Thanks for that post, Greg.
Only Rob's last couple of years of Contest University (CTU) presentations are
archived as videos.
For previous years, just go to my web site and you will find all of his
presentations.
For some there is even audio accompanying the presentation.
Greg, your "Me thinks" are correct for many radios but by far not for all.
There are still some pretty crappy radios being offered, especially in the
under $1K category.
Adam's presentation is probably above the comprehension level of most of us.
When he addresses the problems of "dither", I would suggest that most OM have
no idea what dither is. Indeed it was an outstanding presentation but not for
everyone.
(Notice I said "us" - me included).
Predistortion: forget it. Not going to happen for a long time to come. Even
Flex has not yet committed to a time frame for introducing it, though they are
finally beginning to hint at the will to do it. And just because new radios
have it, that won't stop the millions of older radios out there that will
remain on the bands for a long time to come.
But YES, that would be a wonderful world. Imagine a world without wars!
Our problem is not lack of predistortion in our transmitters. Our problem is,
99% of our hams don't even understand distortion. This whole concept of 3rd
order IMD is VERY misleading.
The spec says, when we blow two tones into an SSB mic and look at the signal
strength of the 3rd order IMD of our transmitted signal, it has to be down by
30 dB. Sounds good, and would be if not for the several "gotchas".
First of all, NOBODY blows just two tones into their mic. Our speech content
has thousands of tones creating thousands of harmonics (and harmonic distortion
products) that are emitted from our transmitters. Besides the 3rd order
products, we NEED to be looking at ALL products... 4th, 5th, 9th, 11th
products, etc. Normally a good transmitter (i.e. the Collins 32S3) generates
the two tones and successive harmonic products, with each successive weaker
than its predecessor. Would be nice. Unfortunately several transmitters are
being sold today that have higher order IMD products higher than their lower
order IMD products. This is disasterous and creates an incredibly wide signal,
ESPECIALLY when driving a linear amp. The worst of all (as measured by Rob
Sherwood) is the YAESU FT-450. And even worse, Yaesu advertises that radio as
having a clean transmitter with MOSfet transistors. Garbage; it's the worst in
the industry. SHAME ON YAESU!
Which brings us to the next problem... bipolar vs. MOSfet amps. 3rd order IMD
is measured into a 50 Ohm purely resistive dummy load. Fact is, bipolar
transistors do not like reactive loads. As soon as the load (antenna) is not
purely 50 Ohm resistive, distortion products increase. Since we have acquired
many new bands, the trend to multi-band antennas is huge...(I'm a contributor
to that, I make and sell such antennas). Unfortunately these will never be 50
Ohms resistive. They are always reactive. But even a dipole is only purely
resistive for a very narrow frequency span. Our antennas are causing IMD!
This can be minimized by always using a matchbox between our transistorized
radios and the antenna.
But wait, every matchbox has loss, so what I am suggesting may result in us
having only 90w into the antenna, rather than the full 100w. Yes, but it will
be 90 clean watts. The QSO partner 3 skips around the globe will never hear
the difference but the hams in your local area as well as those in the first
skip zone may very well hear the negative results if we don't do that.
Finally, broadband phase noise is a problem with many of today's transmitters.
This is not so much a problem at distant stations but can be significant in our
local vicinity (within 5 miles or so). There are transmitters, even very
expensive transceivers such as the IC-7600 which will disturb every ham within
a 5 mile radius when they transmit, regardless of band they are operating on.
Not picking on that particular radio. Most of today's radios are that way!
Until "WE THE PEOPLE" begin to speak out against these easily avoidable
atrocities, our bands will never improve.
Last time I posted a message with this content, I was immediately chastised by
one OM who said as long as the transceiver OEMs are selling product within the
specs (3rd order IMD), we should not complain.
I say, he is not part of the problem, he IS the problem. It is guys like that
who hold our hobby back.
