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Author Topic: Ham Xcvrs' and Amps', Transmit Spectral Purity, IMD Products, vs. comm/maritime  (Read 152752 times)
K6AER
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Posts: 5728




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« Reply #15 on: May 28, 2014, 09:59:54 PM »

All of the 3rd order/IMD discussion is a moot point when the radios being used on the ham bands are older than 20 years. Hams  not going to swap out there trusted radio for 10 dB less spectral noise anymore than the family dog will get put down for oopsey on the  carpet.

Most radios will work just fine if the last ten % of power is not sent up the coax. Yes there are better radios for spectral purity but if you only running 100 watts into a dipole chances are you IMD is lost in the band noise floor.

Where spectral purity and adjacent channel frequency noise comes into play is when have a large beam up high with an amplifier. Now your 30-40 dB stronger and all the dirty laundry is out for all to see.
 
The real question is how much are you willing to pay for 15 dB cleaner signal? I will bet most hams would not spend 5% more on their radio. This is amateur radio and where do you draw the line between experimentation and nanny state overreach to a perceived issue.

I wonder how many hams who worry about IMD so much, actually spend any time on the air. I figure if they don't have a call we can eliminate a lot of postings.
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KA4WJA
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Posts: 1098




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« Reply #16 on: May 28, 2014, 10:09:16 PM »

Ken,
Is this not just "pre-distortion" or "negative-distortion", that has been employed for many years (20 years) now?
Or are some folks working on something new?
The coming IMD control involves feeding back an output sample, shifting phase, delaying and some filtering to cancel distortion to a low level..
While not perfect, it is a quantum leap in the IMD cleanup process.
If a new line of devices were to be developed and circuits designed around them, the IMD could become quite low.
I have been monitoring this discussion and applications by very knowledgeable people on the air and done research on the subject, finding is has been worked on as far back as the late 90s.
It's just now filtering into the present day application.
If this is the former (pre-distortion), it's been with us for quite some time, and I'm not sure what new devices are needed....and I'm not sure I'd call it a "quantum leap"....

So, I assume there is something new that I'm not aware of, coming down the pike?
Please tell us..


73,

John,  KA4WJA



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KI6LZ
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Posts: 738




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« Reply #17 on: May 28, 2014, 10:33:03 PM »

My understanding is that this pre-distortion is now starting to be implemented in DSP coding. Nothing more, nothing less.
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KA4WJA
Member

Posts: 1098




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« Reply #18 on: May 28, 2014, 10:55:39 PM »

Mike,
As I wrote earlier, I have a great deal of respect for your RF engineering knowledge...but, I think you may have missed the point (sorry, my fault for such long rambling posts)....


Perhaps you missed the part where the radios are NOT more expensive?  
The real question is how much are you willing to pay for 15 dB cleaner signal? I will bet most hams would not spend 5% more on their radio.

(and depending on what radio you're comparing them to, are LESS expensive)
But, regardless....I AM willing to pay more and there are others out here like me...





Yes, I use my 35 yr old TR-7, when at home....and some of my friends also have some older radios, but most of the stations I work are all using fairly new / "modern" radios (made within the past few years...)  
All of the 3rd order/IMD discussion is a moot point when the radios being used on the ham bands are older than 20 years. Hams  not going to swap out there trusted radio for 10 dB less spectral noise anymore than the family dog will get put down for oopsey on the  carpet.
Yes, there are a lot of old radios out there....but years ago there were a lot of old cars (w/o air bags, or even shoulder straps) out there as well....and it took a few years, and a combination of market/consumer pressure and new regs, and it's a rare automobile on the road these days that doesn't have air-bags...

Are we supposed to just "give up" and take whatever the manufacturers think we need, or can we (the ham consumers) actually ask/demand better?  
That is my MAIN point here...alternatives currently exist, and with similar or lower costs....so why not demand better and NOT settle?





"just fine"?
Well, that all depends on each and everyone's definition of "just fine", and of course on what radios you're talking about.... Smiley
Most radios will work just fine if the last ten % of power is not sent up the coax. Yes there are better radios for spectral purity but if you only running 100 watts into a dipole chances are you IMD is lost in the band noise floor.

