[TenTec] OT: IP3 and Receiver Performance

[rick@dj0ip.de]

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 at 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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