Why is it that all the major HF transceiver manufacturers set the AM modulation level so low in their radios?
Is 100% AM modulation not the standard in AM broadcasting?
Is 100% AM modulation not the standard in AM broadcasting?
I tried that battery trick. Works.HF SSB rigs on AM
Some newer HF transceivers are excellent on AM, with much less distortion and better fidelity than most older amateur AM rigs. The Ten-Tec Orion and the Yaesu FT-1000D are two examples of very good AM transceivers.
Peak envelope power, with 100% modulation, is four times carrier power. For 100% modulation in a 100-watt radio, a 100W PEP radio must run 25 watts or less carrier. With a 100-watt radio, peak power on voice peaks should be held to 100 watts or less.
I used an IC-751A or IC-706 ICOM on AM. The problem with that ICOM, like with many HF SSB radios, is it uses ALC to limit output power. Turning the output power down or mic control up will not increase the percentage of positive peaks. This is because the ALC system in most SSB rigs almost always detects peak power. If we adjust carrier power to 25 watts and try to modulate 100% (100 watts), the peaks cause the radio to reduce gain until peaks are back at the 25 watt carrier power level. The positive peaks stay at 25 watts or so...and the carrier drops to 7.5 watts when modulated!
The cure is to run the power level all the way wide open and apply an external stable negative voltage to the external ALC input. Adjust the external negative ALC until the carrier is 20-25 watts, and then the mic control until we have 100 watts on peaks using a good peak reading meter.
An external ALC carrier control can be a 9V battery across a 500k pot in a voltage divider. The positive battery lead goes to ground, and the ALC output comes from the pot wiper. P1 goes to the EXT ALC jack on the radio.
Remember to disconnect the battery when using other modes or when not using the radio!
To use this circuit, run the radio's normal power control wide open. Adjust the pot for 20-25 watts carrier. Adjust the mic control for 100% modulation, or 100 watts PEP (on a 100W radio).
Why is it that all the major HF transceiver manufacturers set the AM modulation level so low in their radios?
Is 100% AM modulation not the standard in AM broadcasting?
I would use a scope or a monitor radio to make sure it doesn't sound like a ch19 radio. Isn't there a way to turn the ALC off?
Can someone provide a picture of this device constructed?W8JI wrote:
I tried that battery trick. Works.
Mike
Excuse my lack of understanding the schematic. This is why I wanted to see one already made.It just a potentiometer, battery and RCA plug. It can't go wrong. Schematic is in post #2.
Mike