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From: Phil Hobbs on 21 Mar 2010 19:41
On 3/21/2010 5:06 PM, Joerg wrote:
> Phil Hobbs wrote:
>> On 3/19/2010 11:50 AM, Joerg wrote:
>>> markp wrote:
>>>> "markp" <map.nospam(a)f2s.com> wrote in message
>>>> news:80h62eF4g7U1(a)mid.individual.net...
>>>>> "Grant" <omg(a)grrr.id.au> wrote in message
>>>>> news:2an6q5le2ev2v7o81mqanp9ua14jqu7s5h(a)4ax.com...
>>>>>> On Fri, 19 Mar 2010 03:14:04 -0700,
>>>>>> "JosephKK"<quiettechblue(a)yahoo.com> wrote:
>>>>>>
>>>>>>> On Thu, 18 Mar 2010 18:17:19 -0000, "markp" <map.nospam(a)f2s.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in
>>>>>>>> message
>>>>>>>> news:woydnU4jer8kwz_WnZ2dnUVZ_oadnZ2d(a)giganews.com...
>>>>>>>> <snip>
>>>>>>>>> Spent a day playing around with the optics which yielded no major
>>>>>>>>> improvements. The only thing I was unable to try was the optical
>>>>>>>>> filter
>>>>>>>>> (as
>>>>>>>>> I don't have anything suitable on hand). So, while I wait to get
>>>>>>>>> my hands
>>>>>>>>> on something I thought I'd try a few of the other
>>>>>>>>> suggestions... if
>>>>>>>>> nothing
>>>>>>>>> else it would be a learning experience.
>>>>>>>>>
>>>>>>>>> First I am making a change to my transmitter so that I can use a
>>>>>>>>> watch
>>>>>>>>> crystal as the time base of the modulation. I've basically added
>>>>>>>>> a Pierce
>>>>>>>>> Oscillator with its output going to one input of an AND gate. The
>>>>>>>>> other
>>>>>>>>> input of the AND gate is tied back to the existing
>>>>>>>>> microcontroller acting
>>>>>>>>> as an enable. Upon enabling the signal is fed to the gate of a FET
>>>>>>>>> controlling the LED. Here is a snippet of the schematic...
>>>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg . I've
>>>>>>>>> never
>>>>>>>>> actually constructed a Pierce Oscillator. From what I've been
>>>>>>>>> reading they
>>>>>>>>> may be a bit tough to get going with a buffered inverter (my
>>>>>>>>> case). My
>>>>>>>>> values were derived based on the crystal manufacturers load
>>>>>>>>> capacitance of
>>>>>>>>> 12.5pF. Comments?
>>>>>>>> <snip>
>>>>>>>>
>>>>>>>> As an aside, if you're bandpass filtering 32KHz, could you use a
>>>>>>>> large
>>>>>>>> capacitor from the junction of the resistor and LED to ground,
>>>>>>>> such that
>>>>>>>> when the FET turns on you get a high powered shorter spike? It
>>>>>>>> seems you
>>>>>>>> can't drive more than about 200mA with the LED shown as it's a
>>>>>>>> 50/50
>>>>>>>> waveform. You're allowed up to 2A though with a 10us pulse. If your
>>>>>>>> photodiode can respond fast enough to that shorter pulse it might
>>>>>>>> mean you
>>>>>>>> can turn the gain of the receiver down and reduce background noise
>>>>>>>> effects.
>>>>>>>> You'd need to do a fourier analysis of the 50/50 waveform at lower
>>>>>>>> power for
>>>>>>>> the 32KHz content and compare to the 32KHz content of a shorter
>>>>>>>> pulse but at
>>>>>>>> higher power. Alternatively use a monostable to create a
>>>>>>>> controlled pulse
>>>>>>>> width and up the current. I'm curious whether that would work or
>>>>>>>> not...
>>>>>>>>
>>>>>>>> Mark.
>>>>>>>>
>>>>>>> First OP would need a battery that can deliver the current pulses,
>>>>>>> cr2032 cannot.
>>>>>> So put a capacitor across the battery[1] and it will supply the
>>>>>> current spike
>>>>>> to LED. Duty cycle can be very low for LED drive, as it's the peak
>>>>>> signal power
>>>>>> that provides contrast (signal) at the receiver, not average power
>>>>>> that gets
>>>>>> swamped by ambient light.
>>>>>>
>>>>>> If there's room you could stack a couple coin batteries for 6V to
>>>>>> get more LED
>>>>>> peak current from cap. Or, perhaps a voltage double charging the
>>>>>> capacitor?
>>>>>> Lots of options.
>>>>>>
>>>>>> [1] you might want to disconnect capacitor in between message
>>>>>> sequences to
>>>>>> improve battery life.
>>>>>>
>>>>>> Grant.
>>>>> Yes, I was thinking of something like putting a large cap (seveal
>>>>> hundred uF or larger) with a small series resistor just to limit the
>>>>> pulse curent and connecting it to the resistor/diode juction of the
>>>>> schematic posted:
>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg
>>>>>
>>>
>>> Make sure the capacitor has low enough ESR, else it might limit your
>>> pulse amplitude to some unknown value. Also, measure the voltage dip on
>>> the supply rail because if too deep you crystal oscillator might choke.
>>>
>>>
>>>>> The receiver photodiode has to be fast enough to respond to that
>>>>> small pulse. After that you could filter out the 32kHz, but the gain
>>>>> of that stage may not need to be as high so background noise is
>>>>> reduced.
>>>>>
>>>
>>> Photodiodes are plenty fast if the connected electronics are. You should
>>> have no gain at all at DC, this is very important. Not even in the first
>>> TIA stage.
>>
>> I don't agree at all. Having low gain at DC is fine, to avoid
>> saturation, but if you have zero dc gain you can't tell whether you
>> have no signal or a hardware failure.
>>
>
> Well, for diagnostics you can let a wee bit of DC sneak past or provide
> a FET that breaks the inductive path during a test.

