The PA module Sixty One HVF-1k2 is a modern and powerful amplifier module.
A great deal of emphasis has been placed on high quality and verifiable measurements.

The Sixty One HVF-1k2 module features an optional 15 dB attenuator at the input, allowing it to be used with 100 W class transceivers. This makes the input less sensitive to power peaks.
As an additional protection measure, TVS diodes (suppressor diodes) have been added in front of the 4:1 transformer to further protect the sensitive gates from excessive input power.
Four additional fast switching diodes and four Zener diodes are placed directly at the gates.

Many suppliers omit this protection — it works without it, but one should consider whether it makes sense to take avoidable risks.

To ensure optimal temperature measurement, a digital temperature sensor (DS18B20) is installed next to the LDMOS. It provides the measured temperature via a One-Wire bus at the connector interface. Temperature sensing must take place as close to the LDMOS as possible.
Heat in copper doesn’t propagate at the speed of light!
A clever marketing trick often used is to measure the temperature farther away from the LDMOS, where it is significantly lower, allowing the manufacturer to advertise the amplifier as running much cooler.

The bias stabilization for class AB operation has been implemented using a classic regulated feedback circuit, which has already proven itself in the HF-1200 and HVF-1K2 models.
There are also various “wild” circuits being copied elsewhere — they might work, but their design is far from clean. Some even use cheap general-purpose diodes, and as the thermal characteristics drift far from the LDMOS, the resulting voltage changes unpredictably.

At the connector interface, the bias voltage can be switched for transmission.
The NTC sensor for temperature compensation is connected there, and the bias voltage can be monitored as well.
All materials used are carefully selected: Class 1 low-ESR C0G capacitors with the required current and voltage rating, genuine 17-ohm cable for the 1:9 TLT transformer, and high-quality Teflon coaxial cable for the 1:1 output balun.
Many try to cut corners here, using two or three 50-ohm cables in parallel just to save a few euros — but 17-ohm cable is readily available!