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Author Topic: Better IMD please  (Read 121764 times)
M0HCN
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Posts: 566




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« Reply #165 on: December 16, 2011, 09:39:58 AM »

##  You can easily have the upper and lower tones in or out of phase ..with each other.  That's why spectral phase refractors [ all pass filters] are used for audio processing chains. 
Not quite, With harmonically related tones you can set the phase relationship to any given value at any given phase of the lower tone, but even then the phase relationship is fixed at that value only at that point in the cycle. If I have a tone F1 and its second harmonic F2, I can slip F2 relative to F1 and at say the positive going zero crossing of F1, I can set the phase of F2, but that does NOT mean that that angle is constant over a cycle of F1 (Because the phase of F2 is advancing twice as fast as F1).
Now it happens that for much speech, the bulk of the energy is in one tone plus harmonics much of the time, and by placing a group delay change at about the frequency where on aggregate 50%  of the energy is on either side you can reduce the tendency of the series to sum in phase and thus reduce the peak amplitude and improve symmetry.
Phase rotators have been used since the 50's on AM sites to reduce the asymmetry that is common to much speech and thereby make best use of the power by allowing more symmetrical modulation.

None of this really applies to a two tone test, because the tones are deliberately chosen to  NOT have a harmonic relationship, precisely so that the phase of one will slip continuously relative to the other.
Quote
with loads of audio processing gear, the bass freqs will lag behind the upper freqs.  To 'time align' them, an all pass filter is used, to put it all back in phase. they usually start around 150 hz..and as you slowly progress  higher and higher in freq, you get more and more delay. 
I am aware of using time  alignment in loudspeaker systems (particularly when partially horn loaded),  but I have never seen electronics (except filters which one would expect to have non flat group delay in the transition band) exhibit meaningful dispersion.
I would note that a simple fixed delay line exhibits increasing phase shift with frequency, that is a consequence of constant group delay and is neither here nor there, only changes is group delay matter.
Quote
The point was, using 2 x extremely wide spaced tones will skew the results.
Not really IMHO, it will put the products much further out, but will probably have only a minor impact on the amplitude of those products, which could go either way on test, but will generally result in wider IMD sidebands when modulated with a complex signal.
Quote
##  did you see Zenki's comments  about the ITU insisting that ham gear meet ITU specs ??  Apparently, the worlds member societies, like RSGB/ARRL, etc, etc, were all dead against it. What does that tell you?  It tells me there is an obvious lack of leadership, and short sighted thinking.  They had their chance...and blew it big time. 
Now there we agree!
I can sort of understand however, getting government involved in anything much is seldom a good plan!

Got to hate the RC keying filter in a modern radio thing, just stupid, but the ARRL book still suggests it as a suitable circuit. I would also add not doing proper PA sequencing to the list of infelicities, and there are NO shortage of rigs that do not have the PA up and switched for the full keying envelope, hardly forgivable given the use of micros in the rigs that can easily deal with the simple state machine required.... 
Error function keying is just so much better behaved, and even arranging to transmit through the narrow IF filter would be an improvement.

Regards, Dan.
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GM3SEK
Member

Posts: 99




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« Reply #166 on: December 17, 2011, 06:21:15 AM »


## Now since the ARRL/RSGB/etc, etc all don't want ITU specs..or any kind of imd spec, they will reap what they sowed.  IF QST insists on NOT slamming  xcvr's and amplifiers with lousy imd specs..then they are to blame for this mess.  In essence, they have missed a 2nd opportunity to solve the ONGOING problem.


Some people in "ARRL/RSGB etc" can see these problems perfectly well;  but they can also see other, stronger reasons for not wanting mandatory technical specs:

1. All technical specs are arbitrary numbers, and we would not be the ones who choose those numbers. That would be left to our national authorities, who would be under strong pressure from the manufacturers to choose numbers that are easy to comply with... like -20dBPEP. If that happened, we'd be worse off than before. It simply isn't worth the risk.

2. Mandatory tech specs for commercial equipment would also take us one step closer to amateur radio's ultimate nightmare: mandatory approval for homebrew equipment. This is a very real threat in some parts of the world. In fact it's happening right now in Europe: all the regulatory exemptions for amateur radio have disappeared from the proposed new EU regulations, so we will have to negotiate all over again to have those exemptions put back. We don't want to invite mandatory tech  specs any closer to our own door than they already are.