Down in the kilohertz, it's hard to get enough inductive reactance for
this job. A sub-poissonian current feedback loop works OK.

>
> Now I don't want to be facetious here but: You mentioned the shot noise
> pollution. Wouldn't that present enough signal to ascertain that the
> photodiode is working? I can't imagine it dropping to zilch even at
> night. If there was a full lunar eclipse maybe but then your DC level
> would also drop to zero.

It would if you have something sufficiently smart attached to it. If
you have a DC path, all you need is a comparator.

>
>> But the big problem is nearly always noise--shot noise of sunlight or
>> differentiated amplifier voltage noise.
>>
>
> Ok, true, but we'd have to quantify that. I have seen IR comms (with
> much more data rate than here) work clear across a soccer field in
> Europe. Now I don't have a clue about soccer and field size, but it sure
> was huge.
It isn't that hard to do if (a) you have a sunshade, as you've suggested
already, and (b) you use lenses to corral some reasonable number of
photons onto a reasonably small detector.

RF works better for many of these things because the effective area of
an isotropic detector goes like (lambda)**2. Shorter wavelengths mean
better resolution but require more precise aiming.

Cheers

Phil Hobbs

>


--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net
From: Joerg on 21 Mar 2010 19:46
Jon Kirwan wrote:
> On Sun, 21 Mar 2010 14:24:52 -0700, Joerg
> <invalid(a)invalid.invalid> wrote:
>
>> Jon Kirwan wrote:
>>> On Sun, 21 Mar 2010 14:06:38 -0700, Joerg
>>> <invalid(a)invalid.invalid> wrote:
>>>
>>>> <snip>
>>>>> But the big problem is nearly always noise--shot noise of sunlight or
>>>>> differentiated amplifier voltage noise.
>>>> Ok, true, but we'd have to quantify that. I have seen IR comms (with
>>>> much more data rate than here) work clear across a soccer field in
>>>> Europe. Now I don't have a clue about soccer and field size, but it sure
>>>> was huge.
>>> Baffled telecopic optics, optically narrow-band filtered,
>>> polarized, ...
>> Nope, nope, and nope.
>
> Are you sure? The detector itself might have been chosen for
> its responses over wavelength.
>

I am sure. But I don't remember the photodiode characteristics, it might
have been chosen for the purpose.


