Technical specifications
Supply voltage: 12 V
Supply current: 10 mA in stand-by, max. 80 mA
Input voltage: min. 20 mV rms
Indication range: 30 dB
LED currents: 7 mA
Ref. voltage of IC2: 5 V
Schematic diagram
Parts list
R1 - trimmer 100 k mini
R2 - 2,2 k
R3 - 1 M
R4 - 2,7 k
R5 - 6,8 k
C1 - 0,47 uF
C2 - 10 uF
C3 - 47 nF
C4 - 4,7 uF
C5 - 0,1 uF
C6 - 100 uF
C7 - 100 nF
IC1 - LM386
IC2 - LM3915
D1 - 1N4148
D2-D11 - bargraph or LED's
PCB layout
This simple counter is useful for frequency measurements of various wireless equipments, especially transmitters, receivers and signal generators in VHF/UHF band.
Features
Technical specifications
Supply voltage: 8-20 V
Supply current: typ. 80 mA, max. 120 mA
Input sensitivity: max. 10 mV in 70-1000 MHz range
Measuring period: 0,082 sec.
Display refresh rate: 49 Hz
Schematic diagram
Parts list
R1 - 39 k
R2 - 1 k
R3-R6 - 2,2 k
R7-R14 - 220
C1, C5, C6 - 100 n mini
C2, C3, C4 - 1 n
C7 - 100 u
C8, C9 - 22 p
IC1 - 7805
IC2 - SAB6456 (U813BS - different pin layout, not tested, also maybe R1 value need to be changed)
IC3 - PIC16F84A programmed + socket
T1 - BC546B
T2-T5 - BC556B
D1, D2 - BAT41 (BAR19) - may be ommited
D3 - HD-M514RD (red) or HD-M512RD (green), 4-digits multiplex driven LED display from HP, or four standard 1-digit LED displays
X1 - 4.000 MHz crystal
BNC input connector
To use with a receiver as a digital scale, close the -10,7 pins.
IC3 program download: counter.hex
Programmer settings: Oscillator: XT, WDT: on
For additional changes (eg. IF frequency offset change): counter.asm
The SAB6456 description
The SAB6456 is a prescaler for UHF/VHF tuners. The circuit has an input frequency range of 70 MHz to 1 GHz, has high input sensitivity and good harmonic suppression. With lower sensitivity it's usable down to 3 MHz.
The circuit comprises an input amplifier, a divider stage and an output stage. The divider stage may oscillate during no-signal conditions but this oscillation is suppressed when input signals are received. The voltage-edges of the output signals are slowed internally to reduce harmonics in the television intermediate frequency band.
Printed circuit board
Important!
II
The transmitter includes RDS/SCA input and Audio/MPX input with optional preemphasis. It can be used with or without stereo encoder. Tuning over the FM band is provided by two buttons that control dual-speed PLL. The transmitter can work also without the LCD display.
Characteristics:
Schematic diagram
Part list
Q1 - BF240
Q2 - BFG135 (BFG235)
Q3 - 2SC1971 (2N3553) + heatsink
Q4 - BC547B
D1 - SB260 (1N5822, 1N581x)
D2, D3 - BBY40 (BBY31)
D4 - LED 5mm
U1 - 78L09
U2 - TSA5511 (TSA5512, SDA3202)
U3 - PIC16F627A (programmed)
U4 - 78L05
R1, R2, R11, R17, R20 - 10k
R3, R21 - 270R
R4, R15 - 33k
R5, R7, R12, R13, R16 - 680R
R6, R14 - 18k
R8 - 47R (33R if Q2 is BFG235)
R9 - 18R
R10 - 4k7
R18 - 3k3
R19 - 100k smd 1206
R22 - 91R
R23 - trimmer 5k mini
C1, C4, C9, C12, C13, C14, C15, C30, C31, C32, C33, C35 - 10n smd 1206 (C)
C2, C17, C20 - 15p (C)
C3 - 10p (C) (15p if the PCB is single-sided)
C5 - 1n (C)
C6, C28, C29, C34 - 100u/10V (E)
C7, C26 - 10u/35V (E)
C8 - 22p (C)
C10 - 47p (C) (33p if Q3 is 2N3553)
C11, C27 - 100n (C)
C16, C36 - 33p (C)
C18 - trimmer 50p
C19 - 470u/16V (E)
C21 - 4u7/50V (E)
C22 - 330p (C)
C23, C24 - 47p (C)
C25 - 3n3 (P)
L1 - 3.5 turns on 7 mm diameter
L2 - 1uH/815mA choke, or about 10 turns of thin wire on mini ferrite core
L3 - 2.5 turns on 6 mm diameter (4.5 turns if Q3 is 2N3553)
L4, L5 - 3.5 turns on 6 mm diameter
Y1 - crystal 6.4 MHz or 3.2 MHz
TR1 - rf ferrite transformer 2:1 (3:1 if Q3 is 2N3553), see text
SW1, SW2 - button mini
J1, J2, J3 - BNC connector 90 deg.
