Sunday, October 30, 2016

SDR receiver shortwave.

 The 80 meter band is busy. Being side band you don't see any carriers and the side band bounce as they talk. The strong AM signal on the left may be WWCR.

 The broadcast band appears to be busy. Being AM you can see the carriers.

The dongle will not tune below 24 Mhz as received. The cluster of components in the red circle are a filter designed to block 24 Mhz and below. The black chip with the black arrow pointing to it has a dot in the corner ID'ing pin one. The two capacitors with the yellow lines going to the left are the inputs (pin 1 and 2). The object is to connect to the side of the capacitor away from the chip to your transformer. The other side of the transformer goes to the antenna connector. The blue ring in the toroid. I folded the wire in half and made 5 turns through it. Solder one side to the two capacitors and the other side to the antenna. I have a headpiece magnifier with three lens. it makes the soldering a lot easier. Using #32 wire to wind the transformer helps too.
I've been listening to a rag chew 80 meters while writing this. I am in the middle of the group it covers about 400 mile radius.

HDSDR is the program I am using. You can download the HDSDR for free and a $6 - $8 dongle is what I'm using. The little antenna that came with the dongle will give some listening but I did unscrew the antenna and put a 7 or 8' piece of wire on the screw and tighten it. I put an alligator clip on the end and clipped it to an AC register.
One thing I should point out is the filter is there ti eliminate image signal from the receiver. Bypassing the filter allows the image which is signal below 24 Mhz to pass and a low pass filter should be added to prevent the former desired signal which is the image in our case.
To more simply state it. The LO and the signal mix to produce a  sum and difference of the same frequency. The filter eliminates one signal and you receive the other. Without the filter you receive both signals. It works but you may find an out of band signal coming in strong.

Friday, October 7, 2016

A long battery life reflex receiver with details of its construction.

This one has a good theory of operation in the text.
With 170ua @ 9 volts it is less than 2 mw It should give good battery life.