N3ZI Kits


General Coverage, DDS Controlled
Communications Receiver

Digital Dial

This kit is discontinued and sold out

$39.99, Dual Band GCRX Kit 0.1-11 & 14-30MHz
(Works betwwen 11 and 14 MHz but with reduced sensitivity and image rejection)

Kit includes the bare PC, plus all parts needed for the 2 band receiver
Includes input LPF and HPF, Crystal filter with 2 (input and output) IF amplifiers
Connectors shown in photo (Input, Power, Audio) Included
Dual Band version sold out

VFO not included, but is required for operation.

Also Available Single Band kit, covers 0.1 to 11MHz

$29.99 Single Band Kit
The 1 band kit Does not include the relay or the second IF amp, you will need to jumper around them
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. 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. The manual is written for advanced users, not beginners.

14070 Fixed Frequency version, for PSK31, no VFO required. SOLLD OUT

Complete Fixed Frequency Receiver KIT for PSK31 on 14070 Receives 14070 through 14073, in LSB mode
Excellent receiver sensitivity. Requires 12VDC power, and an Antenna. There is a 3.5mm Audio output you can connect to your computer.

Note: This photo is an older version, the version you will receive includes
an additional IF amplifier stage in the upper left hand corner of the PCB

Also Availble 14100 Fixed Frequency version, for DX Beacons.

$35.00 Via Paypal, either frequency

Note: The Crystal filter is rather wide for the PSK31 version ~3KHz, and narrow, ~500Hz for the DX Beacons version.


DDS-VFO kit can be purchased from this page
History and specifications

Excellent Receiver Sensitivity,
Excellent Image and Spur Rejection
2.5KHz Crystal Filter, receives CW, LSB, USB, AM

To make a complete general coverage receiver, you will need 3 boards, a DDS VFO Kit, LCD Display, and a Receiver kit (GCRX)

The design is relatively straightforward.  It's a SA612 type superheterodybe design with a 11.0592MHz IF. The VFO is my existing DDS-VFO with 0 to 22MHz range thus allowing hi side injection for superior image rejection up to 11MHz. The BFO is placed on the low side, and accounting for spectrum inversion from hi side injection results in LSB reception. The BFO can be moved, or Low side injection can be used when USB is needed (e.g. 60Meters) AM reception is achieved by zero beating the AM signal, given the extreme stability of the DDS, and similar stability of modern S/W broadcasters, this results in highly satisfactory voice reception. The radio covers the standard AM broadcast band and works well there for reception of voice and talk, however music will sound poor because of the narrow xtal filter and the slight carrier offset.

Complete assembled prototype shown with DDS, Above

Another View, Below
See frequency control (rotary controller) and band switches on back of DDS board

Ever since I got my first DDS running late in 2008, I connected it to my ARRL home-brew challenge radio. And soon discovered that this receiver became a wide range general coverage receiver, albeit with limitations. Although designed just for 7MHz, I was able to receive WWV on 2.5, 5 and 10MHz. Shortwave broadcasters on 6MHz, 7MHz, and 9MHz bands, and even the AM broadcast band. 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. 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. For those who do not know, with an 11MHz IF, you can use a VFO at 4MHz or 18MHz to get to 7MHz. 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. So with an 11MHz IF, you would need a DDS that works up to 22MHz to receive anything from DC to 11MHz. 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. For the higher bands, 14MHz through 30MHz, I decided to compromise with low side injection. A fairly decent filter is needed.

The beauty of this approach is that no USB LSB switch is really needed. If the IF is designed with a USB BFO, then the high side injection inverts the spectrum, giving you LSB reception below 11MHz. On 14MHz and above the spectrum is not inverted, and it operates as a USB receiver. This does leave the issue of 60Meters which is a USB band per FCC rules. Also the Canadian time station, CHU Canada uses a weird USB with carrier injected transmission mode on 7MHz. 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. I'm not going to ship the radios that way, but I will accommodate it. 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. I designed a simple high pass filter that solved the problem. It's a simple circuit consisting of two 1000pf Caps in series, and a 1.5uH inductor from the center to ground. 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. I considered a simple audio based one used in my HBC receiver, and I may include it at a later date. But an IF or RF based AGC system would be better. But the radio is perfectly usable without one.

There is only one torrid to wind, used as a broad band input matching transformer. Not very critical. All of the other inductors are commerical inductors.

The audio chain is a simple as it gets. 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. Audio output is not huge, about 1V p-p into 1K ohms. I recommend an old pair of computer speakers with volume control, but It will also drive headphones or an 8 ohm speaker. 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. One filter is a 0 to 11MHz low pass, the other is a 14 and up high pass filter. The DDS firmware will automatically select the appropriate filter dependng on what frequency you are tuning to. Yes it will work betwwen 11 and 14 MHz but the sensitivity and image rejection will degraded.

Preliminary Specifications: Supply voltage: 10 to 15 VDC
Current drain: 55 mA max
Frequency Coverage: 100KHz to 11MHz, 14MHz to 32MHz
Frequency control: State of the art DDS, Continuous coverage in 1Hz steps
Display: 12-digit LCD
Receiver Sensitivity: Approx. 0.2 μV for 10 dB (S+N)/N
I.F. 11.057 MHz, single conversion
Selectivity 4-pole crystal filter, approx. 2500 Hz
Audio output:  Powered computer speakers recommended, but will also drive 8ohm load, or headphones
Computer Interface:  Frequency control and display, along with radio set up  is avaible via the optional RS232 or USB port.

A complete receiver consists of 3 boards

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