AM(SAM) Mode transmit setup

[ke9ns]

Searching around google, I have found these AM transmit settings work well on a Flex-5000:

1) Transmit bandwidth to 0hz to 3K,4K,5k (Leave it up to the band conditions)
2) Disable the ALC: Setup->DSP->AGC/ALC->ALC Attack = 1, Decay = 1, Hang = 10
3) Setup->Transmit->AM->Carrier Level = 40
4) PowerSDR Console->Drive Level = 4 (as a starting point). Adjust for 25 watts out (for 100watt Radio) with no audio input.
5) PowerSDR Console->CPDR = 5 (to boost your audio average level)
6) If using an internal or external EQ, remove any bass boost. But boost the high end slightly if needed.
7) Set MIC Level so your audio output (as viewed on the Panadapter) does rise higher than 3/4 of the way to the peak of the Carrier you see on the screen.


I would like to know what everyone else uses for settings in AM mode?

Darrin ke9ns

[wd5jko]

Darrin,

You got a good start on your settings. I have a couple of things to add.

1.) On AM the phase of the audio can be important. A lot depends on the persons voice, and the microphone used. With analog systems, flipping the phase can have a dramatic effect at the received end when the receiver at the other end does NOT use a product or synchronous detector. The old fashioned diode type detector will follow the negative modulation going to zero, and then follow it when it reverses on the baseline. Some call those points "Wavelets". This is not distortion being transmitted, but the diode detector audio output really sounds dreadful when the transmitted signal contains "wavelets" on voice peaks. Some time back you added a Phase reverse button in Setup. This is nice, but does it do the same thing as flipping the microphone balanced audio wires in the XLR connector?

2.) On AM, the constant carrier draw will drop the voltage from the power supply to the Flex 5000 power connector. To get good positive peaks on AM, I set my power supply such that I get 13.8V as displayed on the PWR SDR screen while transmitting AM at 25 watts carrier. Depending on the DC wire length, and wire gauge, you might need to set the power supply to 15 volts during receive conditions.

3.) With many CB linears out there, it is common to see an SSB/AM switch on the amplifier. For SSB we need to bias the final transistors to get good gain, and low IMD. On AM they remove the bias! Some call this class BC. The idea is that the carrier level with no bias deals with the cross over distortion (class C), and the audio modulation goes beyond that on the linear portion of the curve (class B). The effect is slightly less gain, strong AM positive peaks, the output modulation % increases a little from the drive signal, and higher standing carrier efficiency. The thought here is that with the Flex 3K/5K, the RF power stages are pre biased and the idle current sensed with high side shunts. Just a thought, but would it be possible to turn down the idle current when on AM?

http://amfone.net/Amforum/index.php?top ... #msg253273

Jim
Wd5JKO

[ke9ns]

Thanks

1) The phase invert is done at the MIC pre-amp stage in the code (Mixer). It definitely works. If you put the Display mode into PanaScope (go into setup->Display->Scope Mode = 100 uSec), and PTT the radio and say the word "TEST" I normally get very high positive spike on the T. When I CheckBox the Phase Invert, it clearly spikes negative.
I really wanted to add a "Phase Rotating Asymmetry Eliminator" as code, similar to the multi-stage op-amp. But that might take awhile.

2) Luckily I run a Titan for AM, so I only need to set the Drive to 4 for a 250watt carrier.

3) Not knowing the PA hardware I would not want to mess with changing the bias. Too risky.

Darrin