_108]

Don't know if it means anything, but there seems to me to be a correlation between higher-end units and QFHAs, while cheaper units use patch antennas.

 

Now, QFHAs are most sensetive along their axis, which usually lies in the top-to-bottom axis of the unit, meaning that usually, and I stress usually, they'll get best reception if held vertically - a little annoying. Patches are usually oriented with their axis of greatest sensetivity pointing out of the "front" of the unit, same direction as the screen points, which usually is the face you're showing to the sky. So points there to the patch.

 

I'm sure there are other points I'm missing, but perhaps others can chime in.

 

Seems to me though that a GPS with the new SiRF chip will outperform one without no matter what kind of antenna either unit's got. If you've got geocaching in mind, the only units for you with that chip are the 60/76 C(S)x units.

[+PDOP's]

Don't know if it means anything, but there seems to me to be a correlation between higher-end units and QFHAs, while cheaper units use patch antennas.

 

This is true yet the majority (if not all) external antennas are patches.

[+Prime Suspect]

It's not so much a matter of type, as it is of size.

[+hurley_108]

It's not so much a matter of type, as it is of size.

 

Ah, yes, that's very true too. A patch probably has an aperture on the order of a square inch, a QFHA less than a quarter of that (judging by the size of the casing for my 25MCX, and the antenna protrusion from my 60CSx).

 

So: probably the best solution is an external patch hooked up to a unit with a SiRF.

[robertlipe]

The receiver is more than the antenna alone.

 

Traditional wisdom has it that a QH is "better" than a patch, but it's been demonstrated that it's possible to make good receivers with patch and terrible receivers with a QH.

 

Judge the total car, not just the tires on the car.

[+EraSeek]

It's not so much a matter of type, as it is of size.

 

I think this is really the truth of it. Having been around for a while, the patches got a bad name because the earlier etrex's had a patch that was quite small and so generally under-performed other units with the quad. However, the 12 and the newer etrex have a large patch, and as stated, external antennas are patches and perform well. As to orientation, in real life the quad is actually fussier about how it is oriented than the patch, at least in my experience using a map76. Also the tech studies that I have seen do not favor one over the other.

[+EScout]

As robertlipe said above, there is more than the antenna. And its not the size of the antenna, because antennas have to be a certain size based on the frequency they receive.

 

There is the quality/sensitivity of the receiver and the signal processing that are very important.

 

Regarding the antenna type, for RH circular polarized antennas for satellites, the Quad Helix has more gain lower on the horizon which is where you need it. But, having an eXplorist with a patch and seeing it perform as well as the Meridian with a Helix, and having a Legend (patch) and seeing it perform much worse than the eXplorist: the receiver/processing are the most important factors. This means go with a current generation GPSr and it will work fine.

[Iwuzere]

If anyone has any good links I'd be interested and grateful, it would be interesting to see the gains and directional patterns of both types of antenna. I suspect there's really not that much in it, no more than a dB or two in most directions, just differences in the 'radiation' pattern (if that still applies to a receiving antenna!).

 

In any case, the large losses you get from being under tree cover reduce the signal so much that neither type of antenna is going to cope well. MOST of the time you'll lose signal with either antenna, so why worry about the issue when it's only about 10% of the time that another type of antenna MAY make a SMALL difference?

 

73

[Iwuzere]

(discussed before at http://forums.Groundspeak.com/GC/index.php?showtopic=80114 - but I'm still looking for more technical links .. but not TOO technical, LOL)

[htabdj]

OK, Thanks for all the replies. I have learnt that there are many things which affect accuracy and signal strength aside from the antenna on a GPSR.

 

To cut a long story short, I think I will now look for a GPSR with an external antenna connection, for use under heavy cover. Having the option of plugging in an external would have to be the best solution for heavy tree cover.

 

I'm leaning towards the Garmin GPS 60. Thanks

[+space_man]

How does the SiRF chip works??? why is it sooooooo much better??

[+BigLarry]

How does the SiRF chip works??? why is it sooooooo much better??

 

Good engineering improvements in all directons:

1. Lower noise amplifier to start.

2. More averaging for further noise reduction (like 200,000 signals versus ~1000 on the old chips IIRC?)

3. More processing power to perform more sophisitcated algorithms faster. For instance, on power up my 60CSx finds a lock in seconds rather than 10's of seconds on my eTrex Vista and Quest.

 

Just to name a few.

[+Searching_ut]

Don't know if it means anything, but there seems to me to be a correlation between higher-end units and QFHAs, while cheaper units use patch antennas.

 

This is true yet the majority (if not all) external antennas are patches.

 

Actually, don't virtually all survey grade units use patch antennas? Other than a version of the Meridian that thales put out that was designed to work with post processing I can't think of any high end unit that uses a Quad antenna. Virtually all of the consumer grade units would be considered low end wouldn't they?

 

Just a though.

 

As for the original post, as the others have mentioned, the receiver is a combination of parts with the sum of the parts being what's more important than any individual item. That said, from everything I've seen to date, the Sirf III chip does appear to be a strong indicator of a unit that will give good results and seems to have more impact than antenna choices with the current crop of GPS units available right now.

 

Good luck

[+JohnnyVegas]

I would apper the new GPSrs have better recievers in general than the older units. From my own experiand using both in the past with older models, I have seen better accuracy with untis that have had Quad antennas vs the patch antennas, these were side by comparisons under tree cover. The new SIRF III models from Garmin are an improvment over other garmins.

But many cachers have found thousands of caches with GPSr that have older units.

[+GPSlug]

Actually, don't virtually all survey grade units use patch antennas? Other than a version of the Meridian that thales put out that was designed to work with post processing I can't think of any high end unit that uses a Quad antenna. Virtually all of the consumer grade units would be considered low end wouldn't they?

A patch antenna has a more stable phase center, which is important for precision work. It also has a sharper gain roll-off at the horizon, helping to block out ground multipath.