Obtain the effective radiation power (ERP) in your direction, obtain the receiver power density and receiver antenna cross section, so using Friees equations, so you can easily obtain to power from the receiving antenna.
Why not use a simple passive parabolic reflector and a dipole at the feedpoint ?
On a sunny day (Sat, 04 Apr 2015 21:58:41 +1100) it happened Robert Stevens wrote in :
Things like this get re-invented all the time. Some years ago Nokia had something about powering cellphones from ambient RF. Never to be heard of again (and neither Nokia :-) ). Sure, you can make any bigger antenna, dish even, and point it at a TV tower.
That does NOT guarantee reception indoors, hey I canno teven receive DVB-T indoors here. It would be totally unreliable for something like card based financial transactions. And totally not-practical. Small solar cell and bttery would beat it any time. Even on artificial room light. But, I hope they learned something about RF and communication, those perfessers and their stdents.
I have seen designs from the 1930/50's with a resonant circuit aligned at local transmitter frequency, rectified by a selenium rectifier to generate some low anode voltage for a single low anode voltage RF/AF tube to amplify the signal from a remote station.
Nokia tried all kinds of designs such as solar powered mobile handset. Any pointers to this device ? I would like to take a look at this device.
I had similar problems with DVB-T.
Try two separate DVB-T (active) indoor antennas separated by at least a few meters. Simply combine the signals at RF-level (a passive splitter).
The theory says that in a multipath environment, the combination should be done after the program stream decoding,
However, according to my practical tests, simple RF combining works quite well, as long as the antenna separation is at least a few wavelengths, things work quite OK.
On a sunny day (Fri, 03 Apr 2015 15:33:05 +0300) it happened snipped-for-privacy@downunder.com wrote in :
I was a posting in this group, I think not on April 1, they (Nokia) was developing that) OK, found it with google:
I have a quad bowtie in the attic at 430 Mhz pointing at the next amateur radio repeater that is just as a far as the DVB-T transmitter, the ham repeater comes in great :-) I tried DVB-T several times and no go. I then bought an active DVB-T antenna for indoors, same problem. I gave up, and use cable or satellite.
It is possible DVB-T will simply die... it is either cable or sat here.
OK, but that makes no sense from signal level POV, I mean combining nothing with nothing equals nothing. The decoding will be nothing below some level. I am no DVB-T expert, but in DVB-S there is no ouput if for example Viterbi fails.
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Actually you can make radio receivers with amplifiers that run on harvested AC hum and 'spherics - the more noise the better :-) :
You will get more useful AC hum and 'spherics energy by removing D5 and D6 - and replace C6 by two serially connected electrolytic capacitors and connect the connection point of the two electrolytic capacitors to the earth electrode.
By removing D5 and D6 one diode voltage drop is removed from the rectification.
Please note that the crystal receiver common is NOT DC connected to the earth electrode. The earth electrode and common is connected AC-wise via the lower electrolytic capacitor.
Actually the reciever is a superregenerative receiver, that runs on AC hum and 'spheric !
A "Free-Power", Batteryless, One-Transistor AM Radio that works off of AC hum and 'spherics:
In searching for the superior passive receiver:
Og nu til noget "helt" andet:
Electrostatic Motors Are Powered By Electric Field of the Earth. By C.L. Stong, October 1974:
Glenn
On 04/04/15 12.58, Robert Stevens wrote: ...
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Hi Robert
You should use (onmi-directional?) ultra wide band antennas e.g.:
Even a flat Biconical_antenna - aka Bow-Tie antenna (with measurements):
( Complicated:
Another LPA:
Log-Periodic Tooth Antennas (with measurements):
Glenn
The problem with this idea is that the effective area of nonresonant antennas is small compared with a narrowband antenna of the same size.
There's a 1:1 tradeoff between the solid angle (i.e. angular area) of the pattern and the effective intercepted area, and you have to trade off the directivity to gain bandwidth.
A narrowband Yagi-Uda will give a lot more output for the same physical size, though it still won't be much unless you're right under the tower.
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Not quite. It was a solar charger, not a solar power.
Search for "Nokia Lokki": The link to the original Nokia site is gone, but can be found in the archives:
The basic problem is that you can't put enough solar cells on a cell phone to fully charge a LiIon battery in a reasonable amount of time. Cell phones also don't live in sunlight but prefer the darkness of users pockets and purses. Meanwhile, smartphones have taken over, which have HUGE power appetites, mostly to run the backlighting.
As for the microwave powered phone, it might be possible if live directly in the antenna pattern and you don't mind also being cooked by the power from the cell site. The MPE (max permissible exposure) varies by frequency and service: At 1900 MHz, the GUM (great unwashed masses) can be cooked at: f/1500 = 1900/1500 = 1.3 mw/cm^2 for 30 minutes My smartphone has a frontal area of: 6 x 12cm = 72 cm^2 which under ideal conditions would produce: 1.3 mw/cm^2 * 72 cm^2 = 94 milliwatts of power to the phone charger. The battery in my ancient Rotomola Droid X2 is rated at: 1800 ma-hrs * 3.7V = 6.7 watt-hrs Ignoring conversion and charging efficiencies, and assuming that phone is not drawing power while charging, fully charging a dead battery would take: 7.6 watt-hrs / 0.094 watts = 71.3 hrs Assuming about 3 hrs of available sunlight per day, that would be: 71.3 hrs / 3 hrs/day = 24 days to charge the battery. Not very practical methinks.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
I really doubt that one of those things can flash an LED 6.5 miles away from a TV tower.
