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Frequency Counter 1.3GHz part 2 Print E-mail
Written by IK0OTG   
Monday, 23 February 2009 01:01




Continue from Part 1




The components

Display It is 2 lines 16 characters type with back light. Pay attention to the LCD display type, because in commerce they exist of several models and dimensions, having the connector low on the left, up on the left and with double connector up and low. For the PCB that I have realized and that it is brought back in this article, it serves a display with connector on the left up or double. On the display must be soldered 16 pin of strip male (J3 of the schematic), while on the PCB the 16 pin female (P3) (figure 6).







Fig. 6



The display must be distanced from the PCB through 4 spacers of 12mm and fixed to the PCB with 4 screws 2x20mm, with the hexagonal nuts soldered (or glue) on the PCB copper side.

Connector BNC1 Type angled for printed circuit. They exist with body all in metal or with plastic body and graft of metal. Thinking to 1.3 GHz I have preferred that all metallic one, costs little more, but I hope that it is better.

Relay 5 Vcc. RS with code TQ2-5V and R.F. electronics ( ) sells it with the code SW-G6H-5. They are found also to the fairs.

Push-buttons SW2 SW3 SW4 are those with 7 mm total height (body +button)

LED green 2,5mm

SW1,SW5 They must be of the 90°angled type

Quartz 4 MHz low profile type

The keyboard must be raised 12mm from the PCB. For this I have used two 3mm hexagonal spacers MF type, with the male inserted in the PCB.

The rest of the components are all normal, only the two electrolytic capacitors placed under the display must be of the low profile type.


The box

As already said it is one plastic box of the TEKO (model 10008.9)

It is composed of two identical semi shells. Only on the upper shell, cut the four plastic pegs.

The one which follows is the template, makes a photocopy of it and glue it to on the upper shell. It will serve like foot print of perforation. Since many types of display exist in commerce with various measures, verified that one in your possession corresponds to the window designed on the template, otherwise with one pencil design over it the new dimensions.





fig. 7



Make the window for the display (must be 1mm wider and longer of the display), that one for the keys and the hole for the led.(fig. 8)








Detached the photocopy of the template that you had glue, realize all the other cuts for the connectors and the switches that are on the flanks of the two semi shells and taken the grease out of all with the alcohol.

With a cutter and a metallic ruler, cut the edges of the plasticized template, make the hole for the led and cut the window of display, this time precise to the measures of yours display.

Take a wide (50mm) bi adhesive tape (that one used to glue the carpets), glue a piece of it on the upper semi shell, with the cutter cut it in the edges and around to the windows of the display and the keyboard.

Assemble all the frequency counter like in figure 2, close it with the upper semi shell, take the plasticized template and with a little attention insert it around the display and therefore glue it on the cover.



After to have mounted all the components, and to have controlled that there are not accidental connections of tin between the tracks and the pits, place OFF the power switch, insert the battery, place the switch of filter BF SW5 FILTER towards right (filter off), turn VR1 all CW (screwdriver inserted from the opposite side of CV1) and switch ON the power.

  • The led will be lighted and on the display will appear the written

First line IK0OTG

Second line V2.3A 05-Apr-2007

After 2 seconds the written will change

First line 000.00 KHz

Second line not if * 50M * 10 Hz

If the display is all black adjust VR1 for the better contrast

The asterisks to right and to the left of 50M, will appear in way alternated with duration of approximately 100ms on the left (transfer data) and approximately 500ms to right (reading data)

The first line indicates us the value of read frequency

The second line indicates

Not if  : it has not been inserted some offset of frequency for IF

50M : the upper limit of the range is 50 MHz (counts until to 52 MHz)

10 Hz : the inserted resolution is of 10 Hz

  • Push the button SW3 INC and hold it until (approximately 0.5 second) on the display written 10Hz it will become 1 Hz and the written not if will be replaced by wait and then it will be again not if. Now on the first line the units of Hz will be visualized also.

First line 000,000 KHz

Second line not if * 50M *   1 Hz

The time of reading will be now of approximately 1 second (slower asterisk of right)

  • Inserted the filter of BF (SW5 FILTER on the left)

First line 000,000 KHz

Second line not if * 50K *    1 Hz

It will remain all like before only 50M it will become 50K

  • Push the button SW3 INC and hold it until (approximately 1 second) on display the written 1Hz it will become 10 Hz.

