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Author Topic: Better IMD please  (Read 61151 times)
VK4DD
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Posts: 79




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« Reply #120 on: December 10, 2011, 04:03:14 PM »

One of the ways to force manufacturers to ultimately improve transmitter/amplifier IMD is to petition the FCC requesting they issue a rulemaking proceeding to improve emission standards for amateur radio equipment.  But, starting a session here to gather data for your petition is not a bad idea either.  Good luck!  Seems to me though that the ARRL had asked, or was going to ask, the FCC for tighter emission standards, but I'm not sure what became of that effort.

My opinion... bad, bad idea.

the cool thing about amateur radio is that we have almost no technical standards.  You are free to build as good or bad equipment as you like, and that's the virtue of amateur radio and that whole "advancing the radio art" sort of thing.  I'd hate to have to prove that anything would meet some technical standards before I could put it on the air.  As long as I follow "good engineering practice", then I'm good to go.  Hopefully, I and my fellow hams are responsible enough to not put too much junk on the air.

And I suspect you're not really asking for better emission standards for ALL amateur stuff, just "commercially manufactured" stuff.. but where do you draw the line?  Is someone making 5 copies "commercially manufactured".. what about someone like Comm Concepts, selling copies of Moto Eval Boards?  Or do you just wish that YaeKenCom scale mfrs would have better performance?

Well... I think it's the bully pulpit and reviewers that command respect.  For instance if QST went on a kick of evaluating amplifiers that had IMD of current peformance as being poor, I'll bet that over some few years, performance would get to where QST isn't going to beat on them.

Lets compare IMD with exhaust gases of auto mobiles Grin. If the government didn;t do anything about air quality in the cities than we would have still been poisoned there. Remember all the led and all the NOx in the exhaust gases?  Better emission standards clean up the air not in one year but in 10 years time it did. Remember that people said it is going to be impossible and we should keep on building the same cars and engines?

Even old radios go defect and the present generation rigs will be unable to repair. This will happen quicker than you think. Modern rigs are full of special electronics which are only produced for a short period. So getting spares will become the issue. If we start now that next solar cycle things would look a lot better.

IMD is not an issue for low power. May be 50 or 100W station is an issue?

Why not label equipment in a simple way. Like red for bad IMD. Yellow for moderate, green for good. Home brew equipment would be excluded and that is not a big group any way.
If you drive an amplifier than it should be a green label radio and certainly not a red one etc.

I will remind you when you can't work properly on the ham bands because you wipe out a local or a local wipes you out. May be we can only allocate hams if there is no one in the next 10Km, or do time sharing ham bands. May be it is silly to think we can do better. Don't you feel sorry for these people who invested 10K for a radio and still haven't got something decent?

The least thing we could do is enforce a standard for expensive gear. If the radio is above $3000 than it has to be good. If its below $3000 than anything will do....

Ham radio is CB radio these days. I think back of the days when I was a 12 year old radio pirate. At school we exchange schematics and ideas. I had very little money and was proud of the gear I build and the contacts I made with it. That was great fun and very educational. Those where the real days of experimental radio. Even on CB radio you had two streams. The 40 channel guys and the SSB guys. Where most of the SSB guys later became hams.

Let competition drive down the cost of clean IMD like it did with cars.
Feedback techniques and smart design strategies make it possible. It can all be done.

73 Ron.
« Last Edit: December 10, 2011, 04:19:37 PM by VK4DD » Logged
W4VR
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« Reply #121 on: December 10, 2011, 06:19:36 PM »

Yeah! you're probably right.  But, not too many hams build their own equipment these days.  When is the last time you heard someone running a homebrew radio?  There are people out there building their own amps but they are a diminishing population.  As I understand it, here in the USA the regulatory agency governing standards for ham equipment has taken a "laisse faire" attitude.  They have even done that in the broadcast industry.  There are stringent emission standards but they leave it up to the "market place" to enforce spectrum management.  If a broadcaster, for example, puts out a crappy signal his audience will go listen somewhere else .  In VK land things may be different, but not much different than here in the USA I'm sure.  Ham radios and amplifiers in the USA have to meet minimal standards in order to be acceptable for marketing.  I think that most ham radio gear you hear on the air nowadays sounds pretty good.  There are a few exceptions, as with anything else,  but what I do when I hear someone with poor IMD is get as far away from him as possible.  To complain to the perpretator does nothing in most cases.  Thank goodness we're not crystal-controlled as in the (G)olden days.
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ZENKI
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« Reply #122 on: December 10, 2011, 08:02:51 PM »

Money is just an excuse. Common, you guys your brains are over working here coming up with excuses for something which is a very simple design task. Most of your arguments about costs are invalid arguments because you are making up every possible excuse for problem that has all the design answers already.

