Transceiver power output

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Anonymous (not verified)
Transceiver power output

good morning all,

After browsing the forum for some time I note there seems to be a widespread belief that "My tranceiver can't go below X watts".

RUBBISH!

I know that reading the operators manual will tell you that adjusting the RF power control adjusts the output between 5watts and 100watts for a typical transceiver.

I also know that when you key the transceiver up in cw mode and adjust the knob marked RF Power to minimum RF power you get x watts, (2, 5, 10watts depending on the rig).

The RF Power control adjusts the ALC treshold so you will not go above this set "MAXIMUM" power of x watts!

BUT It does not stop you running "LESS POWER"!

If you are running in SSB Mode and you key the transmitter on with no audio input
(MIC GAIN Wound fully off) you should have "NO RF Output" except any residual carrier leakage, which in a modern transceiver shoud be at least -60db below peak power output, ie Zero power.

Being a linear mode of modulation if you apply an audio tone (of 1.5kHz in the case of WSPR's) suitably attenuated to the mic input you should be able to adjust the power output with the "Mic Gain" from ZERO "NO RF Output" up to a "MAXIMUM" of X watts, at which point the ALC should come in and limit the RF Output to X watts.

By reducing the audio 3db you can halve the X watts output, reducing it by 6db will give one quarter of the X watts output, reducing it 10db will reduce X watts to one tenth,

This of course is based on the assumption that you have got your "Audio Processing" switched "OFF" for digital modes of modulation.

You need to remember that a typical dynamic microphone output is about -45dBm
maximum, and the sound card output will be typically 0dBm so your need to have about 45 dB Attenuation to have a similar input level, and not run the risk of overloading the low level input circuitry of the transceiver.

A suitable T attenuator would be 560 ohm resistor from sound card output to a 5.6 ohm resistor to ground and a another 560 ohm resistor to the microphone input.

Transceivers with an electret mic insert or inbuilt mic preamp, will require a DC blocking capacitor between the attenuator and the mic input connector.

As with any data mode the use of Processing is compressing the audio tone and introducing distortion, operation with ALC often causes distortions and intermod with multiple tone modulation.

Regards
Paul
VK4ZBV