So even though your concerns are valid and undisputable, Jim, there are even stronger reasons why mandatory technical specs are not the answer.

That brings us back to equipment reviews, as a much safer and more direct method of steering manufacturers in the direction we want.


73 from Ian GM3SEK



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KE5JPP
Member

Posts: 0




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« Reply #167 on: December 17, 2011, 06:42:25 AM »


## Now since the ARRL/RSGB/etc, etc all don't want ITU specs..or any kind of imd spec, they will reap what they sowed.  IF QST insists on NOT slamming  xcvr's and amplifiers with lousy imd specs..then they are to blame for this mess.  In essence, they have missed a 2nd opportunity to solve the ONGOING problem.


Some people in "ARRL/RSGB etc" can see these problems perfectly well;  but they can also see other, stronger reasons for not wanting mandatory technical specs:

1. All technical specs are arbitrary numbers, and we would not be the ones who choose those numbers. That would be left to our national authorities, who would be under strong pressure from the manufacturers to choose numbers that are easy to comply with... like -20dBPEP. If that happened, we'd be worse off than before. It simply isn't worth the risk.

2. Mandatory tech specs for commercial equipment would also take us one step closer to amateur radio's ultimate nightmare: mandatory approval for homebrew equipment. This is a very real threat in some parts of the world. In fact it's happening right now in Europe: all the regulatory exemptions for amateur radio have disappeared from the proposed new EU regulations, so we will have to negotiate all over again to have those exemptions put back. We don't want to invite mandatory tech  specs any closer to our own door than they already are.

So even though your concerns are valid and undisputable, Jim, there are even stronger reasons why mandatory technical specs are not the answer.

That brings us back to equipment reviews, as a much safer and more direct method of steering manufacturers in the direction we want.


73 from Ian GM3SEK





Agree.  Some guys just don't get the concept of "Be careful what you wish for" and "Unintended consequences".

Gene
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VE7RF
Member

Posts: 212




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« Reply #168 on: December 17, 2011, 09:28:09 AM »


## Now since the ARRL/RSGB/etc, etc all don't want ITU specs..or any kind of imd spec, they will reap what they sowed.  IF QST insists on NOT slamming  xcvr's and amplifiers with lousy imd specs..then they are to blame for this mess.  In essence, they have missed a 2nd opportunity to solve the ONGOING problem.


Some people in "ARRL/RSGB etc" can see these problems perfectly well;  but they can also see other, stronger reasons for not wanting mandatory technical specs:

1. All technical specs are arbitrary numbers, and we would not be the ones who choose those numbers. That would be left to our national authorities, who would be under strong pressure from the manufacturers to choose numbers that are easy to comply with... like -20dBPEP. If that happened, we'd be worse off than before. It simply isn't worth the risk.

2. Mandatory tech specs for commercial equipment would also take us one step closer to amateur radio's ultimate nightmare: mandatory approval for homebrew equipment. This is a very real threat in some parts of the world. In fact it's happening right now in Europe: all the regulatory exemptions for amateur radio have disappeared from the proposed new EU regulations, so we will have to negotiate all over again to have those exemptions put back. We don't want to invite mandatory tech  specs any closer to our own door than they already are.

So even though your concerns are valid and undisputable, Jim, there are even stronger reasons why mandatory technical specs are not the answer.

That brings us back to equipment reviews, as a much safer and more direct method of steering manufacturers in the direction we want.


73 from Ian GM3SEK





Agree.  Some guys just don't get the concept of "Be careful what you wish for" and "Unintended consequences".

Gene

## Gene, u must be thinking of the ARRL, etc.  They promote various contests, then at the same time, turn a blind eye to lousy imd xcvr's and linears.  Remember the collins KWM-380?  It got a lousy review in qst. That was also the very last issue of qst that collins ever advertised in. They pulled all their ads after that, permanently.

## That yaesu 9000MP [400wpep output]  is  $12K in Canada.  Then toss in 12% sales tax, then a bunch more for shipping. Any end user has the reasonable expectation  that his new megabuck toy will work. -22db pep imd is not what I call working.  yaesu cranked out umpteen thousands of xcvr's with key clix, what a mess that was..[and still is].

