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Author Topic: Ham Xcvrs' and Amps', Transmit Spectral Purity, IMD Products, vs. comm/maritime  (Read 154022 times)
AC2RY
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Posts: 758




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« Reply #210 on: April 06, 2018, 10:12:58 PM »

Soundcards are the [very] weak link in measurements. At the low audio spectrum they can have unflat passbands measuring in the tens of db. They don't couple DC at all and the rollup starting at DC to the mid-audio frequencies is ridiculously not flat. They can have huge gain spikes at specific frequencies anywhere in the audio spectrum. At best they are ok for teeny-boppers to listen to crappy music... the rolloff above 20khz is a given of course. I wouldn't use a soundcard for any type of measurements, in fact it bothers me that my SDR rig works into a soundcard. I've searched for an appropriate substitute and afaik it doesn't exist. I'd like to build something on a card that plugs into a computer mobo directly with a DC to 500kHz flat passband, integrated with GPU processing but a project like that is way over my head... R



Are you serious? Mainstream sound cards are ruler flat up to from 10Hz to 90 kHz. Distortion levels are below -100dB for full range signal. And dynamic range is 110 dB or more.

This is well above anything avalable 20 years ago regardless of cost.
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G0HZU
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Posts: 163




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« Reply #211 on: April 07, 2018, 02:35:21 PM »


I'm not sure if the whole thread should be taken that seriously TBH. One or two claims in the first post seems to be off the planet. I've not been near let alone used an Icom M-700pro marine radio but looking at pictures of it, it just seems to be a basic HF radio aimed at marine use. It looks like it runs from 13.8V so it's probably going to have similar IMD performance to ICOM ham (13.8V) radios of a similar era. It might be tweaked to be slightly better but it's going to be a push pull BJT PA running in class AB. So I'd expect average IMD performance from a radio like that. The ham versions only run 100W PEP so it doesn't make sense that the marine version at 150W PEP will achieve IMD much different to the ham version.

KA4WJA is suggesting that it can suppress all two tone IMD terms to better than -75dB when operated at 150W PEP which is not realistic for a radio like this. Where did the data come from that supports this -75dB IMD claim?
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AC7CW
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Posts: 1356




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« Reply #212 on: April 07, 2018, 06:05:43 PM »

Soundcards are the [very] weak link in measurements. At the low audio spectrum they can have unflat passbands measuring in the tens of db. They don't couple DC at all and the rollup starting at DC to the mid-audio frequencies is ridiculously not flat. They can have huge gain spikes at specific frequencies anywhere in the audio spectrum. At best they are ok for teeny-boppers to listen to crappy music... the rolloff above 20khz is a given of course. I wouldn't use a soundcard for any type of measurements, in fact it bothers me that my SDR rig works into a soundcard. I've searched for an appropriate substitute and afaik it doesn't exist. I'd like to build something on a card that plugs into a computer mobo directly with a DC to 500kHz flat passband, integrated with GPU processing but a project like that is way over my head... R



Are you serious? Mainstream sound cards are ruler flat up to from 10Hz to 90 kHz. Distortion levels are below -100dB for full range signal. And dynamic range is 110 dB or more.

This is well above anything avalable 20 years ago regardless of cost.

Please, suggest some products here, I am looking for the path forward to replace my current soundcard.
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Novice 1958, 20WPM Extra now... (and get off my lawn)
G4ZOW
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Posts: 119




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« Reply #213 on: April 07, 2018, 11:03:10 PM »

Choose the features required then click the left hand menu for full spec: http://www.marian.de/en/products/comparison

Matches or improves on anything AudioScience or Digigram have to offer.

The AD2 is my chosen weapon.

All cards are PCIe and DC coupled and with distortion down to -140db & dynamic range 144dB (A).

US distributors in CA & IN.

David G4ZOW/5B4
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G3RZP
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Posts: 1321




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« Reply #214 on: April 08, 2018, 12:30:51 AM »

G0HZU,

The standards for marine transceivers are in the ETSI Standards, FCC regs and the international Radio Regulations: they are probably in Japanese and Korean regulations, too. Certainly in Europe - I don't know about the US -  a manufacturer can self certify, but does need to have an adequate quality assurance method, usually assumed to be demanding ISO 9000 compliance.

