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I am getting ready to add a GPS to my plane. The two setups that look most interesting to me are the following:

1. Garmin GPS18OEM

2. Garmin GPS15L with a MicroMouse antenna

The GPS18OEM has the following features:

a. WAAS

b. All-in-one weather-resistant unit

c. Cost: $80

Drawbacks:

a. Weight: 115gm = 4oz

b. Size: 61mm diameter x 20mm high

The GPS15L has the following features:

a. WAAS

b. Very lightweight (0.35oz) plus weight of antenna

c. The antenna can be located elsewhere

d. The MicroMouse weighs 1.6oz with 3 meter cable -- I would chop off most of the cable.

Thus overall weight would be under 2oz.

Drawbacks:

a. Cost: $100 + $45 for antenna = $145

b. I would have to terminate the antenna cable myself after cutting it

c. Not weather resistant

I think I prefer the GPS18OEM but would like it to weigh less. Has anyone looked at the GPS18OEM to see if the magnetic bottom plate can be removed to lighten the package? Would doing so break the weather-resistant seal?

Anyone have any other comments about an appropriate GPS receiver to use on a small and payload-challenged plane?

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I use a Royaltek RGM3000.

Dimensions 21x28x15mm, weight under 20gr with integrated antenna. But it has no WAAS.

Bought it for $70 if I remember correctly.

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I use a Royaltek RGM3000 ... But it has no WAAS.

Kilrah, I was about to order one of these for my Telemetry project. The specs say it has WAAS - Did you find that this is not true? In case it matters, I don't believe that WAAS correction signaling is available outside the USA.

Another tiny choice is the Lassen IQ. It is only 1" x 1", 7 grams (not including the external antenna). It does NOT have WAAS.

Edit: The Royaltek REB-7000 looks good too. The specs claim it supports WAAS (RTCA-SC159 / WAAS / EGNOS). So far, this one looks promising; I'm waiting for the programming manual to be emailed to me.

Edited by Mr.RC-Cam

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My understanding is that most of western Europe is also covered by a WAAS lookalike, known as EGNOS, albeit by a different geosynchronous satellite. But the GPS receivers are supposed to know which satellite to get the correction data from.

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That is one that I have had conversations with. I have never ordered from them, so they are an unknown to me too.

I'm still not sure if the stock 3000 or 7000 is truly WAAS enabled. The spec sheets are very vague.

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How important is it to have an active antenna? The antennas built into a small GPS are often passive, while the external antennas are active. They have lots more gain, but they also have a cable which contributes to loss. So what is the overall effect in the environment I expect to be flying in, which is open sky almost from horizon to horizon, but then the plane banks for a turn which suddenly means a huge sector of the sky disappears from the antenna's view. Even an active antenna can't overcome that, but is the passive antenna enough to capture good signal from the satellites that are in view?

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Speaking of banking (turning), does one vendor's algorithm work better than another's when the skyview suddenly changes? I am unclear as to whether an algorithm that is well-tuned to handle a segment of the sky disappearing due to a large obstruction suddenly appearing (large building, mountain, road cut, whatever) is also well-tuned to handle the antenna suddenly not being anywhere near vertical. As far as I know, they are not using phased arrays or other steerable technologies, but I know so little about what they are doing that I can't assume much in my ignorance.

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The specs say it has WAAS

Oops sorry you're right, in fact it wasn't specified where I ordered it, and as I'm in Europe I didn't do much research. But it does support it. Even better than I thought then. Seems to be EGNOS compatible as well. But I haven't found much doc on that system...

I like the integrated antenna idea as it saves space. I don't think the algorithms differ much, as long as the needed minimum signal is not here it can't do much. All those I've seen assume that you're moving straight during a few seconds, and then if the signal is still absent they report the "no signal" condition.

Found it here also, but no price displayed: http://www.jactron.co.uk/royaltek/rgm-3000.htm

The main electronics distributor here now stocks 2 modules that can be interesting:

Falcom JP7-T and Fastrax uPatch02-L1R.

They both are at a reasonable price for here, but still expensive compared to a RGM3000 or 7000. The Fastrax one has an integrated antenna and is 45x45mm, the Falcom is 1 inch x 1 inch, 3mm thick and weighs 2.5g. But there isn't even an antenna connector, must be quite a pain to use.Maybe you can find these somewhere else..

Remember that most of these modules use a 3.3V supply and comm. You need to adapt the levels according to what you'll be using them with.

