Adventures of a broadband amplifier.
Or this low-cost version
These products often change, you can view a similar one here
Some radios are equipped with a 0dBm (1mW) output that can be used to drive an amplifier. The advantage of this output is it usually works over the entire transceiver range. So you can often obtain 1mw from 10 kHz to 60 MHz.
I recently read an article in Radcom from Dave Pick G3YXM and he had purchased an amplifier from eBay. Dave confirmed it was this model with an operating frequency range from 1 to 500 MHz.
Like this one using the search term ” 1MHz – 500MHZ New HF FM VHF UHF RF Power Amplifier For Ham Radio + Heatsink”. If you wanted to use this below 1 MHz that’s possible but you will need to swap the inductors for larger values.
Tests without any changes showed 1mW in @ 1.9 Mhz = 1.6w out. The power out seems to drop to 100 mw below about 500 Khz. I also tested the amplifier at 144 Mhz and the o/p was around 1w.
Hopefully, with a few changes, this will allow me to run a small amount of power on 472 Khz WSPR.