Sunday, June 23, 2019

Simple 10Ghz frequency counter #2

After previous post on the simple 10Ghz frequency counter # 1, here's another option that will be cheaper than buying a full featured 10 Ghz range frequency counter. Again, different functionalities, this way shown it's just to provide an alternative since Ghz range frequency counters are normally very expensive.
This method involves using an old wave-meter.
Now a days you can find some wave-meters ate reasonable prices, in the range of less than 60Eur like this one from HP that I got recently:

It covers roughly 8 to 12Ghz, it's an HP X532B. Diferent models have different ranges, I wanted 10Ghz so this is the appropriate one.
The wave-meter by it self is not enough to measure a frequency, you will need waveguide transition from coax and a waveguide detector. You can build these two components quit echeaply and they will still work, not lab grade but enough for amateur use.

Bellow the ones I build using copper pcb, not an optimal material but will do:
The waveguide detector part:

Most critical measurement is the distance from the diode to the reflection plate on the back (opposite to the front facing side), what I did was measure 1/4 wave from the end and then adjusted the backplate to biggest signal.

View from the back still not covered:
For the flange mount and bolts placement I just used the template of the wave-meter it self but dimensions are pretty much standard.

For the coax to waveguide transition, same method:

 Signal entrance view:

The antenna can be DC connected to ground or open, I preferred the open option in case I need to provide dc over coax.
Basically I used the pin of the sma connector plus a bit of wire to make the correct wavelength
Again, this is not a calibrated devices but on the overall usage it does not make a difference, as long as we can place a signal at the entrance of the wave meter and detect it on the output we are good to measure frequencies.
The only possible downside is if the waveguide transition block loads the circuit we are trying to measure shifting it's frequency, anyhow the actual frequency after load will be measured. 

I used a Russian D405B microwave mixer as detector since was a cheaper alternative (around 1Eur each plus shipping) to 1N23C and 1N21 that are commonly used in this type of application. The diode arrives in lead sealed container, nice touch, no microwaves will "touch" the diode until is unwrapped.

Bellow a test of the diode with a microamp meter

 At this point if you want to see if your diode works, just cook something on the microwave and while it's running place the diode near the door, should see some deflection on a microamp-meter, you can also use a DMM on milivolt scale.

Dimensions are only critical if you need max optimization.

Now on to measurement:
Keep in mind that this method is not as simple as connecting cable to a regular frequency counter and check the result, you need to observe the output value of the detector and look for very small dips on the output, you need to go really slow in order to find it since it's very sharp and small, it's good if you know the ballpark frequency, otherwise it can be very boring rotating the wavemeter knob back and forth until found since the know is quite de-multiplied.

Same values I measure:

 The dip value above
 The frequency on the dial
and the "normal" value at the signal output.

Bellow the test setup:
 I used my home-brew signal generator for testing and validation

Another view from the top knob:

I build recently a millivoltmeter where I added a blinking led if measured value had over 10% change in the average result so I could rotate the knob faster and just look a the led blink to find the dip. That made my life easier when checking for the dip.

It's the led marked "VAR" in the image bellow

 I will post in the future more information on this millivoltmeter.

Meanwhile, have a nice day.


Thursday, June 13, 2019

Simple 10Ghz frequency counter #1

After previous post on the 10Ghz generator we need to measure it.

The following method is probably the cheapest you could find for 10 Ghz measure, still not dirty cheap but considering the price of a real counter on a much lower magnitude order.

This is nothing more than an LNB for satellite TV feeding a UHF frequency counter module.


You inject 12V onto the LNB, DC block it and feed the counter input.

The LNB:

The counter:

...mine is a VFD display module placed in a box with additional crystal testing circuit you have also LED versions (search for PLJ-8LED-H RF Signal Frequency Counter).

To calculate your signal input frequency just sum 9.75Ghz

Keep in mind that this will give you an approx frequency since on most of the LNB's the 9.75 Ghz LO is far from precise. The ones with PLL are a bit more stable.
Anyhow it will let you know if you are in the ball part.

The oscillator feeding the signal was the one from previous post placed in front of the LNB with a piece of wire as antenna:

Total cost will be around 10Eur for the counter plus 15Eur for the LNB and additional components, compare that even for a second hand HP or EIP... ok compare just the price...

Have fun

Monday, June 10, 2019

Simple 10Ghz oscillator with FVC99 hybrid VCO

I wanted to test 10Ghz band, more like a challenge than for any practical application, so started some experiments.

One of the first builds was an oscillator, it's a simple module out of the shelf with just a companion pot for tunning.

The module is an FVC99 hybrid VCO and more data available here:
It's major advantage is price, something less than 10Eur. Cheaper that any other sort of VCO (except probably the cheap motion detector modules that I will show in the future).

Mine is covering 9.5GHz to 10.326 Ghz

I am lucky to have a Ghz capable frequency counter, in a future post will show how to measure in some other ways (cheaper).

Without any care on the output connection it measured -15dBm to -4 on the full frequency range.

So nothing more than power to the module and a pot doing resitive divider connected to the tune terminal of the same module (VT). It's 5V on the picture but I used a 6V regulator.

Keep in mind that i mistakenly connect the 78X regulator on opposite direction.. in case you follow the wiring on the picture....still thinking how I manage to do that the first time...guess i'm getting old.

 ...frequency calibration is more in the "around here" mark than any precision device. Enough for playing around.

These electrical installation boxes/housings are perfect for this type of assembly. just add a piece of pcb.

Have a nice day!

Sunday, June 09, 2019

AC panel voltmeter convertion to DC

Well, this is the first post of 2019.

Since the start of the blog the idea was always to document some of my projects and also as a means that others can be motivated to build something.
This would e a win win situation, the more people building the more need for components so the more shops would keep open since lately the tendency is for hobby electronics to decline. Also I would keep information on my project that could be handy when I have to fix them since I'm not good on taking notes.

Said that, here's a small conversion of a 250V AC panel voltmeter to 25V DC.
The schematic is nothing more than a series diode (using one of the existing from the original PCB) with a resistor and a variable trimmer in series with moving coil meter. The original schematic (for AC) is seen on the background.
Calibration was just using a 9V battery and setting the trimer to read 9V, (90V AC on the original scale). Not critical here since I just wanted a means of checking if one of my DC power supplies was outputting the selected voltage.

Have a great one!