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Author Topic: Ham Xcvrs' and Amps', Transmit Spectral Purity, IMD Products, vs. comm/maritime  (Read 153892 times)
VK3BL
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« Reply #240 on: April 29, 2018, 08:48:48 AM »

Find me a single example of a 12V Ham transceiver where 5th order products (2 tone) DONT dominate at full rated output....

The reality of white noise or SSB voice is different, however.
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J.D. Mitchell BA  - VK3BL / XU7AGA - https://www.youtube.com/ratemyradio - Honesty & Integrity
KA4WJA
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« Reply #241 on: June 07, 2018, 06:36:28 AM »

Just some thank you's and very brief clarifications.  Smiley  (no, I'm not rehashing anything!)

I do appreciate the fine comments and helpful info that some have provided here.  And, once again, allow me to say how much I respect the expertise and experience of guys like Carl and Mike...(even if we do sometimes disagree).  
I sent Carl and Mike some friendly thanks, directly via e-mail...but unable to do so to HZU, so thanks to him as well, for holding our feet to the fire, and accept my apologies if I ever seemed rude (not my intent)...

While some of us have gone 'round-n-'round on some minor issues (and yes, unfortunately I contributed to some of that fairly useless merry-go-round, too)...
I realized that the main point and original impetus of this discussion may have gotten lost.  Sad

So, just for clarification and to sum up:

1)  I personally experience rather poor transmit IMD from (barefoot) ham radio HF transceivers used illegally on the maritime bands (and have seen this for many years now)....30 to 40 years ago, when it was mainly HF maritime rigs and a few Atlas 210x's, Icom 761's, and Drake TR-7's, this wasn't a major issue....but over the past dozen years, it has gotten a lot worse.  (and, for clarity sake, yes I can hear the difference / the splatter is worse....some of the new ham rigs have 10-20db worse IMD products infringing on both adjacent channels and users well down the band / 10khz+ away...)

2)  And, you combine that with my personal experience of seeing/hearing more of the HF ham phone bands with some fairly crappy signals, with poor transmit IMD (gotten worse over the past 10 - 15 years)....compared to what I remember from decades ago! {I have some found memories of the old days, with many "Kalifornia Kilowatts" on-the-air....memories from mid-70's, of studying for my license, listening to clean signals on 75m (when I should've been copying CW in the Novice sub-band)....back then, except for a raucous DX pile-up, even 20m wasn't too bad....But, I digress!}  
In my own personal experience, things have taken a turn for the worse lately (last 10 - 15 years) in regards to my fellow hams HF signals and their poor transmit IMD...(and, again for clarity sake, yes I can hear the difference....except for a quiet weekday, I hear quite a bit of splatter on-the-air these days...)

3)  And, then look at what some of our popular / high-scoring contesters and DX-er's have been saying for the past 10+ years...
Paraphrasing them: "the receivers are better than most hams can effectively use, as the transmit IMD and noisy transmitters are the limiting factor in our HF realm, these days!"  
(and please remember that those are the same guys who were complaining about our poor receivers a decade or two earlier....and their demands of better receive performance is why we have the excellent receivers that we have today!!)


Now, you combine those three things together with the transmit IMD test results of modern HF rigs (both ham and maritime), some of which I had access to a lot of data, some not so much...
And, viola....you have the reasons I started this thread in the first place!

Now, yes....there were some of the oft read frustrations like:
"the tests weren't done right",
"I don't see why some scans are different",
"why are some displayed 'wrong' ",
"where did this come from",
"who are you to tell me this", etc....
....along with the usual ARRL bashing, etc.
And, yep, I get it....these can be valid points....
And yes, I tried to defend 'em, but I just don't have the time / inclination to do much more... Smiley  (you're welcome)


So, the main point here, today, is:

