cf-28 Newbie rim antenna question(S)

i have spent a few hours poking around my cf-28 one thing i found out is that my "siera wireless sb300" cdpd modem has a mmcx connector on the end. doing a little research on the net i found a few wifi cards with both a mmcx and ufl connectors on them. I took the cdpd modem out and it looks as if the antenna cable can be re-routed to the bay where the mini-pci slots are. I know through reading here that the rim antenna is not the best for wifi, and some have reccomended a rim mounted 9dbi gain antenna for better results.
My question(s) so far are can i re-route the antenna cable into the bay under the HDD is without worrying about RF harming anything. Also can i shorten the legnth of the "stock" rim antenna to be more in line with the 2.4 ghz frequency and use it.
i removed the rim antenna and it seems like the threaded connector is a std size have any of you found an antenna that will thread into the rim antenna recptical assuming that cutting the stock antenna will not work. One thing i noticed while removing the rim antenna was that under the rubber grommit there are a few resistors and a flex solderd to the threaded portion of the antenna jack recptical dos this circuitry preclude me from using this for WIFI or can i ignore that.

sincere thanks
john




I am very new to this forum and wanted to thank all of you for your help thus far with my toughbook

 

I have several CF-28 that came with the factory Cisco wireless in the hidden slot. They use a whip antenna that looks identical to the RIM antenna. But the only difference is the circuitry that you discovered. It seems that they are tuned to the correct frequency via those components. I am guessing that shortening the antenna would not make any diffence unless you addressed the circuitry to get the correct filtering. From what i can guess is one uses an inductive filter while the other uses capacitance filter to pass the correct frequencies. It would be nice to be able to retune the RIM antenna for wi-fi as they are plentiful and look much better than the router antenna some people are using.

 

I think I attached a PDF of the RIM modem developers guide. one of the appendices covers how to "electronically shorten" an antenna!

 

Gravitar
would you hapen to have a link to to pdf i looked and could not find it. I assume that "shortening the antenna electronically' means that the stock cellular antenna can stay?

 

take a gander at this:

http://forum.notebookreview.com/showthread.php?p=2615550#post2615550

I don't see why the stock antenna couldn't be made to work. In fact, my plan is to go the OTHER way and use the 7.5" radio modem antenna from a 27. (fits perfect in the stock location on a 28). My wife's uncle is a broadcast engineer, i will see him on thanksgiving and plan on thoroughly picking his brain

 

Radiogeek... I don't mean to flame but a lot of the questions you are asking about can be found with a little searching and reading.

I don't think I've ever seen the resistors you talk about. I've pulled apart a lot of Toughbooks and have never seen them. Could they have been added by the prior owner in an attempt to do ?????

I agree that the stock RIM antenna looks better than the router type antennas... Probably a little more sturdy too. But the little 3 db antennas I install on the LCD pull in 5-6 times the signal that any type of RIM antenna combo I have tried.

The threading of the RIM antenna is the same as some other cellular type antennas. You can find shorter ones and screw in its place. It won't make much difference. The best reception you will get is roughly similar to that of an ordinary laptop... Which I guess is fine if you are always close to a hotspot. I guess I'm spoiled by the router type antennas. I can pull in wifi signals from 2+ blocks away.

 

I wonder what is IN a router antenna. Is it not just a metal rod like the stock piece? could there be some kind of amplification circuit in there?

If the only difference is the length then I think we can overcome the limitations. If however the design is significantly different, then we might be wasting our time.

What's so magical about this darn 2.4GHz band?! Seems like I always could get a halfway decent signal on a radio or TV with a coathanger or cut extension cord!

 

I "think" it is a small metal wire inside the nylon rod... I'm not sure though. I have enough of them I guess I could cut one apart to see. I tried a long time ago to shorten it. It seems that taking it apart would be easy enough... It would be getting everything crimped back to factory specs that would be a bear!

I'm not a radio geek or anything... But it has something to do with RF chokes and impedance or something like that. If your card is too powerful and you feed the signal into the wrong antenna you can burn out your card. At least that is what I read somewhere along the way.