  • Push the button SW4 BND. You will feel the “click” of the relay that change the range, and on the first line of the display they will appear randomises numbers, nothing fear, is the U664 that, to some frequencies, are so sensitive that it tries to count the noise (see the curve of sensibility on the date sheet of integrated SDA 2101, version Siemens of the U664). On the second line we will have the indication  1G3  and100Hz


First line 567 ' 368.3 KHz (random number for example)

Second line not if * 1G3 * 100 Hz

The time of reading will be now of approximately 0.64 second (asterisk of right)

Noticed that in this condition the switch FILTER it does not have some effect.

  • Push the button SW3 INC and hold it until (approximately 1 second) on display the written 100Hz it will become 10 Hz.

On the display the written wait will appear for approximately 6.4 second after of that we will have

First line 569 ' 388.30 Khz (usual random number of example)

Second line not if * 1G3 *10 Hz

The time of reading will be now of approximately 6.4 second (right asterisk)

  • Switch OFF power, exclude the BF filter and newly switch ON power, you would have to be returned in the first condition.

First line 000.00 KHz

Second line not if * 50M * 10 Hz

Push INC and set the resolution to 1 Hz

First line 000.000 KHz

Second line not if * 50M * 1 Hz

Wait five minutes for the frequency counter warm-up; connect on 50Ω BNC1 input a signal of 50 MHz, (signal generator with at least 1 hour warm-up) with a level of -10 dBm and of whose frequency you are sure. A different value of frequency it is also good, but it is important that you know with precision its value.

Adjust VR2 to middle point. With a plastic screwdriver carefully adjust CV1 until reading on display the frequency of the signal that you have applied at the input, ±1 Hz. In the event of 50 MHz you must regulate CV1 in order to read a value comprised between 49'999.999 and 50'000.001.  Now lowered the level of the generator of 1 dB step until to the frequency counter begins to reads values of frequency different of 200 - 300 Hz from those one read in precedence, adjust VR2 until to have again correct values. Still lowered the level and repeat the procedure until to when it is not more possible to get correct values. To this point if the level of the generator is comprised between -20 dBm and - 30 dBm the calibration is ended. In case the level of the generator was higher (- 19 -18 dBm etc), after to have verified that there are not assembly errors, tried to change the Q2 transistor


Programming of the IF

After to have switched ON frequency counter, push the key IF. It will appear the written Set if frequency, release the key and, on the second line, it will appear IF= 000' 000'000 with first 0 underscored. Pushing and releasing newly the key IF, the cursor will be moved towards right of a digit for each step, vice versa if you will maintain it pushed it will be moved with continuity. We suppose of wanting to set up a IF of 10.7 MHz, moves the cursor under second 0, push and release the key INC and you will see that the 0 will become 1, increasing of 1 every time that you will press INC; after the 9 it will return to 0 and so on. Well set it again to 1 and with the key IF go on the third 0 and then on the fourth, press INC until it becomes 7. Now we will have one situation of this kind:

Set if frequency

IF= 010'700 000

Push still IF until carrying the cursor under the penultimate 0 (tens of Hz), the ulterior pressure of the key IF it will provoke the escape from this mask and the entry in that one in which is possible to choose like elaborate the IF.  Push INC and you choose that one of the three options that corresponds to your requirements: VFO - IF, IF - VFO and VFO + IF.

To this point the programming of the IF is finished and pushing once again IF it is returned to the function of counting of the frequency.

Now the value indicated on the first line of the display will be the mathematical result of the operation chosen, in the event of result negative will indicate 0 while, if we have chosen VFO + IF, without signal to the input, will be visualized the value of the set up IF.

On the second line we will have the written that remembers to us which type of counting of the IF, we have programmed. If the value of the programmed IF is zero (all 0) the written will be not if and on the first line we will have the real value of signal in input.

In order to remove the programming of the IF, as you will have realised, it is sufficient that you repeat all the operations of the programming, setting up frequency of IF with all zeros.

The programming of the IF remains memorized also with the frequency counter switched OFF and without battery; therefore it is not necessary to set it again every time you switch ON the counter or after the change of the battery.



For who it has a sure familiarity with the PIC will not be difficult to write a program for frequency counter that realizes the functions described in a this article, in this case a good guide is application notes AN592 of Microchip ( .




I think that the realization of this frequency counter is much easy and to the capacity of all those who are able to make good welds on a printed circuit, for against, compatibly with the stability of the used quartz, the performances of the instrument is remarkable, for it’s dimensions and for the precision of the measures. In the practical one it’s sufficient to solder the components on the PCB, to connect the keyboard with the flat cable (or 5 pieces of wires) and all it works.

For those who they had difficulty with PIC, assembler, programmers etc, to who will demand it, I will send the already programmed PIC to a cost of 12 € plus shipping costs.