These are the honest, real-world, experiences I've had over the past decades...
And test results that I had available (from ARRL, from Rob, NC0B, from a few friends at EMC test lab, etc.)....
And while, yes over-driving an amp could account for some of the crappy signals on the HF ham bands, none of my experiences on the HF maritime bands had any amps at all...
And further, that while I agree with Mike that those with their mic gain, etc., cranked-up are the cause of some (a good deal?) of the horrible splatter we hear, the undeniable fact is that most of our "modern, 21st Century" HF ham rigs have fairly poor transmit IMD, even when operated in their prescribed manner / with good engineering practice, with the mic gain properly set!  
(and btw, my comments regarding the FT-1000 in Class A, as well as the FT-5000 in Class A, were regarding the fact that if you had any ALC at all, the actual result was only marginally better then if you ran the rig in Class B, and certainly not that a maritime rig was "better" than a Class A PA, just that the way Yaesu uses ALC makes the use of Class A fairly moot, if you have any ALC....sorry, if I didn't spell that out clear enough...)

And, that my friends and fellow hams, is/was my primary gist/goal of this discussion....that's it....
Look at the specs (and spectral scans)....we've been through all the ancillary arguments, and I don't think much more can be done further discussing them....so, if you disagree with me, no worries, I take no offense, but please just try to understand that the only agenda I had/have is to bring some info to light, spurred-on by own, real-world, on-air, experience and my research....  Smiley  
{and, just to reiterate, I never wrote that hams need to use maritime rigs, nor that everyone needs to scrap modern technology and go back to a Collins 32S-3....just that we can do better than what we're "being sold" these days....and it's up to us to demand better, by spending our dollars/euros only on rigs with better transmit IMD, as well as educating ourselves and fellow hams of the issues (including keeping the mic gain at the proper level!)...}


Finally, Mike...I will repeat again, I respect your expertise in RF engineering (and have learned from you), and I agree that the mic gain is a problem....but...

(I'm hesitant to write this)...But, perhaps I wasn't clear in that I operate HF these days mainly from my boat (or other location) with my Icom M-802's, barefoot....I got a feeling that you were implying that somehow I'm not "legit", because I have some old equipment at home (Drake TR-7's and Alpha 77SX, for HF....homebrew 144mhz transverter and Henry 2002, for EME, etc...but some tower / antenna damage and lost trees/wire antennas from storms/hurricanes, means that even when I am home I don't operate from there), and haven't added/updated my qrz.com profile in a long while (~ 12 - 15 years?)...
I do hope that I an wrong in this perception??  
As, I really hope that ham radio can be both a service (Amateur Radio Service) and a nice hobby....AND, a great place to learn from each other, etc., without falling into the traps of our modern society, like Facebook/Instagram, etc...
{Oh, and fyi, while it's not as good as some commercial maritime rigs, in my notes joted down in my owner's manual, many years ago I measured my original TR-7 (at 100 watts PEP out?) 3rd order at -38db(PEP) and 5th order at -44db(PEP).....and while I don't have it written down, I believe 7th and 9th were in the mid-50's....these are a fair bit better than some of the more "modern" rigs...but, this was > 30 years ago, and while I have cleaned / aligned the rig over the years, I admit I haven't 2-tone tested in decades, but also haven't used it in years, either. Sad }


Okay, that's all I got for now....hope some here have gotten something out of this.  Smiley


Fair winds.

73,

John,  KA4WJA
« Last Edit: June 07, 2018, 06:43:39 AM by KA4WJA » Logged
W9IQ
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« Reply #242 on: June 07, 2018, 08:34:28 AM »

It seems that throughout this thread, the implied smoking gun of IMD is the tranceiver's output amplification stage. Has anyone quantified the IMD effects of the multiple up stream AF/RF amplification/mixer/filter stages? While these may be more nearly linear by design, I would assume they have a measurable, if not dominant, effect.

- Glenn W9IQ
« Last Edit: June 07, 2018, 08:54:15 AM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
KA4WJA
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Posts: 1098




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« Reply #243 on: June 07, 2018, 09:12:52 AM »

Glenn,
You're correct here....this is mostly about the transceiver's PA...
It seems that throughout this thread, the implied smoking gun of IMD is the tranceiver's output amplification stage.

