GPS on CF28 on the lid's right corner

Hello, i made a new top-right-corner for the lid of my cf28 to allow the installation of a sarantel geohelix antenna, i just want to share it with you, so if anyone want to try i can tell you some tricks:

I made it in poliester resin, mixed with some powdered black pigment, i spent about a week finding the right way to make it, so in the end i chose to spray the lid with some releasing lacquer and then to drip the resin directly on the lid. When dry, i put antoher layer, interleaving with fiberglass, the making the form with a rasp and finishing with sandpaper about with 500 grit.

This is the result:


Now i have a question, it's normal that i have low signals ? I mean that if i am in my house i've NO sigal at all or just one or two satellites, i only get 4 or 5 satelites if i go near a window, on open field there's no problem and it fix quickly, i use OziExplorer software to look at satellites constellation.
Is there a problem if i feed the sarantel antenna with higher voltage, about 4 volt ? Can i have improved gain or just a smocking antenna ?

 

That looks great!

Low signals can be caused by lots of things. IN my house my passive little square ceramic antenna (in the palmrest) gets %85 of the signal received in direct line of sight (outside). An active sarantel should get fantastik reception in a house of standard construction in the US.
I wouldn't mess with the voltage.
I have a 29 and REALLY wanted to put a sarantel in the top right corner (calm down, Rick, I changed my mind ). But one of the hurdles to overcome is the pigment and material for the corner piece. Many materials and pigments absorb or block such RF signals. I don't think polyester resin does, but your pigment might.

Try this test: put a ceramic mug of water in your microwave, and your DIY corner piece next to it (the cup of water is used to absorb excess radiation, so as to not damage the microwave).
Turn on the microwave for 30 seconds. Be careful, if your "pigment" is metalic based, it will now arc inside your microwave. If it does arc, TURN IT OFF. If it doesn't arc, then let it finish running fhe 30 seconds.
Now feel the corner piece. If it arcs or it's warm after 30 seconds, then it absorbs radiation/RF and that is not good.

Good luck, and please report back....

 

Thank you for the fast reply, yes i know, i like to play and mess with rf from some years, making radios for various frequency, i know the problem about using metal pigment near rf antennas, so i used... you will lol i know, powdered coal... i took a piece of coal and pounded it in a jar, until it became of the consistency of flour, just a small amount in the resin (about ten times the amount of hardener) will make a realistic black color, very similar to the original plastic corner, and is satin not lucid like a painted piece.

i made the try that you told me to do, the piece is not hot when i get it after 30 seconds of 1kW of radiation, is it possible that the cause is a deaf receiver ? I have not used a standard board, but a board scrapped from a bluetooth navigator.

 

Great job!

Now; after you conduct the test interestingfellow sugggested and make any changes necessary, start up a limited production on them; and do the same for the CF-29; and you'll have a "cottage industry" for the "moders" in the TGoughbook owners community.

 

Hmmmmm.
What kind of reception do you get without the cover in place (everything else the same, just not your corner piece)?

I have a feeling it's a bad receiver *OR* a bad antenna lead/connection???

 

I agree, you did a very good job on it...looks great

 

Can I have a few comments on your job? IF yes! first you do a fantastic job on that corner piece but your antena installation/mounting is to high. As you can see the sarantel antena provided a black radom cover to specify the max. depth where to be burried the base. The slot on the black radom specify that is the max. in order to have a max. strenght of the base. Your installation doesn't meet that and it is prone into damage very easy. Try to rework the mounting of the antena.

I can see no problem into catching a signal from a satelite based on your setup. May I know what GPS receiver engine do you have. It will prolly need only a retuning.



ohlip

 

For the gps engine it's hard to say, i unsoldered the module from a bluetooth car navigator, that have a sirf star III engine, so i tought "now i've a smartphone with integrated gps, so i no longer need this stuff, i can sacrifice it for the science".

I took the original GPRS board, then i removed the C35 wireless modem and all cable and shortened the pin 37 to a ground, by this way it's recognized by my bios as a GPS.