Where spectral purity and adjacent channel frequency noise comes into play is when have a large beam up high with an amplifier. Now your 30-40 dB stronger and all the dirty laundry is out for all to see.
But, you do have a point....it is the "Big Guns" that can do the whole ham community a great service and be the forerunners here...
They have the money to spend on new radios with better transmit specs, so why don't THEY lead the way?  It will work out as a win-win for everyone!! (heck, how many "Big Guns" don't like having their egos stroked?)





Here we are in agreement....nobody here wants ham radio to become a "nanny state"!!!
This is amateur radio and where do you draw the line between experimentation and nanny state overreach to a perceived issue.
But, why can't we take pride in producing the best signal we can?   And, why can't we ask/demand better from the guys who gladly take or $$$..?





I have a call....and have been proud of it for 35 years....and I try to operate every day (although I DO have other things that take precedence)...
I wonder how many hams who worry about IMD so much, actually spend any time on the air. I figure if they don't have a call we can eliminate a lot of postings.
You may choose to ignore some postings, and that's your choice....but, the facts presented here will not change whether you ignore them, accept them, or choose to come on-board and help your fellow hams and the amateur radio service in whole...
(if you don't have the time/energy/inclination to actually contribute positively, that's fine.....I, myself, have many other commitments too, but at least try not to pour water on others attempts to make positive contributions and/or educate others....being negative / contrary, just seems a bit "un-ham-like", to me... Smiley




Nothing personal....and all in good cheer!!
Fair winds and sunny skies!



73,

John,  KA4WJA
 
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K2GWK
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Posts: 707


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« Reply #19 on: May 29, 2014, 06:02:32 AM »

John,

The reason why I think it would have be easier to pressure the FCC to change (possibly through the ARRL) the spec and force the manufacturers to respond is that I think it will be very difficult to get the average Ham to give up the gear he has and purchase something new especially in light of the aging of our ranks. You may see results but it will take a long time to develop if ever. If the FCC were to change the spec you would see the manufacturers respond overnight. The other side of the coin is that if forced by the FCC the new design or approach for low IMD would be a matter of survival. If pressured by us, the radio operator, I bet the manufacturers would take advantage of the situation and spin it as Low IMD being a new feature of the transceiver and charge more money for it.
« Last Edit: May 29, 2014, 06:10:08 AM by K2GWK » Logged

Guy
Lawn Guyland, New York

K2GWK Website
KA4WJA
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Posts: 1098




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« Reply #20 on: May 29, 2014, 06:10:59 AM »

Guy,
I understand your point, and I do agree that FCC action would force the manufacturers to make the changes.

My "problem" is that in the long-term I really don't think more gov't regulation does anyone any good....(although I'm certainly no anarchist, it's just my personal philosophy here, so I fully accept others' opinions differ)


Thanks for sharing your thoughts.
Now, have 'ya got any "pull" with the ARRL and/or FCC?  Smiley


73,

John,  KA4WJA
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ZENKI
Member

Posts: 1636




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« Reply #21 on: May 29, 2014, 06:47:55 AM »

Government regulations did not bring about better receiver improvements for hams. Hams who discussed this is issue in a sensible manner brought about change.
Lets hope the same robust debate will wake the manufacturers from their design lazyboy positions and fix transmitter spectral purity. Name and shame  works effectively.
All the naysayers in ham community are all enjoying better equipment today because of a small minority of hams who raised the lack of  receiver performance issues in the ham community.

Already we  have  transceiver manufacturers  moving towards pre-distortion  technology in transmitters. At the same time some new manufacturers are improving transmitter IMD
performance. An example is the Zeus ZS1 transceiver. Even though its only a 15 watt transmitter its IMD performance is ahead of radios costing 10 times as much. This is progress.

http://www.remeeus.eu/hamradio/pa1hr/productreview.htm

I can only  imagine how  you would feel owning one of those   8000 dollar and above radios with such poor TX IMD performance. This even before
start talking about the  other transmitter issues that are not even mentioned. Sad really that only 1 or 2 radios on this list could even be considered acceptable.

