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Broadband_VHF_Power_Amplifier.php   6412 Bytes    16-07-2014 00:19:26


Broadband VHF Power Amplifier


3 ... 540 MHz, 1.5 W Power Amplifier using the BGD 804




Broadband VHF Power Amplifier


The CATV Power Amplifier from NXP (Philips) offer high gain as well as high power over a large bandwidth. Unfortunately the datasheets do not specify the maximum available power when using for a single carrier. You may do some sophisticated guess, based on the current consumption. Anyway we measured them all and found, that the BGD 804 has the maximum power at output. You may even increase the supply to + 28 V to get the most out of it. (No failure within 10 years, about 50 devices running in our lab, so far).





Frequency Response



The 20 dB Offset is due to the use of a 20 dB / 20 W Attenuator. (Weinschel, 24-20-43)


Broadband VHF Power Amplifier





Circuit Description



The Circuit uses a GVA-81+ from Mini-Circuits as a driver, operated directly at the +24V
(+28 V) Supply via two 100 Ω, 3 W Resistors. The output of this driver is ac-coupled to the input of the CATV Amplifier BGD-804 from NXP. The capacitors are not critical. We use 4.7 µF, 1206, for ac-coupling of the stages. The coil for biasing the GVA-81+ is a BLM31AJ601SN1L (Murata), obtained from Farnell. In case you need more Gain, you mayst exchange the GVA-81+ with a GALI-74+ or anything else. (Check Bias Resistors !) Online Bias Calculator


As the circuit is that simple, you may have a look at a picture of the PCB, as we don't have a schematic. INPUT is on the right side, OUTPUT left.


Broadband VHF Power Amplifier





1 dB Compression Point



The figure below shows, that compression starts at an input level of + 4 dBm. Data measured at f = 100 MHz. Supply : 28 V, 650 mA


Broadband VHF Power Amplifier





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t1 = 3910 d

t2 = 579 ms

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