[Laser] Some beginner questions

[Paolo Cravero]

Art wrote:

Hi,
thank you Art for the comprehensive answer. Had some email delays, so I 
couldn't reply earlier.

> The remote control receivers used with VCR's are meant for receiving 
> subcarrier  modulated pulses, with the modulation occurring at ~44 Khz 

Interesting. I was actually thinking of "presence" sensors inside VCRs. 
In one model I noticed several couples of diode+detector an inch or so 
apart. Those detectors must be even more crude than remote control RX, 
since they mainly operate in total darkness and very close to eachother.

>> I have seen OPT202 for a reasonable price, but had not the chance to 
> 
> The OPT units are the best deal by far, IMHO. If you get a 5 pin inline 

At "West Florida Components" there are OPT202 and OPT101 sensors for 
sale, both in DIP packages. I compared both datasheets and could notice:
- both have the same 650nm sensitivity, but the 101 has higher "dark 
errors" (7.5mV vs. 0.5mV typ.), how important is this? (a lot I think...)
- 101 has single supply, which simplifies things IMO (ok 202 datasheet 
shows a single-supply arrangment, is this more noisy?)
- 101 has higher IR peak sensitivity, a problem?

I think I'll go for OPT202/DIP.

> They are low cost (ebay) and use little power. To get best results, you 
> need to shield them completely, just as though it was an rf circuit and 
> mechanically (small air currents induce noise).

Do you mean to shield them (202s) so that they look like a 301? Just 
leave a small opening over the sensor, am I right?

> For very serious work, a photomultipler tube is needed. They use high 
[...]
> more sensitive than the best photodiodes. They use much more power, 
> typically 100 to 150 ma from a 12 volt power supply. So, they are much 
> harder to use in portable operations. Unless you get very serious about 
> DX, you should avoid them.

We are more concerned about budget rather than consumption :-)

> Colder air is drier air, and at higher elevations, you have less 
[...]
> I think the current world record is 170 miles, made in Arizona from 
> hilltop to hilltop. The air is much cleaner there, but getting up to

We've already identified some LOS peaks >170 miles apart, they just both 
need to be higher than 1400 masl. It is actually hard to find a peak 
lower than that over here! Anyway, that's for the future. Let's first 
get started!

72,
Paolo IK1ZYW

-- 
| www.paolocravero.tk +  IQRP #476  + skype://pcravero  |
| SpamAssassin-based email antispam/antivirus solutions |
\     Italian/English-to/from-Croatian translations    /