Monday, December 31, 2012

Last post... 2012., for 2013, I wish fellow bloggers, readers and general population: health, peace, love and some money to spend.....


 Now I have to go back and cook something for latter....

Late Santa

For me at least... but it finally arrived...

OK, it's not the latest greatest, it's not new, it's only good to 10Mhz but it works and was within my very very small budget, after all this is a hobby without income.
It has the advantage of a very simple circuit internally and comes with schematic and manual, something I should had thought when I bough the piece of crap of the "Kiotto/Ez Digital/Goldstar" oscilloscope unit.

Anyhow it's only needed for now to check some low frequencies wave shapes. I've been building without an oscilloscope for the past years, only in rare occasions I needed one, in my opinion an spectrum analyzer is much more useful...maybe one day.

Have fun!

Saturday, December 29, 2012

Some changes

I'm doing some changes on the blog layout, hope you like!

Also removing some stuff from the main page an putting it on static pages.

...if you don't like, just say so, if I will change it, that depends....

Friday, December 28, 2012

Marker generator

 I've built a similar circuit to this one for a 500Khz pll circuit some time ago but this one will be used as a dial marker calibrator.

 I works diving a fixed frequency for a fixed value, the square wave output will be rich in harmonics on multiples of the resulting frequency (good, the world isn't perfect).

10Khz spot on from 5.120Mhz:

The oscillator part of the circuit:

The IC was the "HEF" version but basically the same stuff (more or less)...
Resistor between pin 10 and 11 is a 100K Ohm one, the other a 2K. Fixed capacitor was by trial and error, to get crystal on the exact frequency, somewhere near 39pF and the variable one a little more: 39+20var, see 4060 datasheet.
 I didn't had a 10.240 (immediate choice) crystal (only 10.245) but a 5.120 was in the junk box so that was the one used.
Reset pin (12) is grounded.

If you need 1Khz marker then a standard 8192 crystal can be used, just divide by 8192....
Other frequencies... just do some math, "divide ratio" is on the image.

The output part:

The output circuit on the above image wasn't tested (just normal cap coupling was) but I'm sure it will give nice peaks because diode will conduct very shortly on the down flank of the square wave, generating lot's of 10Khz harmonics and more than the simple square wave. I need a scope to verify that....maybe next year...

And the assembly:

 Have a nice weekend...

Sunday, December 23, 2012

Happy Birthday... the transistor...

...and to myself.. (a little bit younger than the transistor)... taken some years ago on a field day

To celebrate the event and the "end of the world" :) this week I built an VFO with my age...

...from 73 Magazine, December 1972 (p114). It worked first time, although I just built the VFO part (Q1,Q2,Q3) there's no reason the buffer/amp part wouldn't work either. The design in itself is very interesting on the Q1 bias part, which is provided by Q3 to keep a constant output level.
As always I changed things a little bit, used 2n3904 transistor but almost any other transistor would work, with the exception on the one of the first photo in this post :)

Season greetings!

Tuesday, December 11, 2012

Signal generator

Here's a little piece of equipment that was missing in the shack. Truth is I already had the Si570 signal generator but it doesn't go bellow 4Mhz and it's not very practical for fast frequency tune/change, so time to put together some components in the oven and see what came out...

This was a kind of the 3 R's project (reduce, reuse, recycle):
The frequency counter is from a "pound shop" radio (so it counts always 455Khz more), the on/off switch is courtesy of US Signal Corps (from a Bendix direction finding set), the coil select switch came with the "Speaky" kit that was replaced by another model, the select button was an ofter of a friend and so was the tune button.
The modulation on/off switch/pot was from a radio of my late grandfather.

Internally, another quality assembly by me....

..the BF's244 I don't remember were they came from but found them in an old box and were bought for something I forgot completely, the output plugs were recycled from old equipment and the variable cap probably bough in some ham fair long time ago.

The schematic:

The only addition to the schematic is a "volume" control in the audio input.
Coils are not specified in terms of value because all of them are different. It's just a matter of build them according to the scientific principle of placing in the circuit and see if it will have overlap ranges.

Power (3V) for the frequency counter module is courtesy of 2 out of the 3 LED's that are in series with an 390 Ohm resistor, not the most elegant solution in terms of energy waste but works nice.

Unfortunately I still don't have the oscilloscope to check the wave form on the output, sure it's not perfect but no problem since it's for simple tests, I know also that I have a strong harmonic at 2f (the usual hum?!).
I'm still struggling to put the oscillator at VLF but will get there...anyhow from about 1Mhz to 31Mhz it works really nice.
I replaced the feedback cap from 33pf to 12pf but both work.

I still have to put more coils for other ranges and put some labeling...

Have a nice week!

Saturday, December 01, 2012

GDM test

Saw this simple GDM:

And decided to give it a try.

 It's just simple because the generator part of the circuit is omitted...

I didn't needed the 2k2 pot (was set to zero) and the diode used although also "Ge" didn't had markings.

"Generator" was the MFJ.

On the following photo is the "dip" on a LC test circuit:

Analog "voltmeter" was the reflected power scale (only had this meter on hand)....

Here's a no "dip" situation:

Control was made using my trustee dip meter...
..."dip" at the same frequency, so it works!

Lot's of info on dip meters at: ,
unfortunately LA8AK is SK but his family still serve's his nice pages at:

Have a nice weekend.

Tap attenuator

...I make no reference to the attenuation exact value because I'm not sure exactly on it...but should anywhere -20 dB

This is nothing more than the inner conductor of a coax cable passing by the center of an 43 type core with 10 turns giving the tap'ed output.

Signal for the tap attenuator input was provided by the MFJ but had to reduce by -10db the output so it didn't went out of the DVM scale.

Here's the input signal value:

And here "tap'ed":

So the math is simple:
Direct signal from the MFJ to a load: 1866mV
Tap'ed value was: 1395mV

So that's: 471mv drop, at 20mV/dB = -23.55dB of attenuation... only the small patch cable attenuation was not accounted... and on my not completely accurate power meter.

Test was only made at around 170Mhz.

There's also the directivity factor that I didn't measured.

Here's one unit similar built by Alan Yates, he got -20db with one less turn (10) than I did (11) and a bigger toroid.

Anyhow in the future I will make another tap attenuator using only resistors.