AM stereo?

KD2AFV
Posts: 2
Joined: Sun Apr 19, 2020 3:05 pm

AM stereo?

Postby KD2AFV » Sun Apr 19, 2020 3:45 pm

Might be a wild idea, but is it possible to TX in stereo in the AM mode? Maybe left channel in the lsb and right channel in the usb with a injected carrier. Feel free to call me crazy lol
User avatar
w-u-2-o
Posts: 2781
Joined: Fri Mar 10, 2017 1:47 pm

Re: AM stereo?

Postby w-u-2-o » Sun Apr 19, 2020 3:56 pm

Theoretically this could be done, but it's not supported in the current version of software. Nor would it be truly useful for mere voice, only for music.

There is some interesting history here, though: https://en.wikipedia.org/wiki/AM_stereo
KD2AFV
Posts: 2
Joined: Sun Apr 19, 2020 3:05 pm

Re: AM stereo?

Postby KD2AFV » Sun Apr 19, 2020 4:14 pm

True the only way would be to have two mic's connected to get stereo voice. And there wouldn't much point in it. Was more of a thought if it would be possible to do in software. The history of AM stereo has been discussed on 3.885 a bit lately and it got me thinking.
User avatar
w-u-2-o
Posts: 2781
Joined: Fri Mar 10, 2017 1:47 pm

Re: AM stereo?

Postby w-u-2-o » Sun Apr 19, 2020 6:02 pm

An often overlooked feature of the software is the ability to do true single sideband AM reception. This is handy for QRM. I'm not in front of my radio PC right now, but you can find that option on the AM setup page.
User avatar
W1AEX
Posts: 329
Joined: Sun Apr 09, 2017 6:17 pm
Location: Connecticut, USA
Contact:

Re: AM stereo?

Postby W1AEX » Sun Apr 19, 2020 8:16 pm

The only person I have spoken with on the air who has actually built an AM stereo transmitter that he uses on 75 meters is Jerry - WA2FNQ. I believe he used the Magnovox system to generate the signal. Unfortunately, the biggest stumbling block seems to be the lack of receivers that can detect AM stereo. He has quite a bit of information here:

http://www.wa2fnq.com/fnq/amstrdoc.htm

Scott, you are correct about the usefulness of the independent sideband receive capability in PSDR mRX PS and Thetis. Warren's implementation of this function does not degrade the fidelity of the signal which makes it far superior to simply grabbing the edge of one sideband and sliding it toward F-0 in the panadapter. Of course independent AM transmit is also very useful in the AM Ghetto around 3885.

Rob W1AEX
"One thing I am certain of is that there is too much certainty in the world."
K1LSB
Posts: 86
Joined: Wed Feb 05, 2020 5:25 pm

Re: AM stereo?

Postby K1LSB » Sun Apr 19, 2020 9:47 pm

W1AEX wrote:Warren's implementation of this function does not degrade the fidelity of the signal which makes it far superior to simply grabbing the edge of one sideband and sliding it toward F-0 in the panadapter.

Rob W1AEX

Rob,

How does a manual sliding of a sideband edge degrade the fidelity of the signal? All of the information in the signal is contained in either sideband.

I've done an A-B comparison of manually-configured single- vs double-sideband reception and can discern no difference other than volume, which is distinct from fidelity.

And if there is no difference in the fidelity, how can the Thetis implementation be "far superior" to a simple manual manipulation of a skirt?

Mark
User avatar
W1AEX
Posts: 329
Joined: Sun Apr 09, 2017 6:17 pm
Location: Connecticut, USA
Contact:

Re: AM stereo?

Postby W1AEX » Sun Apr 19, 2020 11:37 pm

Hi Mark,

Reducing the filter width by dragging the filter edge causes a narrowing Q effect on reception, whereas, the phase cancellation method implemented by Warren in both PSDR mRX and Thetis causes very little change in the recovered audio. In fact, other than a slight click when going from both sidebands to either LSB or USB reception I can't hear any degradation at all.

Take a listen to a random BCB station in the video below. Other than the station transmitting crap audio in the first segment, it pretty clearly demonstrates the superiority of the phase cancellation method.

73, Rob

"One thing I am certain of is that there is too much certainty in the world."
K1LSB
Posts: 86
Joined: Wed Feb 05, 2020 5:25 pm

Re: AM stereo?

Postby K1LSB » Mon Apr 20, 2020 1:32 am

Thanks Rob, that's a pretty convincing video.
User avatar
W3MMR
Posts: 82
Joined: Thu Jul 11, 2019 8:36 am
Location: Chester, PA
Contact:

Re: AM stereo?

Postby W3MMR » Wed Apr 22, 2020 7:55 pm

W1AEX wrote:The only person I have spoken with on the air who has actually built an AM stereo transmitter that he uses on 75 meters is Jerry - WA2FNQ. I believe he used the Magnovox system to generate the signal. Unfortunately, the biggest stumbling block seems to be the lack of receivers that can detect AM stereo. He has quite a bit of information here:

http://www.wa2fnq.com/fnq/amstrdoc.htm

Scott, you are correct about the usefulness of the independent sideband receive capability in PSDR mRX PS and Thetis. Warren's implementation of this function does not degrade the fidelity of the signal which makes it far superior to simply grabbing the edge of one sideband and sliding it toward F-0 in the panadapter. Of course independent AM transmit is also very useful in the AM Ghetto around 3885.

Rob W1AEX


Rob,
How come when i slide one or the other side of the passband, it messes with the volume and tone of the received station? I usally dont do it because of that. But if im to use a websdr or a KiwiSDR online and do the same thing, it has ZERO effect. What causes this and is there a way to defeat it?

