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Author Topic: Ham Xcvrs' and Amps', Transmit Spectral Purity, IMD Products, vs. comm/maritime  (Read 154144 times)
K6AER
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Posts: 5745




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« Reply #285 on: October 17, 2018, 03:03:10 PM »

IMD Specifications and this Holy Grail for the lowest IMD numbers are moot point when the ham uses the VFO and places his SSB signal 2 KHz from an adjacent QSO. Next the mic. gain knob, is a bigger offender of spectrum purity. Today's modern radios are a far cry from the once convent designs of 15 years ago. I see many older radios with products going out 4 KHz on the opposite side band.

If you want to make the phone bands more civilized just require channelization of phone frequencies to be every 5 KHz.

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I4LEC
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Posts: 21




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« Reply #286 on: October 18, 2018, 10:56:19 AM »

John,
I am pleased it serves to clarify some things, I am obviously involved and thus these aspects are much more familiar within my environment.
Here below in red my further comments to your questions

I am curious though, is there some reason (other than cost $$) that a wide-band flat-response directional coupler cannot be used??

Not at all, is actually strongly recommended using a flat wide band one, that will be even safer in order to prevent a possible front-end failure in case of malfunction.

Then there would be no need to set/adjust things band-by-band, either by hand or via software...
And, this would also give the end user a more seamless path to getting the rig (and the PureSignal pre-distortion) properly set-up??

No need to setup anything, at least from when the auto attenuator was implemented, which is a way back (three years or so), prior to that, a manual attenuator setting was required in order to determine the proper feed-back level.

{I have a really cheap coupler in the other room that is flat (+/- .5db or better) from 1mhz thru about 1500mhz....and I used to have a few others that were even better....and I've got a Bird "sampling slug" somewhere (a -50db sample) that is as flat as any ham would need across the HF range, etc..}

Well that Bird sampling slug of yours will be just fine along with few extra dBs pad to be on the safe side when an Amp is on the line.

Again, I love the idea....and I wish every rig made had this....and every amp had a -50db to -60db directional coupler output....and I do hope this happens soon...
But, as of today (Oct 2018) it just isn't here, yet! 

John, I think you have been heard, the latest Amps, Expert, Elecraft, Flex Radio, Acom and others, do have the -60dB tap, which, in my opinion, is just a marketing feature, as you were saying, at the present time, if used for pre-distortion purposes, can only be linked to an Apache Labs radio, some of these manufacturers may don’t even know who they are!

73, Clay
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KA4WJA
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Posts: 1098




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« Reply #287 on: October 24, 2018, 12:46:03 PM »

Mike,
I've purposely not responded to some of the comments, as that might pull us off topic, and cause some that actually wish to learn, to become turned-off and move away... Sad
But, I hope you won't mind me clarifying a few things, in polite and friendly way??
Mike, please understand this is not personal at all... Smiley


1)  Over the years you have repeatedly mentioned the mic gain control as being a (large?) part of the problem of splatter on our phone bands....and I agree with you, that this is a problem...(and I haved voiced that agreement here, many times) Smiley  
And, while I suspect that most here also agree that those running "all knobs to the right" are not actually educated enough to understand this discussion here, the rest of us are...
But, you seemed to have missed the main point of the discussion...

The main point of this discussion is, and has been, that even when operated as prescribed in the manual, many of our "modern" rigs are just crap compared with what used to be standard for the amateur radio service, and inferior to what is being produced for other HF services, today...
(also, that while "higher-voltage PA's" are nice, and can have better transmit IMD, the actual ham HF rigs being made/sold, are not showing much in the ways of "improved transmit IMD", and the fact that some 12vdc PA's are actually better is surprising to many, but the results are right here in this thread for all to read for themselves..)