This email probably won't make me many friends. But I don't need lots of
friends. I need a few GOOD friends who will work with me to help improve the
environment around us... the air that we breath and the RF signal we send into
the ether.
73 - Rick, DJ0IP
(Nr. Frankfurt, Germany)
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Greg S via
TenTec
Sent: Sunday, September 11, 2016 5:48 PM
To: Discussion of Ten-Tec Equipment
Cc: Greg S
Subject: Re: [TenTec] OT: IP3 and Receiver Performance
I would suggest watching/reading, and studying the videos and PowerPoint
presentations archived at Contest University's website, paying particular
attention to those by Rob, NC0B. It is time WELL spent, even if (Maybe
ESPECIALLY if!!) you are NOT a contester. I would also suggest viewing the
presentation by Adam Farson, VA7OJ/AB4OJ given at Friedrichshafen just a few
short months ago:
https://www.youtube.com/watch?v=7kescw0V4rk
Me thinks ALL of the mid-to-upper-tier receivers made today, are capable of
performance better than most of us can, or need to, use. Me also thinks it's
time to start putting the pressure on some of these manufacturers to start
worrying more about their TRANSMITTERS. Food for thought: Imagine how nice the
bands would be if EVERY SSB signal was using Pre-Distortion (ANAN has Pure
Signal NOW). And NO CW transmitter was spewing out wide band trash and key
clicks. Your IC-718 receiver would probably be "good enough!"!!! (No disrespect
meant, the "IC-718" here can be replaced with several low-budget rigs from
several Mfg's, or any of the legacy down conversion rigs from 30 years ago.)
Any way, it sure is fun to be on this ride...... I think it will someday be
compared to the old Ancient Modulation Vs. Slop Bucket wars!
I am finding it hard to know when/where to jump into the SDR transceiver
fray..... Prices are being forced down, and technology is changing FAST on some
of the open source code. I bought an SDRplay, and have had a TON of fun with
it, so I am seriously considering the next level. It still hurts to think
about my 40" LCD, 60Hz, 720P Samsung "dumb" TV that I paid over $1700 for in
2007, but our old TV died, and we jumped in where we thought appropriate. (It
still works perfectly, but draws 3 times the energy of our 60" TV that cost 25%
of that $1700!!) I wouldn't want to be in Mr. Dishop's shoes in this market,
but do hope he comes up with a "winner" the first time around!!! Long Live
TenTec!
73, Greg, KC8HXO
SNIPPED SNIPPED SNIPPED
IMO there is no longer any easy way to rank them based on one or two
specifications alone.
Too many factors affect SDR receiver performance.
I am in favor of removing all SDR radios from the list and placing them in a
separate list, but I have no idea how we should do this.
My best guess would be to use NPR testing such as Adam Farson is conducting.
See: http://www.ab4oj.com/test/docs/npr_test.pdf
Adam has two lists, one for traditional heterodyning radios and another for SDR
radios.
But this is not perfect either.
As you see, the 7300 tops the list and as we all know, it has overload problems
due primarily to improper gain distribution throughout its front end stages.
Adam, Rob, and every test review I have read point out its overload problem.
Note that the two ANANs are ranked above the 6700, even though they do not have
dedicated BPF's for each ham band.
I'm not sure how Adam is ranking the SDR radios. It is not only NPR figures.
At this point we are way outside (above) my pay grade. I have no idea other
than to put these radios in the hands of contesters and let them report on
their experience.
In summary, we have come a long ways since first reporting on IP3 in the 1970s.
We cannot compare SDR radios to heterodyning radios based on their IP3 or
DR3 results.
At this point in time, I am not aware of any agreed method of testing and
reporting performance levels of SDR radios.
There are ongoing discussions between Rob, Adam, Bob Allison (ARRL) and Ken (ex
Ten-Tec president) on how to do this.
ON THE BRIGHT SIDE, this new technology has brought us great improvements in
performance and as we will soon see, at an affordable price.
The 7300 was just the beginning.
73
Rick, DJ0IP
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