[Laser] WB9AJZ laser RX problems

[John Schnurer]

	Dear People,


	The "buzz" .... may come from two primary sources, provide you do
not have some type of internal noise problem from a switching power
supply, or other:

	A)	Electric and magnetic field induced noise from AC mains

	B)	Fluctuation of optical sources from AC mains such as arc
lamps, fluorescent lamps and other non DC, non thermal or non incandescent
light sources

	Solution:

	A) Pay close attention to shielding of ALL high gain circuits

	B)	Make VERY sure you "eye" can ONLY SEE the transmitter, and
this you may wish to call "optical shielding"....

	C)	Use a series of distributed filters along the signal path.

		i]	notch or band-reject filters at 60 cps (or 50 cps
in Europe) and its harmonics, up to the 1,000 cps range.

		ii]	band pass the signal type you desire if possible


	You would be well off to look toward FM modulation and
demodulation.  Each process can be performed with the old standby the
4046 type Phase Locked Loop or "PLL".   You will have to buffer the output
and inputs of same.

	If you intend to do this and do not know PLL circuits, it is well
worth your time and money to buy Don Lancaster's CMOS Cookbook.

							JH



On Sat, 7 Dec 2002, Wendell Smith wrote:

> 
> I built the transmitter/receiver from the web site of WB9AJZ/6:
> 
> http://www.psnw.com/~n7stu/cheapo.html
> 
> I am trying to get 4  units built up for roving during
> the January VHF contest, and these seemed to be rather
> simple. Here in Illinois the best DX is only going to be a
> few miles, unless you are fortunate to live in a Chicago
> hi-rise.
> 
> There is a loud raspy buzz whenever the phototransistor is
> blocked.  Changing the 10Mohm resistance only changes the
> pitch.  Shining the 800 Hz laser produces a 800 Hz tone,
> but much weaker than the buzz.  Turned the laser TX off,
> and the buzz remained. Under normal room  incandescant
> lighting the buzz is gone, and the laser will still give the tone.
> 
> I built a second unit, thinking that I had a bug somewhere,
> and the same result occured. Any thoughts or ideas for
> getting rid of the buzz, or any other hints for these circuits?
> 
> Thanks,
> Wendell N9REP
> 
> 
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