At last I can send the plasticized template and the PCB, (single side, tinned, with serigraphy and solder resist) to the cost of 13 € plus shipping costs.

My address is This e-mail address is being protected from spambots. You need JavaScript enabled to view it and in the limits of my free time, I will answer to demands for clarifications and information.

Hoping not to have bored you and that someone has succeeded in to read until to the end, 73 to all from IK0OTG Pietro



Upgrade      11/02/2009*


Just in these days I have brought one modification to the circuit of the local oscillator, replacing the 4 MHz quartz with a high stability integrated 20 MHz oscillator in SMD technology.

The stability of these oscillator (TCXO) is of ± 2.5 ppm from -30C° to +70C° against approximately ± 200 ppm, for the same range of temperature, of a normal oscillator composed from quartz in free air, fixed capacitor and variable capacitor both of good quality and adapt to work from -30C° to +70 C° (the normal red, greens, etc variable ceramics capacitors, is adapt for temperatures from -25 to +85C°with a thermal drift for the N750 types of ± 300ppm/C°. See catalogue MURATA).

In consideration of the use which it is destined this frequency counter, the employment of this oscillator give us two appreciable advantages:

  • It is not more necessary to wait for the frequency counter warm-up, the variation of temperature of the oscillator between the condition of OFF and ON it is practically null (consumes only 1.2mA), and consequently the generated frequency will be soon to the nominal value.

  • The stability and the repeatability of the measures, in the range of temperatures housewives (+0° ÷ +35°), is comparable to those that could be obtained with an expensive and cumbersome quartz oscillator into a thermostatic oven.

Unfortunately the substitution of the 4Mhz oscillator with a 20Mhz external one, has involved a modification of the SW, that I will free of charge execute for all the friends to which I had sended the already programmed PIC and that they will decide to make this modification.




Practical realization


In order not to make a new PCB, I have assembled the oscillator and relate components on a small PCB (fig 9)






Fig. 9





that must be inserted to the place of the quartz, of the fixed capacitor C14 (33pF) and of the capacitor of bay-pass C13 (0.1µF) that comes moved on the new PCB.

The PCB is a single side top copper with the components surface welded. The terminals of the C13 capacitor (0.1µF), that it has the same function of bay-pass that had before, must be long enough to be threaded and welded in the holes where was inserted the old C13 that has been removed. In this way, through the terminals of this capacitor (+5V and gnd) the feeding will arrive to the new oscillator (fig.10).




Fig. 10



The output of the 20Mhz oscillator will be connected to pin the 16 of the PIC through terminals of C16 (0.1µF), that near VR3 the 10KΩ trimmer, left along enough and threaded in the hole of the old C14 that is connected with pin the 16 of the PIC. It will be opportune to dismount also variable capacitor CV1.

Figure 11 is the new modified electrical schematic.






Fig. 11



Apply on 50Ω BNC1 a signal of 50 MHz, (signal generator with at least 1 hour warm-up) with a level of -10 dBm and of whose frequency you are sure. A different value of frequency it is also good, but it is important that you know with precision its value.

The 10KΩ trimmer VR3 varies the frequency, turns VR3 until reading on display the frequency of signal that you have applied ±1 Hz. In the event of 50 MHz you must regulate VR3 in order to read a value comprised between 49'999.999 and 50'000.001.




Remembering you that, the upgrading to the new version of the SW is free, for all those that I have sended the old 4 MHz version and that will decide to pass to 20 MHz new version,

Best regards.

73 IK0OTG Pietro








Sono ora disponibili, a basso costo, TCXO a 20MHz, tarati in fabbrica al valore nominale. Il modello 924B della FOX, ha le stesse dimensioni del precedente,  tensione di alimentazione a 3,3V e la stessa stabilità. Ho quindi sostituito il precedente TCXO con uno di questi.

In figura 12 il nuovo schema dell’oscillatore esterno.

     freq-exst-osc-09-2008-oscexst.jpg - 20.88 Kb    Fig. 12



Come si può vedere sono stati eliminati il trimmer VR3, le resistenze R17,  R18 e il condensatore C14, inoltre la resistenza R16 è diventata da 270OHM

In figura 13 il PCB dell’oscillatore esterno

freq-exst-osc-09-2008-pcboscext.jpg - 41.21 Kb                                                 

Figura 13



Con questo tipo di TCXO basta fare soltanto la taratura del livellodi segnale (vedi paragrafo Taratura dell'articolo originale). La taratura della frequenza non è più necessaria.


Last Updated on Wednesday, 15 July 2015 15:02