## If they used existing commercial  ITU specs  for IMD, they wouldn't have to  succumb to yaesu, et all.  Exempting all HB gear is  no trick in NA, it probably is in EU. Of course, anything b4 a set date would be grandfathered. [existing yaesu/icom, etc ham gear]

##  IF u want to steer yaesu, icom, etc in the right direction via equipment reviews, they are sure going abt it all wrong. QST single handed, is responsible for that 150w pep output 11m xcvr yrs ago. [ranger]. Remember that xcvr ?  24-30 mhz continuous on RX..and TX on 10+12m.   QST lauded it's ability to also have LSB, and that this was wonderful, since RTTY ops use LSB on the high bands. I don't even think it had a CW key jack. The imd on TX was beyond lousy.  Every 11m op bought one, and did the easy mod to get it to TX from 24-30 mhz, now that entire portion of the spectrum is a mess.  Just a newer version of an old concept. Like the old siltronix 10-11 xcir.  Anybody with 1/2 a brain can see these xcvr's are intended for the 11m market..hence the inclusion of LSB.

## Unsuspecting folks look at these water downed qst reviews [ no more extended lab reports]and since qst doesn't say anything about the lousy imd, joe ham end user thinks it must be a 'good radio'. After all, his proposed new purchase is also  a full page ad on the back cover of qst, etc.  A kwm2 is -48db for imd.  A typ sweep tube xcvr in the 70's was -30db pep for imd.  These days, SS xcvr's are no better than sweep tube rigs from the 70's..and in a lot of cases, are much worse.  Then toss in tetrode amps that only require 20-30w of drive, use poorly implemented EBS systems, and also ALC systems in linears that are not compatible with the xcvr [ different time constants], or are not front panel adjustable, etc, and you still have a mess.

##  yaesu didn't invent Class A  either.  It's been around since day 1.  Perhaps if they had used some sort of sliding bias scheme, like the Class A stereo amps all use, the xcvr would not be in melt down mode all the time.  The short of it is.. easy to get -40 db IMD-3  with any 100w pep out ssb xcvr...and do it in Class AB.  yaesu already proved that with their 767GX yrs ago.  A pair of MRF-422's, but configured to run 100w pep out..and not 200w pep out, like the same 422's used in my 1000-D.

## Zenki is correct though.  You are wasting your time with high dynamic range RX's..until the TX imd is brought under control.  If a yaesu 5000 in Class A is 1/3 the total BW  of an Icom, do the grade 6 maths. With low imd on TX, you could almost stuff triple the number of stations on the bands.  If the bands are getting more crowded, you have 2 x choices. Ask for wider bands, like 14.000 to 14.500 , or use xcvr's with lower TX + RX imd.   They are not making any more real estate, and they are not likely to expand the ham bands any time soon.  I highly suspect that QST is walking a fine line. Don't trash yaesu, et all for lousy TX imd. They will retaliate, and pull their ads.  QST would suffer a massive financial blow. IMO, instead of yaesu spending $25K for a full page ad in QST,[every month] why not just spend that money on improving the xcvr ?

Later... Jim  VE7RF

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M0HCN
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Posts: 566




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« Reply #169 on: December 17, 2011, 10:32:49 AM »

Magazines and advertisers always have something of an incestuous relationship, and the separation of the advertising department from the editorial decision making is usually a hard one to enforce.

Look at the number of mags that have a rating for reviewed products out of 10 (stupid single measure of something complex), where NOTHING gets reviewed as less then about 6/10... Now you would expect that this would be reason to recalibrate the scale so such information as you can get from that sort of thing becomes more useful, but it never happens.

Any change in editorial policy on such things as commenting on poor TX performance would have to be seen to be done across the board, in which case no manufacturer has anything to get sniffy about, and would need significant lab support to very throughly document the results (There could be lawyers!).

Better education, and more emphasis on transmitter performance and issues in the exams might help, after all if you do not understand how to correctly work a receiver that is not a problem to anyone else, if you work "all knobs to the right", it very well may be a problem. Unfortunately I suspect that the US tendency to set exams that can be passed by rote rather then understanding does not help here, doubly so as your technician class get 1.5KW privileges on their bands, so such things would have to be done in that exam rather then the extra.
UK foundation license is far less critical in this matter as they only get 10W PEP, which makes any issues down there rather less annoying, and means that proper understanding of the gear can wait until the advanced exam.

