If you look at Fig4 from the datasheet : http://www.analog-innovations.com/SED/MC1648-DataSheet.pdf

you can use a variable (linearly a saw-tooth) waveform with amplitude ranging from 2 to 7 V at vin and you may obtain the chirped signal at output!

Best of luck!

The MC1648 requires an external parallel tank circuit consisting of the inductor (L) and capacitor (C). For Maximum Performance QL 100 at Frequency of Operation. A varactor Diode may be incorporated into the tank circuit to provide a voltage variable input for the Oscillator (VCO). The MC1648 was designed for use in the Motorola PhaseLocked Loop shown in Figure 9. This device may also be used in many other applications requiring a fixed or variable frequency Clock source of high spectral purity. (See Figure 2) The MC1648 may be operated from a +5.0Vdc supply or a 5.2Vdc supply, depending upon system requirements

If Chirp is the requirement, have you given thought to use a DDS chip to get what you want? There are good chips from Analog Devices which should help you to solve your problem.

Mircea pop : i use XR2206 for generate ramp/triangle signal for input to Mc1648. but until now the chirp signal cannot came out. so confuse. haha

Prasanna waichal : yes, but i have to use vco for generate chirp. and i use IC MC1648 for solve this but now i have a problem when i input the triangle signal for this VCO the chirp signal cannot come out

I think, a triangular wave may not be suitable. Better try RAMP, a positive ramp to generate the Chirp. Please send me your circuit and setup details at "[email protected]" so that I can give you more inputs. Thanks and best Luck!

oke. email sent

are you workink on breadboard? does it oscilate when you apply 2V at input?

i'm working in projectboard. when i input 2 volt dc power supply (not triangle signal) the frequency is change. before input voltage 2 volt the frequency 10 Mhz. after i input 2 volt the frequency be 13 Mhz

Then, can you make the chirp manually by increasing the voltage at the input. Can you check the concordance of the output frequency dependence on the input voltage as Fig. 6 shows? Can you supply the sawtooth waveform from a dedicated instrument (signal generator for laboratory use)?

Hello Friends,

@ Mircea - I had suggested the same steps to check whether the individual circuits are working or not. Let the author conduct these tests and come up with the results. Or I believe that these tests themselves will reveal what's wrong and where.

I will tell you simple tests so that I also understand what is happening there.

Step 1:

1) Test your MC1648 circuit in normal mode without any external input from XR2206.

2) Tell me if you input a DC voltage from say 0-5VDC to the varactor diode input then what is the output you are getting? I mean the waveform (hopefully sine) and the frequency range – minimum to maximum.

3) Next, try to increase this input voltage range from 0-10VDC and see what is the output frequency range you are getting.

4) Tabulate your results and send to me.

Step 2:

1) With the XR2206 circuit running in stand-alone mode see the tri-wave rate, i.e. the frequency and the voltage swing as minimum and maximum level.

2) Then try to use an op-amp based buffer/voltage follower to connect the output from XR2206 to the input of MC1648 circuit.

3) Send the result after testing this.

As I have stated in RG response, a tri-wave would generate your chirp but in low-increase-high-decrease-low fashion. A forward or positive ramp will produce low-increase-high-low-increase-high fashion.

Tri wave input - /\/\/\/\

Ramp input - /|/|/|/|

Step 3:

1) After looking at your schematic, I have another suggestion which I shall tell you after receiving the above results.

Thanks and best wishes!

Where can I find Motorola Brochure BR504/D, Electronic Tuning Address Systems, (ETAS)?

I'm trying to build a Variable Frequency Oscillator with the MC1648 for an 80 meter transceiver VFO.

I need to find the mentioned brochure in the datasheet for more on applications.