May 10, 2006

In no particular order –

A volume control has been added. This was done by replacing R41 (1K on the schematic) with a 10k resistor in parallel with a 10k pot. R41 on the parts list is shown as 10K. The pot is not shown on the schematic, and does not have a designator on the parts list. The easiest way to connect the pot to the board is to leave out C14 (220 pf) and connect the two wires to the mounting holes for C14. You can mount C14 across the pot off the board.

The mute connection (W6) must be shorted for the LNA to work in the receive mode. It is open in the transmit mode.

+12 volts DC is connected to W7 and W4.

Be sure to put jumpers on jp1 and jp2 – otherwise there will be no audio!

I used twisted pairs to make all off-board and inter-board connections.

W9 connects to W3, and W8 connects to W2. If that gives you the wrong sideband, swap the connections.

Be sure to get the 1% and matched parts in the right part of the circuit. They are packed in a separate plastic bag, and the 1% resistors are blue.

C25 is listed on the parts list as 39pf, and is supplied as 39pf. It is on the schematic as 36pf.

The schematic shows only SSB values. If you have a CW version of the microR2, use the values for the CW parts as listed on the parts list. That includes 4 resistors in the audio phasing network and the audio filter components.

C40 is the main tuning capacitor. It is mounted off the PC board, and is connected to the board with short stiff pieces of wire.

With the tap on L7 set at 8 turns from ground the receiver I built covered about 225 KHz. If you want to cover less of the band, move the tap closer to the ground end of the coil. For more coverage, move it a turn or two away from the ground end.

Note that C29 (39 pf chip cap) mounts on the bottom of the board.

The microR2 is very quiet. Don’t be fooled (like I was the first time) into thinking it is not working when you turn it on and don’t hear any background noise.

You will get more volume from the microR2 if you use higher impedance headphones rather than an 8 ohm headset.

For technical info and theory of operation, read chapters 8 and 9 in Experimental Methods in RF Design.