Then i tested all the pinout of the gps module (26 pin of which about 15 are GNDs) i found the serial OUT with my oscilloscope and connected it to the now-is-a-GPS board. If you have no instruments, you can also use a hearphone, like the one used by ipod and similar, they usually have 32Ohm impedance and you can clearly hear the BIP-BIP-BIP of the NMEA-GPS data stream, so you can definitely know what is your OUT pin, because is tho only outgoing information. I left the IN pin on the GPS module unconnected, i'm not planning to use dedicated firmware.

The problem i found is the sensibility of the system, if i open a serial terminal session and set it listening on the COM4 i read NEA data string, without satellites locked, no fix at all, if i go at outside or near a windows then the situation change and it fix at least 7 satellites, the antenna i bought was sold as a 27db gain antenna, so it should gain about 500 times on a non active antenna, in addition to it's geohelical structure that is better itself in respect to a flat ceramic antenna.

if you know how retune a gps engine, please tell me.

 

New idea, when i dismantled the module to extract the gps engine module, i removed the shielding metal plate, do you thin that this can affect reception or noise interference ? I will try to put the plate on tomorrow just to test.
So here is about 1AM i'm going on my bed or on the first plane surface i find to rest, see ya tomorrow.

 

It is normal to have a lower signal of satelite if you are sorrounded by thick wall or concrete. Even if you have a helical antena. The sarantel antena specially the S active antena is the best antena known to all us here.
The right interconnection between the Signal in and out are; from mobo. RX will be connected to TX of the module and TX will be to RX

Usually if the module where came from the car. The antena of the gps is mounted outside at the roof surface of car near at the back.Thats why it can pick up signal quickly.

So, I"ve guess your doing fine enough though.

ohlip

 

In my case my roof overhangs my favoriite chair about 12 feet. The roof is sheet metal. The only reliable, quick gps from the chair is the CF-30 OEM. The CF-19 will get it but takes longer. Also the em-408 in my CF-29 w/ 10x10 active in WWAN corner is pretty quick.
Your best coverage by the window indicates something overhead is blocking. I agree w/Teo.(ohlip)

 

Um.... When I do the Sarantel setup on a CF-28 (or even CF-29 in some cases) I can get fuly pegged satellites in my basement shop with two floors of house above me and I am surrounded by 6 inches of concrete! When I take it outside the signal gets stronger!

I'm thinking a cold solder joint or perhaps even damage to the Sarantel. It is VERY easy to damage them if your soldering iron lingers a bit too long trying to solder the antenna leads on. Anyone here who has done it more than 3 times can testify to that.

 

Mhhh i hope that i havn't broken it... i should test it with a microaperometer to test the current consumption, it's not a decisive test, but can tell me something, if i find another antenna i will try it instead of the sarantel... i should try the original amplified square-ceramic antenna, just to see the differences.

Do you think that a non correct cable can cause the loss ? I have a multi-jointed cable, about 50cm in total, 4 cable sections soldered in 4 points.

 

Teo (Ohlip) was the one who invented a really cool way to add a GPS antenna to the CF-28. Just use a CF-18 GPS bump-out and tap two holes into the side of the laptop and add your antenna inside the bumpout... You'd have to see ehat it looks like on the CF-18 to know what I am talking about... But when Teo did it (And I've done it a few times) the result is a stock looking setup that gets a great signal and is as tough as th rest of the Toughbook... Which is what you want.

I do like the way you molded that part though. Nice to know the process... I'm always dreaming up weird stuff and it's nice to know I can do something like that if I need it.

 

It sounds like you know what you're doing (more than me!)....but I'll say it anyway:

I'm gonna guess one of the 4 joints is grounding out a little.
Can you take pics? I'm interested to see that. I wouldn't even know how to try to solder the jackets together without grounding to the signal wire (AND maintaining proper shielding).

 

I think we're all missing something important; the GeoHelix antenna's active element is in the radome there, well outside the bumper. You could cast that corner piece in aluminum and all it would do is add ground plane.

Obviously if you wanted to use Teo's 10mm patch antenna there would be some concern, but that is such a spiffy bit I might actually have to put GPS in MY Toughbook if he makes a CF-29 version. :wink: Yes, I know all about the sled, etc. I still think I'd rather hack a USB puck style one just for the cheap.

mnem
Where was I?

