Plate Modulation?

[crazybob]

I read about some radios ( & ham transmitters) have plate modulation & some have screen modulation, & then there's phase modulation? Which is better to have? I believe the sonar & Regency's have it? .. Does a Browning tube transmitter have plate modulation? Thanks!

[Sandbagger]

Feb 2, 2012 17:32:49 GMT -5 crazybob said:

I read about some radios ( & ham transmitters) have plate modulation & some have screen modulation, & then there's phase modulation? Which is better to have? I believe the sonar & Regency's have it? .. Does a Browning tube transmitter have plate modulation? Thanks!

Plate modulation is when your audio modulation is coupled to the plate voltage, which then varies with voice peaks. It is the most desirable to have, but the downside is that you have to produce at least half of the Transmitter's RF carrier power in audio watts. Which means for a 100 watt carrier, you need at least a 50 watt modulator. This isn't a problem at the 4 watt level, so most CB rigs are plate modulated.

Grid modulation is when the audio is applied to the grid, and the bias changes with the modulation, thereby varying the output power. The advantage to grid modulation is that you don't need a lot of modulator power to vary the bias, so you don't need a monster sized modulator, for large power output transmitters. The downside of grid modulation is linearity. The tube needs to be very linear or the output will be distorted.

There is also what is called "low level" modulation (what you normally find in a Yaesu FT-101 and other HF rigs), where the modulation is applied to a stage before the final, where there isn't much power yet, so it doesn't take much modulator power to fully modulate. The final section is setup as a strictly linear amplifier, which simply amplifies the low level signal up to the proper power level.

Phase modulation is a form of FM, where instead of the frequency of the oscillator being varied, the phase of the signal is varied. There are some advantages to phase modulation (related to audio frequency response). But it's usually easier to directly FM modulate an oscillator.