400 watt and above transceivers historically needed to be able to work full duplex, receiving in the same band: the duplex split varied between bands.

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SM0AOM
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Posts: 261




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« Reply #215 on: April 10, 2018, 10:22:02 AM »


 It looks like it runs from 13.8V so it's probably going to have similar IMD performance to ICOM ham (13.8V) radios of a similar era. It might be tweaked to be slightly better but it's going to be a push pull BJT PA running in class AB. So I'd expect average IMD performance from a radio like that. The ham versions only run 100W PEP so it doesn't make sense that the marine version at 150W PEP will achieve IMD much different to the ham version.

KA4WJA is suggesting that it can suppress all two tone IMD terms to better than -75dB when operated at 150W PEP which is not realistic for a radio like this. Where did the data come from that supports this -75dB IMD claim?


A previous employer used scores of the Icom M-700TY as drivers for higher powered HF amplifiers. Their output power levels were set about 60 to 70 W. The IM3 requirement was better than -32 dB and an averaged voice loading adjacent channel suppression of about -50 dB for the whole system. Stand-alone,they provided about -36 dB IM3.

The ISB rated 1kW transmitters we used provided -42 dB IM3 and -60 dB adjacent channel. This was using exciters that were better than -55 dB IM3 at the 100 mW level.All IM3 figures are referred to one tone, not the inflated ARRL figures.

A post-power amplifier IMD3 of -75 dB is completely unrealistic with conventional means,and hardly realisable even with SDR and digital linearisation techniques.

There is some current research going on here by SM5HP, former developement manager for HF products at ITT-Standard Radio, using "notched noise" and SDR receivers to evaluate the distorsion properties of current both amateur and professional gear.

It turns out that the transfer functions of LDMOS amplifier chains tend to favour higher-order IM products,compared to bipolar amplifier  chains. If driven near their power limits, the newer LDMOS amplifiers show quite pronounced "shoulders" quite far from the desired channel.

This research will continue, including more HF/SSB transmitter chains of different makes and vintages,and is intended to result in a paper about the real-life transmitter adjacent channel and co-location performance that will be presented at the 2019 Nordic HF Conference next summer.
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KA4WJA
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Posts: 1098




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« Reply #216 on: April 10, 2018, 10:56:09 AM »

Okay, guys....thanks for pointing out a typo of mine that I made almost 4 years ago.. Smiley
Until this afternoon, almost 4 years hence, I did not realize I had made this typo / error!!

What I thought I wrote in regards the old M-700Pro, was that "all higher-order IMD products down better then 75db" (meaning products higher than the 9th order...such as 11th, 13th, 15th, etc...)
Sorry, about the "typo" / "omission" of that critical point!!  Sad
{BTW, how come nobody else caught this???  'cuz, even Zenki would cry BS on a IMD3 of -75db!!  Smiley And, certainly anyone that reads this whole thread could see that this must have been a typo / error!!}

But, even more impressive is the fact (sorry I don't have the scans to "prove" it) that a couple older "12 volt" HF marine transceivers, have even BETTER transmit spectral purity and even lower transmit IMD products....
Such as the Icom M-700Pro (which is a 1990's design, that just ceased production about 7 - 8  years ago, and retailed for ~ $1250...and can be purchased used nowadays for about $500 - $700) had even lower phase noise, and all IMD products down better than 75db...and here again, this is at 150 watts PEP output continuous-duty (FSK/SSB/CW)..

To be honest, I read / proof-read the posting....but when you just got done writing something, sometimes what is in your head is what you think you just read!  
Opps...
Sorry about this!


While as I stated, I don't have the scans of the IMD tests of the M-700Pro, my understanding is that the M-700Pro was built to the old Part 80 standards:




And, the only high-order (above 9th order) IMD spec that I found was a reference to the "higher-order products better than 75db down", from an NTIA page years ago...
If I can find it, I'll post it...
But, for certain a well-designed HF rig can have its higher order products down better than 75db at 100 - 150 watts PEP....it's not rocket science.  Smiley


Again, sorry about the typo!!
But, FYI to all, a simple typo / omission does NOT did-allow all the other factual info I posted, nor the last 4 years of discussing the dismal state of our modern HF ham rigs' transmit IMD!!

