JBOT – An SSB linear amplifier made from Just a Bunch of Transistors

Filed Under (Amplifiers, Homebrew, QRP) by Jonathan on 10-08-2009

Since I lost some time on the site when I broke my foot, I thought I’d drop a few bonuses for you guys this week.

I have an earlier post on the BitX 20 that generated quite a bit of attention.  Farhan has done a lot of great work on that project that has a HUGE online following.

Many have noted that there were some issues with the amplification of this transceiver and it may take a bit to get it going.  Farhan has mentioned this on his site as well:

For many of us, getting hold of high power RF transistors is impossible. They are also expensive and easily blown. In the last decade, hams have pressed the power MoSFETs into use as RF devices. This has been a mixed success. The power FETs (mostly the IRF series for International Rectifiers) have very high input and output capacitance, they need higher drain voltage and they are very non-linear devices. As result, IRF device based RF power amplifiers have remained beyond easy replication for the average homebrewer.

Often, the RF power amplifiers are run flat-out without any attempt at stabilizing the performance, This has to lead to a lot of grief.

The BITX’s linear amplifier painfully illustrates both these issues. The IRF510 takes a lot to get it going. Many of those who scratch build it on their own often found themselves struggling with stability and insufficient power output.

I heard about Farhans’ new project and thought I’d mention it here as it can work pretty well for those of you that have already built a BitX 20.

His JBOT page is at:

http://www.phonestack.com/farhan/jbot.html

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