There are commercial HF radios(marine radios) sold at discount marine warehouses that have much better high order IMD suppression than most ham radios. This very equipment is based on the ham platform from the same manufacturer. Cost is not the issue. These radios are sold below the cost of most ham radio transceivers. The only added cost that the marine radio has in manufacture is the Type Acceptance regime. How much extra would it be for the FCC to tick a box on the current FCC type acceptance paperwork. I don't accept this cost argument.

As for the PA itself again Comon, Who is asking for  a adaptive pre-distorin or Cartesian loop amplifier? I am not so why are talking about million dollar research budgets as if this is a 10 year government project. Jim VE7RF mentioned the YAesu FT767GX. Its radio with -40db 3rd order specifications. The FT767GX  uses MRF422's driven in a very conservative manner. MACOM still makes them. Copy the  FT767GX PA design if you have no RF engineering expertise! Most ham PA's use the same package transistors or FETs across their range. Changing transformers and devices is a easy task if you wanted to do so.

I am not interested  in a standalone amplifier, neither do most hams who are concerned about this issue. The Root cause of the poor IMD is the inherent poor IMD of the PA and and driver stages in the radio. We either need better radios or radios with improved IMD specifications PA's. Standalone PA's are messy and take up a lot of room. The K3s PA is a module, and so is its driver board. These Elecraft PA's could be swapped out for something with improved specifications in 5 minutes. One look at the K3's PA and you can understand why its IMD performance is so poor. So in the context of this discussion  we referring to the radios PA or transmitter not a stand alone PA. I have built my own PA's all solid state all following   Helge's designs except for the BLF175 driver stage.  -44db 3rd order is easily obtained. No rocket science concepts in my homebrew PA's. Any excuses  based upon the arguments of  costs, research, its too hard,  cant be done, technology or lack of skilled people is really non nonsensical nonsense arguments really. Linear PA's have been designed for the last 40 years and nothing has changed much about the designs. Everyone has been copying Helge's work and using his designs commercially since Motorola released his papers.

Why do we need to reinvent the wheel. It takes about a days work to make the proper design decision.  First design decision for the  day is dont  use devices for the PA that have poor IMD specifications. Once this decision is made we  have good basis for moving forward. The  design objective thereafter is too ensure that the IMD performance is preserved through judicious testing. We are not designing a spaceship thats going too mars!

I dont need expensive commercial solutions. If I wanted a clean signal I would use a clean radio with a clean tube amplifier. I have a old TMC SBE transmitter that I can fire up any day I want. It can drive a 4cx600J which can drive any tube I want and I wont have any IMD problems. All my homebrew amplifiers use linear Eimac triodes, the real problem is the transmitters. Here again I  can chose a Collins S line, TS830S, FT1000D, TS930S, TS940S. Most of these radios when used with a decent tube amplifier put out a clean signal. The real problem is the other hams of today who are buying expensive equipment  that cause problems on the bands. Please dont mention  modern radios and Russian Tetrode amplifiers! The ham bands are starting to sound like old days in Europe when every Russian ham was splattering using the infamous UW3DI transceiver.

You are really exaggerating the difficulty of this task. Designing a clean PA for any transceiver is simple task well within the grasp of all the current ham radio transceiver manufacturers. Anyone who says any different is really just being an apologist for  the broader industry who are really destroying the HF bands  by selling poorly designed equipment. Maybe we should ask Tom W8JI how hard it would be too design a PA in a radio that is clean using conventional technology. Tom Designs PA's commercially he would  know.


Quote
Why cant any of the IMD experts publish a amplifier design that we can build? We seem to have incredible experts who have the answers to the IMD problems of the world. At the same time we cant find one example of a clean HF amplifier design published anywhere. Is this all hot air grand standing on a soapbox? Like they say some times  you need to put your money where your soldering iron is!