Someone (And I wish I had the radios and the time) needs to pull a Sherwood table on transmitters.....

Actually I could see a way to take an SDR, laptop, linrad and some software with hamlib wired into it and use the combination to make a briefcase transmitter test set that could automatically do spectrum occupancy tests on all bands (Including testing with real speech recordings). I might have to do it and start taking it to rallies. 

Regards, Dan.
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ZENKI
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Posts: 1648




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« Reply #170 on: December 17, 2011, 03:30:51 PM »

I cant do the standard justice in this forum. You need too refer to the 3 ITU documents to understand exactly what
they  mean. See ITU SM1521, SM328, and SM329. BAsically when you break it down the standard says the reference
bandwidth below 30mhz is 10khz. Then from the center of this 10khz bandwidth you make your IMD measurements at
various spacings defines as % from the center of the bandwidth. You then need to look at the other standards to 
understand  how the peak of the signal is measured and what reference is used.The bandwidth reference of 8 khz
is 150% plus/minus  of 5khz rounded. Now this is about 7.5khz  and its roughly  where the 11th order products fall when
doing a simple 2 tone test.

Regardless of all the complications, you will find that ITU places a emphasis on the adequate suppression of high
order products greater than the 11th order.  In many ways the QST test which reports only products upto the 9th
order gives you really no idea if the radio has wideband splatter products. Ham transmitters have both poor 3rd
order and poor high order product suppression. If it we had average 3rd order product and very good high order
product suppression we probably would not have so much splatter around.
We could simply go  to the extreme of pursuing high 2 tone numbers like the old FCC used to do, or we can do it the
way ITU does it. The ITU's standard would be the least painful for ham manufacturers. If you running 4 high stacks
of beams and QRO+, you would  want to use the best possible 2 tone numbers of something like -40db 3rd order, and
11th order suppressed better than 70db. You would of course optimize the PA bias under dynamic voice conditions not 
2 tone numbers.

I have a number of decent commercial mobile HF radios Skanti, Sailor, Codan and a Icom M710.  The Codans are widely
used by the red Cross, UN and many government agencies. If you do a  2 tone IMD test on them, they have average  2
IMD tone numbers. However when you measure their real dynamic performance all these radios produce a splatter free
signal with no buckshot or crud. The audio on TX is also super clean. Comparing a mobile like a Icom 706 the
difference is night and day, and it clearly demonstrates the design problems that ham transmitters have.


Again, people who assume that meeting the standards is going to be hard thing have not read the ITU standard. The standard does not require adaptive pre-distortion or class A PA's. It just requires that the transmitters and PA's in ham radio transceivers do not have ALC, poor high order IMD numbers, no other design faults and are designed so that their are limits  are set so as to prevent a splattering signal.  We all know hams and especially new hams have the all knobs to the right mentality. Try and find a mic gain control on a commercial radio! You dont need a mic gain control the TX audio is perfect and the levels are always right. This ideal could be achieved on ham radios as well.  You know how well peak limiting works on ESSB, and how its impossible too overdrive once the limiter is set. Commercial radios have this circuitry inbuilt, you can scream as loud as you want and you cant over drive the radio. This is not rocket science its commons sense and works this way in broadcast, telephony and any other area that requires the transmission of audio.

Designing is clean transmitter is not only about 2 tone numbers, it requires a methodical approach too ensure everything is driven to the correct levels. Those who argue against concepts  like ETSI and ITU standards have not bothered to take  the time to read these standards. With the current model transceivers  we just about there. A radio like the K3 could easily  have a peak limiter added to its firmware and have all TX levels hard coded.  A radio like the K3 with better a designed PA would easily meet ITU standards. 

When a ham stations can run 2.5kw from a desktop amplifier feeding a 20dbi stacked array,  80db down suppression of IMD products is not an extreme standard. The ITU requires this for powers greater than 5kw. Calculate the ERP of most contest stations,  when you plug these numbers into the big equation 70 to 80 db down is a reasonable standard. A  IC7800 can meet this standard with its ALC disabled, the class A Yaesu's will easily get there. We already there we just bickering about big stick government sticking their noses into everything. The ham bands are fast becoming a cesspit, it time someone cleans  them up.

