How much does the price of a frequency counter? How about making my own? Well it’s quite expensive, and if you want to create your own, you can not guarantee the precision anyway, such an answer from a friend when he asked about the frequency counter.

Realized the need for this tools is necessary, especially if we play the radio frequency electronics. After collecting references from various sources on the internet, with keyword “homebrew frequency counter”, I chose a project that feels pretty easy , with common components and minimum, and decided to make it.






What can you do with this frequency counter?  Of course measure  frequency output of your oscillator, but further you can compare between what is calculated or designed on paper with the one you measured. If you have a known precision capacitor or known precision inductor use them alternatively in your oscillator as a tool for measuring unknown L or C value, so you now have a LC meter here.

Use formula  LC=25330/F^2, where units are uH, pF and MHz

However it is very funny to see the LED alternatively on off while moving the frequency dial.

Back to my friend opinion, do we really need to buy such a precision counter ? No, since we are amateurs, it’s well worthy to make yourself, even this simple counter means a lot, at least you know where you are when you working on your frequency.


Here is another homebrew counter I have made, A DECIMAL COUNTER also from PA2OHH, this is better from previous counter since frequency reading is more easier.

Note how to read the counter, at 19.8 MHz or 29.8 MHz ( missed type 20.8 MHz ), reading is 9.8 MHz.








Also from PA2OHH site, there are various frequency reading you can choose : a one 7 segment LED, a buzzer for morse code and a RS232 for connection to PC via software.

This counter using Atmel AT90s-1200 as a microcontroller.






This is the first project that I worked after long time absent playing electronics.

I remember when I was at Junior High School, at that time  the source of learning electronics was quite limited here, no internet, just some excerpt article clipping or photo copy from borrowed electronic magazine. But things has been changed, I gathered and understand so much information from various electronics web site. See Ian Purdi – electronics tutorials web site, I am start learning from here, understand such thing named coil or inductor, this coil related thing probably nightmare among us, for example given a schematic, the coil specification was : J. W. Miller 112-H6, or toroid T50-6…. ?? What is this thing ? Where to buy it ? Can I make it ? No one sell it here, I ask a service man, maybe he know something from his experiences, he also did not have an idea and could not give answer that I needed. So mostly the schematic journey was ended here.

My enthusiast passion was at radio frequency project such as walkie talkie, SW radio etc.. Some friend have so much progress than me, but he was into hi-fi amplifier things that I am not interested.

I just feel that radio ( receiver ) thing is amazing, a magic thing !

Back to Ian Purdi’s tutorial, there are lessons about oscillator, he teach how to calculate and constructs such coil, calculate the working frequency  etc. These are the lessons that I want so long !

He also have a nice project to build : Regenerative Radio a la Kitchin. Wow , now reading this schematic is very enjoyment, I could understand even could design my coil for desired working frequency, I recommended this project for: easy to build ( relative ), not so much components, clear explanations and instructions, cheap and the result could be very nice. You will have enthusiasm and confidence to the next projects. And at last getting new experience with art of unusual tuning.

Components are not critical, any available FET can be used, just give attention to coil construction :

1. Note how to wind,  L1, L2 & L3 all must be in same direction. Case of error found in a friend, one coil in in other direction.

2. Another case at L3, coil winding is not enough, for example it mentioned 3 reels, but only 2.5 reels coiled, so the regeneration does not occur or too weak, if necessary make experiment by first adding 1 to 2 reels at L3,  and see how is the result.

3. Space between L1, L2 and L3 according to some article are spaced about 3 mm, but according to my own experiments, space is closed.

4. L3 position is lowest, space between L3 to ground plane pcb not to closed, try at least 2 cm.

This is the first time I try assembling methods so called “Manhattan Island”, where a small piece of pcb glued with super glue to mother board ground plane pcb. Nowadays I preferred “Rat Nest” or “Ugly Construction” assembling method, this is much faster but at some point still use Manhattan Island as a pad, but I do not use super glue any more, I used a double ( adhesive ) tape, very quick. This kind of tape have a black sponge with green insulation, I see glazier used to attach the mirror to the plywood, with time, it become stick very strong. If exposed to soldering heat, let it sit until cool, he will stick again. Scissors the double-sided tape  into small pieces, according to the size of the pcb pad that will be attached.


– Adding FINE REGEN using diode or LED as a varactor, in my opinion is absolute to be added, this addition make regen setting much smoother, much easier.

– Capacitor C3c with value 5 pF is good enough for fine tuning in AM mode, but for SSB mode this is somewhat oversized, replace with 1~2 pF.

– Potensiometer for a long time tend to become dirty and make a noise ” crack – crack” could be replaced the VOLUME potensiometer with fixed resistor with SELECTOR SWITCH , while for ATTENUATOR potensiometer could be replaced by plastic varco, see schematic of AA5TB.

– One thing that has not been satisfying me, is the sound output of the LM386 is too small, I try to add a preamp, the results are not in line with expectations, resulting in the motor boating, and sound output also not increased significantly, please advise from readers. The AF amplifier experiment ended with TBA810, still too weak.

Fortunately I have built my guitar amplifier using LM 1875  ( see my amplifier at, plus a FET preamp.  I can use this with my regen, sound is so powerfull, remembering me to the voice of my grandpa’s Philips old valve radio.

