Actually one does not send cash in the letter. But were only 20 dollar and I an exception there made. On the QRP sides in the web I had gotten stuck with the Small Wonder Labs and their kit supplies. The frequency counter for QRP devices " FREQ MITE " is about as largely as a stamp and had an output of the " displayed " frequency in the form of three or four signs (morse code). The output is released through printing of a key. Interested me, thus the purchase order form printed out, the dollars exchanged into the letter and away with it. Seven days later double letter with me in the mail box. One hour were later encoded in cw the section accurately the digits of the digital display of my frequency generator to my joy.

The structure

The kit consists of 22 parts. The heart is a so-called PIC, which becomes PIC 16C621, a Microcontroller by its ingenious software the frequency counter. There are only few external elements: Quartz, breakdown diode and signal processing Q1/Q2 and the contact strip J1.

A small loudspeaker can be attached directly to the output against ground. For good reason one will grind in the output signal however into the af-way of the device equipped with the FREQ-Mite. For this one uses a resistor of 100 kOhm to 1 MOhm, depending upon desired volume.

Fig. (1) shows the circuit. here not available

Fig. (2) shows the pcb, right the speaker, down the batterie clip.

Max. counting frequency: &# 32.767 MHz

Accuracy: + / - 1.5 kHz to 25 MHz

+ / - 2 kHz with 32 MHz

Output morse code, as 800 Hz tone, 13 or 26 WPM

3 or 4 digits (see setting)

CMOS - logik level (5 Volts) Tristate - output

Input &# high impedance

Operating voltage 9 or 12 Volts (alternatively)

Power input &# approx. 10 mA

Level (input signal) 100 kHz 0.1 V (p-p)

10 MHz 0.2 V (p-p)

20 MHz 0.3 V (p-p)

30 MHz 0.6 V (p-p)

The diagram shows the relationship between the minimum input signal and the incoming frequency for reliable functioning of the circuit. The max. signal level is about 10 V (p-p) up to 30 MHz. Higher input voltages harm the circuit not, cause however measuring errors by the over-regulation of transistor Q2.

Also without incoming frequency the function of the building block can be checked. For this the jumper of the priority " 128 " and " 64 " into the contact strip J1 is put and the voltage is applied. The FREQ Mite asks then in CW: " S? " and means with it, one is to select the rate. If one presses the key S1, then to 26 WPM one switches and the circuit announces " AR ", waits one 2 seconds announces the circuit also to " AR ", but in cosy 13 WPM. If the key S1 is pressed now again, then the output is " 192 ".

The program into the PIC is written by Dave, NN1G. For the application a device must we it still set, i.e. we must determine the offset frequency. This is done via jumpers.

The simplest case is that we want to measure a frequency. The sieved lowest jumper is put. This results in an offset - code of 1008, which is used by the PIC for the suppression of the offset calculation. Examples:

- for an incoming frequency of 455 kHz the output is " 0455 "

- for an incoming frequency of 7,110 MHz the output is " 7110 "

- for an incoming frequency of 21,106 MHz the output is " 21106 "

This application is suitable for devices after the direct mixing process.

If the FREQ Mite in a transceiver or receiver (superhet)is to be used, then must be adjusted the intermediate frequency (IF), more exactly their hundred, decimal and units position in kHz than offset frequency. One can adjust this value over + / - 1 kHz to vary, in order other deviations in transmits - or for rx way.

One must differentiate here whether the VFO swings below (A) or above (B) of the IF.

Example of (a):

If the IF amounts to 4.915 MHz, then must be coded the " 915 " binary, if the VFO between 2,085 and 2,145 MHz swings. The working frequency amounts to then 7.000... 7.060 MHz.

915 = 1 * 512 + 1 * 256 +  1 * 128 + 0  * 64 + 0 * 32 + 1 * 16  + 0 * 8 + 0 *  4 + 1 * 2 + 1 * 1

The coefficients before the powers of 2 result in the binary number:

1110010011

The Jumper must be set to binary priority accordingly in this order.

Example of (b):

The IF amounts to 455 kHz, the VFO frequency 4055 kHz (the working frequency 3600 kHz amount to)

The value, which must be coded binary amounts to:

1000 - 455 = 545

But the following binary coding results: 10001001

With a TRX if the working frequency is formed by subtraction of the VFO frequency of the IF, then the frequency measurement must take place inverting. Example: The White Mountain-75 SSB, a transceiver for 3500 kHz uses a IF of 9830 kHz. The offset must be coded as 830. After switching on, if the question " I? " must the key S1 be pressed, then the PIC calculated the inverted frequency, if the VFO frequency is 6005 kHzs, means the output " 825" a QRG of 3.825 MHz.

The FREQ Mite is a valuable supplement of many self-building projects, for which the expenditure for visual digital displays is not worthwhile itself. Does one think with priority thereby of qrp transceiver, or small short wave receivers, but why one not also a Dipmeter or a Antennascope with RF generator with such is a section is revalued? By the size of a stamp it fits almost everywhere still also purely. The next device, that with DL2LUX thereby is re-tooled is the VLF-RX...