Why are there no output RF filters on the Penelope PCB?
A. This is due to a number of reasons. Firstly, whilst Penelope is primarily an HF ( and VHF/UHF on alias) exciter it can be used for other functions. For example, when used with Mercury it can form a low level signal source as a tracking generator or VNA. For these functions the lack of output filters is an advantage. Secondly, Penelope generates RF directly at the desired output frequency by synthesizing the required RF waveform using a DAC. The lack of mixers, DDS, frequency synthesizer etc means the output spectrum of Penelope is particularly clean. In fact the spurious output at 0.5w meets the FCC requirements without additional filtering. Thirdly, Penelope is an exciter. Whilst we expect it will be used by QRP operators as is we also expect it to be used to drive a higher power amplifier. In the latter case the user will most likely provided external filtering as part of this power amplification. Fourthly, Penelope does provide a 55MHz LPF that can be placed in circuit after the