So, we all get it....you wish everyone would crank down their mic gains....and so do I...
But, if you take the time to actually listen on-the-air (as I do) and listen to what rigs are being used (as I do), and listen to how they are being used, etc....and read what is written here, etc....you may find that there is some important info being imparted here, and that some here may actually be interested in learning... Smiley



2)  And, when you make mention of channelized (HF maritime, HF Fixed / Land-mobile, etc. uses 3khz channels) operation, you seem to imply that requires less stringent transmit purity?? (when in fact these services have required more stringent transmit purity, because of their historical inability to "move" away from interfering stations, although with some private users this is now done..)
But, then also state that we hams like to use tight spacing of our QSO's (which I agree we do!)....but you use 3khz as the "ham standard" (along with 2khz, in tight conditions, like contests??)
This is confusing to me...but, no worries here...
'Cuz we do agree that our ham transceivers' transmit IMD and spectral purity does need to be improved!!  And except for the above-mentioned guys who crank-up their mic gain, how we do that is, by demanding better of the manufacturers....just like we did over the past 10 - 20 years, in regard to improved receivers (both better close-in IMD and better phase-noise/RMDR)...


{As I, and others, have stated here, we are not discussing "contest operations" (where both common courtesy and common sense, seem to get ignored for the weekend)...but rather every day, normal operations....
BUT...
But, to be clear, as long as I'm not trying to dig someone out of the noise, 60db below most other stations, I have no problem if someone with a nice clean signal wants to start up 3khz away from me on the ham bands...it happens all the time!  Smiley
But, if they're using an IC-7600, etc....or maybe an FT-857 and a ALS-600...then I might not like it so much!!  
And, during contest times, stations 1.5khz to 2khz away are quite common....
So, further....while audio fidelity suffers when narrowing the passband much below 1.5khz to 1.8khz....I do have an SL-1000 (1.0khz) IF filter in my Drake TR-7 (along with a 1.8khz and 500hz, as well as the standard 2.3khz)....

And, with the TR-7's imperviousness to overload, and its > 100db of ultimate filter rejection, I can use the passband tuning, and my 1.0khz IF filter and still have a 75m QSO with my best friend (using his TS-830 w/ filters in both IF's and his VBT)....with another station 1.5khz away, just fine!  (heck, a few years back, I think that was during the Nov SS about 10 - 12 years ago, we even had stations 1khz away, and we still had good comms, 100% copy....again, not very good fidelity, but 100% copy nonetheless!!  And, since the other stations were not able to force us to move, and of course they were unable to make much of a QSO-rate, they simply move, and we can then open-up our passbands and enjoy our rag-chew...)
Sorry, for the digression....the above paragraph has nothing to do with transmit IMD....but just shows what can be done on-the-air... Smiley }


My first hand knowledge of US Embassy comms, stops in the mid 90's (I consulted on/off with some USAID folks, from the late 80's thru early 90's....and they were using ITT/MacKay 8000's and 1020's back then...nice rig for the day, but certainly not up to handling the crowded ham bands....but do have a few friends who someone were "given" some of the 1020 amps...Sweet! Smiley)
So, I will defer to your apparent first hand knowledge of 21st Century US Embassy HF comms....and the IC-7800....
(but, I seem to remember that the 7800, even with its 50-volt PA, isn't much better than the 7600?  and the 7600 is a really WIDE transmitter!!  The 7800's 5th and 7th products are about 10db better than the 7600, but the 3rd, 9th, and higher orders are about the same....and this means the 7800, no matter what "filters" Icom might have put in its receiver, has a fairly poor transmitter, especially when looking at the much lower cost "12vdc PA" kenwood TS-590SG!!)

In the US the only operation of radios not channelized is ham radio. Marine, Land Mobile, Public Service, Maritime, Aviation, Military and even CB is channelized.

When the IC-7800 came out the radio was targeted for the US embassy communications which is channelized. When offered to the ham radio market they had to improve the IF filters in the 7800 for we (hams) like to operate 3 KHz away from other stations.

IMD Specifications and this Holy Grail for the lowest IMD numbers are moot point when the ham uses the VFO and places his SSB signal 2 KHz from an adjacent QSO. Next the mic. gain knob, is a bigger offender of spectrum purity. Today's modern radios are a far cry from the once convent designs of 15 years ago. I see many older radios with products going out 4 KHz on the opposite side band.