>>> ... and operating at a crystal-controlled narrow band
>>> modulation rate that was tightly band-passed at the receiver?
>> Yes, there was a filter but not super fancy. Somewhat matched to the
>> data rate but the shape factor was nothing to write home about, simple
>> LC circuitry on the cheap.
>
> Hmm.
>

LC is fairly easy and stable down there. Mechanical filters are sort of
rare antiques by now, I wouldn't even know if anyone still manufactures
them. Back then Collins did.

Heck, nowadays you could even do active filters. Or take a Cypress PSoC
and use the S/C filters in there. The uC part would then almost be a
complimentary bonus.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Joerg on 21 Mar 2010 19:48
Grant wrote:
> On Sun, 21 Mar 2010 14:06:38 -0700, Joerg <invalid(a)invalid.invalid> wrote:
>
>> Phil Hobbs wrote:
>>> On 3/19/2010 11:50 AM, Joerg wrote:
>>>> markp wrote:
>>>>> "markp" <map.nospam(a)f2s.com> wrote in message
>>>>> news:80h62eF4g7U1(a)mid.individual.net...
>>>>>> "Grant" <omg(a)grrr.id.au> wrote in message
>>>>>> news:2an6q5le2ev2v7o81mqanp9ua14jqu7s5h(a)4ax.com...
>>>>>>> On Fri, 19 Mar 2010 03:14:04 -0700,
>>>>>>> "JosephKK"<quiettechblue(a)yahoo.com> wrote:
>>>>>>>
>>>>>>>> On Thu, 18 Mar 2010 18:17:19 -0000, "markp" <map.nospam(a)f2s.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in
>>>>>>>>> message
>>>>>>>>> news:woydnU4jer8kwz_WnZ2dnUVZ_oadnZ2d(a)giganews.com...
>>>>>>>>> <snip>
>>>>>>>>>> Spent a day playing around with the optics which yielded no major
>>>>>>>>>> improvements. The only thing I was unable to try was the optical
>>>>>>>>>> filter
>>>>>>>>>> (as
>>>>>>>>>> I don't have anything suitable on hand). So, while I wait to get
>>>>>>>>>> my hands
>>>>>>>>>> on something I thought I'd try a few of the other suggestions... if
>>>>>>>>>> nothing
>>>>>>>>>> else it would be a learning experience.
>>>>>>>>>>
>>>>>>>>>> First I am making a change to my transmitter so that I can use a
>>>>>>>>>> watch
>>>>>>>>>> crystal as the time base of the modulation. I've basically added
>>>>>>>>>> a Pierce
>>>>>>>>>> Oscillator with its output going to one input of an AND gate. The
>>>>>>>>>> other
>>>>>>>>>> input of the AND gate is tied back to the existing
>>>>>>>>>> microcontroller acting
>>>>>>>>>> as an enable. Upon enabling the signal is fed to the gate of a FET
>>>>>>>>>> controlling the LED. Here is a snippet of the schematic...
>>>>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg . I've
>>>>>>>>>> never
>>>>>>>>>> actually constructed a Pierce Oscillator. From what I've been
>>>>>>>>>> reading they
>>>>>>>>>> may be a bit tough to get going with a buffered inverter (my
>>>>>>>>>> case). My
>>>>>>>>>> values were derived based on the crystal manufacturers load
>>>>>>>>>> capacitance of
>>>>>>>>>> 12.5pF. Comments?
>>>>>>>>> <snip>
>>>>>>>>>
>>>>>>>>> As an aside, if you're bandpass filtering 32KHz, could you use a
>>>>>>>>> large
>>>>>>>>> capacitor from the junction of the resistor and LED to ground,
>>>>>>>>> such that
>>>>>>>>> when the FET turns on you get a high powered shorter spike? It
>>>>>>>>> seems you
>>>>>>>>> can't drive more than about 200mA with the LED shown as it's a 50/50
>>>>>>>>> waveform. You're allowed up to 2A though with a 10us pulse. If your
>>>>>>>>> photodiode can respond fast enough to that shorter pulse it might
>>>>>>>>> mean you
>>>>>>>>> can turn the gain of the receiver down and reduce background noise
>>>>>>>>> effects.
>>>>>>>>> You'd need to do a fourier analysis of the 50/50 waveform at lower
>>>>>>>>> power for
>>>>>>>>> the 32KHz content and compare to the 32KHz content of a shorter
>>>>>>>>> pulse but at
>>>>>>>>> higher power. Alternatively use a monostable to create a
>>>>>>>>> controlled pulse
>>>>>>>>> width and up the current. I'm curious whether that would work or
>>>>>>>>> not...
>>>>>>>>>
>>>>>>>>> Mark.
>>>>>>>>>
>>>>>>>> First OP would need a battery that can deliver the current pulses,
>>>>>>>> cr2032 cannot.
>>>>>>> So put a capacitor across the battery[1] and it will supply the
>>>>>>> current spike
>>>>>>> to LED. Duty cycle can be very low for LED drive, as it's the peak
>>>>>>> signal power
>>>>>>> that provides contrast (signal) at the receiver, not average power
>>>>>>> that gets
>>>>>>> swamped by ambient light.
>>>>>>>
>>>>>>> If there's room you could stack a couple coin batteries for 6V to
>>>>>>> get more LED
>>>>>>> peak current from cap. Or, perhaps a voltage double charging the
>>>>>>> capacitor?
>>>>>>> Lots of options.
>>>>>>>
>>>>>>> [1] you might want to disconnect capacitor in between message
>>>>>>> sequences to
>>>>>>> improve battery life.
>>>>>>>
>>>>>>> Grant.
>>>>>> Yes, I was thinking of something like putting a large cap (seveal
>>>>>> hundred uF or larger) with a small series resistor just to limit the
>>>>>> pulse curent and connecting it to the resistor/diode juction of the
>>>>>> schematic posted:
>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg
>>>>>>
>>>> Make sure the capacitor has low enough ESR, else it might limit your
>>>> pulse amplitude to some unknown value. Also, measure the voltage dip on
>>>> the supply rail because if too deep you crystal oscillator might choke.
>>>>
>>>>
>>>>>> The receiver photodiode has to be fast enough to respond to that
>>>>>> small pulse. After that you could filter out the 32kHz, but the gain
>>>>>> of that stage may not need to be as high so background noise is
>>>>>> reduced.
>>>>>>
>>>> Photodiodes are plenty fast if the connected electronics are. You should
>>>> have no gain at all at DC, this is very important. Not even in the first
>>>> TIA stage.
>>> I don't agree at all. Having low gain at DC is fine, to avoid
>>> saturation, but if you have zero dc gain you can't tell whether you have
>>> no signal or a hardware failure.
>>>
>> Well, for diagnostics you can let a wee bit of DC sneak past or provide
>> a FET that breaks the inductive path during a test.
>>
>> Now I don't want to be facetious here but: You mentioned the shot noise
>> pollution. Wouldn't that present enough signal to ascertain that the
>> photodiode is working? I can't imagine it dropping to zilch even at
>> night. If there was a full lunar eclipse maybe but then your DC level
>> would also drop to zero.
>>
>>
>>> But the big problem is nearly always noise--shot noise of sunlight or
>>> differentiated amplifier voltage noise.
>>>
>> Ok, true, but we'd have to quantify that. I have seen IR comms (with
>> much more data rate than here) work clear across a soccer field in
>> Europe. Now I don't have a clue about soccer and field size, but it sure
>> was huge.
>
> In one of the referenced articles upthread they were bouncing signals off
> the clouds, but they moved up to red to avoid the water absorption of the
> IR.
>

