6500K AM modulator

...Or a "spread spectrum" AM modulator, 390 to 750nm wavelenght, or 400 to 790 THz..... or a white LED AM modulator... now you get it?

Following some LED experiments I wanted to try some light comunication, so decided to do one of the basic forms of modulated light communications, AM, for good or for worst the idea was just to have some fun....

Here's the transmission part, when time permits (I still have a huge backlog on lower frequencies projects) will make some companion receiver and put a mic on this "transmitter".

As you can understand, first I did the schematic and then the final draw on paper...
Any NPN transistor should work but more led's (more power!) will require a more robust transistor, the speaker was just to ear the modulation noise (touching the LM386 input pin), I had no mic at hand.
The pot set's the bias point, and the led should be always on (a steady carrier!?), changing bright by modulation.
LM386 gain was set by an 10uF cap between pin 1 and 8 as standard design.

You can ear noise and see some modulated light in this lousy video:


Have fun!

Powered by led's

I do like led's but aside the fact they are nice to show power on in circuits I only did some minor tests with them. One of the experiments some time ago was to use a led as a poor and small replacement for a solar cell, yes led's can generate small amounts of energy. Some can sense radiation and other types of PN junction can be nice for temperature sensing (like 1n4148 diode)... normaly components have more than one function you know?! The classic example is a resistor used as a camera flash :) One time action of course!

Next images you have an infrared led, (I think, since I don't remember the specs or even when it was bought) the outer case is light blue and emits no visible light when direct biased.

Here in reverse connection getting some direct sun light.
Two of them in series should give 1.4V althoug on a very small current, this multimeter has 10M of internal impedance but if you put some in parallel you end up with a very small power supply as long as the sun shines...

Here's the "power" from a white color paint!:

Incidently this gave me the idea of using one of this for a very crude Sun photometer.... maybe one of this days...

And in the dark:

This led was the best one I tested, other standard types gave worst results.

Have fun!

Mains filter

A friend gave me one of those new computers....a tablet...:)

...never mind the missing screen (there's an vga plug), it works and it was cheap!

My idea was to put Linux in it and use at the weekend shack, it came with windows something installed and for now will stay that way (sure not for long since I'm a bit allergic to that OS).
After some psk and rtty decoding apps installed, decided to hook it up to the FT-102. I was a rainy day and I was getting a lot of interference, I thought it was the weather but after shutting down the computer I notice the interference had gone and the only (confirmed) source was the computer power supply! Rat's! Something had to be done....

So I came up with the idea of making a mains filter idea. The other option includes a Faraday cage for the power supply or getting another computer.

Here's the assembly of the interference filter for the mains power supply:


well....did it worked?.....no and not tested yet, after powering it up (I should had tested before closing the box) the VDR blew up, I guess that it was underrated or I didn't looked very well to the schematic of the donation computer power supply were I removed it and probably the VDR was not on the mains line and was not rated for over 230V.

Now that I removed the broken VDR I have to wait for the next weekend to conduct further tests.

Here's the schematic used:

..never mind the VDR (it's just for spike protection), it's not installed at the moment. If you duplicate this, get capacitors rated for at least 500Vrms, the ones I used are rated 1KV and came from a computer power supply.
The number of turns it's not critical as long as they don't create a lot of impedance on the mains 50Hz....I guess something bellow 1000 turns it's ok :) The idea is to create some high impedance on HF and VHF.

I also placed a ferrite core (the ones used in computer power cables) around the cables as a "won't hurt, probably will help" option.


The white output is the filtered one (it's an old household mains plug), the other two are input and a not filtered output, they came with the donated box (a broken computer power supply).

There's no reason for this schematic do not work at least reducing the level of interference. If it reduces all ,then it's a bonus.

New 10m radio

I don't have much time to do QSO's, in fact time is short even for soldering.... but I have a new radio.... A "Dragon" delta force.... don't you just love the names some manufacteus give to radios? There's also the same radio under the "Magnum" brand. Probably one of this day's someone is going to build the "Kalash terminator" 10m mobile.... :)
Here's the lousy photo:



10m was hot today, I've heard a lot of QSO's and almost pushed the ptt to answear a CQ call from the USA...maybe tomorow!

My first impression on the rig is a positive one, it works and receives nice, vfo operation is not easy on 1khz step since it counts from 1 to 9 but then returns to 0 without increment the 10's Khz...! It's not build like Yaesu, Kenwood etc, in term's of knobs material and front panel (didn't looked inside yet) but enough for the intended function, a receiver for some dowconverter's I will build.

FM crystal radio

I'm back!...Along with the lousy photos and the rusty English...

Having already build a lot of receivers with different approaches I have never tried FM with a "crystal" radio. Now is the time.

This is a simple circuit and honestly I wasn't expecting much performance but is fun and helps getting some momentum for future builds.

I can only get two very faint stations and with an external amp based on an LM386, my "crystal" earpiece I guess is not crystal....

My implementation



The schematic was "borrow" from here. Go on, see the original and nice implementations on that site.

Original schematic from the author site

L: 5 Turns of 1mm silver wire on an "Edding 3000" pen (around 12mm), diode connects to 2.5 turn (half the coil), spacing is around 2mm
D: OA90 or 1N34 (not sure, it wasn't marked) I tried several glass diodes and results were similar.
R: 150 K
C3: 18p
C1: 82p
C2: used one trimmer of 25p (80pf on the original schematic)
Antenna was around 25cm of wire and the 2 station's received are less than 8 km from the shack.

Have fun.

Summer...

Sorry for not posting for the last few months but honestly I've been very busy.

Some 20 years ago I took the training in beach lifeguard, then I did some work on the beach in the following years as a summer job. At that time the training was valid for 5 years and I didn't renew it until this year.
This time, (20 years later) it was not easy from a physical point of view to make the training, most of my colleagues weren't even born when I did my first lifeguard summer on the beach.
I was the oldest in the class (but not the slowest swimming) although my time in the 400m is a little more than the double of the current olympic record :) anyhow I'm not thinking in going for an olympic medal

In June I was counting only to work some days replacing some colleagues on leave but I was offered full time in a near by beach so I end up doing all the summer season from 15 June to 15 September ence not having much time for this blog.

Partial view of the beach


The beach dog with the lifeguard hat and the yellow flag!
By the way in all the beach's were's a lifeguard there's a pole with a flag system for sea water conditions: green for good conditions, swiming is allowed; yellow for moderate conditions were swiming is not allowed but a bath is and red for dangerous conditions were beeing near the waterline is dangerous and is forbiden to go to the water (we have some tolerance during a red flag day).


My observation point and some rescue equipment.


During training! Why swim when you can go by "boat"? Guess who am I in the photo! :)

In the end all went smooth and I only had to do some small rescues.

Now I am slowly getting back to electronics and to this blog. Stay tuned!

What's this ? III

While I don't get time to make a more useful and tangible electronic construction here it goes another "what's this" question....:
What type/model is this and what's the frequency range?


From the last post, here it goes the image on reference point GPS receiving antennas for error correction on GPS signal.

As usual in Peniche there's always a seagull on top of something...