And, while I realize that in ISB service, esp SSB/FSK ISB service the IMD3 spec is crucial....in our ham band SSB service, I find the 5th, 7th and higher order products from many of my fellow hams' transmitters to be the most offending, causing the majority of splatter....not to mention the horrible ALC systems causing lots of spurts and sputters (along with the poor IMD splatter)...
Hmm??
I just wrote some "down-home" tech terms that might not translate well internationally....spurts and sputters are of course not engineering terms, but do aptly describe the results on-the-air... Smiley
So, for those of you that are not USA-based, please be kind to my casual-yankee speech!  Smiley



73,
John,  KA4WJA


P.S.  Those that wish to further discuss SDR's and soundcards, I will gladly read and learn from you!!!
But, please start your own thread on those topics!  Smiley
Thanks!!  Smiley
  
« Last Edit: April 10, 2018, 11:04:31 AM by KA4WJA » Logged
ZENKI
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Posts: 1648




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« Reply #217 on: April 17, 2018, 03:27:00 AM »

When the FCC was in the business of engineering and developing real engineering standards the IMD requirements were most demanding in the world. In particular the OLD Part 80 FCC Marine and Commercial HF SSB IMD standard.

The FCC place more importance on higher order  IMD products that had to be suppressed to the highest levels, IMD products from the 11th order and above.  I cant exactly remember but the formula was very simple. 10log the transmitter power plus 40db for 11th order products or greater.   The requirements for the 3rd to eleventh  order was  very modest  36db below PEP  for the 3rd and 5th order products. The 7th and 9th order products had to be suppressed by -35 below average power or 41db below PEP.

We typically find ham band transceivers whose IMD products  regularly sit on a plateau from the 3rd order to the 9th order  largely being the same with  the 11th order and above being  not much below these figures. Is it a wonder that ham transmitters cause so much harmful splatter.

This old FCC Part 80 Standard would be a good standard to  aspire towards if ever IMD regulations become mandated. There  must be a copy hiding somewhere on the internet. I have a copy somewhere on my old PC.  

We should set the IMD figure on the ERP power rather than the amplifier power, assuming a 10db gain antenna system and a 2500 PEP output it would  be reasonable to have a mandated IMD suppression level  suitable for a 25KW PEP commercial SSB transmitter.

You can see reasonable levels of IMD performance like this on transmitters from Selex and JRC that exceed -36db PEP for 3rd order with the critical high order products suppressed  very well for good engineering practice. These are 10kw transmitters not miserable 100 watt output radios! The JRC Ham radios also had excellent IMD performance that is unmatched to this very day. The JRC245 comes to mind.

We rarely use good engineering practice in Ham commercial  equipment design, its more about cheap and nasty engineering. JRC produce a JR900 10kw HF transmitter thats solid state that use pre-distortion that has  3rd IMD performance  of around -45 db or better.  Pre-distortion is our only hope in the ham service of achieving these kinds of excellent IMD numbers, we certainly cant achieve it with good engineering because the manufacturers are only interested in producing transceivers with rubbish performance  transmitters. How can it be good engineering when we see products reviewed in QST with -15db  below average for 3rd order IMD products? Thats as Class C CB dirty as it gets, totally disgusting garbage being sold to hams.

« Last Edit: April 17, 2018, 03:30:35 AM by ZENKI » Logged
W3RSW
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Posts: 606




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« Reply #218 on: April 17, 2018, 09:41:19 AM »

Of course 10kW (10^5) is  10^3 times greater than 100 Watts (10^2) along with the concomitant 10^3 ratio of IM products.
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Rick, W3RSW
KA4WJA
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Posts: 1098




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« Reply #219 on: April 17, 2018, 10:25:53 AM »

Zenki, my man...
Welcome back!   And, thanks for helping return this discussion to the main point (that we, and the manufacturers can do better!)