J4 - power supply connector
J5 - HD44780 LCD standard connector, 2x8 or 2x16 characters
J6, J7 - jumper
For 0.05 MHz step tuning a 3.2 MHz crystal is required. In other case a 6.4 MHz crystal will make good work (step tuning 0.1 MHz).
Wind all coils (except the L2) by a 0.8 mm wire.
The Y1 package must be tied to ground!
Make sure the Q3 terminals are as short as possible (about 2-3 mm above board). The 2N3553 case/heatsink can't be tied to ground!
To make the TR1 transformer, use specified number of turns on primary side and one turn on secondary side. The secondary wire should be quite thick but the primary can be as thin as you want. Wind on a 2-hole ferrite (material 61 or N1). The picture explains it all:
Alternatively use two ordinary ferrite beads placed side-by-side, something like on the picture:
Be careful when forming the 2SC1971 terminals - you may corrupt its internal structure! Or leave the terminals straight and use another suitable heatsink.
The software for U3 is provided for download here: plltsa.zip (version 1.3). Please read included license text first.
Suitable free PIC programmer is for example here: http://www.members.aon.at/electronics/pic/picpgm/. Actually Pira CZ does not provide the PIC programming or complete kit sale for this device.
Software modifications included: pll64.hex - 6.4 MHz crystal, pll32.hex - 3.2 MHz crystal, pll.asm - for any changes.
Fuses: WDT: Enabled, OSC: INTRC-I/O, MCLRE: I/O.
Use the buttons to set the frequency. After a few seconds of idle the frequency is tuned and stored to EEPROM (icon of diskette). Finally the buttons are locked (icon of key) to avoid unwanted frequency changes. Unlock by pressing any button for a longer time.
The display and LED indicate PLL in-lock state. This state is also provided at pin 1 of U3. It can be used for control of additional power amplifier. When in-lock state is indicated, the PLL is switched to low speed for maximally flat low audio frequencies response.
Placing in operation
After complete parts placement:
Check that there are no shorts bridging adjacent tracks or pads.
Check electrolytic capacitors polarity and semiconductor parts orientation.
Make any duty load and connect it temporarily to the antenna connector. Use for example 2 or 3 bulbs (24V/170mA or 24V/3W) in parallel (see the picture).
Start with smaller power supply voltage, for example 9 V. The bulbs should glow a little. Then it's OK and you may increase the power supply voltage to 12 V. Adjust C18 to max. output power. Adjust right LCD contrast by R23.
Now the L1 coil must be adjusted by stretching or compressing the turns. It affect frequency position of the band, which is the PLL able to tune.
Tune to 107.9 MHz using the buttons.
Measure tuning voltage at Q4 collector. Set the tuning voltage to 8.0 V by adjusting the L1.
Then you are done.
Now tune to 105 MHz and adjust C18 to max. power finally. At this point use about 10 meters of coaxial cable between the transmitter and the duty load!
If you have a problem with stability/spurious oscillations (very improbably if you used standard components and procedures), you may:
decrease R7 or R9 value
increase R8 value
decrease power supply voltage
use another material for TR1
If you want to change the output power, you may do it by changing the R8 value. Don't use smaller values than mentioned in part list!
You may choose between single-sided PCB (only bottom layer) and double-sided PCB (+ ground layer on the top). The difference is in output power. The double-sided PCB gives higher output power (this fact is not so interesting in rf issue).
Parts placement.
Bottom side.
Top side (optional).
The board dimensions are 109 x 54 mm. If double-sided PCB is used, don't forget to solder ground pins of key parts also from top side (mainly Q3, TR1, U1, D1, U4, SW1, SW2, R3, R8, C11).
You may buy the printed circuit board or fully assembled transmitters in the shop.
| Drill chart | |
| Diameter | Quantity |
| 0.8 mm | 151 |
| 1.0 mm | 50 |
| 1.5 mm | 10 |
| 2.0 mm | 6 |
| 2.5 mm | 3 |
| 3.2 mm | 3 |
Double-sided PCB, 2SC1971.
