First 475 kHz WSPR decoding

Tonight I made the first successful decoding of WSPR on the 630 m band. What inspired me was all the talk on the Elecraft reflector on the new synthesizer which in addition to having less phase noise, also allows the K3 to go below 500 kHz. I don't have that synthesizer, but the discussion reminded me of the low frequency converter I built many years ago. It converts 0-1 MHz to 14-15 MHz. Using the KXV3 transverter interface of the K3 it was easy to interface and get up and running.

The first signals I decoded are shown in the water fall above, and their origin in Germany and the Netherlands is shown in the next figure.

According to WSPRnet, PA0A's 2 Watt transmitter is 784 km away from me, and DK7FC's 1 Watt is 1164 km away.

The converter is quite simple and is based on a 74HC4053 switch used as a mixer with a 74HC04 for a 14 MHz oscillator. It is the design of SM6LKM, but with a different oscillator frequency and a simplified output filter compared to his. It is one of many small projects that I have built in Altoids tins.

The antenna used was my trusty old 80 meter horizontal loop which has been the main work horse for making my 8-band DXCC (more than 100 countries on all bands 3.5 - 28 MHz) possible. It is fed with ladderline into a 4:1 Elecraft balun in the shack.

Perhaps the next step is to finish the 475 kHz filter of my Ultimate 3 WSPR transmitter and see if others can receive me? That is going to be more of a challenge antenna-wise.

Show off your project in a clear top tin

We all want to package our electronics projects in some nice enclosure. An Altoids tin is often used - and I have used that a lot myself. But for slightly larger projects, the tin shown below is a better alternative. In addition it has a clear top, so displays can be viewed and the nice layout of your electronics can be admired. 

The simplest possible AM transmitter

Here's a design for a 1 MHz amplitude modulated (AM) transmitter. I've been looking a while for something like this, a simple short range AM transmitter for the medium wave band, as I needed something for demonstration of my collection of old radios.

The result is the AM transmitter shown here in an Altoids tin on top of a Radionette Kurér radio. This is a portable tube radio from the 1950's. Several hundred thousands were produced, and it was exported from Norway to 60 countries. It is still popular among collectors.

The transmitter is as simple as it gets. The heart of it is a 1 MHz crystal oscillator in a can. Its 5 Volt power is modulated via an audio transformer, one taken from the output of a transistor amplifier (primary 147 ohms - secondary 3 ohms). I drive the modulator from my cell phone into the low resistance side of the transformer and get good audio when the phone's volume is set to maximum.

Altoids Projects

Press image for magnification

I like to build small electronics projects and like many others I have found the small Altoids tins to be excellent enclosures. 

These tins are inexpensive, well shielded, easy to work with, and least but not least they enable you to make experimental circuits that are sturdy enough that they can be reused later.

Pictured here is a collection of projects I have built over the years with the hope that  they may inspire others.

Small voltmeter for a QRP rig

AT Sprint rig in an Altoids box, itself contained in a video case.
Digital voltmeter in lower left corner shows 12.0 Volts.
(Click for larger image)

Every battery-operated rig needs a voltmeter. I had a small analog voltmeter for my AT Sprint QRP (= low power), 4 Watt rig, but after it failed I wanted to upgrade it to a digital one. I found a miniature meter on Ebay which is perfect for a QRP rig and which I recommend.

QRPp: Ultra low power operation with the Pixie 2

QRPp is radio amateur jargon for communication using a transmitter with less than 1 Watt power output. That’s less than a handheld GSM mobile phone (max wireless range ~35 km) or a flash light. My Pixie 2 transceiver has so far contacted 15 different countries on 3.5 MHz CW. The first version from 2002 was made in an Altoids tin (picture later), but in 2010 I repacked it in one of the nice clear top tins from the 4SQRP (picture below).

My repackaged Pixie 2

AT Sprint (the original)

Photo: LA8EKA

The AT Sprint is a very nice limited edition surface mount CW transceiver designed by KD1JV Steve Weber. The printed circuit board measures 85 by 54 mm. It was quite a challenge, but a fun one, to build! 

It was designed to be a rig of a size fit for camping. It covers the 40, 30, and 20 meter bands with plug-in modules. The whole transceiver fits in an Altoids tin and outputs about 4 W. The rig in the tin weighs about 85 grams. It uses a DDS - Direct Digital Synthesis - chip for the VFO, it has a superheterodyne receiver with a four-crystal filter, audio AGC, audio filter, and a very efficient class E output stage. It also has a built-in memory keyer and a morse code frequency annunciator. It can take any battery voltage between 5.5 and 13.8 Volts.