 

Any antenna with a dB gain.. is an antenna that has "gain" over a 1/4 wave antenna. What happens if you use an antenna that is not "matched" to the frequency ..is you will have an SWR mismatch. ( Standing Wave Ratio ) You will have more power being reflected back down the coax than power being transmitted. Thus...as Toughbook said.. it will burn out the card.

 

Yeah.... What he said!

 

Toughbook

while i was cleaning all the grime off my laptop, i took the time to remove the top lid and get a better look at the rim antenna and how the cable is routed ect. I took a few pics of the "circuitry " I referd to earlier to better illustrate what i was talking about. It looks to me that if nothing else i may be able to use the existing antenna cable removing the circuitry if that is what is needed.
let me know what you folks think this circuit is for and if i can eliminate it leave it. For thise of you who have mounted the antenna to the sude of the LCD could you post a pic or two if possible.


thanks

 

Hmmm... I can't really see because the picture is fuzzy. Can you post a clearer shot? It doesn't look anything like the RIM antennas I have. Are the resistirs mounted under a cover on top of the LCD?

 

agreed.. doesn't look like my RIM antenna. I was gonna open mine back up tonite (got a cleaner factory black LCD lid to put on) so i will take a pic or two. I don't remember there being ANY circuitry up there.. the same setup on the 27 has a chip resistor or two from what i recall..

 

i will try and get a batter shot of the flex circuit, my camera wont take a close-up that well. It is definetly factory that much i can tell, it is mated to a siera wireless cdpd sb300 modem. I have some stuff on the hunney-do list to knock out and i will try to post soon. On this particular notebook you can see the flex-circuit once you remove the antenna and the rubber grommit that goes over the antenna base that is attached with the two small screws.

 

Well... I can tell you that I've never seen those. I have seen two types of RIM antennas on mine... The longer RIM and the shorter one. The shorter one gives a better signal for wifi. The connector on yours looks strange too. (From what I can make out.) It almost looks like a BNC connection type.

 

Radiogeek97 that is identical to the RIM antenna that I just took out of my CF-28. It was attached to the RIM card with the mmcx connector with blue coax wire to the connector at the back of the laptop next to docking port from there by way of, as was explained to me, an H.fl connector with small black coax and soldered to that flex circuit that you are referring to. I hope this helps shed some light on the subject.

 

is that the way you got it? i just took a good look at my RIM antenna and theres no visible circuitry. the only way any of that could be in there is if it were under the black plastic cap (the part that is visible from the outside) and I wasn't really ready to try to take that apart!

 

I took a few pictures of my antenna. It looks like the same as radiogeek97s'. I hope this helps out. Is it possible that this is some sort of wifi antenna or just a different version of the RIM antenna?

 

so is that stuff inside the black plastic fitting on the outside of the lid? if so, were you able to disassemble it non-destructively?

 

speeddmon
that is the same one i have, the internal blue coax ect is exactly as you describe it. What did you replace the antenna in yours with? Were you abel to use the existing cable after you unsolderd the flex circuit?
if you have any pics that would be great.

 

I'll be damned! I just took mine apart and it is the same way! After seeing speeddemon's pics... I saw what you were talking about.

You have to unscrew the antenna base and then separate the covering from the base. Then you can see it!

Good find Radiogeek! Maybe by modding this we can get a better signal for wifi.

 

Gravitar. Yes it comes apart quite easily all you have to do is rock the rubber piece back and forth while pulling up on it and it will come right off. No destruction.

Radiogeek. I haven't replaced it yet am waiting for wifi card to come in mail and am vehemently searching for rp-sma connector to solder to the black cable to test it first for SWR losses and then I could tell you better. Plan is to use a 5.5db gain rubber duck "router" type antenna like Toughbook and others use in stock RIM location. Just need to find connector first.

 

I was thinking the same mod you were, I have a bunch of Lynksys routers I can rob an antenna off os but as you said finding and putting together the connectrs will be the tougher part. How were you planning on testing the swr/loss. I would be interested in what you come up with as i am in the same boat. What kind of card did you go with? I am still hunting on ebay.

