Yeo Notes 1
These notes apply to the Walford Yeo direct conversion receiver kit.
The circuit diagram and especially the PCB show multiple positions for the band dependant components for the VFO and RF bandpass filter. On first sight these can look quite confusing until you realise how to select and place the component options for your band.
Firstly, the way the kit is supplied is that there are a number of components for every possible band option, as you will be building for one band only there will be components left over.
Each band sensitive section require a specific value of inductance and capacitance, the inductance is provided by a coil. The capacitance required for a specific band (for a particular section of the circuit) is given by Table 1 and Table 2 on page 11 of the Yeo notes. It’s important to realise that the required value of capacitance for your band may be required to be made up by connecting capacitors in series or parallel or may require just a single capacitor and some capacitors may be omitted altogether.
To help with this, the PCB has extra pads etched to provide points for the combination required. A word of warning is that the component layout diagram shows the component layout for just one possible combination (a component layout for one particular band only).
Looking at the VFO diagram on page 13 we see that C26 and C27 are shown in parallel with the inductor L26. Now whatever band you build your receiver for you will need a certain amount of capacitance in parallel with L26 in addition to C3. This amount of capacitance is given in table 1 on page 11 in the column “Capacitors that alter with band” sub column “ Nominal Value”. This “Nominal Value” is made up by connecting capacitors in series or parallel or in one particular case just a singe capacitor (for40m). Whatever combination is required you must end up with one leg of a capacitor connected to one end of L26 and the other leg of the combination connected to the other end of L26.
In the case of a single 150pF capacitor needed for 40m the legs will not be connected to any of the intermediate pads but just to the end pads. When capacitors are required to be connected in parallel they will again be connected to the end pads only with no connections to the intermediate pads.
When a series connection is required then one leg is placed in one end pad then the other leg is placed in one of the intermediate pads. The other series capacitor has one leg placed in the other end pad, then the other leg is placed into the intermediate pad which is connected to the first capacitor’s intermediate pad. This makes the series connection between each end of L26.