WildCat FM /technical station.
attic of station's chief /Top floor /White Room
FM stereo matrix generator /2

Production is advanced with Step by step with the verification of each circuit. If operation cannot be understood, the adjustment that makes the best use of the performance even if the circuit can be done cannot be done. Let's study the operation of the circuit and proceed to the next step.
The power supply of this experimental circuit uses a good quality about single power supply of 12V/100 mA in capacity.

Production of L-R, L+R circuit, and Balanced modulator circuit
 

Well,it hangs in the production of the center part of the modulator in the place where the subcarrier generation circuit can have been done.

This circuit : to Balanced modulator it saw by using double balanced mixer a IC TI/SN76514.

IC is thought that the AM modulation circuit is made before and exists in "Manuke" why though is a thing stocked in some measure, and the data seat of IC is lost, and you do not have the material that can be offered this.
The person who has the PDF data sheet of SN76514 survives when he or she can supply data. it is about SN76514 to break out at hand.
Though it saw suitably attacking it because reeling is not now in a considerable problem if the equivalent circuit in , is understood.

sent to Balanced modulator for modulator of matrix method The signal of L-R is a general circuit to synthesize by usually using the input of +/- the OP amplifier and has been synthesized by using the input of +/- the OP amplifier even if the circuit of various modulators is seen. The modulator circuit of famous orban optimod 8100 has been synthesized with the OP amplifier in the sound processor.
 

This circuit is in an initial design phase with the OP amplifier. A synthetic circuit of the signal of L-R existed.

The thing in which the function that was able to be done was provided was deleted simultaneously with the DSB modulation, and it began to be and deleted a synthetic circuit of the L-R signal from the circuit from an internal equivalent circuit to looking the deletion of SN76514 that was double balanced mixer (DBM) of the synthesis of the signal of L-R with the OP amplifier when seeing examining an internal equivalent circuit of SN76514 again.

Actually, it is a design that has not disappeared the circuit of L-R and is absorbed to an internal equivalent circuit of SN76514. This circuit can be applied to the circuit of the stereo modulator of the matrix type that uses double balanced mixer /LM1396 LM1496 LM1596 uA796 N5596 NJM1496 etc. other than SN76514. When SN76514 cannot be obtained, it is possible to substitute it for this circuit with above-mentioned IC though it is natural.

There is a large advantage by absorbing the L-R circuit to the equivalent circuit in double balanced mixer
The circuit passing can be omitted by one step by the thing that the synthesis of the signal of L-R with the OP amplifier circuit loses.
The reduction of the tone quality deterioration and the improvement of the phase delay cause a decrease in the distortion more than the omission of an active element such as OP amplifiers. In addition, the circuit composition becomes simple
and the thing that the number of parts can be reduced is the maximum advantage.
 
Well, when the above-mentioned circuit can be done, let's put the signal and verify operation to "toriatama" because it thinks the calligraphy that cannot be understood to be trivial.

First of all, the subcarrier signal of 38KHz is injected from the subcarrier generation circuit into 5- pin of double balanced mixer SN76514.
The thing that VR of the subcarrier signal of 38KHz is raised and the signal of about about 70?100mv/P-P is injected with the oscilloscope or VTVM is confirmed.
Because an internal circuit of SN76514 is saturated when the signal of 100mv/P-P or more is injected, 100mv/P-P is assumed to be a limit.

The signal generated in TP-3 of the injection of the subcarrier signal is observed by using the oscilloscope or VTVM, and career suppression is done with VR-S1 and suppressed.
 

[TEST-1]
TP-1 and TP-2 in the circuit chart are put and audio signal (AF_signal/1KHz) of the short-circuit (phase) is put. (Inject it at the level with which an internal circuit of SN76514 is not saturated. ) VR-M1 is adjusted, the signal generated in TP-3 is measured with the oscilloscope or VTVM, it suppresses as well as the adjustment of career suppression, the AF signal is counterbalanced, and L of double balanced mixer enters the state that be able do the balance of R at this point. (The signal is not output to TP-3 in state (L+R) that LorR is short-circuited. )

L-R operation is normally done, the voice signal in phase suppression can be secured by -60 dB more.
 