I would build clean HF solid state amplifier the day someone publishes  a decent design. ...

The answer is money.

As another poster pointed out, going from lab notes on a prototype to a project that someone can build is a lot of work.  Even earlier than that..going from theoretical knowledge or experience on other amplifiers in other bands to a amateur suitable design is also a lot of work. 

You might have a prototype working on the bench using all the stuff scattered around (power supplies, spare components) and that's a long way from a design that you could put into the ARRL handbook or QST/QEX and have people build. It might be single band, for instance, or require a lot of tweaking to get it to work right: one of those adjust 4 different pots every time you change the drive power or frequency or power supply voltage kind of thing, and if you make a mistake, you blow up a pair of $100 FETs.

There aren't a whole lot of people in the world who are capable of doing this, and it's possible that they have other things to spend their limited time on that might be more interesting to them.   I think it's safe to say, though, that if the demand for such things becomes apparent, more and more people will tinker with it, and solutions will become available.

I'd also speculate that ultimately, you're not going to see a standalone "amplifier".. it's going to be a "transmitter" where you feed digital something in, and get high power RF out.   That way, you can do all the automatic bias adjusting, feedforward compensation, etc.

Building a very low IMD amplifier (RF in to RF out) is possible today, but it's expensive, and has a limited market.

The commercial radios with good IMD performance are probably designed as an integrated box, and given the prevalence of DSP, they may be closer to the integrated transmitter model rather than a low level exciter feeding a blackbox PA.
Quote
All we hearing is the whining about how hard and expensive its going to be, these excuses are just that poor excuses by poor engineers.
I think that's unfair.  it *is* a hard problem, or else you wouldn't be complaining about it. Hard problems take resources to solve.  I'm sure that if some philanthropist stepped up and said "I am going to spend $10M to develop an inexpensive ham transmitter with great IMD" that a few years later, you'd have your wishes granted.  So it's not poor engineering: the radios sold today are engineered very well to hit a particular price/performance point: it just happens to be a point you don't like.  A lot of engineering goes into a modern radio: just to get it all to fit in the box and be manufacturable, and have enough ROI to keep the company in business.

Amplifier Research would be happy to sell you a kilowatt amplifier with probably outstanding performance
http://www.arww-rfmicro.com/html/18200.asp?id=908  I didn't see an IMD spec on it, but I'm sure one's available.

However, I suspect that this is a bit out of the usual ham price range, and finding room in the shack for the rack sized box, and arranging for the 5 kW of three phase power might also be expensive.
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ZENKI
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« Reply #123 on: December 10, 2011, 08:07:12 PM »

What hams build anything these days, hams are mostly consumers who go shopping. There FCC allows experimentation outside the legal framework within the ham bands.  If anyone feels that they need their new mode of experimenting approved they can do so through the likes of the ARRL. No legitimate research and experimentation has been ever stopped on the ham bands. The last FCC ruling on ESSB is a good example.

Harmonic emission standards did not make ham  radios anymore expensive than  they needed to be and neither did these rules stop homebrewing. Those who dont want to follow the rules can go to the CB band. There you dont need any standards and you can splatter, use the wrong class of amplifier and cause mayhem. If IMD regulation were introduced for all manufactured equipment the impact on how we go about our hobby would not change. It might just might make the HF bands a better place too be in 10 years time.

""Responsible hams"""Are these the same responsible ones who think its okay to use a Class C CB amplifiers on the hams bands, they obeying the rules right?

Today is not the  yester year of ham radio where when you told a fellow ham radio operator that his equipment  had problem and he would go away and fix it. Nowadays all you hear is people telling you to get lost because they are too ignorant to even know what harm their equipment is doing. When you dealing with this level of technical incompetence you need rules. Its unfortunate that the technical skills and abilities of most hams have deteriorated to the point where ham radio is no longer a hobby of technical skills. Its a hobby of technical aware users not technical skilled users.