 

speed... You want a 3db antenna for the LCD... A 5db or 7db for side mount.

 

I thank you Toughbook. Is that due to the size of the antenna or some other reason? The 5.5db antenna that I purchased only measures 5" long from the connector to the tip of the antenna.

Radiogeek I have a buddy that I went to electronic comm. school with that actually still works in that field and has the equipment for that. I have been working in the residential/commercial electrical field for so long now that I don't know if I would remember how to use an SWR meter.

 

I use the 3 db antenna for several reasons... Number one... They are smaller in diameter and fit very well in the stock location. If you use the 5db they are too thick. Also... The 3 db is shorter. Believe me... You won't want to keep unscrewing it... Especially if you trim the plastic plug that comes in the RIM delete version. Also... Since it is smaller it folds into a smaller space is just looks better and is less likely to catch anything or break off. I keep mine on all the time and toss it around on the couch and chairs... I've never had a problem. PLUS... With a good high powered wifi card... You'll pick up everything there is to pick up with the 3db antenna!

 

Thanks Toughbook. That answers my question. Did you get your 3db from netgate or off ebay? That would make it easy for me to locate, I think.

 

I buy the antennas from Bill at Netgate... They go for $6 each...

 

Toughbook
i went to the netgate site and what I found was a 2.15 dbi tilt/swivvle mount antenna, is this the one you are refering to:
http://www.netgate.com/product_info.php?cPath=23_33&products_id=146

 

Yup... That is the one...

 

Hmm.. I don't think I've been to the netgate site before. good stuff! Just curious what cards you guys are using. The 600 mw card looks like it'll fit and the price isn't too bad, i'm thinking i want to try one of those!

 

Get your antennas and pigtails from Netgate and your wireless cards at www.defactowireless.com... I buy the 400mw card from here...

http://shop.defactowireless.com/s.n...34Pa38Ta38Oc3j0?it=A&id=931&sc=2&category=239

They have the best price for the best card!

 

Ok well let me play the devils advocate then. What's better about that card than the 600mw one on netgate?

 

I see that it is $16. cheaper, a meaningful number if one is using a lot of them.

Does anyone know if either the 400mw or 600mw boards are Linux compatible?

Thanks! doc

 

Mind you I'm not a big baller or anything, but for 50% more output power I'd pay the extra $16. I should have phrased my earlier question differently..

other than cost what's better about that card than the 600mw one on netgate?

 

Both are Linux capable. To my knowledge... All Atheros based cards are.

I have the 600mw card in my personal laptop and they also shipped me one by mistake on my last order when I ordered 8 of the 400mw cards. I see no difference between the two when making comparisons with NetStumbler.

There are noticeable differences between the 100mw cards and the 400mw.. but not so much between the 400 and 600...

 

600 mw output might exceed the max. current the PCI port is able to provide. I remember someone mentioning that.

 

I thought I remembered something about trying to drive that much power through the RIM antenna being a "no-no"...

 

Toughbook/others

FWIW when i looked up the specs on the internal Siera cdpd modem in my cf-28 i found out that the rf output was 600mw. I cant speak for what difference the freq range would effect the rim antenna as far as being mismatched but as far as output power with the stock cable and rim antenna it should handle the power.
When you guys mount the 3dbi gain antennas to the rim of the screne do you use the pannel mounts, if so do you have a link to the ones you use. I looked on the netgate page and there are so many i dont know which would be the best to use as far as making a nice neat job. Also as far as the antennas go do they have to be grounded to the chassis?I put a side mount antenna on my cf28 but it gives poor results. It is mounted to the plastic rj11 faceplate for the dial up modem.

 

I think rim antena is not the right one for mini pci unless you have an amplification device before the signal reaches the mini pci. Here is the simple and easy way to have a reliable antena for mini pci but i will give you a challenge where to permanently installed it on your pc. I solved it to my cf-m34, since it is cf-28 its your job now.

