VCR and TV-tuners
This side will explain TUNER
and Homebrew Spectrum Analyzer Project.

Many thanks to my friend Hugh's who has helped me undestand tuners.
All contribution to this page are most welcome

Spectrum Analyzer is intended for visual inspection of the spectrum of an investigated
signal on the oscilloscope screen. The signal can be continuous or pulsed.

Block diagram
Before we are going to look what it is inside those magic shining
boxes called tuner, I will explain the blockdiagram.
The picture at the right is a "simple" blockdiagram.

Klick on the image to get a larger picture.

Now, let's open the tuner and try to identify the different parts inside.
The tuner I have is a SHARP-modell.
This tuner is a 3-band tuner wich covers the frequency 40MHz - 900Mhz.
The IF output is at 38.9 MHz European Standard.

Klick on the image to get a larger picture.

The photo at the right shows the component side of the tuner.
Some components are idetified as mixer, varactor-diods etc.

Klick on the image to get a larger picture.

The connection to the tuner
The schematic at the right explains the connection to the tuner.
All you need is +12V and +30V. some potensiometers and bandselector.

Klick on the image to get a larger picture.

The scematic of a tuner
I have found one schematic of a tuner.

Klick on the image to get a larger picture.

Frequency standard of TV signal.

IF Frequency
38.90 MHz
45.75 MHz
58.75 MHz
Sound Carrier
33.40 MHz
41.25 MHz
54.25 MHz

Digital tuners UV916
The most common tuners today is digital tuners. The tuner is still analogue,
but the tuning mechanism is digitaly controlled by a PLL frequency synthesizer.
Most often 2 circuits are used:
  • Mixer/oscillator (TDA5630.pdf)
  • PLL frequency synthesizer(TSA5512.pdf)

    This type of tuner is very easy to control and use. The hard part is to get the digital communication work properly. The PLL frequency synthesizer is controlled with I2C, it's a digital standard using only 2 wires.

    Comments to the pic at right:
    The parts around TDA5630 is still analogue. The tuning voltage to TDA5630 reaches from 0 to +33V. This voltage controlls the oscillator wich set the receiving frequency. TDA5630 handles all the RF and LO mixing for all 3-bands. (This is just a simple shematic so haven't drawn the 3-band). The synthesizer TDA5512 probe the LO from the TDA5630. In this way the synthesizer will know the frequency of the oscillator.
    The synthesiser has an internal reference frequency of 7812.5Hz wich comes from the 4MHz crystall oscillator.
    The stepsize is 8 timer higher than the reference = > 8 * 7812.5 = 62500Hz
    What the synthesizer do is to divide the input frequency with the contents in a register and then regulate the tuning voltage until the divided result is equal to the stepsize frequency.
    The synthesizer has also 7 outports wich set the desired band and som other functions.

    Example: Let say you want to receive at 218.750MHz. ==> 218.75e6 / 62500 = 3500.
    The register in the synthesizer should be programmed with the number 3500.
    There are some more register wich has to be set in the synthesizer, you can find them in the datasheets.
    The output from the TDA5630 is the IF-signal.

    How to rebuild a digital tuner to a analog tuner
    If you want to be able to controll the vco in the tuner you must disable the phase detector wich controls the tuning voltage. If we concentrate us to the UV916 wich we have datasheets for, we can see that there is a transistor, a PLL filter and a resistor connected to +33V. Together they controls the tuning voltage. What you have to do is to disconnect the Transistor and the PLL filter. These components are not difficult to identify in the tuner. Now you can control the VCO by the tuning voltage. Just change the voltage from 0 to +33V.
    Next step is to control the desired band, remeber there are 3 bands.

  • BAND I 45 - 180 MHz
  • BAND II 160 - 470 MHz
  • BAND III 430 - 860 MHz

    This can be done in two ways. If you are able to control the tuner digitally you can set the desired band by the I2C communication. If you can not handle this communication you must identify the ports from the synthesizer. According to philips datasheets of the UV916 tuner, P3, P4, P5, P6, P7 controls the band selections. If you still not going to use the synthesizer you my just solder it away. It will makes it easier for you to reach the pads for the P3-P7.
    The truth table below show the band selection.

    BAND P0 P1 P2 P3 P4 P5 P6 P7
    LOW BAND X X X 0 0 1 1 0
    MID BAND X X X 0 1 0 1 0
    HIGH BAND X X X 0 1 1 0 0

    If you want to monitor the VCO frequency with a frequency counter, the synthesizer can be used as a prescaler. Since the synthesizer is connected to the VHF, UHF tuner via the RFin and if you set the programmable divider to 1000 you can monitor the Fdivided via P7 provided that T1, T0, OS = 0, 0 ,0 .
    The result will be that you will have Ftuning/1000 at P7 wich the can be connected to a low frequency counter.
    If you want more infomation or discuss, please mail me and I will help you.