Its time for meaningful IMD standards for ham equipment. The impact and costs on our hobby will be minimal. Whatever standards are introduced I can easily meet them with my homebrew equipment. Who builds a transmitter kit and deliberately leaves out the low pass filter? Only brain dead cbérs do that kind of thing. Hams who build equipment will fine tune their transmitters too comply with the law. Tweaking any piece of homebrew equipment for better IMD performance is a very easy task. I have heard very few completed homebrew solid state transceivers on the air. The signals coming from the current operators HPSDR radios is very good. This bunch of guys seem to be concerned about the IMD issue and seem to have the required skills necessary to build amplifiers and mitigate any IMD problems. So on the homebrew SDR front things look promising.

Everything seems hard and painful when you think about it too much. Just doing it and you soon wonder what all the fuss was about. Its in everyone's nature to oppose change. IMD standards would be a good and welcome change. The good is that we will end up owning better radios, why is that such a bad thing?  Those who dont want change can go buy a old Heathkit HW101, you will sill  be allowed to use it dont worry!


One of the ways to force manufacturers to ultimately improve transmitter/amplifier IMD is to petition the FCC requesting they issue a rulemaking proceeding to improve emission standards for amateur radio equipment.  But, starting a session here to gather data for your petition is not a bad idea either.  Good luck!  Seems to me though that the ARRL had asked, or was going to ask, the FCC for tighter emission standards, but I'm not sure what became of that effort.

My opinion... bad, bad idea.

the cool thing about amateur radio is that we have almost no technical standards.  You are free to build as good or bad equipment as you like, and that's the virtue of amateur radio and that whole "advancing the radio art" sort of thing.  I'd hate to have to prove that anything would meet some technical standards before I could put it on the air.  As long as I follow "good engineering practice", then I'm good to go.  Hopefully, I and my fellow hams are responsible enough to not put too much junk on the air.

And I suspect you're not really asking for better emission standards for ALL amateur stuff, just "commercially manufactured" stuff.. but where do you draw the line?  Is someone making 5 copies "commercially manufactured".. what about someone like Comm Concepts, selling copies of Moto Eval Boards?  Or do you just wish that YaeKenCom scale mfrs would have better performance?

Well... I think it's the bully pulpit and reviewers that command respect.  For instance if QST went on a kick of evaluating amplifiers that had IMD of current peformance as being poor, I'll bet that over some few years, performance would get to where QST isn't going to beat on them.
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ZENKI
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« Reply #124 on: December 10, 2011, 08:10:20 PM »

Well it will take time. Poor equipment does not last long on the hams bands. Once equipment is known to be a dog nobody wants to buy or own this equipment. This in a way ensures that this equipment disappears from the ham bands.

Old equipment will be grandfathered in, nobody is asking for retrospective laws which is very unfair. It will just mark a new beginning. Just like hams rushed to the new generation of radios because of better receivers hams will rush out and buy radios with better receivers and transmitters. There is stigma in ham radio towards equipment that is inferior.

IMD standards wont drive up equipment costs.  If you take some time and read  the FCC or ITU standards, and understand  how they apply too professional HF equipment  you will soon understand that there will be no cost impact. Manufacturers have all the engineering expertise to change their designs. In ham radio design it mostly just mean fixing up the transmitter ALC and better  device selection for the PA. It does not change the business model nor does it require extra investment in equipment or skills. Anyone who just assumes that its going too blow out the costs of equipment is not really taking time out to try and understand what the problem is.

Well you cant ever control the behavior of poor operators, just listen on 14.275 and 14313!  Then you also have the brain dead CB hams who use CB amps and think that because they have a ham license they think they know what they are doing. IMD standards would fix this kind of behavior and we would all have better bands at the end of the day.


Even if the FCC required improved IMD standards, the equipment would only meet those standards when operated correctly, properly adjusted, and properly maintained. Given some time, the majority of equipment on the air will no longer meet those intended specifications. The FCC isn't going to be able to enforce the standards once the equipment is in the hands of the user. All you'll accomplish with such a rule change is to drive up the cost of the equipment.

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ZENKI
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« Reply #125 on: December 10, 2011, 08:17:36 PM »

This is also the reason why we need regulations. When you have operators who have a arrogant   and non technical approach as to how they operate their equipment without due regard to  the harm it does to other peoples ability to enjoy the hobby, its then time to act with regulation.
Hams get their license from the Cheerios box these days, and very few have the understanding  of a complex things like PA's. Just ask many hams what the IMD specifications of their transmitters and amplifiers are, when you get the answer you will understand why we need regulations. I have heard so many hams with Yaesu Class A radios asking their friends to check their audio quality after they switch it into ClassA. Its staggering that hams  think that the Class A bias on a radio has got something to do with audio quality.

