Hi VA2SZM
It's very good to have new colleagues at a club.
The output of SDRs are low power, and generally don't have many filters at the input or at the RF output. This makes it flexible in terms of use (works on multiple bands), and at an affordable price.
We avoid using relays or solid switching devices, as they have a lot of losses, noise, and cost a lot of money.
The idea of switching the input, output, bypass generates many problems. In other words, having multiband equipment at a few GHz is unfeasible for a low-cost assembler.
Ham prefers to assemble separate amplifier pallets. One for each band. These amplifiers have amplification stages, as needed P1dB, IP3, and have band pass filters within the desired frequency. Due to power levels, filters are separated for each stage and desired band.
An comercial HAM equipment (below 1 GHz) is most often built with an output power between 5 and 100 watts. For VHF and UHF satellites with 5 to 50 watts.
With 1 watt and depending on your location, you will make local contacts.
The input and output of an amplifier is a reference to the RF signal.
The variable gain amplifiers that I know of are for use in laboratories (generally under 10 watts) and cost a few hundred dollars. We generally calculate the gain of our antennas (VHF and UHF satellites we use directional Yagi antennas with at least 10 dBs of gain), the cable losses, and use a larger amplifier than necessary. Some commercial radios have adjustable power (0 to 100%) or programmed levels (5, 25, 100 watts).
Sandro Ribeiro
73 de PY1SAN
GG77
Rio de Janeiro - Brazil