Anyway I dont expect much too  change fast, because while technical standards are slipping and when hams are fighting for their existence, standards might be all for nothing in the end. What use is IMD standards when someone can buy  a Solar inverter from China that puts   S9 QRM across the HF spectrum and flouts all known laws when its illegal to do so?. This occurs daily in Europe, we put our own manufacturers out of business with well intentioned laws and turn a blind eye to the fraud from China. The Eurozone is the biggest joke of the century. But this is another subject for another day!

[/quote]

##  8 kz away from WHAT?   The 2 x tone test is convoluted anyway.  Let's say we are using 300-2700 hz TX BW. [2.4 khz wide]   The center  of that mess would be  2400/2 = 1200.  300+1200 = 1500hz.   OK, lets use 2 x tones, 200 hz spacing, and straddle the 1500 hz  center line.   IE: lets use 1400 hz and  1600hz.   OK, now run ur 2 x tone test.   You will now get a real earful, as all the IMD products  from  3-11  will fall WITHIN the pass band on both sides of the 2 x tones. IE: imd-3 = 2 khz...and  IMD-11 = 2.8 khz.    Same deal on the low side.  IMD-3 = 1.4 khz...and IMD-13= 400 hz,  IMD-15= 200hz.

## Now W8JI doesn't  like ESSB, so to bolster his anti-ESSB argument he uses  tones of  100 hz + 3100hz on his anti ESSB website.  [ The yaesu MK-V on DSP  SSB TX  mode will go as wide as 100-3100hz]. So the tones are now 3 khz apart.  Now the IMD-3 is  at  6100hz on the high side...and the IMD-5 = 9100hz..and the IMD-9= a whopping  18.1 khz.   And of course an equal amount on the other side of zero beat.  What he fails to mention is that in order to produce an IMD product, you require the 2 x tones to be equal amplitude and also equal phase..AND also both tones on SIMULTANEOUSLY !!## try as hard as I can, I can not get both bass + treble  AT THE SAME TIME, coming from my mouth !  I tried every trick in the book, and NO words or phrases will do it, none.  Several ESSB ops have also tried it. After a week of this, we all gave up, can't be done.  We even tried nonsensical stuff, like humming, or anything else you can imagine.  You can either get bass OR treble, but NOT both at the same time.   The ONLY thing that will produce SIMULTANEOUS bass + treble is  [A] W8JI's convoluted 2 x tone test, with extreme tone spacing.... or program material, like music.


###  80db down is pretty steep. Heck, most.."'suppressed cxr's" on ssb are only down 40-65db. When was the last time somebody bitched about .."insufficient cxr suppression" ?  If N6--  is say 40 over S-9 on 80m ..and I tune up 1 khz, I sure as heck can't hear his suppressed xcxr.  When Sherwood does his TX white noise IMD tests..he measures the BW  to the -45 db points.  And those Icoms are lousy, at 10 khz wide to the -45 db points.  Meanwhile the FTDX-5000 in Class A  is only 3.5 khz wide [ to the same -45db points]  The imd-5-15  are all -80 to -85db on a mk-v, in Class A.  But Class A  is not a practical answer.  In a mobile or marine set up, you would drain the battery in no time at all. [ battery only]. Lousy 25 % eff, and sky high idle current.   And running a 200w  xcvr  turned down to 100w pep out, in class AB  at 35% eff is not the answer either.


###  You would have to re-design the xfmr's inside the xcvr's PA, so that you get a correct match with say a pair of MRF-422's  or VRF-150'  running 100w out max.  THEN u will get max eff.  But heck, they have already done that...with the old yaesu 767GX.  It uses the same MRF-422's as my 1000-D.  767 is designed to run 100w pep out max.  The 1000-D is designed to run 200w out max.


##  I looked at every ham type kw SS amp recently, using 8x MRF-150's.  All rated for 1000-1200 w pep out on ssb.   Now if you ran  the same 8x MRF-150's at  400-600w pep out..AND designed around the increased load Z. [ it would double] , and also used 50 vdc..and cranked the idle current up a bit, you would have a winner.  Low imd, and an eff amp. Low heat too.  Flip side is the damn thing will only do 400-600w out.   You could however get away with a smaller power supply, and also a smaller combiner and smaller LP filterS.