Yeah! you're probably right.  But, not too many hams build their own equipment these days.  When is the last time you heard someone running a homebrew radio?  There are people out there building their own amps but they are a diminishing population.  As I understand it, here in the USA the regulatory agency governing standards for ham equipment has taken a "laisse faire" attitude.  They have even done that in the broadcast industry.  There are stringent emission standards but they leave it up to the "market place" to enforce spectrum management.  If a broadcaster, for example, puts out a crappy signal his audience will go listen somewhere else .  In VK land things may be different, but not much different than here in the USA I'm sure.  Ham radios and amplifiers in the USA have to meet minimal standards in order to be acceptable for marketing.  I think that most ham radio gear you hear on the air nowadays sounds pretty good.  There are a few exceptions, as with anything else,  but what I do when I hear someone with poor IMD is get as far away from him as possible.  To complain to the perpretator does nothing in most cases.  Thank goodness we're not crystal-controlled as in the (G)olden days.
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VK4DD
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« Reply #126 on: December 11, 2011, 01:04:21 AM »

Zenki,

I counted 4 posts in 15 minutes. Your about to explode about this topic.
Relax mate keep your head cool. Its just IMD, its not the end of the world.

I was watching TV the other day and saw people in Africa who had no rain for the last 7 years. A woman said she used to be rich and used to own 100 goats.
She lost all the goats because there was no water for them. She had some poor quality corn left for the goats with worms in them. So her family lived a while of that food. The last hand of corn has fed 7 people for 2 days. Now she had to walk and search for food and water. This is a problem because she looked like she could hardly walk 100m.

IMD that is just a luxury problem mate. Relax its not worth getting exited about.
Its good that we send a feedback that what;s designed does not meet our expectations. There are IMD issues and if things go well than hopefully this is picked up by the decision makers and producers. If nothing changes... than bad luck so be it mate. If your signal is ok than that's all you have to worry about.

Radio is just radio, it is a hobby, toys for grown ups.

Don't mix up real problems of the world with the minor problems.

Technically your right, the IMD of our radios is messy and things would be better if smart manufacturers manage to find solutions for this. I am very optimistic and think that they will.

73 Ron VK4DD
« Last Edit: December 11, 2011, 01:16:57 AM by VK4DD » Logged
TANAKASAN
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« Reply #127 on: December 11, 2011, 01:17:20 AM »

A couple of observations:

1) If we hear a bad signal on the air we have two alternatives. Refuse to work them or inform them. We've all tried informing hams that they have a splatter problem or keyclicks and the results are not good so perhaps it's time for an alternative approach. If someone with a poorly designed rig doesn't work anyone they're probably going to 'upgrade' and the problem will disappear.

2) I recently helped someone put an Elecraft 500W amplifier together and the small size of the toroids in the low pass filter were an unpleasant surprise. What happens if LPF cores saturate?

Tanakasan
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VE7RF
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« Reply #128 on: December 11, 2011, 03:43:07 AM »

A couple of observations:

1) If we hear a bad signal on the air we have two alternatives. Refuse to work them or inform them. We've all tried informing hams that they have a splatter problem or keyclicks and the results are not good so perhaps it's time for an alternative approach. If someone with a poorly designed rig doesn't work anyone they're probably going to 'upgrade' and the problem will disappear.

2) I recently helped someone put an Elecraft 500W amplifier together and the small size of the toroids in the low pass filter were an unpleasant surprise. What happens if LPF cores saturate?

Tanakasan

## [1] We will end up with no one talking to anyone else!  Joe ham will trade in one $5000.00  rig for another $5K rig, with no improvement at all, since they are all sub standard. One of the fellows on the yahoo forum owns several K3's...sez it's the worse ergonomic front panel layout ever invented.


## [2] Excellent point. For a REAL test then, run a 500 watt dead cxr for say... 15 mins..and cook both the combiner torroids and also the LP filter used for that band... THEN do the TX imd test. And do it on 160-10m too, all bands, including warc, and also 6m if it has it.  That will take a while, no cheating, pre-cook everything 1st, on each band, followed by the imd test, such that they don't get a chance to cool down..and do it with a room temp of 30 deg C.