What's wrong with lithium batteries?
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
You just need to integrate for a few years. ;)
Cheers
Phil Hobbs
-- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
I wonder if a dinky antenna like that could charge a modest capacitor to a few volts in *any* amount of time.
-- John Larkin Highland Technology, Inc picosecond timing laser drivers and controllers jlarkin att highlandtechnology dott com http://www.highlandtechnology.com
The wording in the article is rather odd: "These locations ranged from less than half a mile away from a TV tower to about 6.5 miles away." Ok, it flashes an LED at 1/2 mile from a TV tower. That's possible at
3mw to light the LED. However, it also flashes at an unspecified location 6.5 miles away, that may or may not be getting RF from a different source.Backscatter sounds very much like the way RFID tags currently work.
Also odd: "You can reflect these signals slightly to create a Morse code of communication between battery-free devices". That doesn't quite agree with the video, which claims that the signals are either reflected or absorbed to produce a 0 or 1. Morse code?
Judging by the English, I suspect the article author might not have a good understanding of the technology in the ACM paper.
LiIon power doesn't generate research papers and university web pages.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
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Argh. After a phone call, I reverted back to solar power, not RF power. With RF power, the FCC only allows 30 minutes of RF exposure at the MPE limit per day. Therefore, the charge time would be: 71.3 hrs / 0.5 hrs/day = 143 days to fully charge the battery. However, if you happen to live where the RF is continuously available, and don't care about RF safety, 24 hrs exposure will charge your battery in: 71.3 hrs / 24 hrs/day = 3 days Still not very practical, methinks.
-- Jeff Liebermann jeffl@cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
DVB-T consists of thousands of subcarriers, I am not sure, if you are using the 2k or 8k system in the Netherlands.
Anyway, in an indoor reception system, there are going to be a severe multipath multipath situation and some of these subcarriers become fully canceled out. The DVB-T/T2 system is designed to survive quite heavy loss of subcarriers by spreading the data into multiple subcarriers. The frequency interlace will convert a complete loss of a subcarrier to random bit errors, easily correctable by the ECC (compare with burst error to random error conversion in time domain).
I have an indoor antenna in the window. I had to move the antenna from the left edge of the window to the middle of the window and to the right end of the window to get the best reception of each for different transport stream ("RF-channel").
Having two simple active antennas in adjacent windows combined with a simple power combiner (i.e. a TV-splitter used backwards) works quite well, no need to reposition the antenna, every time I switch a channel.
This is just a simple example of spatial diversity.
The capacitive coupling between the house wiring and some electronic device is in the order of 10 pF so that will have a capacitive reactance of 300 Mohm at 230 V 50 Hz that will pass 0.7 uA or 170 uW.
If your equipment can't live with well below this, I think you should search for a new power source.
On a sunny day (Fri, 03 Apr 2015 19:58:16 +0300) it happened snipped-for-privacy@downunder.com wrote in :
I use this in Linux (part of a script): dvbstream -c $CARD -I 2 -qam 64 -gi 4 -cr 1_2 -crlp 1_2 -bw 8 -tm 8 -f $freq -o $vpid $apid $tpid " so QAM 64, 8k, unless it changed lately ;-) I did some work on dvbstream.. added a beep to tune for max signal strength.
In the previous house I could receive DVB-T with an outside antenna cross country, so I know my hardware is OK. Also the local telco got control of the DVB-T network and IMNSHO completely and totally crapped it. Why? save money on transmitters I guess.
I have 2 DVB-T receivers from Hauppauge, and of course the DVB-T USB sticks with E4000 R820T tuner, that I use for spectrum analyzer:
Yes that makes a lot of sense, on the RF side. Multipath was supposed to be a problem in the US with ATSC, and a lot of clever solutions were made, but I have not really followed that as there is no ATSC here.
On a sunny day (Fri, 03 Apr 2015 09:38:09 -0700) it happened Jeff Liebermann wrote in :
Best is one of those hand-crack charging units I think, I'v seen some on ebay.
cannot beat the price! 2$05 :-) I have to confess I just ordered one, gotto try this, more later!
On a sunny day (Fri, 03 Apr 2015 09:25:31 -0700) it happened Jeff Liebermann wrote in :
I have not seen the paper, but thought they used micro-mirrors (as in LCD projectors) to make a controlled reflector. Or did I just invent that?
OK, so you have the same settings as in most of Europe.
Since the Netherlands have most households connected to cable, the on the air DVB-T system was supposed to be 16/64QAM at 2k to work better with fast moving trains and cars on motorways. 8k is a bit nasty for vehicles moving at high speeds due to Doppler.
At the first DVB-T trials in UK they tried -20 dB compared to analog PEP, but in reality, the DVB-T at -10 dB will give similar coverage compared to analog signals.
The US ATSC 8VSB is a single carrier system, which definitively needs an equalizer to get rid of _most_ multipath issues. Of course, for mobile reception systems, the equalizer needs to be retuned for each step you take.
Not quite related, but backscatter X-rays can be used to see wood beams/supports behind a wooden wall. A bit of doing to engineer from scratch (as they basically do not exist), then build and then be used.. Not exactly small or light to move around as it it were a camera.
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