##  Forget abt ITU standards for a moment, anybody can make a standard. It's trying to meet those standards.  I see that both yaesu and also icom STILL make marine type HF xcvr's that cover 1.8 to 30 mhz..and both put out 100-125 w pep on ssb, and also clickless CW, and data modes.   They tune in 10 hz steps, meet ITU specs, BUT don't have all the bells and whistles on a ham xcvr.  Instead they all offer sellcall, tellcall,TCXO, GPS, data, "where am I", and "this is where I am, even though I'm incapacitated" modes.  They also offer auto e-mail.  Heck, it sounds like we are buying the wrong radio gear.  I found it amusing though, that under the marine options for the yaesu marine HF xcvr....they listed the  VL-1000 kw ham amp!

Later...Jim  VE7RF
[/quote]
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ZENKI
Member

Posts: 1648




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« Reply #171 on: December 17, 2011, 03:58:58 PM »

Well if we chose the ITU numbers they represent a good set of numbers  that would work well. I can guarantee you that if ham transmitters met
ITU out of band emission standards  there would be no problems only a net positive gain.

As for homebrew  transmitters the laws could be adopted much like the FCC laws on the number of amplifiers or transmitters produced etc. Problem solved and most amateurs will be exempted. I cant imagine a bureaucrat turning up on your door saying show me your homebrew equipment or else. They dont enforce any other laws in the ham service, what would really change?

The EEC is joke and the sooner you guys left it the better off you will all be.  The last thing hams would want is a big bunch of jokers in Brussels interfering in a hobby. The ITU is a different matter and their technical standards are devloped by real engineers not bureaucrats.


Mandatory technical standards are the answer. Look at the harmonic standards on transmitters. Who bothers checking the harmonic standards on their transmitters? We all know they meet the required standard. Once IMD standards are law nobody would even bother checking them because the radios should produce a splatter free signal. Except from those who stick their golden screwdrivers into radios.

Hams who homebrew equipment? Its very rare these days for any ham to homebrew  a transmitter or amplifier. We just consumers who rattle off long shopping lists on the air. I even had a ham tell me what brand of cables that he bought that connected his radios and amplifiers, complete with gold connectors! Gold connectors must produce less common mode current and better TX audio!

We have nothing too fear from Type Acceptance or ITU standards. Besides this will only happen if the US FCC makes this law. Since this is unlikely too happen  in any of our lifetimes we arguing about something that is not going too happen. The ARRL  and the RSGB just dont have the stomach for this kind of battle. There are more important issues such as EMC and BPL threats.



[/quote]

Some people in "ARRL/RSGB etc" can see these problems perfectly well;  but they can also see other, stronger reasons for not wanting mandatory technical specs:

1. All technical specs are arbitrary numbers, and we would not be the ones who choose those numbers. That would be left to our national authorities, who would be under strong pressure from the manufacturers to choose numbers that are easy to comply with... like -20dBPEP. If that happened, we'd be worse off than before. It simply isn't worth the risk.

2. Mandatory tech specs for commercial equipment would also take us one step closer to amateur radio's ultimate nightmare: mandatory approval for homebrew equipment. This is a very real threat in some parts of the world. In fact it's happening right now in Europe: all the regulatory exemptions for amateur radio have disappeared from the proposed new EU regulations, so we will have to negotiate all over again to have those exemptions put back. We don't want to invite mandatory tech  specs any closer to our own door than they already are.

So even though your concerns are valid and undisputable, Jim, there are even stronger reasons why mandatory technical specs are not the answer.

That brings us back to equipment reviews, as a much safer and more direct method of steering manufacturers in the direction we want.


