Elektor SDR Shield 2.0 (3): practical use as a measurement tool

摘要

This concluding part of our series on the Elektor SDR Shield 2.0 [1] is also the start of a new beginning. This automatically tunable receiver with two controllable VFO outputs opens up countless new opportunities, several of which are discussed in the article. Developing simple Arduino programs turns tricky tasks into light work. In particular, there's no longer a need to buy expensive test and measurement gear on every occasion; instead you just write a program to do what you need. As soon as you switch on one of the auxiliary channels, a weak signal appears in the receiver. An example of this useful application is the preset frequency at Channel A. 7040.100 kHz is the middle of the WSPR range in the 40-metre band (Figure 1), which is only 200 Hz wide. For accurate tuning, the sideband can simplify hitting the right spot precisely. Without any cable connected, the carrier you have activated is visible in the receiver, because there is always a weak capacitive coupling to the receiver input. It is apparent that sideband suppression is not fully achieved. The signal may appear at +12 kHz and again, slightly weaker, at -12 kHz. This is because there is coupling not only to the input, but also to other parts of the receiver, such as the mixer output.