Modulation

[K5IIA]

What would cause a valiant to have more modulation on the lower side band then the upper. Or vice versa.  I was working a guy earlier. And could see it on the pan adapter.

[Steve - K4HX]

Maybe some FMing of the carrier.

[K5IIA]

I didn't notice any movement of carrier and modulation stayed imbalanced the hole time on the lower side and.  I don't know. This is the second station I have noticed that on in the last fee months.

Every thing seems fine. Sounds ok. But one side and will be noticeably stronger.

[Steve - K4HX]

You stumped this chump. 

[Pete, WA2CWA]

Maybe the sweep linearity of the panadapter is off, some non-linearity in the mixer circuitry of the receiver, AGC anomalies dependent on station strength, unusual atmospheric characteristics.

[W7TFO]

Maybe it is just radio...

73DG

[KF1Z]

Transmitter needs alignment?

I am unfamiliar with the Valiant...
Is is a SSB/AM rig?

I notice that same thing on rice-boxes such as Kenwood 440, 430 etc...
Usually right after the xtal filters were changed ( like installing the AM filter), but
the radio was not aligned afterwards...

After alignment ( IF freq, balance etc..) all was normal.

Just a shot in the mist.


 

[k4kyv]

There could be some phase or frequency modulation of the carrier, simultaneous to the amplitude modulation.  It wouldn't be immediately obvious with the BFO in the receiver, since the modulation index would most likely be well below one. With just the right proportion of AM and PM/FM, emphasis appears on one sideband while the other is attenuated.

When amateurs were first becoming interested in SSB after WWII, there was an article published either in QST or CQ, describing a full-carrier pseudo-SSB technique of phase modulating the VFO of an otherwise unmodified AM transmitter to produce this effect.

The mechanics of modulation and vector analysis of sidebands and carrier relationships are very interesting.  For instance, if you take a full carrier double sideband AM signal and rotate the phase of the carrier 90° relative to the sidebands, all amplitude modulation disappears and you end up with a phase-modulated signal at a low modulation index.

Armstrong's first FM transmitter used this technique to generate frequency modulation.  He started out at some frequency below the AM broadcast band, rotated the carrier phase to convert it to PM, then multiplied it up to VHF to proportionately increase the modulation index.  Then he applied the appropriate de-emphasis to the audio curve of the amplifier feeding the modulator, to convert PM to FM.

[Steve - K4HX]

It's a plate modulated transmitter. No alignment needed.

Transmitter needs alignment?

I am unfamiliar with the Valiant...
Is is a SSB/AM rig?

I notice that same thing on rice-boxes such as Kenwood 440, 430 etc...
Usually right after the xtal filters were changed ( like installing the AM filter), but
the radio was not aligned afterwards...

After alignment ( IF freq, balance etc..) all was normal.

Just a shot in the mist.


 

[Opcom]

How would FMing affect one sideband?

I can see FMing affecting the signal as the modulation half-cycle swings positive or negative and that causes a variation in a B+ to the oscillator (B+ which is not regulated or decoupled). As the frequency is pulled, the sharply tuned tank becomes inefficient when the F is off.

So is there a VR tube for regulating the oscillator and it is not lit?

Is the transmitter RF chain tuned slightly to one side of the carrier causing attenuation of one sideband and possibly emphasizing the other?  (would take lots of Q!)

[W7TFO]

Perhaps it is feeding into a reactive (read bad SWR) load?

That can make the sideband(s) check in, but never check out...

73DG

[flintstone mop]

Is what you are seeing as imbalanced modulation on your panadapter constant and not something like a wave floating through the bandpass of the monitor?
I see that a lot monitoring a SW B'cast playing music. It might be better described as selective fading. It does weird looking things to a modulated AM carrier. The carrier will actually drop out at times while "this wave" is going through.
If it is a constant imbalance, maybe your receiving system needs alignment. I.F. bandpass is not giving a flat response...........dunno

[WD8BIL]

What pan adaptor are you using, Brandon?

