These class AB linear amplifiers were made by Motorola for use in the 800 MHz cellular band.  They will also work very well in the 900 MHz band with some minor limitations.

The amplifier board typical for most of the units listed here is a MRF897 driver and a MRF899 final.  The MRF899 final  transistors are rated for 150W PEP.  Approximately 4-7W drive will be needed for full output.  The SGTF1021B and SGTF1040 have additional driver stages, and can be driven with miliwatts.  Their original application used only a fraction of the power available.  

  Full output is typically achieved up to 910 MHz.  Going higher in frequency the output starts to drop, due to the circulators or isolators used.  Results vary quite a bit between the same type units. The isolators are not easy to remove.  Some minor tuning can be accomplished with a magnet.  The transistors are rated up to 960 MHz. 

Some minor modifications can be made to the amplifiers for Amateur and other applications.  Typically this would be the change out of the RF and power connectors and Bias switching.   VHF south has a good modifications page.


This amp uses a single MRF897 driver and a MRF899 final amplifier board.  The power output is close to 150W on 902 with approx 5-7 W drive.  The power output drops a lot going up in frequency, and it does not appear suitable for 927 MHz.  Power supply required is approx. 26VDC @ 15A.

SGTF1019A, SGTF1019B, SGTF1038A

Same as above, but with two amplifier boards.  The power output is in excess of 200W on 902.  Power supply required is approx. 26VDC @ 30A.

SGTF1040A, SGTF1040B

This amp uses a two stage preamp and a tuned input, will cover a wide range.  The drive required is as low as 50 mW for 100+W output. I tried this amp with 5W drive for a short time, with 150W output, with nothing smoking.  Power supply required is approx. 26VDC @ 15A.


Uses a single stage amplifier with the isolator separated from the main board.  Unlike the other amps this isolator can be easily tuned with a magnet or bypassed altogether.  In this case this amp will work very well for a repeater amp on 927 MHz. Power supply required is approx. 26VDC @ 15A.

The following error amps don't appear to work well for amateur applications, and they only output some 20W or so.  Bypassing some stages and driving the last stage might work, but was not tried 



STF2530A, STF2550A



Copyright  ©  Niko Cimbur - AC6DD 2006.  All rights reserved.