Thanks

Perry

***UPDATE***
Well, now I saw your post with the video and how you mention the narrowing Q effect. How can this be defeated? I cant stand it honestly.
Last edited by W3MMR on Wed Apr 22, 2020 7:57 pm, edited 1 time in total.
Studio "A" - Anan 200D, P2 1.9, Thetis 2.6.9c3, Dell XPS 8700 i7-4770k, Samsung EVO 860 SSD, Nvidia GeForce GTX1050ti, 16GB RAM, Shure SM7B, AL80BX
Studio "B" - Heath-Kit DX100, D-104, National NC-303, Hammarlund HQ-140-X
User avatar
W3MMR
Posts: 82
Joined: Thu Jul 11, 2019 8:36 am
Location: Chester, PA
Contact:

Re: AM stereo?

Postby W3MMR » Wed Apr 22, 2020 7:56 pm

Oh and Rob, that FET fixed my 200d. Thanks for the schematics and pics you sent. You were a life saver.

Perry
Studio "A" - Anan 200D, P2 1.9, Thetis 2.6.9c3, Dell XPS 8700 i7-4770k, Samsung EVO 860 SSD, Nvidia GeForce GTX1050ti, 16GB RAM, Shure SM7B, AL80BX
Studio "B" - Heath-Kit DX100, D-104, National NC-303, Hammarlund HQ-140-X
User avatar
W1AEX
Posts: 329
Joined: Sun Apr 09, 2017 6:17 pm
Location: Connecticut, USA
Contact:

Re: AM stereo?

Postby W1AEX » Wed Apr 22, 2020 8:53 pm

Hey, good for you for warming up the soldering iron Perry! Glad you fixed it!

That Q effect on AM/SAM when narrowing the filter by sliding one edge in the panadapter has always been there, going back to the Flex version of PowerSDR. I believe it happens because you are bringing the very sharp/steep filter edge very close to F0 and that produces the high Q sound effect. You might be able to mitigate it a bit by reducing the RX "Filter Size" setting in the DSP > Options tab to soften the filter edge a bit. Unfortunately, I think that's going to give you a sloppy RX filter with sideband too.

The only way to avoid it cleanly and completely (that I am aware of) is to use SAM mode and the "Sideband Select" receive controls in the DSP > AM/SAM tab. That works beautifully to completely remove the sideband experiencing interference without any degradation to the received signal. Just make sure you leave that menu tab open when you do this until you return it to LSB + USB because it sounds so good you'll forget you shut down one of the RX sidebands and you'll end up operating that way for days/weeks/months until you happen to stumble onto those settings again! I've done that several times...

Rob
"One thing I am certain of is that there is too much certainty in the world."
User avatar
W3MMR
Posts: 82
Joined: Thu Jul 11, 2019 8:36 am
Location: Chester, PA
Contact:

Re: AM stereo?

Postby W3MMR » Wed Apr 22, 2020 10:54 pm

W1AEX wrote:Hey, good for you for warming up the soldering iron Perry! Glad you fixed it!

That Q effect on AM/SAM when narrowing the filter by sliding one edge in the panadapter has always been there, going back to the Flex version of PowerSDR. I believe it happens because you are bringing the very sharp/steep filter edge very close to F0 and that produces the high Q sound effect. You might be able to mitigate it a bit by reducing the RX "Filter Size" setting in the DSP > Options tab to soften the filter edge a bit. Unfortunately, I think that's going to give you a sloppy RX filter with sideband too.

The only way to avoid it cleanly and completely (that I am aware of) is to use SAM mode and the "Sideband Select" receive controls in the DSP > AM/SAM tab. That works beautifully to completely remove the sideband experiencing interference without any degradation to the received signal. Just make sure you leave that menu tab open when you do this until you return it to LSB + USB because it sounds so good you'll forget you shut down one of the RX sidebands and you'll end up operating that way for days/weeks/months until you happen to stumble onto those settings again! I've done that several times...

Rob


Ive been trying out SAM with a single sideband selected and its awesome! Thanks for pointing that out Rob. Its made the AM window in the evening an enjoyable experience again!
Studio "A" - Anan 200D, P2 1.9, Thetis 2.6.9c3, Dell XPS 8700 i7-4770k, Samsung EVO 860 SSD, Nvidia GeForce GTX1050ti, 16GB RAM, Shure SM7B, AL80BX
Studio "B" - Heath-Kit DX100, D-104, National NC-303, Hammarlund HQ-140-X
ron4094
Posts: 22
Joined: Sun Nov 24, 2019 1:16 am

Re: AM stereo?

Postby ron4094 » Sun May 24, 2020 2:49 pm

Rob,
You mentioned that the Q effect on AM/SAM has always been there going back to the Flex version of PowerSDR. During the 12 years that I used my Flex 1000 I never noticed any change in audio quality when narrowing one edge of the panadapter on AM. I used many versions of Power SDR over the years including V1..., V2... and KE9NS. This doesn't mean it wasn't there but I never noticed it. To be honest, I was surprised and disappointed when I instantly noticed this effect with the Anan 7000. I now do use the sideband select feature in SAM which does work but is less convenient than simply sliding one edge of the panadapter.

Ron
WB2RON
User avatar
w-u-2-o
Posts: 2781
Joined: Fri Mar 10, 2017 1:47 pm

Re: AM stereo?

Postby w-u-2-o » Sun May 24, 2020 3:57 pm

ron4094 wrote:To be honest, I was surprised and disappointed when I instantly noticed this effect with the Anan 7000.
It's important to note that the signal processing in question in all openHPSDR versions of PowerSDR has been the same since before the original Hermes board, so this is not something that is peculiar to the 7000, but rather something that is associated with PowerSDR (and Thetis).

Return to “Thetis”