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Lower output from 10W

PostPosted: 10 Oct 2018 14:16
by NQ3RP
I'm looking for an easy way to drop output power for QRPp and BPSK modes. Without going into the software drive setting is there an easy page or additional hardware ad on to make it easy ?


Re: Lower output from 10W

PostPosted: 10 Oct 2018 22:33
Hi ya John!
Have you considered a 50-ohm power attenuator? Ten watts in with a 6 dB attenuator and 2.5 watts out or 1 watt out with a 10 dB attenuator. As long as the attenuator is rated at 10 watts or better. I think suitable ones can be found on Amazon or E-bay for a reasonable cost. However . . . the 'Rube Goldberg' part. You would need an external relay to bypass the atten when in the receive mode. Assuming we're talking TRX2, use the signal from the AUX jack on the rear panel for relay drive?

Just a thought!


Re: Lower output from 10W

PostPosted: 10 Oct 2018 23:31
by NQ3RP
That's exactly what I don't want to do. I was hoping someone had modified the Tx RF Atn and Ist stage PA amp circuit to make changes to the output power. The unit already has 1db, 2db or 3 db attenuation for band balancing in the Tx RF Atn circuit. I'd like to add those and 6db + 9db as user power option selections via button push/software or a hardware switch selected attenuation pad. So 3db would give 5W output, 6db for 2.5W and then 9db for 1.25W. That way it's in the transmit line already. I guess I'll have to look at other schematics to see what's possible.

If you think of anything else ED let me know. Thanks.


Re: Lower output from 10W

PostPosted: 12 Oct 2018 11:28
by NQ3RP
After lookin through the whole forum for an answer because the search form wouldn't search for it, I found the answer on how to lower the output from 10W on both CW & SSB. Thanks Adrian, ∞ 5B4AIY for his explanation from a few years ago. Posted here for an answer so others can reference:

"The output power of the transceiver can be adjusted by means of the carrier level control R28 on the main board for CW output. It is normally set to give an output of 10W, but this can easily be reduce to 5W by re-adjusting this potentiometer if you wish.

The output power can also be set with the on-board attenuator. This is set by selecting the TUNE mode, press the PTT switch, and then press and hold the PWR button whereupon you will be able to adjust the output power by inserting or removing steps of the fixed attenuator. The step setting will be stored in the EEPROM for future use.

You say you are using my firmware version 1.07u, there is now a new version, 1.07x that has a number of improvements that you may wish to install, along with an updated user manual. Drop me an email to: and I'll be happy to send you this latest version. There is also a new version for the PA-100D linear amplifier, if you have that equipment as well.

I forgot to mention R26, which adjusts the gain and hence the output power on the SSB modes, my apologies. R28 sets the CW carrier level, of course. By adjusting these two potentiometers you can easily set the transceiver up for no more than 5W in either CW or SSB modes. The fixed attenuators are really there to equalize the output power across all the bands, and this is most easily accomplished using the serial test suite's Auto Equalize feature. I'll send you the latest versions today. Again, my apology for forgetting R26.

If you are operating RTTY/PSK-31, then you can also set the output power in this mode by adjusting the input drive level as well. When the input source of the Juma is set to LINE and with the speech processor turned off, the input sensitivity is somewhat low and you will have to use a fair amount of drive, but this also means it is hard to really over-drive the power amplifier. I use mine with the excellent NUE-PSK self-contained modem, and when using this its output jumper has to be set to the HIGH position to provide sufficient drive, but it also means that the Juma is relatively insensitive to RF pickup."