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sa612 mixer help please

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matbymay

New Member
hi everbody

i have sa612 mixer and oscillator IC. i would like to mix two signal one is 19mhz another is 20mhz and output will be 39mhz and 1mhz (f1+f2, f1-f2) with theory. but i m not sure how can mix them using sa612.

thank you
regards
 

matbymay

New Member
thank you for answers
but i have read the datasheet i used crystal oscillator tuned (20 mhz)circuit pin 6-7 actually working fine but when i connect to input pin 1-2 (for example 1 Mhz) it dosent give any output
i tried short cut to pin 1 and pin 2 and connected input both aswell but same result

any ideas where i was wrong?
 

RadioRon

Well-Known Member
Some possible faults include:

- you must provide DC blocking capacitors on the input and output so that you don't upset the bias inside the IC
- output impedance is fairly high, so if you try to measure output with a 50 ohm meter or instrument, you would likely lose most of the output signal and it may then not be measurable. Use a high impedance meter, or an impedance buffer or matching circuit of some sort.
- this is a high frequency circuit, so you must construct it on pcb, using good RF practice like for example, keeping connections short. It cannot be constructed on solderless plugboard.

- the simplest input circuit is shown in the Philips data sheet, Figure 5c. this should work ok for you. The simplest output circuit would be to ac couple from pin 5 to an impedance buffer amp, or to a matching circuit or RF transformer. See Figure 6 for ideas.
 

joelby

New Member
I'm trying to do the same sort of thing with a SA602A at 150MHz and am having similar problems to the original poster. The oscillator is working and I can see the transmission from my signal generator at the IC's input pins (I used a tapped inductor and a capacitor) but I don't get anything at the output.

I've connected a spectrum analyser directly to the two output pins, attached a JFET buffer circuit in an attempt to match the 1.5K output impedance to the SA's 50 ohm input, and tried an arrangement of resistors and two capacitors suggested in many SA602A direct conversion audio receivers, with a corresponding change in the LO frequency.

The goal will be to connect it to an ADC, but I was hoping that I'd be able to use the spectrum analyser to see the mixer products before I do that. Can anyone think of any problems with my approach? The circuit my receiver is based on is detailed here, though I've substituted a potentiometer for the PLL at this stage and don't want to demodulate FM signals.

Thanks, and sorry if this is a thread hijack!
 

mvs sarma

Well-Known Member
I don't think the way BF990A is coupled is correct, a capacitor coupling, without a gate termination.
where did you get the firmware of 16F84A from?
i fear Passgen did not release it !!!
 
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joelby

New Member
The oscillator buffer seems to work as described, but it doesn't matter for the purpose of the exercise as I'm not using the PLL or 16F84A - just adjusting Vtune manually with a potentiometer.

The author of the page states that the PIC firmware is available upon request. Other pages have hex files for almost identical PLL-controlled oscillators. Setting registers in a PLL is much easier (for me) than designing a working RF front-end! :)
 
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