MRF151G Amplifier

(Motorola Application Note AR305)

Based upon the Motorola "Gemini" twin MOSFET, this module can provide in excess of 300 Watts from 10MHz up to 175MHz. The devices operate from a nominal 50 Volt supply.

In the Motorola Application Note, the design uses ferrite E and I cores on the input and output transformers. If operation is required only above 75MHz. i.e. for the 2 metre band, as was the intended application for this unit, these ferrite cores can be omitted and an overall increase in efficiency of about 10% can be obtained.

I had planned to use two of these with a 3dB hybrid to get 600 Watts+, but even operating as a single module, I was finding that the MRF151G seemed to be particularly sensitive to VSWR and I have lost a number of these devices in trying to get the amplifier working, which at US $100+ each is not fun. I do use one of these amplifier modules for my infrequent excursions onto 6 metres (with ferrites installed on the input and output transformers) but I only run the unit from a +36V supply rail which provides about 100 Watts output for about 1 Watt drive and seems to be relatively VSWR proof.

It would now appear that Motorola no longer produce these devices, M/A Com having recently acquired the manufacturing rights. However whether they will continue production it to be seen. For the amateur, an amplifier based upon one or more of the ubiquitous 4CX250B, a tube which is widely available and relatively cheap, is probably a better proposition than using the MRF151G .

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Page last updated 7 Sept 2001