AM Operation Using Power SDR with Flex and Other SDR Platforms

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W1AEX:
Hi Mike,

Yah, I forgot to put the washers in there and have paid the price with scratches all over the virtual panel. Thankfully, Photoshop makes it easy to fix!

Lots of SDR-1000 users have tried out the 2.0.22 final release package and many like it. The new software takes some getting used to, and several settings, such as the AGC-T behave differently from the 1.x versions, but there are many enhancements. The biggest change is that they moved the ALC module to the output side of the DSP module. This eliminated issues that many users had with overshoot when driving solid-state amplifiers. If you like to play with Photoshop, you can modify the GUI interface with the 2.x versions and that adds to the fun.

I believe the guys with the SDR-1000 series can float back and forth between the 2.x and 1.x versions without any changes in firmware, so it might be worth looking at the new software to see if it suits you.

Good luck with the FA-66!

Rob

W1AEX:
Creating Your Own "Skins" for PowerSDR:

While this is not exclusively related to AM operation, a number of smug AM Flex users have asked me about how to create custom skins like the one shown in the image above. If you are interested in messing around with this, a brief tutorial along with some custom starter graphics packs are available at this link:

http://www.w1aex.com/psdr/psdr.html

In addition to being able to design your own skins with the custom templates you can download pre-made custom skins. A few vintage examples, such as the Black Wrinkle, National NC-155, and the Collins Retro 32V skins are shown below. Mike - W8BAC collaborated on the Collins skin with some excellent photography and color setting advice. You can take a YouTube video tour of about a dozen custom skins that are available by visiting the link below. What do you make of the station that the Flex is tuned to? Is this an updated 2012 version of a shortwave numbers station with overly processed audio?

http://www.youtube.com/watch?v=U0bv_WYMck4

Have fun!

Rob W1AEX

WA1GFZ:
Rob,
I just bought a second receiver module for HPSDR and doing diversity/ beam steering in software. it is very cool. I lost all my audio settings for TX so need to reload at some point. I'm actually considering a third module once the software guys proves his software works with three.

W1AEX:
Frank,

The second receiver module coupled with the diversity capabilities makes things very interesting. I have no doubt that function will amuse you for a very long time! While you are moving forward and making things more complicated, I'm continuing down the path toward making things simpler at this place. I only have to throw about 15 switches to get on the air instead of 30 or 40. Yah... that's much better!

Flex just released the beta version of PowerSDR 2.2.2 Tuesday night. It appears to be rock solid, and they have a new tunable notch filter to go along with the auto-notch filter. The new TNF is awesome for use on AM as you can lock it to a carrier that's any distance from your operating frequency, adjust the width of the notch to whatever you want, and adjust the depth to the point where an S-9 carrier simply disappears. It's perfect for when propagation causes our QSO's here in the northeast to collide with the mid-west guys. It also will completely notch out SSB monkey chatter that shows up in either sideband, without having to remove the whole upper or lower sideband. You can make a permanent notch that stays active on any assigned frequency if you wish. That takes care of the annoying spurious crud from someone's stupid baby monitor that shows up here close to the beacon frequencies on 6 meters.

So many toys, so little time!

Good luck with the diversity/beam steering setup!

Rob

W1AEX:
Notes regarding AM Operation with PowerSDR version "2.2.3 Final Release"

This release of PowerSDR includes the long awaited fix for the AGC problem that plagued AM users with all versions of 2.x that were released previously. At some point during the end of the 1.x versions, Flex altered the way that the AGC responded to AM signals. Instead of responding appropriately to the carrier of a signal, the AGC responded instead to the energy in the sidebands. This caused the receiver to detect AM signals in such a way that they sounded horribly over-compressed. By riding the AGC-T control, and using a very slow AGC repsonse time, users could sort of compensate when strong signals were present, but when a weaker station showed up it became necessary to constantly fuss with the AGC-T levels. Fortunately, with the 2.2.3 release Flex has fixed this so that the AGC now responds appropriately to the carrier of an AM signal and ignores the sidebands. The AGC-T level now behaves very much like an RF gain control, strong and weak AM signals sound fine together, and you can pretty much set it and forget it.

This is an important note regarding the potentially disastrous behavior of the Drive control in versions 2.2.2 beta and 2.2.3 final release while in the AM mode. Previously, the maximum carrier power with the drive control set to 100 for both AM and FM was roughly 35 - 40 watts. An AM carrier setting of 50% pretty much guaranteed that you could not inadvertently exceed a carrier power of 20 watts even with the drive control set to 100. This left plenty of head room for modulation, and made it possible to drive an amplifier without too much worry about over-driving things. When Flex completely re-wrote the FM module to add new features and to correct issues with that mode in the 2.x versions of PowerSDR, the behavior of the drive control changed radically for both AM and FM. At this time, if the AM carrier control is set to 100% and the drive control is set to 100, the Flex will produce a carrier at full output (+100 watts). This would result in a horrendous AM signal for the obvious reason that there would be zero headroom for modulation, but more importantly, this could be disastrous for those with amplifiers that only require a small amount of drive power. Keep this in mind when upgrading to either of these versions when creating TX profiles for AM and FM! Once my amplifier (2 x 3-500's) is tuned and loaded, I typically run with my AM carrier setting at 40% and my drive level set between 15 and 30 to run anywhere from 150 watts to 250 watts of carrier power depending on conditions. When modulating heavily, I see peak power reaching between 1000 - 1500 watts regularly and the scope reports a healthy looking signal.

Rob W1AEX

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