## zenki and somebody else mentioned standards for ham gear.  This would be stuff made by yaesu/alpha etc..and NOT home made gear.  Home made gear is NOT type accepted.  I'm under no obligation to even use type accepted ham gear. I can take type accepted ham gear, say Like yaesu model XXX...then turn around and modify the daylights out of it, if I want to.  With any homemade HF amp, I don't have to meet the 44db down harmonic suppression spec either.  I prefer to use a slightly lower loaded Q on the tank circuits,[tube amps] and reduce the circulating current in the tank coils, and bandswitchs, plus it's broader, and less  re-tuning required.  OK, so I lose a few db of harmonic suppression, who cares. My ant's are not resonant on their harmonics anyway.

Later... Jim VE7RF
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ZENKI
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« Reply #129 on: December 11, 2011, 03:50:56 AM »

Dont worry Ron, I have a bottle of Grange Hermitage which I am now sipping  for lunch while  reading some good porn. The porn is the NXP BLF574 datasheet. Look at those sexy IMD curves, WOW -39Dbc for the 3rd order almost holds continuously upto 400 watts of output. One of these devices in a 200 watt transceiver would be just what the doctor ordered. Will you be building a board for this device?  You  should be able to get 100 to 150 watts of good class A output from it.  Maybe someone can send the datasheet to Elecraft, Ten Tec, Kenwood, and Icom.

I am more worried about my retirement fund disappearing  from the the thieves in the financials markets than the IMD performance of ham radios. We certainly have no problems when compared to the other peoples of the world.


Zenki,

I counted 4 posts in 15 minutes. Your about to explode about this topic.
Relax mate keep your head cool. Its just IMD, its not the end of the world.

I was watching TV the other day and saw people in Africa who had no rain for the last 7 years. A woman said she used to be rich and used to own 100 goats.
She lost all the goats because there was no water for them. She had some poor quality corn left for the goats with worms in them. So her family lived a while of that food. The last hand of corn has fed 7 people for 2 days. Now she had to walk and search for food and water. This is a problem because she looked like she could hardly walk 100m.

IMD that is just a luxury problem mate. Relax its not worth getting exited about.
Its good that we send a feedback that what;s designed does not meet our expectations. There are IMD issues and if things go well than hopefully this is picked up by the decision makers and producers. If nothing changes... than bad luck so be it mate. If your signal is ok than that's all you have to worry about.

Radio is just radio, it is a hobby, toys for grown ups.

Don't mix up real problems of the world with the minor problems.

Technically your right, the IMD of our radios is messy and things would be better if smart manufacturers manage to find solutions for this. I am very optimistic and think that they will.

73 Ron VK4DD

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ZENKI
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« Reply #130 on: December 11, 2011, 03:56:27 AM »

Interesting information on IMD testing by W0QE.

http://www.bnk.com/w0qe/Technical_Topics/imd_testing_of_amplifiers.html

Using 2 Icom radios you can even test Class A amplifiers.
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VE7RF
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« Reply #131 on: December 11, 2011, 04:30:40 AM »

This is also the reason why we need regulations. When you have operators who have a arrogant   and non technical approach as to how they operate their equipment without due regard to  the harm it does to other peoples ability to enjoy the hobby, its then time to act with regulation.
Hams get their license from the Cheerios box these days, and very few have the understanding  of a complex things like PA's. Just ask many hams what the IMD specifications of their transmitters and amplifiers are, when you get the answer you will understand why we need regulations. I have heard so many hams with Yaesu Class A radios asking their friends to check their audio quality after they switch it into ClassA. Its staggering that hams  think that the Class A bias on a radio has got something to do with audio quality.

###  whoa!  A bunch of us were on 80m, at midnight, and all using ESSB. One of the fellow's toggled between class A and class AB.... and I could just hear the difference from 1300 miles away. That surprised me. It's def cleaner.  The inband IMD drops like a rock.  Off freq, it's blatantly obvious. Remember your 2 x tones tests?  If the tones are say 200 hz apart, then all your odd order products, like 3-5-7-9 etc, will also be all 200 hz apart...and they will all be INband.  


