Final transistor robustness

[Jens Wilke]

Hi,

I am just making my first steps with RS-HFIQ and also as a ham as well.

How sensible is the final transistor? Is it easy to fry it or would it withstand a bad SWR or open connector for some time?

73, Jens

[jcve...@gmail.com]

Hi Jens,

The final in the RS-HFIQ is a Mitsubishi RD16HHF1 MOSFET; the same device that we use in the Hardrock-50 amplifier (which has four of them). According to the datasheet, the RD16HHF1 is rated at 16W output and can withstand a 20:1 SWR. So running at 5W, it should be virtually indestructible. That being said, the heat sinking on the RS-HFIQ could be better so under adverse conditions the MOSFET gets hot and that can cause premature device failure.

If you expect to be running high duty cycle transmissions using constant amplitude digital modes or FM, you should consider beefing up the heat dissipation capabilities of the radio. If you have the enclosure, you can eliminate the bottom heatsink, drill two holes in the case and attach the board to the case with 1/4" aluminum stand-offs and apply heatsink compound to the surfaces. This will more effectively conduct heat into the case lowering the MOSFET temperature.

In summary, if you are running SSB or CW into a fairly well matched load; say 2:1 or less; the RS-HFIQ will work just fine. It can gracefully tolerate the occasional open or short condition without any issue. If you plan to run PSK31, FT8, WSJT-X, RTTY or FM with long key down times into questionable matching, add more heatsink.

73,

Jim WA2EUJ

[Jens Wilke]

Hi Jim,

many thanks for the quick response.

I am not planing for high duty cycles, I was just concerned of my typical clumsiness and what might happen when I have to high output level when tuning the antenna.

So now I am at ease. Maybe there is a free ADC on the Arduino which could monitor the temperature?

73, Jens