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Author Topic: SS Amplifier IMD Testing (New Start rolled from Command Technologies Thread)  (Read 11085 times)
VE7RF
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Posts: 212




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« Reply #15 on: January 26, 2012, 05:15:57 AM »

I will bow down and let the arguments fly , However I will do some testing on the 3 amps soon (IMD) and post results as soon as they are complete (soon as possible when I can get into our lab with the radio equipment)

The bottom line is  , "IMD" applies to a limited amount of folks, Most buy an ALS-600 or FL-7000 or VL-1000 and could care less about it as long as the amp works however as an interesting task , I will take it on. As a matter of fact , the majority of ham operators (99.9%)probably think IMD some new drug to enhance hair growth...

I am already setting things up (preliminary ideas)  with a lab guy here who is a also a ham and is interested in the results...
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N4ATS
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Posts: 851




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« Reply #16 on: January 26, 2012, 07:12:41 AM »

"If you're smart, you'll get multiple parts from multiple lots to characterize the spread.

And pray that the mfr doesn't change the process, or that your parameter of interest happens to be tied to something that they DO care about."

VERY intelligent !

Not to jump off subject , however I design flight termination systems (FTS) and changing a part requires a tremendous amount of work , funds and re-qualifiction of the assembly after the new part is installed. Example, a simple Merrimac power divider change in potting compound resulted in a 6 figure cost when I had to develop the qualification test plan and execute the testing (about 4 months) so it was flight worthy again. The power divider itself costs a mere $300

Counterfeit parts need to be added in as well. Just because you get "one" part with a IMD report means absolutely nothing , it may be real or it may be counterfeit. We have a complete department just looking at parts for counterfeit identity.

Again , there is an elite group only that's interested in the complexity of IMD, most hams have no clue nor do they care about it.
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VE7RF
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Posts: 212




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« Reply #17 on: January 26, 2012, 07:34:44 AM »


 It would be certainly better than the ARRL's simplistic approach which tells you absolutely nothing by reporting IMD products only to the 9th order level.


SM5BSZ has produced the largest  database of the IMD  performance of radios. His LINRAD  TX test most produces meaningful results. This is the approach that the ARRL should take.

http://www.sm5bsz.com/dynrange/dubus205/dubus205.htm

Only the ADAT transceiver comes close and radios like the Elecraft K3 are right at the bottom of the IMD performance table with figures that are 30db worst than the above! We have a long way to go before hams will actually see a radio on the market that is  really clean. We just using glorified Cb radios in the terms of IMD performance


Your results will be interesting I am also interested in a clean solid state amp that has exceptional IMD performance. Its really idiocy spending huge dollars on a solid state amplifier then running it at low power to achieve a clean signal when I can achieve better results with a SB220 and a clean radio driving it at low power. Amplifiers need to be designed from the ground up to produce clean signals.



##  ZENKI, my imd buddy..... ur here at last !   Yes, quoting imd out to IMD-9 is absurd. It has to go way out past that..like out to IMD-19.

##  Did you see Leif's results  on the 1000-D  vs  MK-V.....astounding to say the least.

##Did you notice that Leif TWICE mentions the use of injecting a fixed DC voltage into the xcv'rs alc buss.  I have been harping on about that since the mid 80's now.  It works damn good. No need to wait to develop alc voltage from the xcvr, just inject it into the alc buss on the xcvr.  Scream all you want, and the po  will never go higher than XXX watts pep out.   You don't have to worry abt alc attack time..and developing alc voltage ..after the fact, you already have it, so no overshoots either.


##  The K3 with it's -29db imd3 is pure junk for ssb..and not worth the $4K fully loaded price tag. Folks outside the usa  pay huge $$  for ham gear...and are not getting a good bang for their buck. The adat is fine..if they were actually in business selling it.  For $4k..and it's 50w pep output...it too, is no bang for the buck.  

## l use a load of external rack gear as well, on my essb set up.  At the tail end of it all, the aphex compressor  feeds a constant level of audio into the aphex  3 x band split limiter/ distortion cancelled clipper.  Using that method, I can get 1.5 kw pep out of the linear..and have NO alc action showing at all on the xcvr....ever.  Both methods work well  however.  

##  Yes, spending huge $$  on a 1 kw pep amp, then reducing the po down to 50-70%, just to get better imd is silly...BUT, the SS amp does not need to be re-tuned..where as the sb-220 /L4-B  does need to be re-tuned.  On 20M, I can tune the L4B's  at 14.200  and they are good from 14.1  to 14.300  like 200 khz, with no re tuning required.  Different story on 40m..and esp 80m.   I have a hb amp for 160m..and it's worse still.