This old FCC Part 80 Standard would be a good standard to  aspire towards if ever IMD regulations become mandated. There  must be a copy hiding somewhere on the internet. I have a copy somewhere on my old PC.

I'm pretty sure this is the old Part 80 mask....and as you can see it's pretty darn good....all transmit products beyond about 11.2khz away (2.8khz bandwidth x 4) from your transmit signal down -80db! and everything beyond +/- 5% of your freq, down -100db!  (I doubt anything can meet that spec today...but it's a nice goal!)

  



As for the JST-245....I think I mentioned it a while back??  But, if not, yep it's quite good for a 150-watt ham rig!
3rd/5th/7th/9th =  -39 / -56 / -57 / -60db(PEP)

Have a look...




Along with a current production Icom (M-802), we can easily see that good IMD for HF rigs is not only possible but is actually being done every day by the same manufacturers that make some of our ham gear....and at 12vdc, no less!  Smiley
And, as I pointed out years ago, this doesn't add much to the cost of the radio....about $50 to $100, MAX!


Icom M-802's IMD (at 150 watts) =  -47 / -50 / -58 / -60db(PEP)  [and, note the roll-off of the higher-order products...]




Zenki, thanks again!  (but, I still wish you'd ID yourself!)


73,

John,  KA4WJA
« Last Edit: April 17, 2018, 10:32:06 AM by KA4WJA » Logged
KA4WJA
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Posts: 1098




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« Reply #220 on: April 17, 2018, 10:48:24 AM »

Rick,
If you're writing exponents, you're off by one order...

Of course 10kW (10^5) is  10^3 times greater than 100 Watts (10^2) along with the concomitant 10^3 ratio of IM products.

10kw is 100 times 100-watts....not 1000 times...
{btw, even though your math is off by a factor of 10, I haven't seen "concomitant" used in decades!  Good on 'ya!}

73,
John,  KA4WJA
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G0HZU
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Posts: 163




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« Reply #221 on: April 17, 2018, 04:49:43 PM »

Quote
But, the point I'm trying to make is, there ARE currently full-featured, HF transceivers, that provide excellent service on the ham radio bands, that have excellent transmit spectral purity and extremely low IMD products, with the IMD products that actually cause most of the splatter (5th and higher order products), completely non-existent....
And, these radios are now currently on the market (and have been for years), at a reasonably "affordable" price...(< $2000)

Here's another possible 'typo' you made 4 years ago? Your old keyboard managed to suggest that there are sub $2000 radios out there that have 'completely non-existent' 5th order distortion terms Smiley

One solution would be to turn the transmit power down because then it would become more realistic to run a PA in class A. 10W PEP is only 10dB down on 100W PEP but a wideband class A PA at 10W PEP could have >=11th order IMD terms nearly 30dB better than the JST245 plot when measured wrt PEP. They will be even better in absolute terms because of the obvious difference between 150W and 10W PEP. So the interference level to other users could be about 40dB lower. But the class A PA will be expensive and will probably run at a steady 60W DC input power just to get 10W PEP. So it would need a decent heatsink and a fan.

Which radio PA is the ham going to buy if they both cost the same? The one that takes a steady 60W DC input power that only gives out 10W PEP or the one that runs at a similar average DC input power (with human speech) that can deliver 100W PEP?
« Last Edit: April 17, 2018, 04:57:10 PM by G0HZU » Logged
KM4AH
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Posts: 963




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« Reply #222 on: April 17, 2018, 07:08:11 PM »

You can run Class A with a Yaesu FT1000MP Mark V which you can buy for $1100, or at least I did.
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KA4WJA
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Posts: 1098




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« Reply #223 on: April 17, 2018, 07:27:16 PM »

G0HZU (I would politely address you by your name, but you don't wish to provide that to us here, nor to qrz.com...and ofcom says you requested to not disclose...so...I cannot be as friendly as usual.)

So, sir, I'm taking you seriously....one last time... Smiley

Though, I wonder if you have read this whole thread??
Because it appears that you haven't??
If you have, I'd think you could easily have read enough of my ramblings (and facts) as well as much input from many others, that would certainly have clarified any "errors" or "outrageous" statements as typos...