 

[CHECK-1]
When the short-circuit of TP-1 and TP-2 is released and audio signal (AF_signal) of about 1KHz is put in TP-1 and TP-2, a beautiful DSB signal is promoted to the output of TP-3 as follows.
 

 

When you can confirm the thing that the DSB signal is promoted The circuit that synthesizes the L+R signal is added and the stereo/MPX signal is generated in TP-3.

 

When VR-P is adjusted by injecting signal (AF_signal) into TP-1(L-ch) or TP-2(R-ch), the following MPX signals are synthesized.
 
Test sound source and promotion signal 'The thing that the signal of the test sound source can be correctly reproduced is a condition.
'Though it thinks the possession of that has put the link of the test sound sources oscilloscope to have the signal generator
 

[CHECK-2]
1KHz AF_signal /L ch signal of promotion image

 

[CHECK-3]
1KHz AF_signal /R ch signal of promotion image

 

[CHECK-4]
1KHz AF_signal /L+R ch signal of promotion image(phase signal)

The thing that the side band signal has been completely suppressed is confirmed. !
 
 
 

[CHECK-5]
1KHz AF_signal/L-R ch signal of promotion image(SUB)/opposite phase signal

The thing that the peak of the double side band signal is suitable is confirmed.
 

The base of a high Separation characteristic is obtained by the balance and adjusting the circuit. When you do not obtain the shape of waves of the above- mentioned image by the confirmed signal Because the balance is not suitable or the circuit doesn't function normally, it is necessary to readjust.
 

The correction of the following signals is adjusted with VR-M1/VR-M2 in CHECK-2 and CHECK-3. (LorR /each channel can do an independent adjustment. )
 

Bad example of signal of 1 (under)	Bad example of signal of 2 (Over)

The above-mentioned signal image is bad. Each signal also obtains neither limit nor a straight stereo Separation characteristic that the center line doesn't become a straight line.
 
 
 
 

it verifies it in each frequency of the audio signal. The Separation characteristic (In the thing that the line doesn't become a straight line) of deterioration in the characteristic etc. can be confirmed.

The case of a general modulator of 50Hz or less, especially the low region signal and the high region signal of 10KHz or more fall into disorder, and the Separation characteristic of each frequency is deteriorated.
 

experimental circuit of synthetic signal (measurement environment-3)
characteristic of high region signal

5KHz/AF_signal/L-ch signal

10KHz/AF_signal/L-ch signal

15KHz/AF_signal/L-ch signal

Characteristic of low region signal

100Hz/AF_signal/L-ch signal

50Hz/AF_signal/L-ch signal

20Hz/AF_signal/L-ch signal

10Hz/AF_signal/L-ch signal

5Hz/AF_signal/L-ch signal


 
 

The circuit enters after this back and forth, and it changes to VCO slightly though the signal wave form has been slightly distorted still by the connected state. When connected with VCO, a final adjustment will be severely done. A final evaluation is decided with everything went out over the air.
 
 

Was a basic part of FM modulator able to be understood though it became a considerably heavy content?
it is necessary to obtain the above-mentioned characteristic to achieve an efficient FM modulator.
 
 
 
 

Next Page /Do you advance to the following experiment circuit ?
FM stereo matrix generator /3  Production of Pre-emphasis /input filter/buffer amplifier circuit
 
 
 

FM stereo matrix generator  introduction
FM stereo matrix generator /1  Production of pilot signal and subcarrier generation circuit
FM stereo matrix generator /2  Production of L-R, L+R circuit, and Balanced modulator circuit
FM stereo matrix generator /3  Production of Pre-emphasis /input filter/buffer amplifier circuit
FM stereo matrix generator /4  Connection to VCO/exciters and phase of pilot signal
FM stereo matrix generator /5  FM stereo modulation signal Spectrum seen from side of electric wave
 
 

document of yamamoto by WildCat FM