If you want to make the phone bands more civilized just require channelization of phone frequencies to be every 5 KHz.
FYI, the only way modern ship-to-ship maritime SSB Voice comms survives today on-the-air (with many sailors using ham rigs "opened-up" to transmit out-of-band) is by them using "non-standard" maritime HF freqs (away from the standard / int'l assigned HF channels)...

Example: for decades I (and many, many others) have used 12.359mhz daily for long-range, transocean HF SSB Comms (typically at 150 watts PEP)....with 12.362mhz and 12.365mhz being used as SSB Voice Weather broadcasts (at 1000 watts PEP) from shore stations, at bottom and top of the hours....and never has anyone experienced interference...
BUT...

But, fast-forward to the past two years or so....and now we have many baby-boomers retiring and 100's of them using modified ham rigs on their boats....and they have indeed caused a great deal of interference....so, in order to keep interference away from some users of the 12mhz simplex freqs (12.353, 12.356, 12.359, etc. as well as those Voice Weather broadcasts), 12.350mhz (a non-standard maritime freq) was allocated to a few HF coast stations and also authorized for use by vessels licensed under the maritime mobile service....(and this channel will be in use daily now, mostly in late afternoons, by many boats sailing across the oceans)

Further...I (and many others) used to use 8.294mhz as a secondary long-range channel (and now-a-days, with low solar activity it should be a primary HF, transocean SSB Comms channel)...but, due to the adjacent channel interference, most users have migrated to "shared"/'"secondary" HF channels...
{the FCC and ITU, allocated these "fixed/land-mobile" HF channels on a "shared" / "secondary" basis for all licensed maritime mobile stations to use, for specific purposes....again on a "shared, secondary" / "non-interference" basis.....to be clear, these addition channels were of course not allocated because of interference caused by maritime users (whether using ham rigs or commercial maritime rigs)...it was just a "happy" happenstance that as more an more hf ham rigs began to be used on-board more boats, that these "new channels" were available...however the USCG and the IMO pushed heavily for this, as to improve the situation of adjacent-channel interference....as 8.291mhz is the 8mhz GMDSS SSB int'l safety/distress calling freq...and 8.294 and 8.297 were the only other allocated 8mhz simplex freqs....}
These HF land-mobile channels (just like the primary maritime channels) are spaced 3khz...
Starting at 4.000mhz, 4.003mhz, etc....up to 4.060mhz.....and from 8.101mhz, 8.104mhz, etc....up to 8.191mhz....
FYI, the specific reasons for these new allocations were:
Quote
for supplementing ship-to-shore channels for duplex operation;
for Intership simplex (single-frequency) and cross-band operation;
for cross-band working with coast stations;
for duplex operation with coast stations working in the band 4438-4650 kHz or with Channels 834, 835, 836 and 837;
for ship-to-shore or shore-to-ship simplex operations (8100-8195 kHz only).

Mike, of course, now-a-days with maritime HF-DSC (and lower cost sat comm) there are fewer and fewer public coast stations, and as such not much traffic on the duplex / ship-to-shore channels, but in recent years there has been an uptick in simplex ship-to-ship (and simplex shore-to-ship) Voice SSB comms....and with the increase in ham rigs being used on these maritime channels, there have been quite noticeable issues...

Again, I cannot speak about modern US embassy HF comms (my personal, first-hand experience there ended in the mid-90s')....but, I can speak of our modern 21st century HF ham comms, as well as maritime HF comms (which I use almost daily) as well as HF Fixed/Land-mobile comms...


To be continued below...

73,
John,  KA4WJA
« Last Edit: October 24, 2018, 12:54:15 PM by KA4WJA » Logged
KA4WJA
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Posts: 1098




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« Reply #288 on: October 24, 2018, 12:58:35 PM »

Continued from above....