Recently I read an article at QRP-SWL Homebuilder web site ( this is one of the very good site ) about LM1875 and e-mail to owner site Todd VE7BPO. I asked him a suggestion for a preamp that suit for this configuration ( homebrew rx + pre-amp + LM1875 ). A homebrew rx could be : kitchin regen, PA2OHH shortwave rx, PY20HH DSB TRX etc.

Not too long, he replied my letter explain that he make and tweak a pre-amp for me ( thanks ! ) :

Hi Indra:

I liked your blog.
Based on some work by Douglas Self; a prodigious Audiophile EE/author — This is the best “popcorn” AF pre-amp I’ve built — in that with a load R of ~1K or greater the output stays clean until above 7.04v peak-peak with only ~ 5 mA of current . Low distortion at .002%. The boot-strapping boosts Q1 gain and the current source on the emitter follower extends the ability of this amp to drive even smaller load impedances quite well.

This should boost up your signal nicely. The 1K input resistor called “R” can be increased or decreased. The minimum would be 100 ohms as to prevent oscillations. If your input signal is too large and gets distorted, increase R to between 1K5 to 4K7.

The output 1K resistor can be your volume control pot or any load greater than ~ 1K

I know it looks a little “busy” but this amp is staple, very clean and can swing a large AC signal




This is another regenerative radio from Onno ( PA2OHH ).

The results were not too good, noissy compared with Kitchin regen. There is interference from FM broadcasts, but this can be overcome by adding a 10 pF capacitor in transistor T1. But I like it smal size.


First time read an article from PA2OHH’s web site about DDS VFO , I was curious, what is this thing called DDS VFO. Further reading  tells that this is basically a LC – VFO but is controlled by a microcontroller, indeed it is very stable because there is a locking frequency mechanism, also it has a minimalis frequency display.

Next step is to check whether the components are available in the market here or not, especially:
10mH coil, varactor BB212, uC AT90S1200.

AT90S1200 is available, I can not find 10mH coil in the market, fortunately I have a friend who gave me a toroid ( marked KDK ) from switching power supply, then as measured by LC meters can meet the 10mH, I only have one toroid, I seek the same toroid and it could be found on the market.

No BB212 varactor available in the market, I have some varactor from TV tuner and some MV209 maximum capacity only 30 pF, ok I think these could be paralleled.

Because I never have any experience with microcontrollers before, I asked to PA2OHH how, and he responded by posting the article about HOW TO PROGRAM THE AT90S1200 MICROCONTROLLER. .

For implementation to be neat, I prepare on shop drawings first, sketching from schematic part by part . After finished drawings of each part, then I arranged the components ( by part ) in pcb, if all the parts are finished, then connect each part with connecting cable. All done in ugly construction method.

Once all components are neatly mounted on pcb, it’s time to program the UC, as I remember, the WRITE speed to be set at slowest, because the computer speed is quite high. Currently, I lost my UC programmers and software tools, so I can not give more details on this.

There is a modification in my VFO, since my varactor maximum capacity only 30 pf, I have to parallel four varactor, then series it with a 1 nF capacitor ( value from experiment ).

For the coil, to save space I wound it on a rubber donut-shaped, first make just one coil, measure it with LC meter and record the value, monitor and note the output frequency. Then make the next coil,  inductance must meet to follow the frequency generated previously, of course with a little frequency overlapping. And so on until completed a frequency range that we want, in this case the HF.

To overcome the unavailability of varactor, currently there are some ideas, but I’ve never tried, as follows: use varactor for locking mechanism with a small capacity, can use LEDs, or 1N4007 diode, may be mounted back to back. Then parallel these with plastic Varco with big capacity ~ 300 pF, this Varco served as a coarse tuning, I think we need to add Varco wheels to be more smooth.





The first time switch on, the circuit does not work, after 2 weeks of dizziness search, found there was an error on schematic, at pin number 10 of UC, the scheme is not reflected connect to the ground, once connected, the circuit works fine. The scheme has now been updated by PA2OHH.

The easiest way to test this DDS is to use a shortwave radio, sweep DDS frequency around the tuning frequency SW radio, you will hear strong zero beat, and very slowly sweep up (or down) the DDS, while tuning up ( or down ) the SW radio, this way until you reach upper ( or lower ) frequency range of coresponding coil is known and noted on paper.

Then make the next coil, and so on.

The DDS power output is quite flat, about + 15 dBm ( 30 mW ), above 20 MHz start slighty down, up to 29 MHz output power down to +3 dBm ( 10 mW ) , power output level is adequate to be injected into diode ring mixer. Measurement done with simple calibrated Wattmeter at 50 Ohm environment.

Better use a good quality selector switch, the body is from white & blue plastic, mechanism is wrapped inside, “click” is smooth not heavy, price about US$ 2.5 at ELTECH store – Pasar-Genteng-Surabaya. I already use ordinary brown selector switch, sometime switch behaviour does not connected correctly.

I have tried this DDS VFO with PA2OHH’s  SIMPLE PC RECEIVER WITH THE MICROCONTROLLER DDS with satisfaction result.

If you want to display certain frequency range , PA2OHH mention in his email as follows:

How to change the display setings works as follows. In the software the .ASM file, readable in ASCII, there are 2 lines, one for minimum frequency of 1 MHz and one for the maximum of 39 MHz. This last one is a test for the value 57 as 57 = 3×16+9…….

The minimalis frequency display is very good QRP idea indeed, but I prefer LCD display for frequency counter.



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