Reinventing the wheel

Reinventing the wheel....

Will post more details as soon as I finish this prototype.

In the oven

Some random projects awaiting conclusion....


A new coil for the antenna tuner...

 A "configurable" bridge

And here's what happens wen you have to many broken printers around...

....probably a future micro CNC machine...


have a nice week!

Box for the voltage reference circuit

Nothing special.... just boxing some stuff, here's the voltage reference IC in a box.

The board is very small and it could be lost in the shack mess so I used one IF transformer box from an old Bendix ARDF equipment for housing.

Regarding the voltage reference, it's not a voltage cell but for the nature of my measurements and calibration it's more than enough, my DVM doesn't have enough digits for measuring to the millivolt unit.

Maybe one day I could get a better DVM...

Random projects

Just some photos on projects waiting calibration and a decent front panel decoration:

The AD8307 power meter bellow on the photo. On top an store bought LCD panel meter placed in a box for measuring the voltage output of the power meter, here with -10dbm input signal but lacking calibration....

Looking back I should had placed the AD8307 signal input on the front and the measure voltage on the back....hum...I have an UHF panel mount plug somewhere....will see.
The box of the DVM was one that housed my first ever working transmitter, an 88-108Mhz FM one...at least more than 22 years already passed...

 Bellow, another power meter:
 A simple qrp power meter for the FT-817, two scales and internal dummy load, a reuse of an old USSR 7.5v dc panel meter, unfortunately the internal dummy load from 20 1K Ohm resistors is just good to 50Mhz... they just don't do carbon resistors like they used to do...

The 90º angle silver plated BNC plug near the Kantronics was a kind donation from a friend and fits nicely on the FT-817 front panel, leaving space for the select button.

Variable capacitor idea

Spotted this page and decided to try this unusual variable capacitor idea, I had an 20cm heat sink laying around so splited it in two to see the results.

We can "juice" just a little bit more getting the plates closer.

Now fully open....

There's just a small problem, it takes some space and the mechanical parts are not easy to make but should be easier to build than a classical unit. Regarding the price, this "unit" cost'd me 7 Eur some years ago. Now the 20cm heat sink costs 11 Eur (dam inflation), total cost for a typical 400pF for an ATU should be around 22 euros, plus the hardware for turning.... sometimes we can get cheaper caps in ham swaps.
One big advantage of this design is that there are no wiper connections so lower losses and no risk of bad connections.
As far as breakdown voltage, considering 30Kv/cm in normal conditions we can assume that at least 1mm separation gives 3Kv... but on a safe side I would consider just 1Kv...

....I think in the future I'm going to rebuilt my antenna tuner/matcher.

The unobtainium light bulb

This particular light bulb model is getting each time harder to find. The one I have as the bench head lamp just broke about 2 years ago and I've been using a "normal" one ever since. Been looking all over the city shops in the past months an not one stock them anymore.

 So, what's different about this particular light bulb, well for a start the light color, daylight blue, is very good for long reading periods and I found that is extremely nice also for for long periods of soldering at the bench so I use it as the main head lamp over the soldering area. For me it works really nice, there are similar lamps in the marked but their of painted glass, not this model, it's the glass that has the blue color. I also found this particular lamp to be best suited for reading small components markings.


Luckily last week during some garbage removal I found one that I had kept as spare! Lucky me to keep a spare, anyhow will continue to search another unobtainium light bulb.

-10db attenuator pad

Some days I like to build radios, others fix things, now I am in the mood to make and fix test equipment. I started with my oscilloscope, not fixed yet but I think I will get there.... also doing a rebuilt of the AD8307 meter, after, I will calibrate it. For that (and other stuff) one thing needed is an attenuator pad.

Here's my build of a -10db pad and some results as measured on the MFJ-259B:

 Not very good at 145Mhz

Good until 28Mhz, then starts decreasing.

 Not very critical for the intended propose.

The BNC plugs came from an old telco modem, I had the pcb pieces and the foil, the resistors some were from old boards (I am recycling lot's of components) and others from my stock.
It's not perfect but was cheap and will do!

The original schematic:

Came from here, by the way, a great place with lot's of useful information.