On 2015-05-22 2:23 PM, Mike Waters wrote:
What bugs me is that most (if not all) SS amps that are overdriven
generate considerably more IMD than most tube amps would if
overdriven by the same amount.
First, tube amplifiers (except for the sweep tube variants) have more
headroom than a SS amp. Second, the tube amplifier saturates slowly
while the gain curve of solid state devices have a very pronounced
"knee".
I can pick out an overdriven SS amp almost as soon as I hear the
signal. And when we tune 3 kHz away and the signal is still fairly
strong, there's almost zero doubt that there's an SS amp behind that
trash.
If you want an easier way to tell ... just tune to the "opposite"
sideband or look at the other side of the suppressed carrier on a
panadapter/spectrum analyzer. Overdrive/IMD causes the suppressed
sideband to be regenerated. That was one of the reasons analog (NTSC)
TV transmitters required predistortion - to keep the signal in the
channel.
> ... The band will not get better until the signals get clean.
The signals will not get clean until ARRL Labs stops being a lap dog
of the manufacturers. They need to be very loud in condemning rigs
with IMD worse than -36dBc (-42dB PEP), the rigs with really terrible
transmitted phase noise, rigs with "wide" (> 2.7 KHz) transmit audio
response, those with user menus that allow CW rise time to be set in
such a way as to guarantee terrible key clicks and those with FSK
that is two to three times wider than necessary.
73,
... Joe, W4TV
On 2015-05-22 2:23 PM, Mike Waters wrote:
Well stated. However, at the risk of sounding pessimistic, I think that's
wishful thinking.
What bugs me is that most (if not all) SS amps that are overdriven generate
considerably more IMD than most tube amps would if overdriven by the same
amount.
I can pick out an overdriven SS amp almost as soon as I hear the signal.
And when we tune 3 kHz away and the signal is still fairly strong, there's
almost zero doubt that there's an SS amp behind that trash.
I think most people on this list know exactly what I mean. But I don't
think there's a single thing we can do about it.
73, Mike
www.w0btu.com
... The band will not get better until the signals get clean.
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