Freq Generator

bigkim100

Apr 17, 2013
265
Ok, Im driving myself crazy trying this, and this is a general statement on my inability to design this...please help!
I have frequency generator that i am using to drive whatever this component is called....so my question is...what the hell is this device (supplied in pics) that Im starting to see in AM/FM Radios. it is being used as a tuner instead if a Good old Variable capacitor. Is it a shaft encoder,, an endless variable resistor (it is marked 100K after all)????. Schematics for this unit are unavailable (Surprise!!!)
That being said, I am driving it with a frequency generator (22056 or 555) on the middle pin, in sine wave mode, but while it works, and works well, it seems easily overdrive the circuit.

Is there a way to lower the output of the frequency generator?????

Thanks in advance for any help

"I only know enough to get myself into trouble"*

PPS I have attempted to upload pics from my phone, and they will not load for some strange reason

*=My Dad (T.M., R. us pat office, as seen on Bugs Bunny)

Last edited:

Harald Kapp

Moderator
Moderator
Nov 17, 2011
12,778
they will not load for some strange reason
resize to < 300 kB/picture.

bigkim100

Apr 17, 2013
265
Thank you Harald, I appreciate that, now I have to figure out how to lower my resolution on my camera

73's de Edd

Aug 21, 2015
3,437
what the hell is this device (supplied in pics) that Im starting to see in AM/FM Radios

FAR BETTER . . . . that you could have given an applicable model number of radio so that its circuitry could have then been analyzed.
INSTEAD . . . i'm going to have to say that you have run into the 1st GENERATION of the abandonment of the all to familiar multi gang variable air tuning condenser.
They are using a voltage variable, adjustable, semiconductor junction, which they cal a varicap or varactor diode.
Put a variable voltage to its junction and its capacitance varies . . couple it into your inductor thru a HIGH value capacitance like a 0.01 or .0.1 cap ( so that variable voltage doesn't get shorted out by the "dead short" of the coils SHUNTING inductance) and then, you have yourself a . . .voltage controlled . . . variable capacitance + the fixed inductance = tuned circuit.

Replicate it with another varactor diode in the local oscillator of the mixer section, and operate it at a specific reduced voltage / higher frequency operation (~455 khz above received frequency).
Then you have a voltage controlled front end tuning section of an AM band superheterodyne receiver.

????? the 100 k marking ?????????? is a variable pot that voltage divides down to provide that variable tuning voltage to the two separate . . . . .varactor tuned circuits.
SO ITS A 100K VARIABLE POT !

73's de Edd . . . . . .

It seems . . . . . the faster the plane, the narrower the seats.

.

bigkim100

Apr 17, 2013
265
what the hell is this device (supplied in pics) that Im starting to see in AM/FM Radios

FAR BETTER . . . . that you could have given an applicable model number of radio so that its circuitry could have then been analyzed.
INSTEAD . . . i'm going to have to say that you have run into the 1st GENERATION of the abandonment of the all to familiar multi gang variable air tuning condenser.
They are using a voltage variable, adjustable, semiconductor junction, which they cal a varicap or varactor diode.
Put a variable voltage to its junction and its capacitance varies . . couple it into your inductor thru a HIGH value capacitance like a 0.01 or .0.1 cap ( so that variable voltage doesn't get shorted out by the "dead short" of the coils SHUNTING inductance) and then, you have yourself a . . .voltage controlled . . . variable capacitance + the fixed inductance = tuned circuit.

Replicate it with another varactor diode in the local oscillator of the mixer section, and operate it at a specific reduced voltage / higher frequency operation (~455 khz above received frequency).
Then you have a voltage controlled front end tuning section of an AM band superheterodyne receiver.

????? the 100 k marking ?????????? is a variable pot that voltage divides down to provide that variable tuning voltage to the two separate . . . . .varactor tuned circuits.
SO ITS A 100K VARIABLE POT !

73's de Edd . . . . . .

It seems . . . . . the faster the plane, the narrower the seats.

.

bigkim100

Apr 17, 2013
265
These radios are am fm sw, and all the components are in the master chip rather than on the board, which makes pplaying with tuning only available at the middle pin of the tuning pot.

73's de Edd

Aug 21, 2015
3,437
THEY WERE BEING ONE HELL OF A MECHANICAL COMPLEXITY . . . . . . . . .compared to the varactor diodes . . .1N4148's comparative physical footprint profile.