In the commercial and military  HF industry the IMD performance of transmitters are  improving for the technical requirements of digital transmission.
An example is the Codan Envoy transceiver from Codan. 12 volt operation with -40Db per 3rd  IMD figures of -40db PEP for 125 watts of output.
You can clearly see why ham radio manufacturers are really many decades behind in their design expertise.

http://www.codanradio.com/product/envoy/

Hams who continue to have  have their heads buried in the sand against being proactive about improving standards are really just being argumentative for no good reason.
The reason for improving TX IMD is long term good  on many fronts even if these hams dont  really fully understand the debate fully. 








Guy,
I understand your point, and I do agree that FCC action would force the manufacturers to make the changes.

My "problem" is that in the long-term I really don't think more gov't regulation does anyone any good....(although I'm certainly no anarchist, it's just my personal philosophy here, so I fully accept others' opinions differ)


Thanks for sharing your thoughts.
Now, have 'ya got any "pull" with the ARRL and/or FCC?  Smiley


73,

John,  KA4WJA

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K2GWK
Member

Posts: 707


WWW

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« Reply #22 on: May 29, 2014, 06:55:36 AM »

Guy,
I understand your point, and I do agree that FCC action would force the manufacturers to make the changes.

My "problem" is that in the long-term I really don't think more gov't regulation does anyone any good....(although I'm certainly no anarchist, it's just my personal philosophy here, so I fully accept others' opinions differ)


Thanks for sharing your thoughts.
Now, have 'ya got any "pull" with the ARRL and/or FCC?  Smiley


73,

John,  KA4WJA


I agree that we certainly do not need the government heaping any more regulations on us. IMHO government is much bigger than it needs to be. The fact is that the specification exists. I see no harm in changing an existing spec for the better. Heck, it would be nice for once having the government stick their nose in something and it do some good.  Grin
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Guy
Lawn Guyland, New York

K2GWK Website
K2GWK
Member

Posts: 707


WWW

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« Reply #23 on: May 29, 2014, 07:03:44 AM »

Government regulations did not bring about better receiver improvements for hams. Hams who discussed this is issue in a sensible manner brought about change.
Lets hope the same robust debate will wake the manufacturers from their design lazyboy positions and fix transmitter spectral purity. Name and shame  works effectively.
All the naysayers in ham community are all enjoying better equipment today because of a small minority of hams who raised the lack of  receiver performance issues in the ham community.

Already we  have  transceiver manufacturers  moving towards pre-distortion  technology in transmitters. At the same time some new manufacturers are improving transmitter IMD
performance. An example is the Zeus ZS1 transceiver. Even though its only a 15 watt transmitter its IMD performance is ahead of radios costing 10 times as much. This is progress.

http://www.remeeus.eu/hamradio/pa1hr/productreview.htm

I can only  imagine how  you would feel owning one of those   8000 dollar and above radios with such poor TX IMD performance. This even before
start talking about the  other transmitter issues that are not even mentioned. Sad really that only 1 or 2 radios on this list could even be considered acceptable.

In the commercial and military  HF industry the IMD performance of transmitters are  improving for the technical requirements of digital transmission.
An example is the Codan Envoy transceiver from Codan. 12 volt operation with -40Db per 3rd  IMD figures of -40db PEP for 125 watts of output.
You can clearly see why ham radio manufacturers are really many decades behind in their design expertise.

http://www.codanradio.com/product/envoy/

Hams who continue to have  have their heads buried in the sand against being proactive about improving standards are really just being argumentative for no good reason.
The reason for improving TX IMD is long term good  on many fronts even if these hams dont  really fully understand the debate fully.

Zenki,

Therein lies the problem. I would bet that most Hams do not share your view and are happy with the status quo. As long a this is the case it will be very difficult to change things from this end. The truth of the matter is that as long as there is no incentive for the manufacturers to change, they won't. Getting the FCC to change the requirement will take care of that immediately. Otherwise what motivation is there for the manufacturers to change.