I mean, seriously??
Can you not infer that what I meant (and thought I had written) was that most of the splatter was nonexistent....not that all IMD products were nonexistent.
I realize that we are separated by a common language, and I know that sometimes my mind is running at a different speed than both my fingers and my eyes (dyslexia)....but, I think if you take the time to read through things, the few odd typos will become apparent and easily understood...


Oh, and as for running a 100-watt rig at reduced power?  And/or Class A??
Yes, this has been discussed at length....

--- as you are aware, most find Class A operation of medium or high power PA's, to be a waste of power / produces heat-generation issues, etc. (yes, I know to you purists, there are ways to adapt to these issues, but at what cost?)...and if you care to read all the info here regarding the horrible ALC systems employed by the few production rigs with Class A PA's, you'd see that unless you operate without any ALC at all, there is little if any advantage in operating them in Class A...(the old MarkV did allow you to adjust the drive level and operate Class A without driving any ALC....and it's a nice rig...but long-since discontinued)

--- also, as can be easily seen, there is much more to this than just "turning the power down"....yes, many modern HF ham rigs will produce somewhat lower IMD products when operated at 60% to 75% of their rated power, some do not (and recent tests on youtube, of some newer rigs show fairly poor IMD when operated at QRP power, can't find the links at the moment, and they're not ARRL tests, but do show a frustrating result)....further my mentioning of the various PA designs / biasing / tuning that can provide lower higher-order IMD at the sacrifice of the lower-order products and vice-versa....but, even more on point here was the part of this discussion between Carl and I regarding the fine work done by Eimac, where their paper shows that drive levels (and varying biasing levels) / output levels can all be manipulated to produce PA's that "spec out" well, but fail to produce actual cleaner transmit spectra (another reason Carl, and others, hate two-tone testing)


HZU,  I hope you are seeing my point here...
You mention some obvious points, that all been fully discussed here, but have failed to grasp the gist of this thread:  That there are current production 150-watt / 12vdc PA, IF-DSP, HF transceivers, selling for less than $2000 USD, with fairly good transmit IMD....made by the same manufacturer that sells other HF rigs (our ham rigs), with inferior transmit IMD...


I scratch my head at times, wondering why some wish to find solutions (like running a PA in Class A, running QRP, only using SDR rigs with pre-distortion, etc.) that cost money, cost power output, cost heat, cost inefficiency, etc....when these same manufacturers already make reasonably priced radios that require none of these "solutions"??  Smiley
Just saying....your ideas are not bad ideas, but they've all been discussed at length, and fact is they aren't necessary to solve the problem....all that's needed is for hams to stop buying rigs with crappy transmitters and demand the manufacturers produce rigs with better transmit IMD!!
Problem solved!  Smiley



You ask the question of which rig the ham will buy??
Of course with just the two choices you give, if the ham doesn't understand the issues of transmit IMD, etc., he'll buy the 100-watt rig.
Which radio PA is the ham going to buy if they both cost the same? The one that takes a steady 60W DC input power that only gives out 10W PEP or the one that runs at a similar average DC input power (with human speech) that can deliver 100W PEP?
But, what if the ham had a choice to buy (for the same $$$) a 100-watt (or 150-watt) rig, with 10db to 20db better transmit IMD products??  (like an Icom rig, using the PA from a current-production Icom M-802)
I'd say, he'd buy this one...
But, if you're not informed that these radios, and these PA's, really exist....well then you're gonna' be stuck following expensive (in either money or transmit power, or both) trends like "Class A PA's", "running QRP", "SRD's with pre-distortion", etc...



Okay, enough for now....
HZU, I wish you well....but since I'm not really interested in going over all of this again, take care and 73.


John,  KA4WJA
 
« Last Edit: April 17, 2018, 07:45:00 PM by KA4WJA » Logged
W3RSW
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Posts: 606




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« Reply #224 on: April 18, 2018, 08:01:14 AM »

John,
4-2=2:  yer right , I got excited with the 5!

At any rate, a 10kW amp puts out serious signals along with somewhat serious IM products, even when properly down.  Grin

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Rick, W3RSW
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