3)  But, directly on point to what you were asking / commenting on...regarding how close do hams operate, etc....
Of course as Carl mentioned, it all depends on conditions, etc... Smiley
But, please have a look at what was posted here this summer....and you might just see the gist of what we have been discussing... Smiley
And, yes....if everyone adjusted their rigs better / turned their mic gains down a bit, we would have less splatter....but, again that is not what this whole discussion has been about....rather it is about how poor our "modern" rigs are in regards to transmit IMD even when operated properly (as most hams do)...and about what rigs (ham and maritime) are actually better than most...


...no powerpoint and no photoshop...just a couple pics from NC0B's talks (some courtesy of W6XX), etc., with some of my crude drawings to help...[Please forgive my crude drawing, and understand these drawings are not precise/absolute!]

Also, please note that I debated whether to use just the few scans using white noise, that I have, rather than try to use some two-tone scans (and draw-in the actual occupied bandwidth)??  If I use some two-tone scans and draw stuff in, some will just cry foul and some/much of all this effort will be for not....and I do not wish to run off on more tangents about transmitter testing, tone freqs, etc. etc...I just want to address Brian's legit question, asking what are the compelling reasons to improve our transmit IMD / spectral cleanliness... Smiley

So, I think I will just include the few white noise scans and use them as comparisons, and these are NOT meant to insult any specific radio, they're just what I have available....hope this is okay??
Now before anyone balks, and says that striving for 60db S/N (or S/interf) ratios is a ridiculous idea on our HF ham bands...no worries here, I'm not saying that is the goal!  Smiley   Although, it would be nice, what I'm just saying is that we can do better than what we're being sold these days, and if we can get a 10db to 20db improvement in average transmit IMD (do-able and affordable) from our HF rigs, the bands would be easier to use, and friendlier, too!  Smiley

{Although, in the world of commercial HF / maritime HF ~ 60db S/N is done all the time....we are not in that business, we're hams....and getting a 20db to 30db S/N on HF SSB, is good with most of us....but remember that there are many times where there are stations close in freq (even directly adjacent) that can be 30, 40, 50, 60db, or more, different in strength...heck, on some of my 75m operations, I've had a couple guys S-9 +30db (or more), and one or two only S-7 or less...and that's as much as 50db difference, in the same round-table!  and this is one reason that I give one or two of them some good-natured ribbing for not having a decent antenna and/or a nice amp (hi hi)....'cuz it's a pain to run the RF gain up to hear the S-5, S-6, or S-7 guys, when the others are 20 to 30+ over...Smiley  So, even if you think your transmitter isn't so bad, remember there are others on adjacent freqs that might be in QSO with signals significantly weaker, and your transmit IMD could be seriously detrimental to those guys!!}

[The final preface here is a reminder that these are not worst-case scenarios, but rather just average everyday situations....no extremely crowded conditions, nor seriously offensive transmit IMD, nor super wide variations in signal strengths...just showing average normal stuff, from average rigs...]

This first image (courtesy of W6XX, from a paper presented by Rob Sherwood), show two rigs running at 75w PEP....one is an FT-1000 MkV in Class A;  the other is a K3;

 

The FT-1000 MkV in Class A @ 75 watts PEP, shows a nice clean (and narrow) spectrum...only 6khz wide, at -60db down!!! (that's about 1.6khz to 1.8khz from the transmitter passband)

The K3 @ 75 watts PEP, in comparison, is fairly wide...about 15khz wide, at -60db down...(that's more than +/- 6khz beyond the transmit passband)


This second image shows two different rigs, operated at 100 watts....one is a modern IC-7600;  the other is a bit older / legacy IC-756ProIII;

 

The 756ProIII isn't too bad, but still pretty wide...14khz wide, at -60db down...(about +/- 5.5khz from xmit passband)

But, the IC-7600 is really wide...20khz wide, at -60db down...(that's about +/- 8.5khz from xmit passband)


In this third image, I took the original image of the FT-1000 MkV  vs.  the K3, and I drew in some other signals (red, yellow, and blue), and if the top line of the spectrum analyzer display (ref level) is at say S-9 +20db to S-9 +30db (considering approximations and normal HF fading), and the other signals, +3khz (yellow),  -3khz (red),  and -6khz (blue),  are of accordingly weaker strengths....

