RF - Broadband Amplifiers

Radio frequency broadband amplifiers are mainly used in radio technology (CATV, amateur radio) or in measurement technology.

I've built a few of these amplifiers, all in push-pull with either bipolar transistors, MOSFETs, or LDMOS (BLF188XR) semiconductors.

Power Amplifier - 100W: This module is constructed with 2 bipolar transistors and is intended as linear amplifier (SBB) and equipped with a transmit/receive switching which can also work as VOX.

 

Technical Data:

Full Power (100W) Frequency Range: 1.8MHz to 30MHz

• Power Supply: Typ. 13,5 Volt (12 Volt)
• Current Consumption: max. ca 10 Ampere (12 Ampere)
• Power Gain: min. 10dB (see table attached)
• Harmonics: 2nd <30dB, 3rd <10dB (see table attached)
• Input SWR: < 1 : 1,8 (see table attached)
• Efficiency: Apr.max. 70%
• Bias Current: 250mA
• VOX sensitivity: 15dBm resp. 30mW
• Weight: ca. 200g
• Fuse: 10 A delayed, 5 x 20mm
• mechanical Dimensions: 114mm x 60mm x 24mm

Power Amplifier - 250W: This module is constructed with 2 MOS transistors and is also intended as linear amplifier (SBB).

 

Technical Data:

• Full Power (250W) Frequency Range: 1.8MHz to 60MHz
• Power Supply: Typ. 50V Volt
• Current Consumption: max. ca 7 Ampere
• Power Gain: min. 18dB (see table attached)
• Harmonics: 2nd <30dB, 3rd <10dB
• Input SWR: < 1 : 1,8
• Efficiency: Apr.max. 60%
• Bias Current: 250mA
• Weight: ca. 300g
• mechanical Dimensions: 115mm x 80mm x 24mm

Measureing Amplifiers: When it comes to using highly linear amplifiers in the frequency range between 1MHz and 500MHz, so-called RF Linear Hybrid Amplifiers are often used. Essentially, these are symmetrically constructed cascode units. To ensure that these units not only have a high frequency bandwidth but are highly linear, the transistors used usually operate in Class A mode.

I have build some versions of cascode high frequency amplifiers and here are the technical data of a "smaller" cascode amplifier:

 

• Energy Supply: Voltage 18Vm, Current 140mA
• Input SWR: < 1 : 1,8
• Power Gain: approx. 22dB

• Frequency response: approx. 1MHz - approx. 200MHz (at approx. 14dBm output power)

• Maximum output power (1dB compression): approx 24dBm

• IP3: Output IP3 = 42dBm

And here are the technical data of a "greater" cascode amplifier:

 

• Energy Supply: Voltage 28Vm, Current 380mA
• Input SWR: < 1 : 2
• Power Gain: approx. 21dB

• Frequency response: approx. 1MHz - approx. 55MHz (at approx. 20dBm output power)

• Maximum output power (1dB compression): approx 34,5dBm

• IP3: Output IP3 = 50dBm