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.

Thursday, November 29, 2012

New dummy load and the BNC problem

While making a small impedance bridge I came across a small issue in one of the female BNC plugs, the central pin would turn/rotate while being attached by a male plug, I sorted the issue soldering a strong wire from the center pin to another plug since that was according to schematic, a pcb island preventing rotation and anchored would be another solution.

Now reworking my UHF capable dummy load ("Cogent" mints box) to a new shape  (top one on the picture)....

...the same issue arrived making me break one of the eight 100 Ohm SMD resistors (4 || 200 series), in the end I reworked all the load, because I was out of 100 Ohm SMD, to tree parallel 150 Ohm 1/4W carbon resistors. Probably will not go to UHF but goes nice to high VHF.

In the end this was the result:

Not pretty, but for now it works...

Another issue I got due to the poor manufacturing tolerance and construction on BNC plugs/adapters is this:

 The middle pin is just press fit on the stripe line between the two female plugs of the T adapter.
It failed probably after the second insert in the dummy load, one advantage of this happening is that if you made a small coupler link you can make a bird style plug...

...always optimistic but next time will have to get a better brand of BNC's.

Monday, November 26, 2012

Pescada de rabo na boca...

This Portuguese expression it's equivalent to a "no win situation" in English, as the image states. By the way, it's also a traditional dish!

This relates to the AD8307 power meter, without calibration it's "mostly" useless, well you measure something in this case power but you will never know how close or how far you are from a real value...or you blindly trust the datasheet.

Most people that build this circuit tend to calibrate against a know source, that is also my idea in the mean time for simple tests and for relative power it works, sort of, let's exemplify:

An unknown power source to the input:

 Now let's attenuate by 10dB the same source:

Let's do some math:

(Supposedly the power meter should give me 20mv/dB)

So a 186mV drop translates to: 9.3dB

I had measured my 10db pad as 10db at 28Mhz and 9.7 at 70Mhz on the MFJ...again not calibrated. Also my signal source is full of harmonics (noise generator)...

So I have a pad that should be somewhere near 10db, more or less 1 db, no big deal?! Could be the difference between 100 or 125 Watts...

Should I assume the pad is correct and calibrate the power meter to the pad?

...I could measure the attenuator pad on DC against my voltage reference, but the voltage reference it's not calibrated and would only give me the DC behavior......OK...back to the beginning......I will calibrate one of this days against a know calibrated signal generator.

Have fun and measure, doesn't matter if the voyage is 100 or long as you make it!

Random projects II

Between old projects getting finished, a lot more left behind, even more get in the horizon...

...I finished (for now) the AD8307 power meter:


 it was rewired in the inside and placed the input signal on the front. With the switch on this position it indicates the internal battery voltage, 9V, still good.

I also placed a rear input for the companion DVM:

There's also the option of using the front panel plug (on the DVM):

Get back to the midle picture... notice the DC motor and the IR slot sensor, had this recovered from a cassete player and a scanner and will proably be used in a NBTV mechanical receiver project I stunbled upon this week...

And when you don't have plugs for 9V bateries, just grab a used one and recover the top, easy:

Not all 9V batteries are equal but you can recover the plug from all of them.

Here's an idea for a measuring grab plug

It works but I have to get a stronger clip...

Some time ago I decided I would only buy new components when stock is empty or can't be recovered from old boards, truth is: I can't remember last time I bought was 2 days ago: 1N5711 diodes, had none and found none in the pile of old rf boards. It takes some time searching and recovering but no money is spent and you can always say: it was junk before, now it's a transceiver :)

Have a nice week!

Saturday, November 17, 2012

New box for the noise-bridge

Decided to separate the noise and the bridge for convenience.

Here's the new box for the noise generator, again an old if transformer can:


I could had placed the battery inside but would be a little crammed and difficult to change so a small patch was made:

For the bridge itself, I had no small (in size) variable cap to put inside so improvised with an polivaricon and the shaft of a defunct pot

 Some grinding was needed for the rotating knob of the polivaricon (it was from a pound shop radio).
Some "Araldite" glue after...
 ....allmost perfect

 And here's the the bridge. Scale is to be finished, I only placed the 50 Ohm mark and the 68p "unknown" internal cap (close to half the varicon) on the reactance side:

 Main capacitor is of 146pF and I had no more bnc plugs so used a cable for the "rx" part.

Inside, lot's of space left if chose latter on to put an internal noise source.
 In practice it's preferable to use the MFJ analyser but you learn a little more building your own test equipment and can always cross-check the measurement made.

Preliminary tests made to my dipole have the same result as on the MFJ equipment.

Have a nice weekend.


Wednesday, November 14, 2012

Reinventing the wheel

Reinventing the wheel....

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

Monday, November 12, 2012

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!

Wednesday, November 07, 2012

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...

Wednesday, October 31, 2012

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 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.

Tuesday, October 30, 2012

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.

Monday, October 29, 2012

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.

Sunday, October 28, 2012

-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.