 

The "white" signals (at 14.200) =  S-9 +20db to S-9 +30db

The "yellow" signal (at 14.203) =  S-8 to S-9  (30db weaker than the "white" signals)

The "blue" signal (at 14.194) = S-8 to S-9 (30db weaker than the "white" signals)

The "red" signal (at 14.197) = S-7 to S-8 (40db weaker than the "white" signals)

If you look at how much of the various colored signals are "above" the "white" signal, you can see the approximate S/N, or S/I (Signal-to-Interference) of those QSO's....and you can certainly see how easy / difficult those QSO's will be...

The "yellow" QSO guys would need some IF shift and probably a narrow SSB filter to have an acceptable QSO when the K3 is transmitting....but not much of a problem, when the FT-1000 MkV is transmitting... Smiley

The "blue" QSO guys might be okay, when the K3 is transmitting...although, they'd still want to narrow their rec passband and adjust their IF shift a bit...

The "red" QSO is not going to be long-lived here....they'll likely QSY or they're done... Smiley

If you can increase power or antenna gain in the desired direction on some of the color QSO's (or, even better, if they can rotate their antennas to place their nulls onto the K3's signal), that can help...or get the "white" QSO guys to reduce their power, turn their antennas, etc...or any combination of these....this can all help...but....but, except for the "color" QSO guys turning their antennas to null out the k3's signal as best they can, there's little chance of these other things being done...

But....If you can narrow the occupied bandwidth of these transmitters, everyone's QSO's improve!!  Hmm....what a novel idea....let's reduce our occupied bandwidth / improve our transmitters' IMD, and everyone wins!!

If it was just someone's mic gain being cranked up to max, or serious amp over-drive, that would be an easy fix....but, you see these scans of transmitters are not with mic gains cranked all-the-way up...nope these are with the rigs operated as designed/proscribed....and these are the best they're gonna get!  Smiley  These are not worst-case....not even close....This is just "normal" / "everyday" operations....


If you want to see what it could be like, have a look at the 4th image...look at just the narrow "white" transmission (the FT-1000 MkV) and look at the dotted lines of the "color" transmissions...and what-do-you-know, you now have 4 different QSO's, at different signal strengths, all spaced about 3khz apart, and nobody is interfering with their neighbors...[Again, please forgive my crude drawing, and understand these drawings are not precise/absolute!]

 

Hmmm....is this compelling??  Not sure about everyone here, but it is to me... Smiley


And, for those that might think Class A operation is needed, or that we need to go back to vacuum tube PA's....I highly disagree with both of these...(see earlier posts for info on what is easily possible to accomplish in solid-state Class B PA's)....

{I know some are waiting for all HF rigs to have active pre-distortion, but as of 2018, Apache Labs is the only one doing it...and with literally 100's of thousands of hams (millions) on the HF bands using analog rigs and/or DSP rigs, and only a couple thousand using SDR's, active pre-distortion is a LONG way from being ubiquitous!! A REALLY LONG WAY!!  So, maybe we hams can vote with our wallets, and demand better transmit IMD, now....not wait 'til some manufacturer decides they'll grace us with that "privilege"??   I mean it's really up yo us, the technology is there (been there for decades) and it doesn't cost a lot....it's up to us to demand it! }

Have a look here at this 5th image....which shows an FTdx-5000 in Class A operation...(FYI, this is a10khz wide image, rather than the above 20khz wide images)

 

Note the vast difference in the occupied bandwidth between having 1/2-scale of ALC, versus No ALC at all....

1/2-scale ALC = it's almost 11khz wide at -60db down...better than any of our "modern" rigs that have Class B SS PA's, but not what most think of as that wonderful Class A advantage..(that's because of Yaesu's ALC)

No ALC = it's only 5.8khz wide at -60db down!!!  (just about 1.6mhz from xmit passband, it's 60db down!)  And, that is very nice!!


