Hello homebrewers,
I am building a universal receiver kit from partsandkits.com for the 40m band. I followed the sequence in your Chuck's excellent video series - started from the audio amp and up from there. At this point, I have the VFO soldered up. I can hear the distinct narrow band CW sound. However I can't hear any stations when I hook up an antenna. I have a Elecraft XG1 50uV signal generator that generates a tone at 7040. But no, I can't hear that too.
So, I acquired a frequency counter from aliexpress. PIC based with a good LCD display, meant for rig displays I guess, but I am using it as a measurement tool.. The VFO is generated out of the SA602AN's pin 6 and 7 in a colpitts configuration. On the website, I couldn't find any values for the actual VFO output or the inductance, but I calculated the frequency as follows.
Center frequency of the crystal filter is 5067400 Hz. We would want our input RF to be shifted down to this intermediate frequency by the VFO. Input RF is from 7006000 to 7079000.
So, VFO range should be from 7006000 - 5067400 = 1938600 to 7079000 - 5067400 = 2011600.
When I look at the VFO output, with the potentiometer from one end to another, it is going from 1929000 to 2000000. So, the input RF I am tuning is 5067400 + 1929000 = 6996400 to 5067400 + 2000000 = 7067400. 7040000 falls well within this band, but it didn't appear when I tuned the VFO. I am unable to explain why that is the case.
I found a couple of wrongly soldered capacitor values around the VFO, but I think those are not too important ones. From my reading of the circuit, C6 and C8 and L2 are the ones that determine the VFO frequency. I am guessing that the variation in my VFO frequency is because of the inductance difference, probably because of the way I wired up the toroid. The one I have wrongly soldered are these:
Wrongly populated C9 with 180pf.
C10 is not populated.
C11 has a 470pf one instead of 180pf.
I will fix these and check again.
Universal Receiver circuit: <>
Has anyone else tried this little receiver? I really liked the simplicity of the receiver and want to figure out what is going on, but I don't have an oscilloscope or any other fancy test equipment. Any help/ideas/directions appreciated.
73
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Ramakrishnan VU3RDD
Ramakrishnan Muthukrishnan (VU3RDD)