73 from Ian GM3SEK




[/quote]
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M0HCN
Member

Posts: 566




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« Reply #172 on: December 17, 2011, 04:56:07 PM »

Mandatory technical standards are the answer. Look at the harmonic standards on transmitters. Who bothers checking the harmonic standards on their transmitters?
Walks over to a book case, pulls out a ring binder... Last checked two and a half months back when a taxi company set up down the road and started bitching about me getting into their VHF setup. Odd how quiet it went when I handed them the SA printouts (Including the one showing that their TX was not exactly blameless) and suggested that they take it up with their gear supplier or Ofcom. 
Quote
Hams who homebrew equipment? Its very rare these days for any ham to homebrew  a transmitter or amplifier.
Speak for yourself mate, plenty of us been known to build (and in some cases even design), loads of CDG2000, Picastar, SDR of all sorts and the like out there, and if weak signal VHF or UHF is your trip you got no choice but to roll your own.
Quote
I even had a ham tell me what brand of cables that he bought that connected his radios and amplifiers, complete with gold connectors!
It is a broad church, but that is just embarrassing.
Quote
We have nothing too fear from Type Acceptance or ITU standards.
Agree about the ITU, some good engineering there, Type Acceptance is a more complicated argument, but actually does not Commercial ham gear have to meet EN301783-1 which does at least put some kind of limit on energy more then 10Khz away from the carrier (by my reading).

Regards, Dan.
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TANAKASAN
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« Reply #173 on: December 18, 2011, 01:10:43 AM »

"Odd how quiet it went when I handed them the SA printouts (Including the one showing that their TX was not exactly blameless) and suggested that they take it up with their gear supplier or Ofcom."

Nice  Grin

Tanakasan
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VE7RF
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Posts: 212




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« Reply #174 on: December 19, 2011, 12:47:40 AM »

Mandatory technical standards are the answer. Look at the harmonic standards on transmitters. Who bothers checking the harmonic standards on their transmitters?

Walks over to a book case, pulls out a ring binder... Last checked two and a half months back when a taxi company set up down the road and started bitching about me getting into their VHF setup. Odd how quiet it went when I handed them the SA printouts (Including the one showing that their TX was not exactly blameless) and suggested that they take it up with their gear supplier or Ofcom. 

## I just can't fathom the manager/owner of any taxi co, being able to understand a SA printout any time soon. 

Jim  VE7RF
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VE7RF
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« Reply #175 on: December 19, 2011, 03:37:23 AM »

Zenki sez....." What use is IMD standards when someone can buy  a Solar inverter from China that puts   S9 QRM across the HF spectrum and flouts all known laws when its illegal to do so?. This occurs daily in Europe, we put our own manufacturers out of business with well intentioned laws and turn a blind eye to the fraud from China. The Eurozone is the biggest joke of the century. But this is another subject for another day!"

### same thing here in NA.   We had a recent case of defective extension cords....all made in China, complete with UL/CSA stickers on them. They are supposed to be 18 ga wire inside, when in fact they were only 22 ga wire, with heavy insulation on em.  After a few homes burned down, somebody finally figured it out.

##  The noise floor on HF ham bands is steadily rising.  I gave up on astronomy because of light pollution, now the same thing is happening with HF radio.  160m is one big mess.  Installing directive RX ant's  on 160m is a trick at the best of times on a 90' x 130'  suburban lot.  Since the qrn is coming from all directions, the rx ant is always pointed at a noise source.  Folks used to do fairly well with just 100w on any HF band.  Not these days.   The noise is  getting worse...and the amps are just getting bigger. I don't blink an eye using a couple of kw  to talk across town.  Some of the rag chew groups I belong to, everybody in the group runs an amp.  The idea being everybody can hear everyone else.  If a 100w station breaks in, and we can't copy him too well, we suggest he get himself a big amp, or at least 500-600w, than come back.  If they start up abt the 'evils of hi-power', the easiest way to shut em up is to flip to standby.  Then they will bitch about poor copy at their end, case closed, end of story.  Back in the late 60's, early 70's, the odd fellow had a 2-el shorty 40 yagi.  These days, you are lost with out one...+ 2 kw.

Later... Jim  VE7RF

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VK4DD
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Posts: 79




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« Reply #176 on: December 21, 2011, 08:19:38 PM »

Contribution from exciter to IMD when used in combination with amplifier.

see http://www.ab4oj.com/quadra/sshfamp.html
Have a read what AB4OJ writes about IMD near no 8.

In other words.
 
- if the PA has bad IMD, don't worry about driving it with a clean radio.
- you will not get better IMD because of your amplifier.

