As Jim said, IM products are a really big deal!
Most of the rigs on the bands have very poor signals. Along with
bipolar transistors and sweep tube amps, we have been inundated with
many thousands of cheap rigs with poor signals for roughly 40 years..
Had we stuck with good design, the bands would sound quite different
today. HOWEVER that is the price growth often brings.
Today's rigs are marvels of technology with the capability of meeting,
or exceeding the signal quality of the old top end tube rigs for the
first time. Add predistortion or better yet, dynamic predistortion and
you can run a LOT of very clean power. Unfortunately those very rigs
give the user access to parts of the signal chain that would have been
better left alone. So now we have top end rigs capable of exceptional
signals that give the user control over things that can generate signals
that sound off frequency to horrible quality. For SSB the first thing
is following the setup directions precisely as given in the manual.
Excess compression and clipping are endemic during contests. I often
hear signals wiping out 10 to 15 KHz. Loud, does not require wide, or
excessive compression, or clipping. A loud, clean signal will win over
the horrible sounding broad signal most of the time. I heard one DX
station tell one such station to stop calling as his call would never be
entered in their log!
Tetrode amps have gained a bad rap for dirty signals when the problem is
the person tuning said rig didn't know how to tune a Tetrode. There is
very little difference in the settings between tuning up for max output
(Proper method for a GG Triode) and max screen current in the Tetrode,
but there can be a very noticeable difference in signal quality.
I blame much of this (ll) on the dumbing down of the exams to earn the
licenses. On top of this, they want to develop an entry level license?
What a wast of resources!
Also, some exciters use ALC to limit the output, meaning if you set it
to run half power to drive an amp the exciter comes on at full power to
develop that required ALC limitation. That hits the high gain amp with
lots of over drive for a brief time leading to splatter and poor IM
products.
73, Roger (K8RI)
On 4/10/2017 3:14 AM, Jim Brown wrote:
On Sun,4/9/2017 8:24 PM, Steve Wright wrote:
Surely most multi-band yagi's, 1/4y verticals, plain ol' dipoles, and
any other competitive HF antenna that you would WANT to poke some
horsepower into is gonna have <1.5:1 SWR?
At one frequency, perhaps. But it takes some real tricks (good ones)
to get a dipole apparent SWR (as read at the transmitter) under 2:1
for 400 kHz of 80/75. Ditto for 160M.
Maybe you alligators want to
tune up your half size g5rv on 160M or similar?
It's almost as baffling as the fixation with IMD..
IMD is a VERY big deal if you care about not making a mess on the band
when you transmit. IMD ==> wide clicks on CW and splatter on SSB. If
you read FCC Rules, it says that we must use the minimum bandwidth
required for the mode of transmission. Since Elecraft introduced their
P3 spectrum display (almost a lab quality instrument, by the way), I'm
repeatedly disgusted (and QRMed) by many of the dirty signals I hear/see.
A disgustingly large number of SSB signals have almost as much
splatter in the bandwidth of their suppressed sideband, and an equal
amount above where the sideband filter in the rig cuts off. That's ALL
IMD, much of it in the amps, but some in the rigs themselves. Causes
include the output device driving a mismatch, overdriving the amp,
driving the amp at full output of the rig and letting ALC throttle it
back, and even IMD produced in the rig itself through bad design of
"processing" that includes the RF chain. W4TV has written about this.
K6XX taught me that a mis-tuned amp (or a solid state amp working into
a mismatch load) produces a lot more clicks and splatter than one that
is properly tuned. We're both serious contesters, and when I moved in
3 miles S of him, he made damn sure that I knew how to tune my Titan
amps. Bob is an engineer working at Elecraft, where he works as a
production engineer. As a result, we can work with 500 Hz of each
other on CW at legal limit and hear the other as simply another strong
signal, and easily work fairly weak signals. We're both running tube
amps.
Isn't the goal to get on the air, work some DX and bend some
jealous locals' S-meters?
I'm and old fart, and when I was young, I was taught that with rights,
we have responsibilities. We have the right under FCC Rules and our
license to run big power to big antennas, but we also have the
responsibility to keep our signal CLEAN.
Cmon people.. Make a resonant antenna already!
I'm a VERY strong believer on that score. All of my TX antennas (about
a dozen) are resonant.
On a separate topic, sort of -- the amp sold for use with the 6700
Flex can run SO2R. For those who don't contest, that means there are
two radios on different bands, and one radio is always calling CQ
while the other is listening. Or, when things get slow, dueling CQs.
Think about this with RTTY -- it could be damn near solid keydown at
the end of a contest when you've worked almost everyone. The Flex 6700
is set up so that that single radio can function as two complete
receivers, and transmitters than can be switched between two outputs.
If a single amp like the one announced does SO2R, it's going to see a
duty cycle that approaches twice that of an amp connected to only one
of those outputs.
As to CCS and ICAS -- it's been a long time since I've looked at the
definition, but CCS clearly means that you turn the transmitter on and
it stays on 24/7. Think broadcast, or a repeater that stays up for
very long periods. As I recall, ICAS means intermittent commercial and
amateur service. But I could be wrong. And these ratings are for the
output devices, which when I was knowing about it, were hollow state.
73, Jim K9YC
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