Single-sided PCB, 2N3553.
Bottom side with smd parts.
Source : http://pira.cz/entx4.htm
This stereo encoder advisedly does not contain any preemphasis circuit. Remember the key fact: a compressor/limiter/clipper device must be always present between the preemphasis circuit and the stereo encoder or modulator. Only this configuration ensures loud sound without exceeding the maximum frequency deviation limit (75 kHz). The stereo encoder is designed to provide really good sound. This always needs to use the compressor/limiter/clipper device where the preemphasis is precisely assured. The Pira CZ Compressor/Limiter/Clipper is highly suitable for this task.
Basic block diagram:
Characteristics:
| Supply voltage: | 9-16 V (stabilized) |
| Quiescent supply current (12 V): | 34 mA |
| Audio 19 kHz rejection: | 40 dB |
| Channel separation at 1 kHz: | >55 dB (see details) |
| Subcarrier rejection: | >60 dB |
| Pilot sampling frequency: | 1.843 MHz (19 kHz x 97) |
| Subcarrier sampling frequency: | 1.843 MHz (38 kHz x 48.5) |
| Pilot sync. output: | TTL |
| Max. audio input voltage: | 5 V pp (1.75 V rms) |
| Pilot tone level: | linear adjustable 0-0.5 V pp |
| Output voltage gain: | linear adjustable 0-1.5 |
| Audio input impedance: | 2000 ohm |
| RDS input impedance: | 1000 ohm |
| MPX output impedance: | 500 ohm |
| Pilot sync. output impedance: | 10000 ohm |
| Signal-to-noise ratio: | >70 dB |
Schematic diagram:
Part list:
U1-U3 - TLC272, TS272
U4, U5 - 74HC4053 (74HCT4053)
U6 - 7805
U7 - PIC18F1220-I/P with stereo.hex file inside
Y1 - Crystal 7.3728 MHz (7.372 MHz)
SW1 - Button
L1, L2 - Coil 15 mH (09P-153J)
RN1, RN2 - SIL resistor network 3x 1k (discrete, 6 pin)
C1, C2 - 47p (C)
C3, C4, C5, C9, C24, C33-C35 C37 - 100n (C)
C6 - 82p (C)
C7, C19, C20, C30, C31 - 270p (C)
C8, C11, C14, C22, C23 - 220u/10V (E)
C10, C21, C25, C32 - 560p (C)
C12, C36, C38, C39 - 100u/10V (E)
C13 - 470u/25V (E)
C15, C26, C40 - 22p (C)
C16, C27 - 2n7 (C)
C17, C28 - 4n7 (P, 5%)
C18, C29 - 10n (C)
R1, R24 - 20k (1%)
R2-R9, R30, R31, R38, R39, R49, R50 - 2k (1%)
R10 - 160k
R11 - 330k
R12, R16, R27-R29, R40-R42 - 39k
R13 - 82k
R14, R17, R18, R20, R21, R25, R32, R43 - 10k (1%)
R15, R26 - 1k
R19 - 470R
R33, R34, R44, R45 - 30k (1%)
R35, R46 - 16k (1%)
R36, R47 - 47R
R37, R48 - 680R
R22, R23 - Trimmer 5k
HEX file: stereo.zip (WDT: on, Osc.: HS PLL, MCLRE: RA5), version 2.0.
Suitable free PIC programmer is for example here: http://www.members.aon.at/electronics/pic/picpgm/. Actually Pira CZ does not provide the PIC programming, PCB nor complete kit sale for this device.
Adjusting elements description:
Pilot level adjustment: The pilot level should be set to 9 % of the total deviation (75 kHz), measured in peak-to-peak values. For example, if audio input level is 2 V pp, set the pilot tone level to 0.2 V pp (the adjustment is linear with the max. of about 0.5 V pp).
Output level (gain) adjustment tip: If possible, it's recommended to set high output level and adjust lower sensitivity on the transmitter/exciter rather than set low output level and adjust high sensitivity. This way gives getter S/N ratio. Is it clear?
Note: The output level adjustment has no effect on pilot-to-audio ratio.
Mode selection: Click and hold the button until the mode change is indicated by acoustic signal (number of beeps indicates the mode set). The device will remember the setting.
Mode table:
Mode 1 is the default and recommended. Mode 2 switches to monaural operation. Modes 3 to 5 can compensate transient characteristics in some cases and improve channel separation, but have no reason for nonspecialists.
PCB:
Connection to the RDS encoder:
Source : http://pira.cz/eng/stk2en.htm