Finally #4  (yeah, there was supposed to be only 3!)

#4 -  While I was writing all the above, it dawned on me that I probably should include a few other comments regarding a "compelling reason" to improve our transmit IMD...but some of these final points are opinion, rather than the many facts above...so, wasn't sure whether to write these or not, but here goes:

--- It makes good sense.

--- It's efficient use of the airwaves.

--- It is the polite / courteous thing to do.

--- And, that it meets 4 of the 5 basic reasons/tenants for the existence of the amateur radio service.

After all, from Part 97, the 5 basic reasons / purposes of the Amateur Radio Service are:

"The rules and regulations in this part are designed to provide an amateur radio service having a fundamental purpose as expressed in the following principles:

(a) Recognition and enhancement of the value of the amateur service to the public as a voluntary noncommercial communication service, particularly with respect to providing emergency communications.

(b) Continuation and extension of the amateur's proven ability to contribute to the advancement of the radio art.

(c) Encouragement and improvement of the amateur service through rules which provide for advancing skills in both the communication and technical phases of the art.

(d) Expansion of the existing reservoir within the amateur radio service of trained operators, technicians, and electronics experts.

(e) Continuation and extension of the amateur's unique ability to enhance international goodwill."

--- So, to advance the radio art, advance the skills in both the communications and technical phases of the art, expand the reservoir of technicians and electronic experts, and enhance international goodwill....4 of the 5 purposes above...having a clean transmitter and allowing others to use the airwaves without adverse interference, and learning about how this is done, etc., actually does accomplish 4 of the 5 of these....so...

--- How about we look at what we are trying to accomplish here...inform and educate our fellow hams, regarding reduction of on-air transmit interference (and hence allow those who bought "90db to 100db dynamic range radios", to actually get close to being able to use some of that potential).


I do hope this here, and all the rest of this thread (please read it), gives some of you compelling reasons to improve our ham rigs' transmit IMD, improve our transmit spectral purity...if not, that's okay....not going to go off on a rant, nor engage in any arguments, so I will just agree to disagree, politely.  Smiley

Fair winds and 73,

John,  KA4WJA


So...
So, aside from the guy with "all knobs to the right", who would rather operate next to??

?? Some guys with modern rigs like the K3 / K3s, the IC-7600??  Or even a FTdx-5000 adjusted as the manual prescribes (w/ ALC)??

??  Or some with IC-756ProIII or FT-1000MkV (in Class A)Huh  (or maybe even a nice Icom M-802, or JST-245, or TR-7, IC-781, etc.??)

?? Or maybe some with ANAN-8000's w/ "pre-distortion" on??

??  Or, if you want to look at tube rigs....how about guys with TS-830's or Collins 32S-3's??

Again, aside  from the guy with "all knobs to the right", who would rather operate next to??
The facts are there for you to read and look at....
The choice is yours...
Who do you want to operate next to??  
And, how wide of a signal do you want to transmit??  How much on-air pollution do you choose to transmit??

Do, we hams want to learn / educate ourselves??
Do we want to use our wallets and "demand" manufacturers make better transmitters??

The choice is ours....
If some here wish to dismiss this as a "non-issue", that is their choice, and I will not argue with them...
But, to imply that we hams are "too demanding"??  That, in my opinion is just sour-grapes BS!!

We used to have much cleaner transmitters....we used to have much worse receivers, too...
We "demanded" better receivers and we got 'em...

What if the 1000's upon 1000's of hams clamoring for better receivers actually read what Rob Sherwood (and many others) have been saying for years (instead of just looking at some list)....if they understood what he (and many others, myself included) have been writing for many years now??  

That it is out TRANMITTERS that are the limiting factors of our RECEIVERS now..
What do think could happen??