Except for mis-adjusted mic gain, and/or overdriving of amps, etc...For SSB operation, etc., it's mostly (all?) about the PA stages....
Although anything (including filters) can be non-linear, and contribute to transmit spectral issues (IMD, etc.), to the best of my knowledge, the IF's, filters, and last mixer (1st mixer) contribute little, if anything, to the transmit IMD issues of our modern HF ham rigs...and the rigs' oscillators' noise contributions are a very small factor to the rigs' transmit spectral purity in SSB operations...(but, I could be wrong??)
{although, in CW operation the transmit noise (oscillator phase noise) does play a significant part in th rig's transmit spectra....although in most cases the hard-keying (short rise and fall times, of less than 4 to 5ms) plays the major role...see reference to K9YC's article, regarding this..}
But...


But, I actually don't have an absolute answer for you... Sad
Has anyone quantified the IMD effects of the multiple up stream RF amplification/mixer/filter stages? While these may be more nearly linear by design, I would assume they have a measurable effect.

- Glenn W9IQ
To be honest, I've never looked at my low-level (0dbm) output of my rigs, directly....

But, I did look at my spectral purity of my 144mhz transverter (which uses a 0dbm output of my TR-7, on 28mhz), and found no issues....(but, honestly that was 30 some years ago, and I don't remember what I found...except for a frustration with a "spur" that developed from my transverter's 144mhz PA....turned out that the VMP-4 that was supposed to be good for 7+w, was producing a spur of about -30dbc a few mhz away, when output was > 4 watts....but, disappeared altogether at outputs <3 watts...luckily all I needed was 2 watts, so I was golden! Smiley )


So, I cannot say that I have any real-world quantitative data for you.  Sad
But, Carl and/or Jarrad might???
Perhaps they will chime in...

Since there is no reason to assume that the output of the mixer (at ~ 0dbm) that goes to the pre-driver, driver, and final PA of our rigs, is non-linear....I (like everyone else) assumes there is little contribution from them to transmit IMD...


But of course, for CW operations, the transmit noise (oscillator phase noise) is a significant contributor to the rig's transmit spectra....although, in many cases the hard CW keying (rise times < 4ms to 5ms) is the major component of the rig's transmit bandwidth and close-in spectra...


Glenn, I hope to learn from your question....

73,
John,  KA4WJA
 

 
 



« Last Edit: June 07, 2018, 09:18:07 AM by KA4WJA » Logged
KM1H
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« Reply #244 on: June 07, 2018, 09:35:28 AM »

It seems that throughout this thread, the implied smoking gun of IMD is the tranceiver's output amplification stage. Has anyone quantified the IMD effects of the multiple up stream AF/RF amplification/mixer/filter stages? While these may be more nearly linear by design, I would assume they have a measurable, if not dominant, effect.

- Glenn W9IQ

With the low level audio and RF amp stages being Class A, modern filters and mixers being far better than even 20 years ago, their IMD contribution does not fall into the GIGO category of yesteryear.

Even so the mid 80's TS-830 is capable of a real IMD in the low -40's; I dont know about the other KW hybrids.

Carl
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K6AER
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« Reply #245 on: June 13, 2018, 04:48:38 PM »

KA4WJA,

You have posted on this thread 59 times. Do you ever get on the air?

Mike
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KA4WJA
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« Reply #246 on: June 14, 2018, 02:47:26 AM »

Mike,
Yes, I do get on the air, but in case you missed it, not nearly as often as I used to, nor as often as I'd like to!
I do have much more pressing priorities, such as some family matters (that I'd rather not discuss publicly, if that's okay), and sometimes find that I have a few minutes to spare when I can get on-line (such as doctor's offices, or late at night but cannot disturb anyone, etc.)....and I'm not online much....

BTW, you did get my personal e-mails of respect and explanation, but instead of politely accepting, you choose to show a rather harsh outlook on your fellow man here, instead of understanding that we all are individuals and have different priorities??

In the world I live in, we can all be different, have different opinions and share them with each other and still respect each other....perhaps you do not live this same philosophy??  But, I do still wish you well.