1.0 Provide a certain lenght(its up to you where you place it) of u.fl ca with connector at the other end for mini pci.
2.0 At the other end Open the outer insulation about 2.5" long exposing the outer conductor.
3.0 cut the outer conductor 1 1/4" long at its end so you still have at least 1 1/2 " long still remain of open outer conductor.But be careful not to damage inner conductor on the process.
4.0 So now, the inner conductor is also expose 1 1/2" approximately. Provide a copper tubing with a dia. of 2mm about 1 1/4" in lenght.
5.0 Insert the copper tubing on the conductor all the way to open outer conductor overlapping the outer insulation about 2mm.
6.0 Crimp the cooper tubing where it overlap.
7.0 Make sure that outer conductor is inside the tubing at the other end and crimped it the other end of copper tubing but as i said be careful not to damage the inner conductor.
8.0 now you are almost done and product look like this: 1 1/2" inner conductor with insulation exposed followed by a copper tubing 1 1/4" crimped bothe end.
9.0 Provide any srinkable tube materials covering the internal conductor where you work on all the way to copper tubing and your done.

Install the antena to you mini pci just place the antena outside temporarily. Boot the pc to test the signal. Good Luck



Before my cf-m34 got only two network signal now i've got 9network from my nieghboorhood. I just rip off the rim antena got what maybe usefull. Taken out the twisted wire inside insert my improvised one and stack it permanently on the side of the panel

 

ohlip, it sounds like you are making what is called a dipole antenna. It has a 1/4 wavelength attached to the center conductor, and another 1/4 wavelength attached to the shield. I have made them for 144 Mhz (ham radio, 2 meters) by opening up the braid at 1/4 wavelength, and then pulling the center conductor out. In general terms, it looks like a T (the crossbar of the T is the antenna, the vertical part is the coax. You could probably fold the top of the T over onto the coax, and have it be one single "prong", for lack of a better word.

The formula for a diple (which is a half-wave, total) is 468 divided by the frequency in Mhz. Just very broadly figuring 2400 Mhz for 2.4 Ghz, it is:

468/2400 = .195 feet, which is about 2.34 inches. To do it right, you should find the frequency for channel 6, which is in the center of the 11 USA wifi channels.

 

Yup! your right as i remember almost 15 years ago during my school days, I just cut it out coz i don't wanna damage the outer conductor instead of twisting it back, i place a copper tubing instead its some kind of a filter if i am not mistaken. Sorry! for my english coz i am not originally english speaking person.

Rim antena is same as loop antena, you can see on its small board that there are two capacitor on it.

 

If a 1/2 wave antenna = 2.34", why don't we try for a full-wave antenna? should be 4.68" right?

 

Hey! no feedback yet? how's the result is it good enough for your pc?

 

I don't know for sure, Gravitar about a full-wave. While it's certainly very easy at these frequencies (very short wavelength) to try it, there's always _something_ about center-fed dipoles always being a half-wave. I don't recall enough about it to know what that _something_ was. My ham license is long-expired, and the brain is feeble. It would be very easy to try, but standing wave ratio would be hard to measure at these frequencies. Antenna experimentation is best carried out with an SWR meter, else transmitter damage can occur. Granted, the transmitter output of all of these cards is very small, and they may well shut down to protect themselves.

For a very rough approximation, perhaps have another pc/laptop/something that can measure signal strength, and you could get an approximation of 'better or worse'.

 

A 1/2 wave does not require a ground plane.... ( although the metal casing of the 28 would work....)

 

But it works for me! better than the older pc. I can even use my neighboor network, if i wish.

 

Anyone ever use one of these?
http://www.netgate.com/product_info.php?cPath=21&products_id=33

 

If you're thinking of using that in the factory rim location, have a look at internal gps thread. TB couldn't get a 19" lead to reach the rim daughter board location, too short!

 

You need a 24" pigtail to run from the wifi mini-pci card to the RIM location. (If that is what you are thinking about. Netgate is the only place I know of that has that pigtail. BUT... It is not an SMA bulkhead connector.... So you will need to find a way to secure it.