Yeah, it probably wouldn't be so great in a thick London fog. Unless you
have enough energy to vaporize the water content :-)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
From: Grant on 21 Mar 2010 19:49
On Sun, 21 Mar 2010 17:39:15 -0500, "krw(a)att.bizzzzzzzzzzzz" <krw(a)att.bizzzzzzzzzzzz> wrote:

>On Mon, 22 Mar 2010 08:29:03 +1100, Grant <omg(a)grrr.id.au> wrote:
>
....
>>In one of the referenced articles upthread they were bouncing signals off
>>the clouds, but they moved up to red to avoid the water absorption of the
>>IR.
>
>...and every time they turned it on Batman showed up.

Oh yeah... :o)
>
>It would seem that they'd need a *lot* of transmit power to make up for the
>scattering, which they must be counting on since clouds are quite amorphous.

It was big, side by side fresnal lenses (tx & rx) each about a foot square,
I think it might've been a 5W LED they used.

Grant.
From: Joerg on 21 Mar 2010 19:53
Phil Hobbs wrote:
> On 3/21/2010 5:06 PM, Joerg wrote:
>> Phil Hobbs wrote:
>>> On 3/19/2010 11:50 AM, Joerg wrote:
>>>> markp wrote:
>>>>> "markp" <map.nospam(a)f2s.com> wrote in message
>>>>> news:80h62eF4g7U1(a)mid.individual.net...
>>>>>> "Grant" <omg(a)grrr.id.au> wrote in message
>>>>>> news:2an6q5le2ev2v7o81mqanp9ua14jqu7s5h(a)4ax.com...
>>>>>>> On Fri, 19 Mar 2010 03:14:04 -0700,
>>>>>>> "JosephKK"<quiettechblue(a)yahoo.com> wrote:
>>>>>>>
>>>>>>>> On Thu, 18 Mar 2010 18:17:19 -0000, "markp" <map.nospam(a)f2s.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> "eeboy" <jason(a)n_o_s_p_a_m.n_o_s_p_a_m.jasonorsborn.com> wrote in
>>>>>>>>> message
>>>>>>>>> news:woydnU4jer8kwz_WnZ2dnUVZ_oadnZ2d(a)giganews.com...
>>>>>>>>> <snip>
>>>>>>>>>> Spent a day playing around with the optics which yielded no major
>>>>>>>>>> improvements. The only thing I was unable to try was the optical
>>>>>>>>>> filter
>>>>>>>>>> (as
>>>>>>>>>> I don't have anything suitable on hand). So, while I wait to get
>>>>>>>>>> my hands
>>>>>>>>>> on something I thought I'd try a few of the other
>>>>>>>>>> suggestions... if
>>>>>>>>>> nothing
>>>>>>>>>> else it would be a learning experience.
>>>>>>>>>>
>>>>>>>>>> First I am making a change to my transmitter so that I can use a
>>>>>>>>>> watch
>>>>>>>>>> crystal as the time base of the modulation. I've basically added
>>>>>>>>>> a Pierce
>>>>>>>>>> Oscillator with its output going to one input of an AND gate. The
>>>>>>>>>> other
>>>>>>>>>> input of the AND gate is tied back to the existing
>>>>>>>>>> microcontroller acting
>>>>>>>>>> as an enable. Upon enabling the signal is fed to the gate of a
>>>>>>>>>> FET
>>>>>>>>>> controlling the LED. Here is a snippet of the schematic...
>>>>>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg . I've
>>>>>>>>>> never
>>>>>>>>>> actually constructed a Pierce Oscillator. From what I've been
>>>>>>>>>> reading they
>>>>>>>>>> may be a bit tough to get going with a buffered inverter (my
>>>>>>>>>> case). My
>>>>>>>>>> values were derived based on the crystal manufacturers load
>>>>>>>>>> capacitance of
>>>>>>>>>> 12.5pF. Comments?
>>>>>>>>> <snip>
>>>>>>>>>
>>>>>>>>> As an aside, if you're bandpass filtering 32KHz, could you use a
>>>>>>>>> large
