N3zi kits general coverage receiver
The PCB for the single band kit is the same as the 2 band kit, so it is a simple matter to buy a few extra parts, all readily avaaible from sources like Mouser and Digikey, to expand your single band kit into a 2 band RX.
These kits are for EXPERIENCED kit builders. High pass filter explained Although the kit is relatively easy to build, calibration and operation requires knowledge of Superheterodyne recevier theory, SSB communications theory and Crystal Filters, amoung other things. High pass filter symbol The manual is written for advanced users, not beginners.
Ever since I got my first DDS running late in 2008, I connected it to my ARRL home-brew challenge radio. High pass filter derivation And soon discovered that this receiver became a wide range general coverage receiver, albeit with limitations. Capacitor high pass filter Although designed just for 7MHz, I was able to receive WWV on 2.5, 5 and 10MHz. High band pass filter Shortwave broadcasters on 6MHz, 7MHz, and 9MHz bands, and even the AM broadcast band. A high pass filter This is with no modifications to the radio, just the replacement of the VFO with a DDS-VFO.
So I decided to tweak the design for better performance, and low cost, with the hooks to add additional features. High pass filter bode plot After several prototypes, and much design calculation and redesign, I ended up with a rather elegant but simple radio.
I have an IF of 11.0592 MHz (this is a common frequency for microprocessor crystals, thus they are readily available at low cost) I wanted to use high side VFO injection. Uses of high pass filter For those who do not know, with an 11MHz IF, you can use a VFO at 4MHz or 18MHz to get to 7MHz. High pass filter theory The difference being that with a 4MHz VFO there will be an image at 15MHz, but with the 18MHz VFO the image is at 29MHz, which makes it much easier to filter out. Rc high pass filter calculator So with an 11MHz IF, you would need a DDS that works up to 22MHz to receive anything from DC to 11MHz. High pass passive filter Its pretty easy to push my 20MHz DDS to 22MHz, and still keep the supurouis response down though the combined attenuation of the DDS filter and the receive input filter. Frequency response high pass filter For the higher bands, 14MHz through 30MHz, I decided to compromise with low side injection. High pass filter code A fairly decent filter is needed.
The beauty of this approach is that no USB LSB switch is really needed. What is low pass filter and high pass filter If the IF is designed with a USB BFO, then the high side injection inverts the spectrum, giving you LSB reception below 11MHz. High pass filter noise On 14MHz and above the spectrum is not inverted, and it operates as a USB receiver. What does high pass filter mean This does leave the issue of 60Meters which is a USB band per FCC rules. High pass filter on vocals Also the Canadian time station, CHU Canada uses a weird USB with carrier injected transmission mode on 7MHz. High pass filter c However, it turns out that the crystal I am using are easily pullable by ~2.5 KHz to accommodate USB/LSB selection for those who demand perfection. High pass filter online I’m not going to ship the radios that way, but I will accommodate it. Rc circuit high pass filter You can also switch to low side VFO injection for 60M with some compromise in image rejection.
I did incur a problem with overload from AM broadcasters on certain frequencies. Difference between high pass and low pass filter I designed a simple high pass filter that solved the problem. High pass filter laplace It’s a simple circuit consisting of two 1000pf Caps in series, and a 1.5uH inductor from the center to ground. Butterworth high pass filter theory I will not be including this in the kits, but its fairly easy to add if you see overload.
There is no AGC in the design right now. High pass filter working I considered a simple audio based one used in my HBC receiver, and I may include it at a later date. High pass filter noise reduction But an IF or RF based AGC system would be better. Active high pass filter transfer function But the radio is perfectly usable without one.
There is only one torrid to wind, used as a broad band input matching transformer. High pass low pass filter Not very critical. High power low pass filter All of the other inductors are commerical inductors.
The audio chain is a simple as it gets. High pass filter photoshop download Rather than use a de rigeur LM386, I opted for a single transistor class A audio amplifier that’s uses less than a dimes worth of parts. What does high pass filter do Audio output is not huge, about 1V p-p into 1K ohms. Low pass and high pass filter transfer function I recommend an old pair of computer speakers with volume control, but It will also drive headphones or an 8 ohm speaker. High low pass filter It requires that you use a well filtered power source, any AC ripple on your 12 v power line will be audible in the output.
The standard PCB has space for two input filters switched by a relay. Op amp high pass filter One filter is a 0 to 11MHz low pass, the other is a 14 and up high pass filter. High pass filter amplifier The DDS firmware will automatically select the appropriate filter dependng on what frequency you are tuning to. 2nd order high pass filter transfer function Yes it will work betwwen 11 and 14 MHz but the sensitivity and image rejection will degraded.