[K5IIA]

Pmsdr with Hdsdr software. I'm pretty sure it is the transmitters. Shows up good in waterfall. There will be one side and with more audio power then the other. It's not common. But I do see it from time to time. One was a valiant. The other was an elmac or how ever you spell it.  It was clear as day. And there were other stations in at same time. That did not show that.  Not sure. I just thought there might e a simple explanation.

[KM1H]

I am unfamiliar with the Valiant...
Is is a SSB/AM rig?

Its a 3 pill box and if you work on one you will need other pills

Carl

[w1vtp]

How would FMing affect one sideband?

<snip>

It is the result of instantaneous FMing as the result of some voltage regulation problems.  This can frequently be observed on ARC-5 transmitters where there are voltage regulation problems.  Q of tank circuits or alignment of a high level class C transmitter could not produce this effect.  

Having said this, I wonder of some sort of phase difference of a self-modulated screen grid circuit in a push pull final could be made have this effect but the transmitter in question does not have a push-pull final.  I’m putting my $$ on the effect of instantaneous FMing, having seen this with ARC-5 transmitters.

It would be easy enough to confirm. Just use the FM button on the PowerSDR and compare that signal with an AM transmitter that does not have an imbalanced sideband appearance. You will hear the FM component with the station of interest.  The "normal" transmitters will have either no AF or a much lower demodulated AF

Al

[kb3rdt]

I seen it before here is k3sqp on his valiant

http://www.youtube.com/watch?v=C6Penl7RFWk

[flintstone mop]

I seen it before here is k3sqp on his valiant

http://www.youtube.com/watch?v=C6Penl7RFWk

Good presentation!
It did not affect the TX audio.

[w1vtp]

I seen it before here is k3sqp on his valiant

http://www.youtube.com/watch?v=C6Penl7RFWk

Good presentation!
It did not affect the TX audio.

All things being equal and reasonably adjusted, you won't.  You should hear / watch KA1ZZC's SBE transmitter.  The audio quality is great, surpassing many stock EJF's, Collins gear.  The only time you would have a problem is if the wobble (instantanaeous FM plus wobble due to swaying antenna) exceeds the bandpass of the IF filter you have selected.  I don't even try to put on the Sync AM detector when HLR's SBE is on - it's awful! 

[w1vtp]

Here's my final commentary on unsymmetrical sidebands on an AM signal.  This is from an uncopyrighted document put out by Agilent (formerly Hewlett Packard)

AM plus FM (incidental FM)

Although AM and angle modulation are different
methods of modulation, they have one property in
common: they always produce a symmetrical sideband
spectrum.

In figure 33 we see a modulated carrier with asymmetrical
sidebands. The only way this could occur is
if both AM and FM or AM and phase modulation
existed simultaneously at the same modulating frequency.
This indicates that the phase relations
between carrier and sidebands are different for the
AM and the angle modulation (see appendix). Since
the sideband components of both modulation types
add together vectorially, the resultant amplitude of
one sideband may be reduced. The amplitude of the
other would be increased accordingly. The spectrum
displays the absolute magnitude of the result.

[KZ5A]

I've seen this apparently asymmetrical modulation before from a Ranger 2 on 40M.   

The effect goes completely away in that transmitter if it is switched from VFO to Xtal.

73 Jack KZ5A

[steve_qix]

What would cause a valiant to have more modulation on the lower side band then the upper. Or vice versa.  I was working a guy earlier. And could see it on the pan adapter.

Assuming the pan adapter was working correctly, at these frequencies the only real cause of this is incidental FM or PM on the signal.  Seen it MANY times, and have had it in my own transmitters when the VFO was insufficiently shielded.

[Steve - K4HX]

To me that would indicate an instability in the VFO that is producing some PM/FM.

I've seen this apparently asymmetrical modulation before from a Ranger 2 on 40M.   

The effect goes completely away in that transmitter if it is switched from VFO to Xtal.

73 Jack KZ5A

[w1vtp]

Put an AC coupled scope on the plate and / or SG supply for the oscillator.  Bet you see some modulation component showing up.  I don't have a manual for that xmtr but it might be either a VR tube not firing due to a supply resistor changing value upward or the VR tube itself not firing

Al