[Gta04-owner] GTA04 hardware suggestion and discussions

Glenn glenn.mh.dk at gmail.com
Sat Jan 22 23:34:50 CET 2011


Hi All!

Here are some hardware suggestion for discussion:


1) Possibility of IR RC5 receiver/transmitter


2) Possibility of IRDA transceiver


3) Possibility of a "video-link"? Use 
touch-screen as a color matrix (2D) barcode video 
transmitter - and the camera as a receiver (half 
or full duplex). Let the link automatically adapt 
to to half duplex, if you need to turn your 
smartphone to establish the other half duplex 
connection. The link should also adapt frame rate 
and if the camera and/or screen is dirty - or the 
link is through a dirty window. I have no idea 
how fast the link can be as a function of 
distance. The link should automatically adapt if 
the video color matrix (2D) barcode is mirrored 
in any way - or "played" backwards.


4) Antenna diversity of (preferably pattern, 
space - or polarisation diversity):

* GSM/UMTS? (receive diversity incl. external antenna).

* 802.11(a)bg(n) (diversity) (W2CBW009Di: "For 
Dual Antenna application") Almost every laptop 
has diversity.

* FM-receiver (receive diversity requires 
2*Si4721 - uC selects the best signal (listen to 
one - let the other turn on and scan when the 
listen-signal has to low S/N ratio) - or you can 
listen to one and record another).

* GPS? (receive diversity including external antenna).

For FM-diversity you can use a 180 degree hybrid 
(two loaded LC-circuits?) to separate common-mode 
and differential-mode - for diversity - if three 
space divided poles are available. I know that 
there is a capacitance between ear-wires and 
their ground, so I do not know, how well it will 
work. Note that some impedance matching might be 
needed.

For VHF/FM the head-phone cable might be used. 
The diversity might be implemented isolating 
ground by a adequate inductor (100MHz parallel 
LC-circuit) - and two high-pass filter from left 
and right earphone non-ground wires - and the 
GTA04 itself as a kind of "ground"/third-wire.

-

Links:

Matrix (2D) barcodes:
http://en.wikipedia.org/wiki/Barcode#Matrix_.282D.29_barcodes

PCB-antennas (small):
http://www.numatechnologies.com/pdf/foilantennas.pdf

An antenna that can be sized for 100MHz reception 
around the perimeter of the PCB? Use two loops so 
ground is not needed:
http://www.hard-core-dx.com/nordicdx/antenna/loop/k9ay/k9ay_orig.pdf
http://www.hard-core-dx.com/nordicdx/antenna/loop/k9ay/index.html

Also for 100MHz:
(T2FD -- The Forgotten Antenna: 
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fd.html 
)


1/3/2003 Antenna Diversity Strengthens Wireless LANs:
http://www.eetimes.com/design/communications-design/4008941/Antenna-Diversity-Strengthens-Wireless-LANs
Quote: "...While detailed implementations of 
dynamic diversity can vary widely, it's possible 
to summarize the simulated performance of a 
conceptually simple scheme relative to that of a 
single-antenna mode, as well as full diversity 
and selection diversity (Figure 6)..."


http://en.wikipedia.org/wiki/Antenna_diversity
Quote: "...
Spatial diversity employs multiple antennas, 
usually with the same characteristics, that are 
physically separated from one another. Depending 
upon the expected incidence of the incoming 
signal, sometimes a space on the order of a 
wavelength is sufficient.
...
Pattern diversity consists of two or more 
co-located antennas with different radiation 
patterns.
...
A polarisation difference of 90° will result in 
an attenuation factor of up to 34dB in signal 
strength. By pairing two complementary 
polarizations, this scheme can immunize a system 
from polarization mismatches that would otherwise 
cause signal fade. Additionally, such diversity 
has proven valuable at radio and mobile 
communication base stations since it is less 
susceptible to the near random orientations of 
transmitting antennas.
..."


http://web.archive.org/web/20060427002449/www.tvhandbook.com/support/pdf_files/Chapter17_7.pdf
Quote: "...
Diversity is only of value for the relatively 
rapid fading caused by multipath. This kind of 
fading is encountered extensively at HF and for 
tropospheric and iono- spheric scatter 
propagation at higher frequencies. Similarly, 
mobile vehicles passing through a static 
multipath field at VHF and UHF encounter such 
fading as a result of their motion.
..."


180 degree hybrid:
http://upload.wikimedia.org/wikipedia/commons/6/62/Combine2.svg
"Sum" uses sum of ear-wires - and third-wire.
"Difference" to some extent uses only ear-wires.


Pattern Diversity:
90 degree hybrid:
http://upload.wikimedia.org/wikipedia/commons/6/62/Combine2.svg
"X" uses ear-wires in one direction.
"Y" uses ear-wires in the other one direction.

180 degree hybrid and 90 degree hybrid might be 
combined. One 90 and two 180 degrees? Then you 
have 4 receive pattern diversity output ports.


http://www.option.com/en/products/products/embedded-mobile-broadband/lgamodulegtm601-609/specifications/#start
Quote: "...
Simultaneous Equalization and Rx Diversity on all 
bands (Advance Receiver Type 3i), except for 
GSM/GPRS/EDGE
...
Primary, diversity and GPS antenna contact pads
..."

regards,

Glenn


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