A 28.8MHz RTL-SDR TCXO that's easy to build, and designed entirely from readily available and inexpensive components. Schematics and project files: www.analogzoo.c...
Instead of a band pass filter for 28 MHz, it is better to use the 28 MHz high pass filter, the output signal will have sharper edges, and higher harmonics are therefore an advantage - lower phase noise when gate detection within RTL2832.
You could just use a flexible small diameter teflon coax with a connector on the end to plug into your oscillator. That way you can put the circuit board back in its case and have the coax coming out of a small hole. Not so frankensteiney :)
Some of the single band Softrock RX only radios use the same Taloe mixer divider (not using one of the IQ channels) and 3rd harmonic filter approach. It keeps the kits simple and easy to alter 😊
You should have gone for the gold medal award and used a TNC connector instead of that dinky small BNC connector on your RTL-SDR. That BNC connector was such an overkill that it was hilarious.
Another way to come to the third harmonic is double and double the frequency, thats the fourth harmonic. After this subtract (mixing) the original frequency. Subtracting find place when you use a low pass or a bandpass filter.
Is there a way to keep the 28.8MHz harmonics out of the front end of a rtl-sdr? There is one right in the 2M band that is affects the reception of weak signals.
My first reaction was just like: 15m 01s - such a nice dongle ^^ 15m 10s - WHAT THE.... O_O Thank you for another really good video showing something unusual and new! Also, could you tell us what do you plan to use your RTL-SDR for? I've heard of it some years ago in some article about GNU Radio, but that's all I remember.
+Michal “Dreit” Kundrát Haha, yeah, the BNC looks a bit like a growth on the back of the PCB. Useful for testing though! :) I don't have any specific plans for the RTL-SDR at the moment, but I think it will be a nice tool to have in the lab for signal analysis and processing. It even covers some frequencies my spectrum analyzer doesn't.
devttys0 But still not that bad. I've seen much worse things in circuits produced in bigger series (hundreds pieces per year). I can remember to circuit with PIC, there was bridge of two resistors to somewhere and from same pin there was also connected capacitor to totally different place. And they were producing it with this design for many years and are still producing it O.O edit: Of course with all components at one place. Some resistors were lying on side, capacitor was on resistor under it,...really really bad design, of course unable to make on pick and place machines. I see. Well, then, good luck with it and other projects in future ;)
I'm a bit confused about your filter. You say it's a third-order Butterworth bandpass filter, but everywhere I've looked shows a different topology for that filter--usually similar to one of the two shown here: www.changpuak.ch/electronics/butterworth_bandpass.php In addition to the fact that yours has more shunt/series stages than the one above, I notice that the series stages on your filter are capacitors only. It almost looks like you've taken a seventh-order highpass Butterworth filter and added resonant capacitors to the shunts. I haven't been able to find any references that show a design similar to this for a bandpass filter. I wonder if you can shed some light on this for me--I'm just learning about filter design, so I'd love any clarification you can offer. Thanks!
+Michael Cooper This configuration is often called a direct coupled filter, top-C coupled filter, or a triple-tuned filter (or, if there were two resonant tank circuits, a double-tuned filter, etc). It's just multiple tank circuits connected via coupling capacitors; the actual component values are determined by the type of filter response you want. This filter was designed to provide a Butterworth response, but others are possible (Chebychev, for example). www.changpuak.ch/electronics/Direct-Coupled-Resonator-Bandpass.php
Hi Shaker M. What happens here is that harmonics are created when there is any "non linear" response in the semiconductors. The shape of the sine is changed. In fact, diodes (switches) are very non linear, so the output spectrum is no longer the fundamental freq, but now the fundanental + harmonics.
