Making contact with another "Ham", whether in the next village or on the other side of the world, on equipment you have built yourself, either from discreet components or from a kit of parts is one of the most enjoyable aspects of our hobby. This is  "Home Brewing".  

There  are a number of sources of circuit diagrams of everything from simple pieces of test equipment to complex multi-band multi- mode transceivers.

A number of companies producing kits for the Amateur market have come and gone over the years, Heathkit and Wood and Douglas to name but two. 

There are still a few companies who produce kits of various degrees of complexity for anyone who wants to "have a go" but prefers to use a proven design with ready made printed circuit boards and a kit of all the necessary components.

One such company is Cumbria Designs, their WEB Site can be found at http://www.cumbriadesigns.co.uk/

Another company who produce a number of products, including a basic frequency counter, a Direct Digital Synthesizer (DDS) signal generator and an SDR receiver, can be found at Vintage Components

Tim Walford G3PCJ of Walford Electronics also produces a wide range of kits, including receivers and transceivers of varying degrees of complexity, which can be seen on his web site Walford Electronics