« Last Edit: May 29, 2014, 07:05:57 AM by K2GWK » Logged

Guy
Lawn Guyland, New York

K2GWK Website
W1BR
Member

Posts: 4189




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« Reply #24 on: May 29, 2014, 07:07:59 AM »

It looks like Palstar is making some effort to market a transmitter with decent IMD specs. The new TR-30 uses a 50-volt FET in the PA and the specs are pretty decent.  Not exactly a power house, but it is a start.


The TR30 has one of the industry's best transmit IMD performance, provided by a 50 Volt RF LDMOS FET transmitter final. 20 watt PEP output with IM3 of -48 dB PEP or -42 dBc is 10 to 20 dB better than today's popular transceivers. The TR30 is an ideal exicter for high-performance Linear RF Power Amplifiers that can provide 100 Watts PEP.
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AF6WL
Member

Posts: 224




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« Reply #25 on: May 29, 2014, 08:22:37 AM »

It looks like Palstar is making some effort to market a transmitter with decent IMD specs. The new TR-30 uses a 50-volt FET in the PA and the specs are pretty decent.  Not exactly a power house, but it is a start.


The TR30 has one of the industry's best transmit IMD performance, provided by a 50 Volt RF LDMOS FET transmitter final. 20 watt PEP output with IM3 of -48 dB PEP or -42 dBc is 10 to 20 dB better than today's popular transceivers. The TR30 is an ideal exicter for high-performance Linear RF Power Amplifiers that can provide 100 Watts PEP.


But wouldn't  backing off a -30 dBc @ 100W PA by 6dB to 25W also yield -42 dBc IMD performance  ?
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KH6AQ
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Posts: 7892




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« Reply #26 on: May 29, 2014, 08:29:40 AM »

Getting the FCC to add a marine-transceiver like IMD requirement to amateur gear would work. I think that gear already in production would be grandfathered in. Clean transmitter IMD would run up against the IMD of many amplifiers. They too would need to be included in the new rules. There would not be an immediate improvement and significant on-the-air results could take a decade or more.

Who here has gone out of their way and paid more for a transceiver having marine grade IMD performance?

How much are we willing to pay for good IMD performance? It would raise the price of transceivers and amplifiers. Would $100 more for a transceiver or $1000 for an amplifier bother us?

The ICOM-M802 appears to achieve good IMD performance by using big and more expensive transistors. It's brute force and doing it at 11.5 volts with no 50 volt rail and no predistortion. Using the 1:4 manufacturing mark up rule a $25 increase in the PA cost raises the selling price by $100.
« Last Edit: May 29, 2014, 08:33:10 AM by WX7G » Logged
W1BR
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Posts: 4189




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« Reply #27 on: May 29, 2014, 08:35:08 AM »

It may or may not... many amps have sweet spots where the IMD performance is best.  Third order IMD imay look good, while the odd order distortion products for the 5th, 7th, etc. that may go on forever.  That is the biggest problem with the RMI amps. You can reduce the drive and get decent (comparable to many rigs being sold) specs for the third order IMD products, but the other odd order products continue and wreck havoc for 10's of kHz. W8JI shows the results of IMD tests he ran on a RMI 300 watt PEP amp on his webpages. Most rigs and amps are analyzed using static two tone tests, while three tone tests can yield much more informative dynamic IMD analysis.

FCC regulations sound good on the surface, but they don't address hams who use ALC for aggressive speech processing, excessive mike levels, or simply over driving amps for some extra "PEP" on a wattmeter.  You would have to educate hams on proper transmitter operation; and the current licensing system is lacking in that regard.

Pete
« Last Edit: May 29, 2014, 08:38:57 AM by K1ZJH » Logged
KH6AQ
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« Reply #28 on: May 29, 2014, 10:06:27 AM »

Good point on operator error. Operator error can be overcome by designing transceivers to always be clean.

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DL8OV
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« Reply #29 on: May 29, 2014, 10:19:20 AM »

I have a suggestion (and I hope that someone from Icom is reading this thread). As the Icom 7800 is modular why not bring out a new version IC-7800M where the electronics and firmware are to marine specification, charge a little extra and then see if the rig is taken up?

Also there is one thing that maybe nobody has noticed, marine transceivers do not have a microphone gain control. I'm sure that this explains some of the better IMD figures.

Peter DL8OV
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