## My solution/fix...for now is to string all 3 x L4B's in series, nose to tail..and if on 80/40m at night...just tune each one for a different part of the band..which is a pita.  Still, the L4B, on the low  1900 vdc no load position..with zero bias...is a very clean amp..squeaky clean for IMD.   I have 3 of em right now..and a 4th on the way.  3 of em could blow up..and I still have  a spare !

Later... Jim  VE7RF
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ZENKI
Member

Posts: 997




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« Reply #18 on: January 28, 2012, 02:51:28 AM »

All good stuff Jim. The is  K3 appalling, the high order IMD products go on forever. Elecraft ruined a good radio putting such a poor PA in the K3.

The HPSDR group is doing the same with all their solid state PA projects. The Penelope/Pennylane produces superb IMD then they tack on a 12 CB transistor IMD,  some engineers just dont get it!

The ALC voltage fix is a good work around, however you cant fix the IMD which is a shame!
The K3's ALC is very good in this regard, shame the PA is so crap.

Leif has been chasing the IMD demons for  a long time, people like the ARRL just ignore his expertise. His Linrad software is free and offers ham a excellent spectrum analyzer when used with a decent SDR receiver. IMD problems are instantaneously spotted in Linrads TX test mode.

I think the L4B's when driven with a equally clean radio is a good way to get a clean driver. Either a MK5 pr FT5000 in class will do the job.
If ADAT finishes and refines including a crap IMD PA within the adaptive pre-distortion system that might be a easy fix.

If all else fails just use a KWM2A with DDS, thats as clean as you can get without going class A.



 It would be certainly better than the ARRL's simplistic approach which tells you absolutely nothing by reporting IMD products only to the 9th order level.


SM5BSZ has produced the largest  database of the IMD  performance of radios. His LINRAD  TX test most produces meaningful results. This is the approach that the ARRL should take.

http://www.sm5bsz.com/dynrange/dubus205/dubus205.htm

Only the ADAT transceiver comes close and radios like the Elecraft K3 are right at the bottom of the IMD performance table with figures that are 30db worst than the above! We have a long way to go before hams will actually see a radio on the market that is  really clean. We just using glorified Cb radios in the terms of IMD performance


Your results will be interesting I am also interested in a clean solid state amp that has exceptional IMD performance. Its really idiocy spending huge dollars on a solid state amplifier then running it at low power to achieve a clean signal when I can achieve better results with a SB220 and a clean radio driving it at low power. Amplifiers need to be designed from the ground up to produce clean signals.



##  ZENKI, my imd buddy..... ur here at last !   Yes, quoting imd out to IMD-9 is absurd. It has to go way out past that..like out to IMD-19.

##  Did you see Leif's results  on the 1000-D  vs  MK-V.....astounding to say the least.

##Did you notice that Leif TWICE mentions the use of injecting a fixed DC voltage into the xcv'rs alc buss.  I have been harping on about that since the mid 80's now.  It works damn good. No need to wait to develop alc voltage from the xcvr, just inject it into the alc buss on the xcvr.  Scream all you want, and the po  will never go higher than XXX watts pep out.   You don't have to worry abt alc attack time..and developing alc voltage ..after the fact, you already have it, so no overshoots either.


##  The K3 with it's -29db imd3 is pure junk for ssb..and not worth the $4K fully loaded price tag. Folks outside the usa  pay huge $$  for ham gear...and are not getting a good bang for their buck. The adat is fine..if they were actually in business selling it.  For $4k..and it's 50w pep output...it too, is no bang for the buck.  

## l use a load of external rack gear as well, on my essb set up.  At the tail end of it all, the aphex compressor  feeds a constant level of audio into the aphex  3 x band split limiter/ distortion cancelled clipper.  Using that method, I can get 1.5 kw pep out of the linear..and have NO alc action showing at all on the xcvr....ever.  Both methods work well  however.  

##  Yes, spending huge $$  on a 1 kw pep amp, then reducing the po down to 50-70%, just to get better imd is silly...BUT, the SS amp does not need to be re-tuned..where as the sb-220 /L4-B  does need to be re-tuned.  On 20M, I can tune the L4B's  at 14.200  and they are good from 14.1  to 14.300  like 200 khz, with no re tuning required.  Different story on 40m..and esp 80m.   I have a hb amp for 160m..and it's worse still.


## My solution/fix...for now is to string all 3 x L4B's in series, nose to tail..and if on 80/40m at night...just tune each one for a different part of the band..which is a pita.  Still, the L4B, on the low  1900 vdc no load position..with zero bias...is a very clean amp..squeaky clean for IMD.   I have 3 of em right now..and a 4th on the way.  3 of em could blow up..and I still have  a spare !

