Problem with modulating the oscillator (POS 150) with an MPX audio signal

[savnik]

I use POS-150 as oscillator for FM band (87.5-108 MHZ).
When modulate the oscillator with a MPX sound it plays well but does not make segregation in the channels , if I receive the oscillator with a stereo radio for Fm band. Only turn on the LED which is for to show when the station is stereo.
Why happen it ;

 

[E-design]

pos-150 schematic pll

If you do modulate this VCO you should make sure that the level will provide enough deviation of the FM carrier. The stereo led will come on at low levels of pilot tone 3-4kHz of the optimal 7-10kHz required for good stereo separation. Also frequency response should be flat from about 20Hz to about 50kHz

 

[savnik]

pos-150 vco

When modulate the oscillator (POS 150) with a MPX audio signal , don't make separation , if I receive the oscillator with a stereo fm radio band , but only turn on the LED , which is to show when the station is stereo.

 

[Borber]

schematic pos-150

For stereo separation of 40dB your FM oscillator must have flat frequency response within 0.1dB up to 100kHz if you plan to use RDS also. In front of varicap diode there may be resistor connected to DC input and it is together vith diode capacitance forming LPF. Question is is POS suitable for MPX modulation at all. You should check it first. You should check your circuit in front of POS for frequency response also.
Stereo LED is driven by 19kHz pilot tone in MPX and it is on low frequency side so less attenuated.

 

[savnik]

stereo mpx lpf

For stereo separation of 40dB your FM oscillator must have flat frequency response within 0.1dB up to 100kHz if you plan to use RDS also. In front of varicap diode there may be resistor connected to DC input and it is together vith diode capacitance forming LPF. Question is is POS suitable for MPX modulation at all. You should check it first. You should check your circuit in front of POS for frequency response also.
Stereo LED is driven by 19kHz pilot tone in MPX and it is on low frequency side so less attenuated.

I have test and the newer model MOS 114 but the result is the same and i don't know why;
With other oscilator i don't have problems.The separation is ok.

 

[Borber]

pos-150

OK if you testedd with MOS-114 then post your circuit. There must be something wrong. Just a suggestion: your modulation and PLL output to POS should be low impedance.

 

[savnik]

pdf pos-150

OK if you testedd with MOS-114 then post your circuit. There must be something wrong. Just a suggestion: your modulation and PLL output to POS should be low impedance.

I use with pll and without pll , but the result is the same

 

[savnik]

pos 150 modulatie

And the MOS-114 inside.
Why use two varicaps;

 

[savnik]

tl082 lpf

And the circuit without PLL

 

[Borber]

pos150 signal circuit

If POS connected as in the last circuit (no PLL) has low stereo separation then POS is not capable to be modulated with MPX (modulation bandwidth is smaller than specified 100kHz) or it has additional capacitor connected between DC input and ground. In this case insert voltage follower in front of DC input (pin 8).

 

[savnik]

vco pos-150

If POS connected as in the last circuit (no PLL) has low stereo separation then POS is not capable to be modulated with MPX (modulation bandwidth is smaller than specified 100kHz) or it has additional capacitor connected between DC input and ground. In this case insert voltage follower in front of DC input (pin 8).

I have test the same circuit (no PLL) and with MOS-114 , but the result is same.
Where is the problem or my mistake;

 

[Borber]

pos150 fm pll

As I presume the problem can be the input capacitance of POS or MOS.

 

[savnik]

pos150 rf out

As I presume the problem can be the input capacitance of POS or MOS.

I have post the circuit of the MOS-144 inside and haven't any capacitor in input.

Added after 3 minutes:

Look at this:
**broken link removed**
I have send email and his answer was:

The TXFM-01 is "transparent" for the stereo multiplexer. If you MPX, can separete and not only send de 19Khz pilot signal, you will have separate "L & R" chanel in your receiver.

 

[Borber]

pos-150 vco receiver

Anyway your kit has low impedance drive to VCO imput and correct circuit for PLL-AF combinning. You circuit above has 6dB peak at 100Hz.

 

[savnik]

pos150

Anyway your kit has low impedance drive to VCO imput and correct circuit for PLL-AF combinning. You circuit above has 6dB peak at 100Hz.

I don't have buy this kit.
In his circuit the LF353 (IC6B) for who reason him it has.

 

[Borber]

Re: POS 150

Left Lf353 is PLL filter and the second is low impedance drive.

 

[savnik]

Re: POS 150

Left Lf353 is PLL filter and the second is low impedance drive.

If i use this circuit is ok;

 

[Borber]

Re: POS 150

Only under one condition: PLL out must have low impedance like in kit schematics. After 3.3kohm resistor put another follower.

 

[savnik]

Re: POS 150

Only under one condition: PLL out must have low impedance like in kit schematics. After 3.3kohm resistor put another follower.

Ok , i will try it.

 

[savnik]

POS 150

I test with a TL082 and now make separation.