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Author Topic: Help identify this 900 MHz antenna and its pattern  (Read 938 times)
WB4WZR
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Posts: 17




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« on: January 26, 2013, 12:58:52 PM »


My son is developing a blood glucose monitoring / insulin injecting system for diabetics.  He's obtained a gadget that communicates between a USB instrument and an insulin pump.  The frequency of operation is in the 900 MHz range and the antenna is clearly visible on the device's circuit board (link below).  He'd like to know the type and directional characteristics of the antenna so he can position his insruments for maximum received power. Alas, I'm challenged by HF wire antennas and can't be of much assistance.

Would someone please look at the JPG photo of the circuit board at

<http://www.cvkimball.com/Tanach/PreviousVersions/Summary/Dongle.JPG>

and identify the antenna type and location of the maximum lobe(s)?  There doesn't appear to be any antenna foil on the reverse of the board at

<http://www.cvkimball.com/Tanach/PreviousVersions/Summary/Dongle-reverse.JPG>.

Thanks for your assistance,

Chris
NQ8Z (formerly WB4WZR)
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KZ1X
Member

Posts: 3228




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« Reply #1 on: January 26, 2013, 05:40:34 PM »

At less than a wavelength away from this type of antenna, multipath will predominate in most every environment you'd use this in.  So, there won't be any discernible pattern. 

Check out me in a video of a system at 900 MHz designed to work differently than this, and see how large the antennas have to be to have realized indoor patterns:

http://www.wral.com/lifestyles/healthteam/video/8930431/#/vid8930431
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WB6BYU
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Posts: 13244




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« Reply #2 on: January 26, 2013, 06:15:24 PM »

A quarter wave whip on 900 MHz is about 3" long.  I'm guessing the antenna is
basically a folded quarter wave.  Radiation will be mostly horizontally polarized
when the antenna is horizontal, or a mixture of horizontal and vertical polarization
when the USB slot is vertical in the side of a computer.  Given the circumstances,
mostly omnidirectional, especially at close ranges.

You aren't going to get much directivity in a package that small.
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K5LXP
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Posts: 4482


WWW

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« Reply #3 on: January 27, 2013, 07:30:32 AM »

It's a meander antenna.

http://www.google.com/url?sa=t&rct=j&q=meander%20antenna%20theory&source=web&cd=2&cad=rja&ved=0CDkQFjAB&url=http%3A%2F%2Fpiers.org%2Fpiersproceedings%2Fdownload.php%3Ffile%3DcGllcnMyMDEyTW9zY293fDJBOV8wNTk0LnBkZnwxMjA1MTcwODI4MjU%3D&ei=jEcFUfj_LeWbygGltIGwCw&usg=AFQjCNGWMihx-IWlvvLuuMHVjp9b9U6M9Q&bvm=bv.41524429,d.aWc


Mark K5LXP
Albuquerque, NM
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G3RZP
Member

Posts: 4574




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« Reply #4 on: January 29, 2013, 03:41:23 AM »

Chris,

if your son is developing a commercial product, make sure he knows that he can't sell in Europe using that frequency, and that anyone using it in Europe is doing so illegally, plus the fact it may not work because of interference from cellphones etc.
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KE3WD
Member

Posts: 5689




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« Reply #5 on: January 29, 2013, 10:19:24 AM »

Likely working like a linear loaded quarter wave or possibly half wave. 

Certainly a nearfield situtation, but vulnerable to hacking from the general area to include the next room over, or from just outside.  Boo. 

I also question the choice of frequency band, you should tell your son to investigate carefully on this issue, also I hope he is aware of the problems incurred by hackers with these types of devices. 

An Insulin Pump hacked to turn on and keep pumping can and will kill the user. 

There are also the "inadvertent" situations to consider carefully here.  For example, RF interference from another device should never be able to activate - or inactivate - the medical device. 

System design should then be governed by factors that pay attention to absolute failsafe, to include both hardware and software design.  And, of course, RF considerations suc as frequency band, modulation scheme, password encryption and protection, this is not a trivial matter. 

I am assuming that it is very likely that your son is in development to answer these problems, as not only Insulin Pumps, but Pacemakers have recently been in the news as being unsecured in several ways. 

http://www.technewsdaily.com/7696-firewall-prevent-pacemaker-hacking.html

Websearch can bring up a whole lot more, including the findings at the last hacker's convention, in which not only the basic and rather easy radio comm situation, but the bad situation of passwording which blames both users for picking easy to crack passwords as well as designers for not encrypting same or using better programming schemes. 

73
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G3RZP
Member

Posts: 4574




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« Reply #6 on: January 30, 2013, 04:41:06 AM »

There are insulin pumps working at 900 MHz on sale in the US - one manufacturer I know of is Medtronic. Although there has been one manufacturer using 900 MHz for a pacemaker, most implants use the more or less internationally available 401 to 406 MHz, following ITU-R Recommendation RS 1346. There is also an band available for implants in Europe of 2483.5 to 2500 MHz: this is currently undergoing compatibility studies at the CEPT for use also  by MBANs - Medical Body Area Networks. The frequency range 2360 to 2400 MHz used for MBAN in the US is not likely to be completely available in Europe and studies for sub bands in the range 2300 to 2500 MHz are under way.

The hacking problem is known: more of a problem is a suggestion from the European Commission that the method of putting radios in to a test mode should be on a 'secure' (ha!) web site available to administrations in all 27 EU countries.  The concept that such information could be used to switch the radio in a pacemaker to test mode and run down the battery doesn't seem to worry the proponents! Modern security approaches limit the length of time that the implant can be in test mode, plus enhanced encryption. As the erp is limited to 25 microwatts, you would need to be very close to hack the pacemaker, as there has to be handshaking to re-programme or to download telemetry: this means that you have to reliably pick up the signal from the device.
You also have to know the address of the device, so to hack it, you would need to be within  2 or 3 metres of the patient in the operating theatre while it was installed, or be in the doctor's office when it was addressed. A weaker link is where there is home monitoring because there, it would be possible to get the address: however, encryption can be made pretty good - PGP, for example.
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