    My Spectrum Analyzer
    (This project is still under construction and is calculated to be finished in the end of may! 30/5 2001.)
    The information on this side will be uppdated with the same speed as my hardware work!

    I will explain my construction for a Spectrum Analyzer. I like to store and analyze information, so this Spectrum Analyser will be connected to a computer where the information will be stored and displayed. If you don't like this concept, don't worry, I will also explain how you can build the Spectrum Analyser to display the information on a oscilloscope.

    This project has several parts :

    1. The Tuner and IF part.
    2. The measurement of the RSSI-signal.
    3. The DC-sweep generator.
    4. Software for the computer.
    5. How to connect to a regular oscilloscoper.

    1. The Tuner and IF part
    The tuner I have used is a SHARP model. You can use almost any tuner, the important thing is to identify the pin from the tuner. The easiest way to do this is to look at the circuitboard before you dismount the tuner. Most often there is some text on the board saying "UB" , "TU", "VHB", "AGC", "VLB", "AFC", "MB", "IF" or something equal. The "IF" output is most often a bit away from the other pins. If you follow the IF strip from the tuner you will come to a IF- preamplifier and some filter. After the filter the IF- signal continue to the video IF- Circuit. Close to the IF-circuit you will find some IF-cans. These cans is tuned to the IF frequency. Inside the can is a coil and parallel to the coil is a capacitor connected. Most often the capacitor is outside the can, but some times it can be inside the can. You should be carful with this can and the capacitor, becasue it will be used as an oscillator to the IF-demodulator later in this project. If you don't have this can or can't find it, don't worry, I will explain how you can make the oscillator work.

  • So what you need to do first is to identify the pins on the tuner and dismount it from the circuitbord in the TV or VCR.
  • Identify the IF can and it's capacitor and dismount it from the circuitbord in the TV or VCR.

    The IF-output from my tuner is 38.9Mhz (European standard), American standard is 45.75 MHz.
    The IF-can I dismounted is 186.6nH and the capacitor is 82.5pF. The resonans frequency is 1 / 2*pi*(LC)1/2 = 40.5Mhz pretty close to the 38.9MHz. By tuning the ferrite slug in the can I will be able to adjust the resonans frequency.

    As IF-demodulator I have used a high performance low power mixer FM IF circuit called SA615 from PHILIPS.
    The RF input on this circuit will be connected to the IF-output from the tuner. The oscillator in the SA615 will be set to 38.445 MHz. The oscillator is made of a coil and a capacitor, it is here the previous discussed iF-can comes in handy.
    The mixer in the SA615 circuit mixes the RF input (38.9MHz) and the LO (38.445MHz), the product from the mixer will be the difference between the two frequences which will be 455kHz. The IF section in this circuit has a gain of 90dB.

    2. The measurement of the RSSI signal.

    A log signal strength (RSSI)completes the circuit (PIN 7). The output range is greater than 90dB. It is the RSSI signal wich will be measured and indicates the level of the RF-signal. The RSSI will be the Y-axle of the oscilloscope.
    The RSSI-level will be measured by a fast AD-converter and send to a computer.

    3. The DC-sweep generator.

    The sweep voltage is constructed around an OP-integrator. The OP works with +/- 18V so the V-tuning will have a range from 0 to 36 volt. The Integration time depends on the capacitor c1 and the total resistance from R1 to R3.
    R1, R2 and R3 have different values.
    The PIC processor can control the RC constant of the integration by selecting on of the resistor R1-R3.
    Example: Let's say you want to sweep slowley between 8-10 Volt. The PIC choose a resistor with low value (R1). The V-tune is constantley probed by a AD and the PIC is monitoring the AD. The V-tune will rise fast from 0 Volt to 8 Volt. When the V-tune is 8 Volt the PIC switches the resistor R1 to R2 wich has a large value and the Integration time will be much slower so the V-tune rise slowley until 10 Volt is reached and the procedure restarts.
    There is another AD converter wich probes the RSSI-level from the SA615 circuit.
    Both the RSSI value and the V-tune value will be sent to the computer. The RSSI is the Y-axle and the V-tune is the X-axle.
    The V-tune is a voltage but you want it to be a frequency, so what you have to do is to measure the LO frequence in the tuner depending on the V-tunes and make a reference table in your computer.
    The PIC will also control the band-selection.

    Tuner and Spectrum Analyzer links

    SF1216 Tuner info and specs.( 900 - 2000 Mhz )
    Low Cost Spectrum Analyzer, from Zanko NL
    Homebrew Spectrum Analyzer Project, from PA0ZN
    Hugh's web site.

    Copyright © Last modified on 18h April 2001.