im getting a signal on 1640 where i want it, but theres a stronger spur present on 1240. unsure of what i can do to clean that up. hopefully my chips aren't junk.
I have seen a similar problem with a PLL circuit which is very similar to the $12 design. Viewing the transmitter output on a spectrum plot on a scope showed a strong signal about half the frequency of operation. A careful examination of the divided down reference frequency and the divided down output frequency waveforms showed a lot of phase jitter between the two. The loop response appeared to be too slow.
Try removing the .01 uF cap from the 14046 IC pin 9 to ground. My circuit is a bit different but this fixed the problem I had.
I used the 74HC series of these chips. My loop filter component values are different so I don't know for sure if this fix will work.
Neil
cool, i'll give it a whirl. that may be my problem with the SStran circuit that i got too. thanks! i think it's time to bring the anklebiter into the modern age since i'm clean out of fundemental crystals
no dice. this just brought the spur down to 1210
Too bad you don't have a spectrum analyzer so you could see what is going on.
yeah, poh boy over here. prob should mess with that area im thinkin
Just one question radiodirtysprings1700: Where did you get that signal 400 kHz below?? Is it on your receiver, and if it is, what is the MF of your receiver??
Rob V.
on the output of the PLL unit. hooked to a freq counter, it reads that too, so apparently it's way stronger than the signal on 1640
I don't understand how you can read two frequencies at once with a frequency counter. Could you describe your test setup and what you observe in more detail? I am thinking that this may be a counter artifact or you are overloading the counter input.
You could try bringing an AM radio close to the circuit ant checking if the radio can hear the signals at various frequencies.
Neil
the freq counter is reading 1.240, but there is a signal present on 1640
But how do you read that 1640 kHz as your counter reading is 1240 kHz??? You can't read two frequenties at once with one counter. So tell us how you messure that 1640 kHz??
Rob V.
it was present on a radio in the room, audibly weaker than the spur on 1240
What I think is that your counter is right, so 1640 khz is a spur wich is probably a mix in your receiver (1240 kHz + 400 kHz MF). So check out your PLLif it's really on 1640 kHz.
Rob V.
i re-checked the switch settings, def set to 1640. this is weird
It is possible that your counter input is being overloaded. I suggest using a voltage divider to bring the output voltage down to less than a volt.
Failing that, the next best thing is to use an oscilloscope to check the circuit waveforms. If you don't have a scope then use a DVM on the DC volt scale and measure the output voltage. It should be half the supply voltage. If the circuit is misfiring then this will not be the case. If it is about half this doesn't mean everything is OK but if it is not then there is a problem.
Neil