 

Ok, thank you to everybody for the tips.
I think that these joints introduce some unbalancing on the line, that can alterate the impedance of 50 Ohm on the cable.

I used some pieces of military cable, coming from a old army radios dismantled, that is fire proof, just to make it tough, i will look for the cf18 solution on google, thank you.

 

I'm wondering... is your GeoHelix antenna the active one or the passive one? The active one will have an amplifier module attached directly at the base under a small tin box. The active one is the one we recommend; it's the one that gets killer signal. I know you've said it was marketed as an active module, just wanted to be sure.

Also, if the GPS module doesn't provide power for an active antenna module, that could be it too. They use an L-C decoupling stage the separates the DC from the signal without disrupting the signal; if you're just hacking DC 3-5V to the antenna, that can also cause a lot of signal loss.

As for your antenna wire, I'm going to recommend you just get an old WiFi antenna with a long enough single bit of cable and a uFL end to plug into your GPS; it's the best way to ensure a balanced load.


mnem
Satellite signal-lossed.

 

Tell me, Mnem; how do you know if your GPS engine can support an active antenna???

 

It will provide 3-5VDC output along the same coaxial antenna connector to power the antenna; you can test for that voltage with a DMM. The GPS module decouples the DC internally to protect the pre-amp stages.

Some will have a separate antenna connector or a jumper you can solder to activate the power subsystem; this will be outlined in the engineering notes for the module when you buy it. My old Magellan 760 GPS worked that way; my Garmin Nuvi is a cheaper model, so doesn't have an external antenna connector.
If it has a MMCX connector for external antenna, it's usually a powered port.

mnem
Port-ed.

 

Perfect answer!

 

There is an easy solution for every corner that we want it to be in our own design If somebody among you who has a friend with 3D printer. I am thinking buying one of this printer but as I summarized everything it will cost around 2gran. the printer alone cost around $1,200.00 or less but of course you need an scanner and software. Anybody?


ohlip

 

Or use this program to print on flat paper and make your prototype with it. It even makes the folds and stuff for you. http://http://www.tamasoft.co.jp/pepakura-en/
I am also a 405th member, this is how they make those life like halo costumes, you load your 3d model and this program makes it where you can print it on paper, then cut it out and make it full 3d life size or what ever size you scale it too. Then they usually bondo or fiberglass it to get the prototype to cast.

 

Yes, my antenna is preamplified and the module is emitting +3.3 volt dc, there was a preamplified flat-ceramic antenna, before i installed the sarantel.

Sometimes it work great, yesterday it fixed about 9 or 10 satellites inside my home, now just 1 or 2, i think is a problem of loose contact

 

Yeah, then I would suggest replacing the cable as I described earlier. Does your GPS board have a uFL connector on it ?

mnem
Right THERE.

 

Ok i found the problem, it's the sarantel antenna, it must be damaged in any way, the cable is attenuating a little, but not too much, i made a comparison with a normal rg174 cable (about 1mt) and the difference is not big.

Switching the sarantel module with a normal preamplified antenna gave me an increase in signal strenght of about 4 times (6db) or better, so i'm wondering on the cf18's like solution, i should find a left side cover to make y mods, i noticed that in the cf18 gps, the antenna is mounted not facing the sky, but facinf forward (forward the side of the machine)... is it right ?
Do you know if and where i can find one original GPS left side cover, or at least a normal cover to modify ?

 

Before someone says my name sorry I am sold out but I will be getting some in but its going to be 3 weeks. You could try ebay but the last time I checked I have been the only one selling them for the last few years.

 

The patch antennas show a large surface plane to the sky; they'll get a useable signal even oriented perpendicular to the horizon. My Garmin Nuvi's built-in antenna is like this.

I'm more of a mind to think maybe a bit of soldering slag than an intermittent fault on that Sarantel; unless, of course, you think it might be possible you crushed the PCB somehow while working with your resin corner.

mnem
Okay, RIGHT THERE then.