ANTENTOP- 01- 2008, # 010

Matching a Transceiver

with PA on several GU50

By: N. Filenko, UA9XBI ua9xbi@online.ru

Credit Line: www.cqham.ru

Matching input of PA that contained several tubes GU50 with a transceiver is not a simple matter as it seems at first look. Sometimes for simplicity of the design PA the driver power from a transceiver going straight away to several connected to bridge cathodes of the GU50.

However, input resistance of a PA containing 2 tubes GU50 (that is close to 50- Ohm at major amateur HF- ranges) is differed from input resistance of a PA with 3 tubes GU50 (the resistance lower in 1.5 times compare to 2xGU50- sample), and of course differ from input resistance of 4xGU50- PA (the resistance lower in 2 times compare to 2xGU50- sample). So, the input resistance for those PAs with 3 and 4 tubes is differ the 50-Ohm that requires proper matching of the PA with driving transceiver.

UA9XBI

Radio club "Arktika" Championship 2004

Photo Credit Line:

http://www.arktika.komi.com/Champ_2004.htm

Figure 1 Matching Autotransformer

Figure 1 shows a simple autotransformer that helps match input impedance of the PA to 50-Ohm in wide frequencies range.

The autotransformer was made on a Russian ferrite toroid with permeability 60. It is possible to use Amidon T-50-2 (OR t-50-6). At some cases it is better to use 2 toroids putting together. Coil contains 12 turns of wire in diameter 2-mm (12-AWG). Tap is chosen for best matching of the transceiver with the PA in wide frequency range. Experience shows that best matching for 3xGU50 PA gives tap from 8^th turn (from "cold" end). For 2xGU50 PA best matching gives tap from 5^th turn (from "cold" end). Anyway, try to find best tap and best quantity of coils in the autotransformer for your design of the PA.

73!

www.cqham.ru

http://www.antentop.org/

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