Later... Jim  VE7RF
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ZENKI
Member

Posts: 997




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« Reply #19 on: January 28, 2012, 02:58:04 AM »

Well good IMD performance is not only a ham requirement. As the military moves over to a totally digital platform on HF, the IMD requirements are even more stringent. Even using adaptive pre-distortion and cartesian loop amplifiers is not a cure all of the device IMD performance is poor to begin with.

The problem these days is that you have venture capitalists running the semiconductor business's not engineers. Thats why good engineering data that was routinely provided. This fact combined with zero inventory operation makes bringing new  and improved products to the  market very difficult.

There are still good companies like NXP and a few others who still do the proper engineering research. Just lets hope that Tyco does not swallow up NXP.

If you visit these manufacturers  web pages they dont even bother publishing IMD data which is very unprofessional. At least MACOM when they produce RF devices publishes some IMD data.



If you're selling the part into a market which doesn't care about IMD, then why would you bother characterizing and publishing the data.  Surely not to just satisfy the curiosity of a casual observer.

This is why amplifier design isn't cookbook. The data sheet only lets you identify candidate parts, then you get to buy samples, and test them for what you really care about.

If you're smart, you'll get multiple parts from multiple lots to characterize the spread.

And pray that the mfr doesn't change the process, or that your parameter of interest happens to be tied to something that they DO care about.

And, if you want the manufacturer to guarantee performance on some new parameter, you can pay for it separately (which is what makes MIL and Space parts expensive..)   radiation tolerance is a good example of something that can change radically with small changes in process.
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W6RMK
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Posts: 672




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« Reply #20 on: January 28, 2012, 06:17:36 AM »

Well good IMD performance is not only a ham requirement. As the military moves over to a totally digital platform on HF, the IMD requirements are even more stringent. Even using adaptive pre-distortion and cartesian loop amplifiers is not a cure all of the device IMD performance is poor to begin with.
Unlike hams, though, commercial and military users are willing to pay more, which can cover the cost of test/characterization either at the semiconductor mfr or the radio mfr, and they can buy in sufficient quantity to mitigate some of the process variation issues. (although.. it's nothing like 30 years ago, where running 883B lines, etc. was a big fraction of the sales.)
Quote
The problem these days is that you have venture capitalists running the semiconductor business's not engineers. Thats why good engineering data that was routinely provided. This fact combined with zero inventory operation makes bringing new  and improved products to the  market very difficult.
Actually, not so much VCs (who are willing to bet on a huge return), but more downstream investors on a larger scale who are looking for small incremental changes.  Can you reduce cost by 5% kind of things?  Deming (among others) has bad things to say about cost accounting and control as  management philosophy.  Fine if you're running an established product on an assembly line, not so good for new technology development.
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G3RZP
Member

Posts: 4965




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« Reply #21 on: January 28, 2012, 08:30:05 AM »

The British Army introduced a whole series of mil radios in the early 70's, called Clansman.  Plessey designed a lot of integrated circuits for them including some using a gold doped process for speed for the synthesisers. Gold doping is not good for devices not intended to have it and contamination and reducing demand led Plessey Semiconductors to put  all the gold doped Clansman prodiuct on 'last buy'. So the mil did. And then stored them all in one warehouse.

And it caught fire........

Bit of redesign in some cases, cannibalism in others.....

Clansman has been replaced by a system called 'Bowman'. The soldiers say it is actually an acronym for 'Better Off With Map And Nokia'.

So even storing obsolete devices can be a problem. Plus, when it comes to analogue integrated circuits, second sources very rarely actually are.
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VE7RF
Member

Posts: 212




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« Reply #22 on: January 28, 2012, 09:38:34 PM »

The British Army introduced a whole series of mil radios in the early 70's, called Clansman.  Plessey designed a lot of integrated circuits for them including some using a gold doped process for speed for the synthesisers. Gold doping is not good for devices not intended to have it and contamination and reducing demand led Plessey Semiconductors to put  all the gold doped Clansman prodiuct on 'last buy'. So the mil did. And then stored them all in one warehouse.

And it caught fire........

Bit of redesign in some cases, cannibalism in others.....

Clansman has been replaced by a system called 'Bowman'. The soldiers say it is actually an acronym for 'Better Off With Map And Nokia'.

So even storing obsolete devices can be a problem. Plus, when it comes to analogue integrated circuits, second sources very rarely actually are.