Could we end up with 10's of thousands of hams actually willing to spend an extra $25 to $50 for a rig with a clean transmitter??
Goodness, what are the odds that that would happen??
That someone would actually sell a product that the consumer wanted?  Is that possible now-a-days, or are all consumers now just sheep being led to the trough and being fed whatever some designer and marketing guy tells them they "need"
 (like Apple / Steve Jobs, and the iPhone, etc....don't get me wrong, Steve Jobs was a genius!!  Just that he had a knack for convincing folks that they "needed" something that they didn't even understand....pure genius! Smiley )
 


What's that old saying?
"With hard work, much is accomplished....but, with faith, All is possible!"


I choose to have faith in my fellow hams...


73,
John,  KA4WJA
« Last Edit: October 24, 2018, 01:13:12 PM by KA4WJA » Logged
KM1H
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« Reply #289 on: October 24, 2018, 03:00:30 PM »

Back in early August a long time ham friend was well into Alzheimers and his wife wanted me to get his ham gear ready to sell or give to a son in DE who was also a ham.

He had messed up the IC-7800 he had bought new and rather spend considerable time learning this beast I sent it to Icom-Michigan.

When it came back I put it on the bench, turned on the SA and just made some basic "Hola Radio" tests. The IMD from 3 to forever was far from spectacular and went from ~ -32 3rd real dB in a steady progression down to ~ -60 dB.  Nothing scientific as I was just curious as to what a $12K radio would do.  My slightly modified TS-940 run at 80W and stock TS-950SD at 100W both started about 10 dB better and had a slightly slower curve to -60 which was a bit further out. Those power levels were the best sweet spots.

The 7800 had much lower TX noise with no drive than the 940 while the 950SD was only slightly worse. Both KWs are mid to late 80's designs with the 950 their flagship model.
I didnt bother lugging over a TS-830 as I knew Id be highly pissed off...been there done that with several brands of rice boxes plus TT crap.

My 1959 CE-100V phasing rig with USA Tung Sol 6550's is also in the superb class.

Carl
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KA4WJA
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« Reply #290 on: December 03, 2018, 10:42:20 AM »

Just a brief update / anecdote...and a reminder (to me as well) that we cannot "hear" splatter / poor transmit IMD "on-freq"...
Of course if it's really bad there are usually corresponding distortions in the transmit audio, this is not always the case, and most importantly the lack of audible distortion "on-freq" cannot be used as an indicator of a "clean" transmit signal... Smiley

This past month, operating on the maritime HF bands I heard a friend (a seasoned ham and long-time maritime op as well) with a weird audio problem, he was operating a private maritime coast station and as such was of course required to use only FCC Part 80 type certified transmitter, so I was concerned that he had a problem that he was not aware of....(he had a somewhat harsh sounding audio and a rather abrupt sound on the end of some words and at end of transmissions, not actually distorted but sounded overdriven?)

My first thought was maybe he's got some RFI or RF feedback into his rig?  Or maybe he added something? (a new mic, or an external amp that is causing problems?)

Being on 12mhz, late afternoon, about 1000 mile path, his signal was strong (S-8 to S-9+), and I have low noise level so S/N was excellent!  But he had this weird audio issue....so, as he was in comms with another station I tuned up and down to check his spectral purity, transmit IMD, splatter, etc....and as I tuned up and down, I found nothing!  No splatter, no spurts nor sputters....(3khz away was clean and silent!)
And, as I tuned up/down further, I still found no issues!  
Everyone else's signals on this Net were also good as well, with no issues heard anywhere off-freq from 3khz out to +/- 15khz...(but, did hear two other coast stations from Australia, 9000 - 11,000 miles away, with clean signals too!)

So, I assumed he had some audio issue...
And, brought this to his attention (on-the-air and followed-up in email)....he found and fixed the problem!
 
Turns out he was running an Icom M-802 maritime rig remotely, via an IP connection....and it was his computer mic / audio that was a bit harsh and overdriven....not sure if he found the input to his computer or the output to the rig to be where the overdrive was causing the most of the problem, but he found both to be issues....and corrected them.

