SAM Mode

[wd5jko]

The SAM mode works pretty well as it is. One negative is when the received signal is off frequency a little, or if propagation QSB induced fading occurs, then the result is a squeal until the receiver sync's up with the received carrier.

There is a thread on AM Fone talking about early synchronous detectors, actually tube type circuits. Here is a post from Kevin, WB4AIO that I found most interesting:

"And I also remember W3DUQ's tube-type sync detector and tried it out a few times when I was visiting him. His detector was a true Costas Loop, and had three capabilities that modern SDR sync detectors so far lack:

1) It could sync on a DSB suppressed carrier signal -- no carrier was required to lock it on frequency. It did this by generating a DC correction voltage from a phase detector. John P. Costas' original 1957 articles in Proceedings of the IRE discuss this method and Bill used it.

2) It could output stereo, with the QRM from the USB panned hard right, the QRM from the LSB panned hard left, and the desired signal in the center of your head. This allowed the brain to distinguish the desired signal amazingly well in the presence of strong QRM.

3) It could cancel the QRM from either the LSB or USB (switch selectable) while -- amazingly -- still receiving BOTH sidebands of the AM/DSB signal. This worked because the detector's Q output contained zero audio from the desired signal, which was in a quadrature null. Modern software sync detectors, like the Anan's, lose 6 dB compared to a true Costas Loop, because they are coded to use bandwidth filtering, not true phase nulling, to achieve sideband filtering."

I am wondering if the stereo and center effects mentioned above can be reproducible within PowerSDR?

Thanks,
Jim
Wd5JKO

[ke9ns]

Jim,

I am not very knowledgeable on the subject, but I can take a look at what I can do.

SAM in PowerSDR will just look for the largest carrier to sync on, so if someone is transmitting AM within your passband and its a stronger carrier, it will lock onto them. From what I can tell of the code, SAM (on receive) is just DSB with a carrier lock.

With QRM, usually I just pull the Right or left side of the receiver passband closed (with the mouse) but leave the intended carrier within the passband.

BUT.. I also added the ability to use SSB on RX, and AM for transmit.
Just pull the rx passband (right or left side) "across" past the carrier. Now you will still transmit AM, but receive it as SSB. This helps with weak AM stations and QRM.

I know in SSB & DSB you can still activate "BIN" (I/Q to Left/Right), but you cannot in SAM mode.

Darrin ke9ns