(tr)uSDX Forum

Hi,

I have just finished building a *Rxxxx* batch B3 kit. As seen with other kits from *Rxxxx*, efficiency is extremely low, i.e. in my case I get 4 - 5 watts@12V, but efficiency varies between 45 and 65% depending on band. That values are far below the specs!

While I could live with the output power, what would actually happen if one would operate the transceiver at those low efficiency numbers, in particular in CW mode? Will it blow the PA transistors of the class E transmitter even if a resonant antenna is used having a SWR <1.5 - 1.0 ? Is it better not to use the transceiver at those efficiencies and wait until *Rxxxx* comes up with a solution?

I follow the other thread on this topic (which is now 6 pages long), but I am not sure what would be the actual consequences if one intends to operate the transceiver anyway.
Regards,
Chris

Hi Chris,

You can of course work with it, especially in CW Mode on a low SWR Antenna.
I would not advise to do WSPR for example, as this includes 2 Minutes of continuous TX.
But use it with confidence, and if your PA blows anyway, 3x BS170 are just a few cents.

73 Manuel; DL2MAN

Great to hear that the radio is basically usable even at low efficiencies. I have spare BS170s from Fairchild and it would not be a problem to replace them if one or more fail on the RF board. I am just hoping that nothing else will blow up.

Would be great to know though how likely it is that those transistors fail at the above-mentioned low efficiencies. If there is a high risk for failure I will not take the radio with me on a SOTA summit without backup. Changing BS170s on a summit is obviously no option.

Cheers,
Chris

I take this opportunity to ask for clarification regarding the transmitter's power efficiency,
I have read that the ideal would be to have 80% efficiency. But if, regardless of the emitted power, I work in a range between 60 and 70 percent, it is correct to use a transmitter?
I ask this because I have a VNA to attempt a calibration as indicated by Manuel. But let's say I can't and perform the calibration to bring it to 80% I could be safe (TX final) with a 60-70% efficiency?
Best regards

It is safe. It is a question of efficiency only (power out / power in).