[amsat-bb] RF Designers? 30W UHF Transistor PA?
jamesduffey at comcast.net
Tue Apr 5 16:09:08 UTC 2016
Not sure what you want to do. It would help to have more details as sometimes the application drives the trade studies used to choose a device. UHF covers a wide range. I assume that you want to build a class AB or A RF amp for 435 MHz that puts out 30W and costs less than $X? $X is important and the materials that are used to build the amp may well equal or exceed the cost of a transistor when you figure in a enclosure, heatsink, connectors, PCB, and miscellaneous adjunct components. If you need to switch the amp out of line for receive, you need a fairly good relay at those frequencies. If you chose a cheap device that requires a higher voltage, like 24VDC, than the usually available 12V-13.8VDC in the ham shack, you will need to figure in the cost of a power supply. If this is a commercial or semi-commercial application, you should probably figure in the cost of design, assembly, and distribution. You probably know the drill.
Also, not sure of your definition of cheap, but $30 isn’t out of line for a good RF UHF transistor. While cheap switching MOSFETS can be used at HF, they usually have too much gate to source capacitance to be useful at UHF, and most need higher voltages than 12.5 - 13V, and some can be unstable at high frequencies.
Probably the cheapest and most effective way to generate 30W on 432MHz, is to use a pair of Mitsubishi RD16HHF1 RF MOSFETs at 16W, priced at $4.75 each, lower in quantity. A single RD30HUF1, will put out 30W and costs $23.95 each, again lower in quantity. These will run with good efficiency on 12V-13.8V, are specifically designed for UHF RF applications; unlike the switching MOSFETS.
At $45 you can get a Mitsubishi RA30H4045MR 30W RF module that requires a PC board and a few simple external components to make a good amp, but might be cheaper than buying a transistor and components.
If you can get by with a Class C amp, there are other design possibilities, and .
Again, a lot of these suggestions are based on conjecture as to your actual requirements and applications, but if you give us a better idea of what you want to accomplish, it would be easier to make useful suggestions. - Duffey - KK6MC
On Apr 5, 2016, at 7:31 AM, Robert Bruninga <bruninga at usna.edu> wrote:
> Asking AMSAT RF experts.
> What is the cheapest garden variety UHF Power Transistor good to 450 MHz
> and suitable for 20, 30W or more? Im finding transistors can cost $30 and
> up. That’s steep for an idea we are pursuing…
> Bob, WB4APR
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