Yeah! you're probably right.  But, not too many hams build their own equipment these days.  When is the last time you heard someone running a homebrew radio?  There are people out there building their own amps but they are a diminishing population.

###  That's nonsense.  There are more HB tube amps being built these days than ever before.  There are loads more vac tune and load caps available, and ditto with HV caps, and surplus tubes like YC-156's, 8877's pulled from MRI machines etc. You can find anything on the internet. It's easier now, than it ever was back in the 70's.  A smile comes across  my face when I know I just beat Alpha, et all, at their own game. If you want to spend $7k on a 1.5 kw amp, go ahead on it. 1/4", 3/8" and 1/2" copper tubing is dirt cheap at home depot down the street. I silver plate all mine with that cool-amp glop . Toss in the ceramic vac tune and load caps, and the manually tuned, tuned inputs, digital readout turns counters, humongous dahl plate xfmr's, ceramic vac relays on the input, output, and bias, plus some real connector's ,like 7-16 Din, then it's a winner.  I just got in a few 10-1000pf @ 15 kv ceramic, motor driven jennings vac caps...and the mating 35-4000pf @ 5/10 kv ceramic vac caps.  A GG triode amp is pretty simple stuff, no rocket science.   My 3CX-3000A7  has -59db pep  IMD-3, and the tube is rebuildable. The 225 watt CCS grid can be used as a dummy load for a FT-1000D.

Later...Jim  VE7RF


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ZENKI
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« Reply #132 on: December 11, 2011, 04:30:56 AM »

What Rf devices are used in the KPA500? Just about every solid state amp on the market has marginal IMD performance thats why I wont use one.

What I also see is wide variation in IMD performance across amplifiers from  different manufacturers. This is particular so with the MRF150 amplifiers. The MRF150 has relatively good IMD performance however there seems to be a wide variation in the IMD performance depending on the brand of amplifier.

The KPA3 is also a marginally built amplifier. Some people have suggested that the some of the IMD problems of the K3 is related to the marginal transformers and cores  used in the KPA3. If a IMD bottleneck  has been found in receiver bandpass filters, it would not be a surprise if this is the case on TX.

http://martein.home.xs4all.nl/pa3ake/hmode/bpf_intro.html

More knowledgeable hams might have a better answer.

A couple of observations:

1) If we hear a bad signal on the air we have two alternatives. Refuse to work them or inform them. We've all tried informing hams that they have a splatter problem or keyclicks and the results are not good so perhaps it's time for an alternative approach. If someone with a poorly designed rig doesn't work anyone they're probably going to 'upgrade' and the problem will disappear.

2) I recently helped someone put an Elecraft 500W amplifier together and the small size of the toroids in the low pass filter were an unpleasant surprise. What happens if LPF cores saturate?

Tanakasan
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ZENKI
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Posts: 934




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« Reply #133 on: December 11, 2011, 04:38:40 AM »

Jim,,,, I was talking about ON FREQUENCY AUDIO quality not wide band  off channel IMD products. Are you saying when you switch too class A bias on Yaesu that you can hear a difference in on channel transmit audio quality from miles away?

This is also the reason why we need regulations. When you have operators who have a arrogant   and non technical approach as to how they operate their equipment without due regard to  the harm it does to other peoples ability to enjoy the hobby, its then time to act with regulation.
Hams get their license from the Cheerios box these days, and very few have the understanding  of a complex things like PA's. Just ask many hams what the IMD specifications of their transmitters and amplifiers are, when you get the answer you will understand why we need regulations. I have heard so many hams with Yaesu Class A radios asking their friends to check their audio quality after they switch it into ClassA. Its staggering that hams  think that the Class A bias on a radio has got something to do with audio quality.

###  whoa!  A bunch of us were on 80m, at midnight, and all using ESSB. One of the fellow's toggled between class A and class AB.... and I could just hear the difference from 1300 miles away. That surprised me. It's def cleaner.  The inband IMD drops like a rock.  Off freq, it's blatantly obvious. Remember your 2 x tones tests?  If the tones are say 200 hz apart, then all your odd order products, like 3-5-7-9 etc, will also be all 200 hz apart...and they will all be INband.  


