Max power recommended for digi modes?

[N0LX]

I was hoping to find a definitive answer to the recommended max power we should run for digi modes.

[gatorjj]

I think it depends greatly on the efficiency and SWR, which is different on every radio and every band.

That being said after blowing my FET at 13.5v on 10m (lower efficiency) with FT8 at about 6 watts I have been running digi modes with 10v happily the last several months with no problem (3-4 watts) on both the low band and classic band (tr)usdx. So not the max but pretty safe and only losing a couple db which doesn’t matter too much for digimodes.

Hope that helps,
J.J. KF4VE

[DL2MAN]

I was hoping to find a definitive answer to the recommended max power we should run for digi modes.

There is no definitive answer as there is no hard lines.
It depends on the efficiency of your individual rig, and the SWR of your individual antenna, stability of your power supply, common mode currents in your shack, condition of your PA FET, Type of PA Fet, in case of BS170s: How well are they matched and much more.....
So noone can take away your responsibility.
You can either risk it and live with the consequences (good or bad) or you stay on the safe side....
Your choice. Don´t ask anyone else to take your risk !

73 Manuel; DL2MAN

[finco]

I don't get it, how did you blow up a FET at 13.5? I thought it's safe to operate up to 13.8?

[gatorjj]

It may be safe if you take the time to optimize efficiency and your SWR is way low. I didn't, and learned the lesson from that

The higher bands are more difficult to optimize since there's not many coil turns. Even though I've optimized all the toroids now, I still run at around 10v for digital just to be safe. No blown FETs for months and maybe a db or 2 less on signal reports, a good tradeoff for me.

J.J. KF4VE

[finco]

So this is a problem only for higher bands? for lower (20, 40) it's safe to use 13.8 with no issues? what if there is a high SWR?

[gatorjj]

As Manuel stated pretty clearly, "There is no definitive answer as there is no hard lines." Better to be safe with digital, as the long transmit times are harder on the FETs.

[finco]

There is no definitive answer as there is no hard lines.

This makes no sense. They made a product rated for 13.8v and it's not cheap, it's 200 dollars. It either works as stated or it doesn't in which case I like my money back.

[VE3RRD]

Off hand, I can think of 3 important variables - and input voltage is only one of them. The input voltage will determine the Watts output. BUT, you must have checked efficiency is 80 to 85% using an external current meter and external wattmeter (the remaining 15 to 20% is heating up the final amp). Also the antenna SWR must be low or the reflected power will affect the final amp (maybe an antenna tuner will be needed).
So it's not as simple as just the supply voltage.