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Right. In this circuit I think the jfet buffer amp is to provide the high load, is it not? But I did try to load the output with 1, 10 and 100k anyway but with no obvious difference. Right now there's no further circuit behind yet to load it.
Just a minute ago I found one possible cause or...
This is what I see. Hopefully the measurement makes sense and I didn't screw it up. Because the first harmonic is even a little bit stronger than the second I guess the selectivity of the tank circuit is somehow missing altogether. Furthermore it looks like the signal was very noisy too.
Thanks for all your answers guys! I wasn't aware of some things and now focused on E-designs input. I was able to replicate the simulation in LTspice very well but in the real world no way.
I built the exact circuit with the exception that I didn't have any J310 but J112 and no 180 Ohm but 200...
FFT is what I can use right now and sure enough the second harmonic is there about 8 dB below the first. However I may not have correctly understood the concept of a frequency multiplier. I thought the tank circuit's purpose was to select the second harmonic (in this case) over the others. Is...
Hi
The current task I have trouble with is building a bjt frequency doubler. Unfortunately I haven't been able to find a lot of practical hands-on design information but the circuit I built seems to be considered a working one in general. If someone knows a hands-on design guide somewhere...
Thanks for this input, I was able to observe a difference when using the resistor method; however 100k were too much so I used 10k.
In the meantime I have also changed my VCO topology for a fixed inductor/variable capacitor one so there may also be some coincidental differences from this.
Here...
Yes, I do and I'm basically aware that it can cause trouble but the alternatives are limited. Maybe you or someone else can suggest a better way? As long as it doesn't involve buying additional big-bucks equipment suggestions are certainly welcome ;-)
My scope does support active probes but so...
Maybe it was not practical to use said signal generator because the signal distorts badly at the input as I found out afterwards. This is probably an impedance mismatch effect but I didn't have a matching device at hand to find out. The signal (at the input) looked pretty similar to the output...
Good point, I actually hadn't paid much attention to this. To find out I did drive the mixer with a signal generator and I may in fact be overdriving it but this problem seems not to be primarily a result of it:
@ -30 dBm
@ -20 dBm
@ -10 dBm
At -20 dBm the output should be pretty clean if...
E-design, many thanks for your design, unfortunately I wasn't able to test it due to the lack of the necessary inductors. And you're certainly right that it's better to use off-the-shelf filters, however if this thing is to be used as a TX mixer (with no further mixing or multiplying behind)...
You're right, it is flapping in the breeze there, however they do it like that in every AN I saw and also in many more circuits using this chip I looked at. Therefore I'm not too sure whether this is really necessary or even recommended with this particular chip. When I quickly tried with a 1k5...
It seems that I finally got that bloody ripper working, using 2x 39p, a 2-20p trimmer and the 22k resistor proposed by E-design. I'm not completely sure what made the difference in the end though.
Now on to the next challenge, maybe I should open a new thread for this but I first ask right...
Finally it seems that these crystals are just crap for some reason. The new chip on a new pcb didn't change anything until I tried a 10.245 RX crystal and this one gave a result very much like E-design's. Unfortunately these are old stock crystals and I don't know their exact specs but they're...
Thanks to both of you for your new inputs!
E-design, thanks for trying this out and the additional tips, however I'm completely out of luck. Is my chip dead? I need to find out but I only have SMD ones and will also make a new pcb first at the same time. I'll let you know.
Well... there's not really much more around for fundamental mode crystal oscillators.
This is from the datasheet:
Fundamental crystal mode is not mentioned at all...
This is from the above mentioned document "NE602 primer":
I did try version B with the trimmer cap in series with the crystal...
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