One additional note ... it is not necessary to be running ESSB to
generate the "false carrier". Bandwidth is not an issue - only that
there be *excess* low frequency drive to the modulator (analog or
DSP). False carrier (ringing below 50 Hz) tends to be most common
in situations where low frequency audio has been "enhanced" or high
frequencies have been cut and the mic gain increased for more "talk
power". Low frequency ringing is more prevalent with electret mics
due to their higher output and additional low frequency response
but it can also be noticed on dynamic mics when males with voices
that are particularly low pitched "close talk" a mic due to the
increased low frequency response from the proximity effect.
This low frequency ringing is a major reason (in addition to hum and
background noise reductions) professional audio guys use a (typical)
100 Hz low cut filter in "talk" radio. A six to 12 dB reduction in
the strong fundamental does not upset the voice's overall tonal balance
but the 10 dB or so reduction in low frequency energy prevents overload
problems in the electronics.
73,
... Joe, W4TV
On 4/29/2014 10:04 AM, Joe Subich, W4TV wrote:
A "spike" on the left of a USB signal is normally an indication of
insufficient carrier suppression (carrier leakage). Signal to the
left of that is generally insufficient opposite sideband suppression
(sideband leakage) or regenerated sideband due to excess IMD in the
transmitter.
However, if the other station is using ESSB with excess low frequency
content below 150 - 200 Hz, the spike can be a "false carrier" due to
ringing in the modulator when it is over driven by the excess low
frequency content. "False carrier" or modulator ringing is almost
always accompanied by IMD and regenerated opposite sideband.
Most SSB users will tend to zero beat the false carrier. That will
cause a "robotic" or "hollow" sound because excess low frequency
content, the signal is actually tuned slightly off frequency, and
the normal/regenerated sidebands are not producing the same/in phase
audio.
73,
... Joe, W4TV
On 4/29/2014 9:31 AM, Slava Baytalskiy wrote:
Hello everybody!
Ever since i got my new P3 - i've been looking at people's signals
(naturally).
And i've noticed the following:
When using USB on 10 meters, talking locally, there are a couple of
folks that use ICOM radios and i can see these spikes on the left of
the carrier.
Normally, in USB, all the signal shows up on the right, correct?
But with these guys there's a lot of signal on the left as well.
And they sound a bit robotic, as if they were off frequency a bit. But
they aren't.
When they switch to, say, Yaesu or a Kenwood i don't see that same graph.
But on the ICOM its very pronounced (except the older ones like 756
Pro III).
Saw it last night with an ICOM IC-7000.
Is this normal? Has anyone else noticed this?
This P3 is certainly giving me a lot of insight i didn't have before...
Thanks in advance!
Slava B
W2RMS
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