Finally, you have more than 5 times the number of posts than I do, over the same number of years.
What does that have to do with anything?

73,
John,  KA4WJA

« Last Edit: June 14, 2018, 02:58:47 AM by KA4WJA » Logged
K6AER
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« Reply #247 on: June 14, 2018, 10:58:26 AM »

My postings are on all subjects. I don't have my panties all in a wad over IMD which I cannot control any more than bad behavior on 80 meters.

I have been posting on E-Ham since they started. 60 postings on one thread would indicate you like to keep the thread alive at all cost.

Through all of the verbiage on IMD I have not any evidence that having an station IMD number better than -35 dB would improve the band operating with our current band noise floor of -108 dBm. With summer lightning that number drops to -90 dBm.

I noticed on QRZ.com your main radio is a TR-7. These radios have never had better than -30/-34 dB IMD on their  3rd and 5th IMD two tone numbers at 100 watts out. If IMD is your main concern why not a better radio?

This IMD thread is nothing more than a tempest in a tea pot.

« Last Edit: June 14, 2018, 11:12:30 AM by K6AER » Logged
VA7OJ
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« Reply #248 on: June 14, 2018, 11:20:38 PM »

Find me a single example of a 12V Ham transceiver where 5th order products (2 tone) DONT dominate at full rated output....

The reality of white noise or SSB voice is different, however.

Hi Jarrad,

Here is an example of a radio I tested in which TX IMD5 < IMD3.

http://www.ab4oj.com/icom/ic7600/7600notes.pdf  p. 21

All this fuss about IMD performance of amateur transceivers overlooks the fact that the ITU-R guideline (SM.326-7 §1.2.3) specifies -25 dBc for single-channel J3E, and -35 dBc for B8E (ISB). This is quite modest. I do not think an OEM will 'bust its hump' trying to exceed this guideline unless the radio set is type-approved for radio services requiring a tighter transmit IMD spec.

73, Adam VA7OJ/AB4OJ
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HAMHOCK75
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« Reply #249 on: June 15, 2018, 02:20:41 AM »

Here are what some of these products look like on a public access SDR. Notice in the image below that there is a station occupying more than three times the spectrum of other stations. Listening to the LSB as shown sounds fine.



There is nothing heard listening below the LSB until that station comes on, then there is what sounds like garbled audio.

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KM1H
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« Reply #250 on: June 15, 2018, 06:13:25 PM »

Quote
http://www.ab4oj.com/icom/ic7600/7600notes.pdf  p. 21

All this fuss about IMD performance of amateur transceivers overlooks the fact that the ITU-R guideline (SM.326-7 §1.2.3) specifies -25 dBc for single-channel J3E, and -35 dBc for B8E (ISB). This is quite modest. I do not think an OEM will 'bust its hump' trying to exceed this guideline unless the radio set is type-approved for radio services requiring a tighter transmit IMD spec.

73, Adam VA7OJ/AB4OJ

Even using the ARRL PEP method the 3rd sucks and the 5th isnt much better. Sweep tubes could do better in the 60's.

What is the reference point of the ITU spec?  BTW the commercial SSB is channelized so close in IMD isnt a problem plus there is no mike gain control, no audio processor, and no access to the internals for Hammy Hambone to get his dick skinners into.

Carl
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K6BRN
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« Reply #251 on: June 15, 2018, 07:21:36 PM »

Carl:

Tube finals could do better for many reasons (see below), but what they were better at was not quite as desireable as what a solid-state amp provides in return...

1.  The simple analog oscillators of the day had phase noise that was determined largely by the quality of their crystals, not the jitter of their DDS/NCOs as in modern radios.

2.  The RF final amps in radios and external "linear" amps were as dirty as heck (usually push-push architecture with just over 180 degrees of conduction angle), but they had the major advantage of a tuned, narrowband relatively high Q filter (tank circuit) right after them, vs. a broadband amplifier with "no-tune" broadband filters on the output.

