Portable FM as FSM.

[radium98]

I need some help.
In practice ,because i am a bit confused .
I have a portable Sony China radio FM AM ,that i need to convert it to a tuneable field meter .in same time i can listen to modulation
the receiver radio have a 1 block monolithic IC : CD1691CB. As i was looking at the datasheet pin number 19 is the meter cadran so i have to take from there to the scale meter .i saw that the three pins 18-19 and20 are grounded ,so i will isolate the ground from pin 19 ,but i still have 1 more problem .that confused me ,because i need to try to use it to locate a transmitter, that i know in advance ,where it is located ,and is interfere with our pirate radio lol .
My question isnt i need to attenuate the signal because it is amplified in the radio ?
i have removed the aerial antenna ,should i put some kind of atenuator with some resistor ,help me please.

[radium98]

ANyone ?

[sinus trouble]

Hello Radium

I had a look at the Datasheet which did not make much sense as it was all in Chinese?

I would think you would need some kind of old VU meter or a digital display meter (Maybe a cheap multimeter) to detect field strength with any degree of accuracy?

The best tracking antenna would be a YAGI or something similar?

You could possibly use a dipole horizontally and rotate it around to get general idea of the direction of which the signal is comming from?

[Albert H]

I really wouldn't use a plastic-cased receiver to try to track signals. You need to build a basic superhet FM receiver, probably with a PLL local oscillator and a variable gain input stage. Use an IF chip like a CA3189, and use the RSSI output to drive a meter.

[sinus trouble]

Yeh to be brutally honest Radium, Its not looking good.

I would be surprised if that is actually a real SONY?

You could do what some UK Pirates would do and send them threatening messages saying "TURN YOUR RIG OFF NOW!!! OR I WILL KILL ALL OF YOU!!!!"

[radium98]

thank so ,what it be a diy project as a tuned filed meter ?

[sinus trouble]

There are many field strength meter circuits out there for inspiration.

Working with what you have? As Albert mentioned, fitting the PCB into some kind of tin box would help block any unwanted interference.

Maybe fit some connections from the signal pin to a multimeter to test the sensitivity.

[radium98]

thank you freind sinus happy new year ,i will see if i put a tuned circuit to a simple one with some kind of attenuation ,but i faced is the selectivity of the tuned circuit ,because it is an outdoor use ,just hobbie ,i know where thoses are transmitting from.i have an old sk-2200 wattmeter 150mhz that have fsm field strength ,but it is just indoor use next a tx ,that is not good for outdoor ,even an good fsm is not also good ,only triangulation can do it or some kind of doppler

[Albert H]

Doppler DF is quite easy to build. Look up "Whistling Dipoles" for a simple handheld location system. There are loks of designs around the 'net.

[Rfdiva]

I have one to build but the switching antenna is a nightmare .i think i still have the hardware files only .because the site is no more onl8ne.but someone told me that the doopler work as a narrow band only .but 8t shouldnt be a problem with some knowledge .the doppler have 4 antenna to kept the signal.from.all dorection with the reflection echo too .how then it can omitted with only one antenna ?

[Rfdiva]

Building now with etching pcb is f9r now a dream with problem here .i wish you all a happy new year 2021 full of r8gs build .

[Rfdiva]

Rfdiva is radium98 but from another ip and another location cause on the mobile i dont have the password of radium to login.