##  amazing info.   Here's my .."fix"  for stuff like this.  Get  a mess of spare parts  for what ever you have.   RL Drake, a few years ago, found a bunch od spare L4B amp parts in some old cabinet, buried in their warehouse.   The bandswitch's have always been unobtainium.   They had 2 x left..a  long and short shaft version. Sort shaft goes into the amp, the long shaft version goes into the mating 2 kw tuner...so i bought the long shaft version [ has 2 x sets of flats  ground into it].   Then it can be used on either my 4 x L4B's  or  on my MN-2000 tuner.   I bought  a bunch of other parts like meter switch, bezels  etc, etc.

##  IF buying an amp, like the ten tec, with now unobtainium SS finals, I would have bought at least one spare set of finals.   Even if u never use the spares.. it increases the re-sale value down the road.   I'm one of these guys... if you need one, buy two !   Stuff either [A] becomes unobtainium, that piece of gear is no longer made..or [C].. parts go way up in price.

## The only good news these days is... jackson bros is now making their infamous ball drives once again.  A buddy just got his new jackson bro's  4" diam ball drives.. real nice.   I had stashed 4 x away yrs ago.

later... Jim  VE7RF
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G3RZP
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Posts: 4965




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« Reply #23 on: January 29, 2012, 03:22:09 AM »

Jim,

It's not actually the Jackson Bros that it was. Somebody bought the tooling and maybe the name.

Amazing when you realise that the design of that drive goes back to the 1930's.
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M0HCN
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Posts: 473




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« Reply #24 on: January 29, 2012, 06:43:39 AM »

Mainline electronics brought Jackson Bros. some years back, then had a major fire!

The fire was in their main business at the time which was all sorts of really cool surplus, but did seriously impact getting things up and running with jacksons.

Regards, Dan.
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G3RZP
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« Reply #25 on: January 30, 2012, 06:14:46 AM »

When Jackson Bros was Jackson Bros, some 40 or so years ago, they were very good at doing specials for free for development - like fitting ball bearings to a standard cap to make it easier to drive from a motor. I guess that's an old fashioned approach now.....
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TANAKASAN
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Posts: 933




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« Reply #26 on: January 30, 2012, 06:45:53 AM »

Gentlemen (and Allison KB1GMX if she's around), we've talked enough about IMD so how about if we show the manufacturers a good example.

The Challenge
=========
Build an amplifier chain with 0dBm input and 50dBm output. Any technology can be used but the amplifier chain must cover 1.8 MHz to 30 MHz and be easily constructed using standard parts.

The Test
======
A two tone signal at 14.200 and 14.210 MHz fed into the amp, lowest IMD wins. No prize, bragging rights only.

We have a lot of expertise on these forums and it's about time we put it to good use. Who's interested?

Tanakasan

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KE5JPP
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Posts: 0




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« Reply #27 on: January 30, 2012, 06:54:04 AM »


The HPSDR group is doing the same with all their solid state PA projects. The Penelope/Pennylane produces superb IMD then they tack on a 12 CB transistor IMD,  some engineers just dont get it!


This is a prime example of a COWARD who hides behind a CB handle and casts dispersions on other designers/engineers.  John aka "Zenki" is like those COWARDLY LIDS you hear on the bands who make snide comments and then refuse to identify themselves with their callsigns.

Gene
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M0HCN
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Posts: 473




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« Reply #28 on: January 30, 2012, 12:51:03 PM »

A two tone signal at 14.200 and 14.210 MHz fed into the amp, lowest IMD wins. No prize, bragging rights only.
We have a lot of expertise on these forums and it's about time we put it to good use. Who's interested?
I am deep in the throws or a 350 mile relocation and starting a new job, but once that is out of the way I might be willing to give it a shot (More so if I can enter a complete transmitter rather then just an amp strip, in which case that 10Khz spacing is too wide, 14.2 & 14.201 would mean audio input could be used). Likely to be summer before the workshop is properly re-established however.

Oh, add a requirement that a schematic, parts list and possibly board layout be published so the work is reproducible.

The real problem with this sort of thing is that it ignores things like production cost & efficiency (Anyone can build a clean 100W by burning 500W DC input in a class A stage).

73, Dan.
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VK4TUX
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Posts: 37




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« Reply #29 on: January 30, 2012, 01:00:36 PM »


##  The K3 with it's -29db imd3 is pure junk for ssb..and not worth the $4K fully loaded price tag. Folks outside the usa  pay huge $$  for ham gear...and are not getting a good bang for their buck. The adat is fine..if they were actually in business selling it.  For $4k..and it's 50w pep output...it too, is no bang for the buck.  

Later... Jim  VE7RF

See here Jim;

http://forums.qrz.com/showthread.php?331524-K3-with-the-sb-220&p=2452824#post2452824

Adrian ... vk4tux

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