SOLD OUT

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.