73's de Edd

Aug 21, 2015
3,437
These radios are am fm sw
Still would need a brand / model / schematic to fully analyze . . . as you are now talking 2nd GENERATION design.

kellys_eye

Jun 25, 2010
5,145
Those radios also use a fixed voltage divider (long chain of resistors) to set the band of operation as well as a variable resistance to deliver a tuning voltage. There are many, many examples of this type of receiver these days.

The tuning resistor (variable) is often connected to the tuning indicator (tuning dial) via a cord and some wheels (that the cord runs through) to move the dial pointer. The tuning resistor should NOT rotate past 0-270 degrees (or thereabouts) and if yours does then it has been forced past its limits. This doesn't always damage them but means you can't determine the end points of movement thus rendering it impractical for setting levels.

Practically 'any' potentiometer can be used to create a voltage divider (reducer) and these are found in may older electronic items or even new for a few $- many experimenters will have a box of assorted values and I myself have a junk box containing 50+ assorted devices. You could persist with your defective potentiometer however if we knew the actual application we could suggest one that better matches your requirements. bertus Moderator Nov 8, 2019 2,734 Hello, now I have to figure out how to lower my resolution on my camera You can resize the pictures using a paint program on your computer. Also some photo editor programs will allow you to resize. My paint program has a tool like this: Bertus Harald Kapp Moderator Moderator Nov 17, 2011 12,778 Is it a shaft encoder,, an endless variable resistor (it is marked 100K after all)????. Probably not a potentiometer. Potentiometersa aren't "endless". More likely a rotary encoder that delivers a digital signal to the tuning circuit on the chip. bigkim100 Apr 17, 2013 265 Probably not a potentiometer. Potentiometersa aren't "endless". More likely a rotary encoder that delivers a digital signal to the tuning circuit on the chip. What confused me sir, is that it does have a resistance printed on it like a pot Harald Kapp Moderator Moderator Nov 17, 2011 12,778 Take it out of the circuit and measure, then you'll know what it is bigkim100 Apr 17, 2013 265 Hello, You can resize the pictures using a paint program on your computer. Also some photo editor programs will allow you to resize. My paint program has a tool like this: View attachment 55419 Bertus Thank you for this. My son also suggested a posting to a hosting forum, which I shall also try bigkim100 Apr 17, 2013 265 Take it out of the circuit and measure, then you'll know what it is Once I am done with this, I shall actually open one up, and take pictures of its innards. This tests like a pot. on my VOM. Those radios also use a fixed voltage divider (long chain of resistors) to set the band of operation as well as a variable resistance to deliver a tuning voltage. There are many, many examples of this type of receiver these days. The tuning resistor (variable) is often connected to the tuning indicator (tuning dial) via a cord and some wheels (that the cord runs through) to move the dial pointer. The tuning resistor should NOT rotate past 0-270 degrees (or thereabouts) and if yours does then it has been forced past its limits. This doesn't always damage them but means you can't determine the end points of movement thus rendering it impractical for setting levels. Practically 'any' potentiometer can be used to create a voltage divider (reducer) and these are found in may older electronic items or even new for a few$ - many experimenters will have a box of assorted values and I myself have a junk box containing 50+ assorted devices.

You could persist with your defective potentiometer however if we knew the actual application we could suggest one that better matches your requirements.
This one does rotate almost 360 degrees, and all the ones that use this tuning, on all these radios.... as I have used many brands, do

bigkim100

Apr 17, 2013
265
The radios are also void of all those pesky tuning slugs in cans, that we are so used to seeing in radios of this ilk.

Moderator
Nov 17, 2011
12,778

Apr 17, 2013
265

Moderator
Nov 17, 2011
12,778

hevans1944

Hop - AC8NS
Jun 21, 2012
4,762
The radios are also void of all those pesky tuning slugs in cans, that we are so used to seeing in radios of this ilk.
Sounds like this is an SDR or Software Defined Radio since all the "majic" happens inside a single chip. These are a lot easier to produce since they do not need or use those pesky RF transformers with the tuning slugs. I happen to own such a beast for my amateur radio hobby. It uses a rotary encoder to select the transmitter/receiver operating frequency. Maybe yours does too?

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