Page updated 16.12.2004
10W HF amplifier story
Our (OH7SV and OH2NLT)Direct Conversion HF Transceiver project faced first obstacles when we decided to make wide band power amplifier for it. As writing this we are still stuck with amplifier design. We have found this subject challenging. More you know you also know more things about what you do not know anything! Matti OH7SV has done lots of thinking to enable us to understand meaningful phenomenon in a low voltage push-pull HF amplifier. More about this rescuers in our DC Radio pages.
One evaluation platform was withMitsubishi RD15HVF1 MOSFET transistors. This particular prototype never made its way in to our radios. Main reason is lack of power. With proper transformers this amplifier is however excellent add on for your HF generator. Amplifier is very wide band and provides about 20dB gain. With +20dBm generator output you get 10W signal for drive demanding experiments.
Amplifier is constructed intoold NMT900 cell phone enclosure.
Only control is bias current on/off switch.
Final transformer primary is brass tubes and two loops coaxial type low ohmic Tyco Spec 44 cable connected parallel between drains. Secondary are two rounds of low ohmic coaxial inner conductor. Core is two pieces ofWurth 74270030 ferrite tubs. Input transformer is 10 bifilar turns on Amidon FT50-43 core.
This construction delivers clean output without any filters.Oscilloscope picture about output looks nice. Output harmonics are also under control.
Clean Drain signals are also sign of healthy push-pull operation.
Amplifier frequency response (without any corrections) looks good.
10W Linear HF Amplifier Schematic Diagram