Variable Freq Oscillator

**forever99482** · 12th December 2007 11:39 PM

Hi, I've got a question about the circuit below

As it is using a TCA440, the oscillator and mixer is actually in it, and I cannot test to see the output from the Variable Freq Oscillator(kank3333r part), any ideas of how I could test to see the output of the VFO is correct?

By the way, can anyone find the datasheet of kank3333r?? I googled it and can't seem to find the datasheet of it.

Thanks in advance

**on1aag** · 13th December 2007 01:17 AM

Hi Forever99482,

You can try to measure at pin 5 of the TCA440.

Data for the BKANK3333R :

between pins 1 and 2 14 turns
between pins 2 and 3 41 turns
between pins 1 and 3 55 turns
between pins 4 and 6 14 turns, pin 5 is not connected !

Inductance 45 µH, Q = 60 probably measured between pins 1 and 3.

on1aag.

**forever99482** · 13th December 2007 11:40 AM

Originally Posted by on1aag

pin 5 is not connected !
on1aag.

pin 5(toko) is not connected?? but the circuit shows that it is connected to pin 5 of tca440. Please explain a bit more, I might be confused.

some more questions,
1. what frequency should I be looking at before the input to the lm386 (pin 3)?
2. What frequency should I be expecting on the mixer output of tca440, as I'm seeing frequency as high as 100MHz.....

Thank you

**Leftyretro** · 13th December 2007 02:53 PM

Originally Posted by forever99482

pin 5(toko) is not connected?? but the circuit shows that it is connected to pin 5 of tca440. Please explain a bit more, I might be confused.

some more questions,
1. what frequency should I be looking at before the input to the lm386 (pin 3)?
2. What frequency should I be expecting on the mixer output of tca440, as I'm seeing frequency as high as 100MHz.....

Thank you

1. Audio frequencies only, as this is after the signal has been detected and filtered by the detector diodes, for AM audio modulation content only.

2. 455khz that then feeds to the ceramic IF 455khz filter to remove any other mixer products.

Your local osillator will have to cover a 3.045 to 3.545mhz range to convert the 3.5-4mhz ham 80 meter band to the 455khz IF frequency of this design.

Lefty

**forever99482** · 13th December 2007 03:10 PM

As I'm not inputing any RF signals to it, so shouldn't the mixer output be around 3.5MHz? Unless my VFO is not working correctly....

**Leftyretro** · 13th December 2007 03:24 PM

Originally Posted by forever99482

As I'm not inputing any RF signals to it, so shouldn't the mixer output be around 3.5MHz? Unless my VFO is not working correctly....

Most mixer designs use a balanced mixer that only outputs the sum or difference between RF and LO. If no RF or no LO then there would be no mixer output at all. You can normally not troubleshoot mixer problems easily without a spectrum analyzer.

Lefty

**on1aag** · 13th December 2007 03:48 PM

Hi Forever99482,

The pin 5 mystery is only a typo that probably sneeked in because
pin 6 of the KANK3333R is connected to pin 5 of the TCA440.
As with most Toko 10K coils pin 5 is missing, so it can't be connected
to pin 5 ! The general rule is if it isn't necessary pin 5 is always
missing, the same goes for KANK3334R, KANK3335R and a lot of other
Toko coils.

on1aag.

**forever99482** · 15th December 2007 11:30 AM

about the trimmer cap in the VFO part, is it used for impedance matching with the toko?

What frequency should I be looking at for pin4,5 and 6 of TCA440 with an AM modulated sinewave of 3.5MHz fed in to pin1/2 of the TCA440

**on1aag** · 15th December 2007 02:33 PM

Hi Forever99482,

The trimmer cap C11 is used to set the frequency of the local oscillator
that it will cover the 80 m band.
It has nothing to do with impedance matching.
The signal measured at pins 4,5 and 6 will always be the oscillator
frequency no matter what signal you apply to the inputs of the TCA440.
I've checked the internal circuitry of the TCA440 and pins 4 and 5 are
differential inputs, pin 6 is the open collector output of the oscillator.
Try to measure the signal at pin 6 of the TCA440.
Make sure you haven't mixed up the connections of the KANK3333R,
I measure 0,7

hm: between pins 1 and 2
and 1,9

hm: between pins 2 and 3 which seems to agree with
the schematic.
The Toko catalogue doesn't give a specific footprint for the KANK3333R
but from what I can measure I think that the pins are numbered like
integrated circuits.

on1aag.

**electrocompo** · 19th December 2007 07:16 PM

Hello,
Can anybody please help me out with oscillator configuration of the tca440.
the internal oscillator circuit can be controlled by pin 4 5 and 6. my questions are

1) how do you control the frequency of the signal produced by this internal oscillator by using this three pins?

2) am i suppose to build a whole new oscillator circuit to control the internal one?

3) how do i build an oscillator circuit that controls another oscillator circuit?

Thanking you i advance

**Nigel Goodwin** · 19th December 2007 08:42 PM

Originally Posted by electrocompo

Hello,
Can anybody please help me out with oscillator configuration of the tca440.
the internal oscillator circuit can be controlled by pin 4 5 and 6. my questions are

1) how do you control the frequency of the signal produced by this internal oscillator by using this three pins?

2) am i suppose to build a whole new oscillator circuit to control the internal one?

3) how do i build an oscillator circuit that controls another oscillator circuit?

Thanking you i advance

You use a tuned circuit to set the frequency, like almost every RF oscillator there is - it's clearly shown on the diagram above.

**electrocompo** · 19th December 2007 11:37 PM

Thanks for the reply!

the oscillator circuit above is just too confusing (I'm kind of new to this.. ).

So there are many kinds of RF oscillator that I can use with the tca440?
Arent RF oscillator meant to be connected to the mixer directly... I mean if it is an RF oscillator and we are connecting it to another oscillator (the internal one) then its like two oscillator connected together? does that make sense?

I really need help with this topic

**on1aag** · 20th December 2007 12:13 AM

Hi Electrocompo,

Originally Posted by electrocompo

So there are many kinds of RF oscillator that I can use with the tca440?
Arent RF oscillator meant to be connected to the mixer directly... I mean if it is an RF oscillator and we are connecting it to another oscillator (the internal one) then its like two oscillator connected together? does that make sense?

I really need help with this topic

The TCA440 is a single chip single conversion AM receiver.
All active components are inside the chip and the oscillator
is allready connected to the mixer. Only the frequency dependant
components are external.

http://www.alldatasheet.com/view.jsp?Searchword=TCA440

on1aag.

**Nigel Goodwin** · 20th December 2007 09:43 AM

Originally Posted by electrocompo

So there are many kinds of RF oscillator that I can use with the tca440?
Arent RF oscillator meant to be connected to the mixer directly... I mean if it is an RF oscillator and we are connecting it to another oscillator (the internal one) then its like two oscillator connected together? does that make sense?

Like on1aag says, there's only one oscillator circuit there, with the active part inside the chip, and the LC tuning part outside the chip - two halves make a whole.

You're making it far more complicated than it is!.

**mvs sarma** · 24th December 2007 10:30 AM

Originally Posted by forever99482

pin 5(toko) is not connected?? but the circuit shows that it is connected to pin 5 of tca440. Please explain a bit more, I might be confused.

some more questions,
1. what frequency should I be looking at before the input to the lm386 (pin 3)?
2. What frequency should I be expecting on the mixer output of tca440, as I'm seeing frequency as high as 100MHz.....

Thank you

Hi Forever99482,

where did you get the TCA440 in Malaysia and at what price-- as I need few pieces for a friend in Malaysia. plse try to give shot contact if you had purchase recently sir

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