Both PA and exciter need to be good other wise IMD will be limited to the worst.

It is just like your home stereo at home.
If you have good speakers but a bad amplifier than the sounds like a toilet.
If you have a good amplifier but no good speakers you still have the toilet sound.
If they both are good quality, than you got nice a nice sound in your hifi Cheesy

73 Ron
« Last Edit: December 21, 2011, 11:54:35 PM by VK4DD » Logged
M0HCN
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Posts: 566




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« Reply #177 on: December 22, 2011, 03:47:46 AM »

Well kind of, except that in reality the speakers are almost always the bottleneck!
All engineering is trading off the compromises, but speakers are basically a box of compromises.

Regards, Dan.
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AA4PB
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« Reply #178 on: December 22, 2011, 05:07:14 AM »

Just like the IT saying "garbage in, garbage out". The output of an ideal amp should be an exact copy of the input, except larger.
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Bob  AA4PB
Garrisonville, VA
VE7RF
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Posts: 212




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« Reply #179 on: December 22, 2011, 05:20:25 AM »

Contribution from exciter to IMD when used in combination with amplifier.

see http://www.ab4oj.com/quadra/sshfamp.html
Have a read what AB4OJ writes about IMD near no 8.

In other words.
 
- if the PA has bad IMD, don't worry about driving it with a clean radio.
- you will not get better IMD because of your amplifier.

Both PA and exciter need to be good other wise IMD will be limited to the worst.

It is just like your home stereo at home.
If you have good speakers but a bad amplifier than the sounds like a toilet.
If you have a good amplifier but no good speakers you still have the toilet sound.
If they both are good quality, than you got nice a nice sound in your hifi Cheesy

73 Ron


##  This is all blatantly obvious.  K3  with -32 db pep IMD-3  driving an 8877 with -40 db IMD-3  will  result in lousy imd. The K3's imd is no better than any sweep tube XCVR  from the 70's.

## yaesu FT-9000MP  with it's CB -22db pep IMD-3  driving a 3CX-3000A7  with -59db pep IMD-3  will result in lousy imd.

##  yaesu in Class A with -49db pep IMD-3  driving a RM Italy 1.5 kw SS wonder bar CB amp = lousy IMD.

##   http://www.nikkemedia.fi/juma-pa1000/   Does anybody know  what the imd is on this amp ? It uses a SINGLE LDMOS device  made by freescale, which is all the rage these days.  Freescale also has devices in 300/600/1200 watts.

##The link to the VA7OJ article was interesting though.  Using a yaesu in Class A  can improve IMD by 2.97db....since the total imd will consist of the amps IMD, plus the IMD from the XCVR.  The kicker is, any and all IMD from the XCVR gets amplified by the amp..and adds to it.  EG: XCVR has say -30db pep IMD-3.[class AB] Lets say the xcvr is 100w pep output. IMD-3 will now be .1 watt.   Amp has say 10db of gain.  The amp will amplify the .1W of imd from the xcvr by 10db.  So the IMD from the xcvr is now up to 1watt.   Lets say the amp is 1000watts.   And amps IMD is also -30db pep IMD-3.  Amps IMD-3 alone is 1 watt.  IF the 1 watt of amplified imd from the xcvr adds in phase with the 1 watt of imd from the amp.. then we have 2 watts of imd.   And now TOTAL imd has just been de-graded to -27db.

## OK, switch to class A  for the XCVR.  IMD-3 is now -50db pep.  IMD = .001 watt.   It then gets amplified by the amp by 10db.   Xcvr's imd is now .01watt.   Amp's IMD alone is 1 watt.   Total IMD is now  1.01 watt.  That's a 2.97db improvement.

## Now this all assumes the  imd from the xcvr and also the amp are in phase..and additive.  They could easily be outa phase..and then subtract. [ distortion cancelling distortion].  I think the ADAT xcvr works on a similar principle with it's pre-distortion scheme. Class A has it's drawbacks though. 25% eff + a whopping 10A CCS of idle current.

## The real way to get the xcvr clean is to run a 300w pa..at 100w...AND design it around that 100w level.  2 x VRF-151's at 120w pep out would be the ticket.  These new LDMOS devices, when backed way down, also show good imd.

Later... Jim  VE7RF
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