A couple weeks later, I was on-the-air with him and all was good!  Smiley

I just wanted to write this so everyone can see that even those that should know better occasionally have issues that they caused themselves and it takes someone on the air to notice and help 'em out....and also wanted to remind myself that just 'cuz I hear a crappy signal, that doesn't mean they're splattering, nor vice-versa that just 'cuz I hear nice clear audio, that dosen't mean he isn't splattering!!   Smiley


Fair winds and 73,

John,  KA4WJA

  
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« Reply #291 on: December 03, 2018, 08:10:53 PM »

A question for John,  KA4WJA (or anyone else, I guess)..

How do the modifications made to transmitters for ESSB (notably by Voodoo Labs) relate to signal bandwidth and purity ?

Glenn AE0Q
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« Reply #292 on: December 04, 2018, 07:45:52 AM »

Glenn,
First off, I have no knowledge of "Voodoo Labs"...

But, secondly, as for ESSB (Enhanced SSB) where increases in low-freq audio response, and wider audio and RF bandwidths are designed/encouraged, this is (in general) a very bad idea for both transmitter bandwidth and spectral purity...
A question for John,  KA4WJA (or anyone else, I guess)..

How do the modifications made to transmitters for ESSB (notably by Voodoo Labs) relate to signal bandwidth and purity ?

Glenn AE0Q

Glenn, in general:

a)  the enhancement of (or even the flattening of) the standard audio passband of an SSB transmitter, results in higher levels of lower and higher freq audio, there by increasing the levels of IMD products...

b)  the increase in bandwidth, increases the spacing / width of the various audio tones of speech, thereby spreading the resulting IMD products out farther/wider....

c)  the increase of the low freq response, has an even further detrimental effect....in that opposite sideband emissions are worsened (as can be carrier suppression and carrier noise)

d)  of course, just the fact that you're making the signal wider in the first place means that it is wider!!  (and, of course those ESSB guys always use only this one point to make their argument....usually saying that they're narrower than the AM guys...but if you point out the 3 main issues above, they are left looking fairly ignorant...)

e)  and, while this point is more radio-specific...fact is that these wider, and higher level higher/lower audio tones, can drive the succeeding stages of the rig into further non-linearity...AND also can further tax the rigs PA and power supply, even further exasperating the situation....




Opinion alert:
The "enhancements" they are doing, are, in my opinion, certainly 180 degrees away from "good engineering" and "good amateur practice"...and if you add in the fact that some of these ESSB guys are  using rigs that don't have decent transmit IMD to start with, it starts to look pretty bad in regards to intelligence / knowledge of these operators... Sad
But, as I write, this is just my opinion...


Hope this helps answer your questions??

73,
John,  KA4WJA



BTW, I still think the Alpha 77x series were the best amateur HF amps built (I know some will say Henry Radio's were better, but unless you get to the big 3k, 4k, 5k, 8k, console amps, nothing compared to a Alpha 77 as a desktop amp)...I love my 77Sx, it's > 35 yrs old, with original Eimac tubes....very clean in the IMD area, stable as a rock, high-gain, easy to tune, runs all day long (Brick-on-the-Key, etc.)
And I can't figure out why anyone making amps these days wouldn't consider making such a model?
No need for auto-tune, nor "protection circuits", etc.. Smiley

« Last Edit: December 04, 2018, 07:52:16 AM by KA4WJA » Logged
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« Reply #293 on: April 17, 2019, 10:43:35 AM »

Yeah, it's been a few months, there is not much new to add...and I'm sure some will not be too happy about resurrecting this thread (but it is almost Easter).

But, with all the recent talk of amps for FT-8, amps for some particular rig, etc...and those looking for reasonably-priced amp, etc...
I thought this might be useful for some to read...especially as I see some folks mixing up "harmonics" and "IMD" these days...

If you can't wade thru the whole thread (even I can no longer do that!), have a look at page 8 and page 18...(see links)

https://www.eham.net/ehamforum/smf/index.php/topic,97093.105.html

https://www.eham.net/ehamforum/smf/index.php/topic,97093.255.html


73,
John,  KA4WJA
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