I've designed a board for the RGM3000 with a MAX3232 + 5V -> 3.3V Vreg if this can help.

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Another tiny choice is the Lassen IQ. It is only 1" x 1", 7 grams (not including the external antenna). It does NOT have WAAS.

Speaking of the Lassen IQ, I have some of the older SQ's I'll sell if someone is interested in using them for experimenting. They're 8 channel receivers.

Michael

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Hi all.

For my small input, I'm using the Laipac UV 40 with a passive antenna I built on the board.I quite often get 7 plus sats at a signal strength of 49-51,which is pretty good especially at ground level. I'm now working on integrating it with an AVR to store waypoints and guidance information.

Lyn

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For my small input, I'm using the Laipac UV 40 with a passive antenna I built on the board.

That is good to hear. I was afraid to use a passive on my new project because I had bad luck when I tried it a few years ago (hard to get a signal lock sometimes).

I just ordered a REB-7000 with a active antenna. Once things are running well I will try a passive on it to see if it is reliable for me.

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The REB-7000 GPS arrived today. The size is perfect ("tiny" hardly describes it). If I can successfully weight reduce the mag antenna that I also received, it will do fine too.

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I got to wondering why the Garmin GPS18OEM weighed more than their Geko-201, especially as the Geko included an LCD screen and batteries. So I used Garmin's query link and asked them. Here's the correspondence:

On 12 May 2005 at 16:14, Garmin Sales Support wrote:

Dear bluegill,

The weights given for the GPS 18 include the cable.  The GPS 18

without cable is about 1.9 oz (54 g).  It's fine to shorten the

cable, but I would not recommend other weight saving measures.

Regards,

Garmin Sales Support

-----Original Message-----

From: bluegill

Sent: Thursday, May 12, 2005 1:29 PM

To: Garmin Sales Support

Subject: Sales support request for GPS 18 LVC OEM (hardware only)

I am looking at both the GPS18LVC and the Geko 201 to put on a small

radio-controlled plane. I am surprised the GPS18LVC weighs more than

the Geko. Does the weight of the GPS18LVC include the weight of the

cord? If so, what does the unit weigh when the cord is shortened to 6

inches or so? Are there other ways of reducing the weight of the GPS18LVC

without violating its weatherproofing or warranty?

Thank you,

  --bluegill

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A friend of mine did buy the Garmin GPS18OEM and let me look at it for a few minutes before he ran off. It is cute in the sense that it is completely self-contained and sealed (a feature here on the coast where the grass at the landing area is often wet with salty dew). So I'm torn between using a unit that has intelligible manuals and specs, great product support, is weatherproof, but weighs nearly 2 oz, or something lighter, much more vulnerable, and whose spec sheet shows the ill effects of translation into English. Shucks, I guess I answered my own question.

I am interested in how well the REB-7000 turns out -- it will be a while before I am actually ready to use a GPS. Mr.RC-Cam, did you buy it at http://www.w-innovations.com? And what antenna did you get for it?

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did you buy it at http://www.w-innovations.com? And what antenna did you get for it?

I bought it from Lance at w-innovations. The antenna is the mag mount that he sells for it. The GPS module has an I-PEX connector on it. It is the smallest coax connector I have ever seen (slightly bigger than a pin head). The antenna is SMA equipped, so their $9 adapter cable is needed to connect the two.

If you do not have plans to integrate the module into a special custom design then skip going that route. A consumer GPS is what you would want.

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I am interested in how well the REB-7000 turns out -- it will be a while before I am actually ready to use a GPS.

Update: It is a very small GPS and works fine. It is 9600 Baud, rather than the traditional 4800 Baud that other GPS use. The updates are still 1Hz, but the faster com speed allows sufficient time to send the $GPGGA, $GPGLL, $GPGSA, $GPGSV, $GPRMC, and $GPVTG data strings. Despite Royaltek's claim to having WAAS compatibility, it does not. They continue to advertise that it does, which seems a bit odd to me.

And what antenna did you get for it?

You can use any 3V ACTIVE antenna with *at least* 25dB of gain. The magnetic antenna sold by w-innovations is fine. Just plan on taking it out of the heavy plastic case and reduce the long coax cable length to about 16 inches (you'll need a quality SMA connector and the proper crimp tool to do this). Antenna weight will be under 1oz if you hack it as suggested.

When you order the REB-7000 be sure to get the SMA antenna cable pigtail adapter and the special SIP SMT connectors. Budget about $90 for everything.

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