No reason that a similar tunable, resonating narrowband filter could not be attached to a solid state amp to improve performance.  With a lot of extra parts.  And significant loss of efficiency (lower voltage amps means much higher current in the tank - or a broadband transformer - ack!).  And the need to always take the time to "tune up" the amp.  So I guess the marketplace decided it could live with poorer IMD (some of the time - tube amp performance always depended on an operators skills in tuning/loading) to receive simpler operation and longer life in return.

I've still never heard what the immediate, obvious and critical value a 10 db reduction in IMD would yield for the user of, say an FTDX-3000.  Usually the reasons listed are pretty squishy.

Brian - K6BRN

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VA7OJ
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« Reply #252 on: June 15, 2018, 08:04:40 PM »

What is the reference point of the ITU spec?

The ITU-R guideline is referenced to one of two tones of equal amplitude. The ARRL PEP spec is 6 dB lower.

73, Adam VA7OJ/AB4OJ

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VK3BL
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« Reply #253 on: June 15, 2018, 11:57:40 PM »

Find me a single example of a 12V Ham transceiver where 5th order products (2 tone) DONT dominate at full rated output....

The reality of white noise or SSB voice is different, however.

Hi Jarrad,

Here is an example of a radio I tested in which TX IMD5 < IMD3.

http://www.ab4oj.com/icom/ic7600/7600notes.pdf  p. 21

All this fuss about IMD performance of amateur transceivers overlooks the fact that the ITU-R guideline (SM.326-7 §1.2.3) specifies -25 dBc for single-channel J3E, and -35 dBc for B8E (ISB). This is quite modest. I do not think an OEM will 'bust its hump' trying to exceed this guideline unless the radio set is type-approved for radio services requiring a tighter transmit IMD spec.

73, Adam VA7OJ/AB4OJ


Nice find.

Its interesting that my IC-7610 testing at full output doesn't mirror that, given the PA stage is the same I am lead to believe.

I will have to test my current radio again.

I agree there is much fuss about a natural part about radio, and people frequently misinterpret the manufacturer spec of -30 and the real life performance of some stations at -10.

73,

Jarrad VK3BL
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SM0AOM
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« Reply #254 on: June 17, 2018, 01:00:37 PM »


2.  The RF final amps in radios and external "linear" amps were as dirty as heck (usually push-push architecture with just over 180 degrees of conduction angle), but they had the major advantage of a tuned, narrowband relatively high Q filter (tank circuit) right after them, vs. a broadband amplifier with "no-tune" broadband filters on the output.


The IMD and close-in noise of linear amplifier chains is quite unrelated to the existence of any tuned filter at the output of the amplifier. No realisable filter would be narrow enough to suppress IM3 or IM5 products, and noise within +/- 1% or so from the centre frequency.

Instead, the good IMD and noise (both close-in and broadband) performance of professional-grade equipment comes out of other design considerations:

- Gain distribution
- RF negative feedback
- Use of absorptive (harmonic dump) low-pass filters at the PA output, especially
  necessary with MOSFET and LDMOS devices
- Level setting and ALC circuits with carefully controlled dynamic properties
- Noise properties of active devices at every power level
- Noise properties of attenuators and level-control stages
- Selectivity in low- and intermediate level parts of the chain

Most amateur gear is designed with little or no concerns regarding the above,
ending up with the quite poor noise and IMD performance of contemporary equipment.

As an example, if there is improper gain distribution and lack of RF selectivity in the low-level stages of a transmitter, it is possible to end up with a transmitter that has a close-in sideband noise in the order of only - 65 or 70 dBc in an SSB bandwidth, as compared to the -100 dBc which is attainable in a top-of-the line design.

To get such performance, all parts have to be carefully engineered to reduce both the PM and AM components of the sideband noise.

In co-located systems, it often becomes necessary to limit the RF bandwidth in the low-level stages by using post-selector filters at selected points in the amplifier chain, often at the +10 or +20 dBm points before the pre-driver stage.

If one wants really "clean" signals, careful attention to detail will be necessary.

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