>>>>>>>>> capacitor from the junction of the resistor and LED to ground,
>>>>>>>>> such that
>>>>>>>>> when the FET turns on you get a high powered shorter spike? It
>>>>>>>>> seems you
>>>>>>>>> can't drive more than about 200mA with the LED shown as it's a
>>>>>>>>> 50/50
>>>>>>>>> waveform. You're allowed up to 2A though with a 10us pulse. If
>>>>>>>>> your
>>>>>>>>> photodiode can respond fast enough to that shorter pulse it might
>>>>>>>>> mean you
>>>>>>>>> can turn the gain of the receiver down and reduce background noise
>>>>>>>>> effects.
>>>>>>>>> You'd need to do a fourier analysis of the 50/50 waveform at lower
>>>>>>>>> power for
>>>>>>>>> the 32KHz content and compare to the 32KHz content of a shorter
>>>>>>>>> pulse but at
>>>>>>>>> higher power. Alternatively use a monostable to create a
>>>>>>>>> controlled pulse
>>>>>>>>> width and up the current. I'm curious whether that would work or
>>>>>>>>> not...
>>>>>>>>>
>>>>>>>>> Mark.
>>>>>>>>>
>>>>>>>> First OP would need a battery that can deliver the current pulses,
>>>>>>>> cr2032 cannot.
>>>>>>> So put a capacitor across the battery[1] and it will supply the
>>>>>>> current spike
>>>>>>> to LED. Duty cycle can be very low for LED drive, as it's the peak
>>>>>>> signal power
>>>>>>> that provides contrast (signal) at the receiver, not average power
>>>>>>> that gets
>>>>>>> swamped by ambient light.
>>>>>>>
>>>>>>> If there's room you could stack a couple coin batteries for 6V to
>>>>>>> get more LED
>>>>>>> peak current from cap. Or, perhaps a voltage double charging the
>>>>>>> capacitor?
>>>>>>> Lots of options.
>>>>>>>
>>>>>>> [1] you might want to disconnect capacitor in between message
>>>>>>> sequences to
>>>>>>> improve battery life.
>>>>>>>
>>>>>>> Grant.
>>>>>> Yes, I was thinking of something like putting a large cap (seveal
>>>>>> hundred uF or larger) with a small series resistor just to limit the
>>>>>> pulse curent and connecting it to the resistor/diode juction of the
>>>>>> schematic posted:
>>>>>> http://img717.imageshack.us/img717/8467/transmitter.jpg
>>>>>>
>>>>
>>>> Make sure the capacitor has low enough ESR, else it might limit your
>>>> pulse amplitude to some unknown value. Also, measure the voltage dip on
>>>> the supply rail because if too deep you crystal oscillator might choke.
>>>>
>>>>
>>>>>> The receiver photodiode has to be fast enough to respond to that
>>>>>> small pulse. After that you could filter out the 32kHz, but the gain
>>>>>> of that stage may not need to be as high so background noise is
>>>>>> reduced.
>>>>>>
>>>>
>>>> Photodiodes are plenty fast if the connected electronics are. You
>>>> should
>>>> have no gain at all at DC, this is very important. Not even in the
>>>> first
>>>> TIA stage.
>>>
>>> I don't agree at all. Having low gain at DC is fine, to avoid
>>> saturation, but if you have zero dc gain you can't tell whether you
>>> have no signal or a hardware failure.
>>>
>>
>> Well, for diagnostics you can let a wee bit of DC sneak past or provide
>> a FET that breaks the inductive path during a test.
>
> Down in the kilohertz, it's hard to get enough inductive reactance for
> this job. A sub-poissonian current feedback loop works OK.
>