Yeah! you're probably right.  But, not too many hams build their own equipment these days.  When is the last time you heard someone running a homebrew radio?  There are people out there building their own amps but they are a diminishing population.

###  That's nonsense.  There are more HB tube amps being built these days than ever before.  There are loads more vac tune and load caps available, and ditto with HV caps, and surplus tubes like YC-156's, 8877's pulled from MRI machines etc. You can find anything on the internet. It's easier now, than it ever was back in the 70's.  A smile comes across  my face when I know I just beat Alpha, et all, at their own game. If you want to spend $7k on a 1.5 kw amp, go ahead on it. 1/4", 3/8" and 1/2" copper tubing is dirt cheap at home depot down the street. I silver plate all mine with that cool-amp glop . Toss in the ceramic vac tune and load caps, and the manually tuned, tuned inputs, digital readout turns counters, humongous dahl plate xfmr's, ceramic vac relays on the input, output, and bias, plus some real connector's ,like 7-16 Din, then it's a winner.  I just got in a few 10-1000pf @ 15 kv ceramic, motor driven jennings vac caps...and the mating 35-4000pf @ 5/10 kv ceramic vac caps.  A GG triode amp is pretty simple stuff, no rocket science.   My 3CX-3000A7  has -59db pep  IMD-3, and the tube is rebuildable. The 225 watt CCS grid can be used as a dummy load for a FT-1000D.

Later...Jim  VE7RF


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VE7RF
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Posts: 212




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« Reply #134 on: December 11, 2011, 05:38:45 AM »

Money is just an excuse. Common, you guys your brains are over working here coming up with excuses for something which is a very simple design task. Most of your arguments about costs are invalid arguments because you are making up every possible excuse for problem that has all the design answers already.

As for the PA itself again Comon, Who is asking for  a adaptive pre-distorin or Cartesian loop amplifier? I am not so why are talking about million dollar research budgets as if this is a 10 year government project. Jim VE7RF mentioned the YAesu FT767GX. Its radio with -40db 3rd order specifications. The FT767GX  uses MRF422's driven in a very conservative manner. MACOM still makes them. Copy the  FT767GX PA design if you have no RF engineering expertise! Most ham PA's use the same package transistors or FETs across their range. Changing transformers and devices is a easy task if you wanted to do so.  


## Let's cut to the chase. We don't require schemes like pre-distortion, nor Blast furnace Class A tricks.
If yaesu can build the squeaky clean 767GX.. BACK IN  Sept, 1987...[24 years ago!]  it can easily be done again.  It's a 300w PA..that's being run at just 100w out. BTW, it uses the SAME MRF-422's that are in my FT-1000D. The 1000-D will do an easy 200-300w pep, without breaking a sweat.

## OK, what about this 'concept'.  If the xcvr is to put out a clean 100-200w pep out, then use SS devices that are good for 300-600 watts out.  Now think about it for a minute.  All the stuff in there only has to handle the 100-200w, and NOT 300-600w.  IE: the combiner, heat sinks, LP filters,  cooling, and power supply.   Then crank up the idle current a bit more, like they did on the 767GX.

##  other than perhaps selecting more modern devices, maybe the VRF-150, etc, or perhaps the device that contains 2 of em on one die, then just size the other stuff for the 100-200w level.  Run it in AB, and you are done.


### BTW, has anybody done imd tests, with the yaesu 1000-D or the 200w mk-v, or the 9000/5000...but run at 100w level..and NOT the 200w level ??..[and I mean in Class AB].  I'll bet anything if the idle current  was increased a tiny bit, that the imd would drop like a rock.

##  For a real eye opener, check out the kenwood TS-870..on the arrl extended lab reports. TX imd on 12m is pure crap, -18db pep, [IMD-3]..and  -20db pep [IMD-3] on 10m !   It's -40db pep on 80m [IMD-3]..and the 5-7-9 drop like a rock. On 20m, they did it at 3 x power levels, 100w [-31]...and also 80watts [-36]...and also with just 50watts. [-48db pep, IMD-3]

## as u can see on 20m, the 870 is junk with 100w, then cleans up with 80w..and really clean with 50w !!         All that's needed  is to just de-rate SS devices...but at least start off with the cleanest device to start with.

later..Jim  VE7RF
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