If you want tons of gain in the TIA that's a problem. Jim could design a
gyrator though :-)

>>
>> Now I don't want to be facetious here but: You mentioned the shot noise
>> pollution. Wouldn't that present enough signal to ascertain that the
>> photodiode is working? I can't imagine it dropping to zilch even at
>> night. If there was a full lunar eclipse maybe but then your DC level
>> would also drop to zero.
>
> It would if you have something sufficiently smart attached to it. If
> you have a DC path, all you need is a comparator.
>

Not too much smarts needed, just monitor wideband AC.


>>
>>> But the big problem is nearly always noise--shot noise of sunlight or
>>> differentiated amplifier voltage noise.
>>>
>>
>> Ok, true, but we'd have to quantify that. I have seen IR comms (with
>> much more data rate than here) work clear across a soccer field in
>> Europe. Now I don't have a clue about soccer and field size, but it sure
>> was huge.
> It isn't that hard to do if (a) you have a sunshade, as you've suggested
> already, and (b) you use lenses to corral some reasonable number of
> photons onto a reasonably small detector.
>

Yes, you've got to shade it via a tube.


> RF works better for many of these things because the effective area of
> an isotropic detector goes like (lambda)**2. Shorter wavelengths mean
> better resolution but require more precise aiming.
>

With RF the wavelength doesn't really matter but you have to stay within
an ISM band and pick one that's not crowded. If directionality isn't
desired and you can't shade then yes, RF would be the ticket here.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
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Prev: Microeconomics 5e Jeffrey M. Perloff test bank and solution manual is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today.
Next: Essentials of the Legal Environment 2nd Edition 2008 Roger LeRoy Miller Test bank is available for purchase at affordable prices. Contact me at alltestbanks11[at]gmail.com to buy it today.