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Author Topic: Better IMD please  (Read 121762 times)
VE7RF
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Posts: 212




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« Reply #150 on: December 13, 2011, 08:15:45 AM »

## actually, they would be ideally suited for  ZENKI !  He could take it..and reduce the power to say 1/2..and get even better TX IMD.  His signal would then be so clean..and narrow, that the brain dead contesters would then snuggle up on both sides of him..so you still can't win.

That's why you need a "splatter" button that cuts you back to class C.

You know these people who run really lossy 75m antennas and gush about how "quiet" they are... these people are in severe need of a lesson on how to use the attenuator button with a high efficiency dipole.  You don't want to ALWAYS have to have your attenuator switched in, especially on TRANSMIT.

Same for excessive IMD for contesting ... you don't want it on ALL the time, just some of the time Grin

## per W8JI's excellent site, here is how the 11M ops do the biasing on GG triodes.  Instead of the usual zener/string of diodes for bias, instead they use a big WW resistor !  Now with normal idle current, the amp looks like it's in AB mode, pulling say 180ma  on a SB-220 [ just like the stock heath 5 V zener].  IE: use a 27 ohm WW @ 25 watts CCS.  It will diss .87 watt on idle.

## Now when u hammer it up to 800 ma, the bias will INCREASE to .8 x 27 ohms = 21.6 volts
[diss is now 17.28 watts.]. Now this is wonderful, and the 11m ops love it..esp when using the amp as a linear on AM.  You get lotsa "swing" on the wattmeter.   Of course with 21.6 volts of bias on peaks..and  only 5 volts at idle, the bias regulation is horrid, but who cares. Now to further enhance the effect, you then stick a big electrolytic cap  across the 27 ohm resistor.  A 47,000 uf should do the trick nicely.  Now what that does is sustain the bias V higher, so it won't sag down to 5 v between syallables etc.

##  Imd is probably -14db pep, but who cares, eff goes way up, and u get lotsa talk power.  Just wire a simple SPST toggle across the 27 ohm resistor, and there u have it...done.  The next time  you are having [or trying to have] a nice ragchew on 75m..during the NOV SS contest /wpx/arrl/CQWW/ etc....and with fools to the left and jokers to the right...simply hit the spst toggle, and you can rub em all out in one fell swoop...slick idea.

##  yrs ago, I used to do a lot of contesting, but back then, none of us were stupid enough to start cqing...1 khz away from an ongoing round table or net.  A group of us gets together on 75m SSB..and all running 2 kw into good ants..and every contest, we gets bozo's starting up 2 khz down, then 1.5 khz above us, then 300hz below us..then finaly smack on our freq.  One of us would ask em if they can hear the 7 of us..and the reply is.."sure, I can hear all of u, ur all 20 over".   75m late at night is dead for the most part on the west coast.  Come the weekend, then the 10,000 brain dead contesters gotta start up.  The folks that really tick me off are the ones running split..and can't RX on their TX freq !!  [ or just ignore].  The dx station will say 'listening on XXX freq.'   Of course, we just happen to be on 'XXX' freq for the last 2 hrs.  Then 16 x guys start screaming at the top of their lungs. The fix for that of course is for me to TX on the DX stations TX freq..and tell the bozo's to hit the road..or at least buy a radio with real dual RX.

## IMO, TX imd goes right out the window come contest season.  Now use the above bias technique [ wire the resistor in series with stock zener, and  wire a SPDT toggle such that the zener OR the resistor is in the circuit, by shunting either one]  in conjunction with 6 khz wide ESSB..and you have the ultimate ticket to... 'keep the freq clear' .


later... Jim VE7RF
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M0HCN
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Posts: 566




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« Reply #151 on: December 13, 2011, 08:31:20 AM »

I can beat that behavior with my experimental rig, a 'massive loop instability' button, 300Khz of chaotic oscillation!
Yes, there is a detector for it that causes automatic shutdown, but I have seen it on the bench, and the spectrum is a wide and very impressive mess.  Fortunately my dummy load does not care!

Actually the ideal thing for the too close contest crowd is to inject a 4Khz tone AM component after the sideband filters...... A lovely S9++ blank carrier right in their passband, or you could produce a synthetic IMD3 component with a knob on the front of the radio to turn it up..
Wouldn't be any worse then some of the QSD you hear.

Regards, Dan.
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VK4DD
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Posts: 79




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« Reply #152 on: December 13, 2011, 03:06:04 PM »


Actually the ideal thing for the too close contest crowd is to inject a 4Khz tone AM component after the sideband filters...... A lovely S9++ blank carrier right in their passband, or you could produce a synthetic IMD3 component with a knob on the front of the radio to turn it up..
Wouldn't be any worse then some of the QSD you hear.

Regards, Dan.

I am sorry this is disgusting.

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M0HCN
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Posts: 566




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« Reply #153 on: December 13, 2011, 03:14:25 PM »

Yea, I know I shouldn't post things like that, might give folks ideas.

Also sarcasm comes across badly on line.....
Regards, Dan.
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VK4DD
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Posts: 79




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« Reply #154 on: December 14, 2011, 01:51:51 AM »

http://www.freescale.com/files/rf_if/doc/data_sheet/MRFE6VP6300H.pdf

This is one of these fets with real potential. I predict that this will be a very common fet in ham radio equipment. It is almost impossible to destroy, provided that it is properly cooled.
This fet has got potential to make a clean HF amplifier or VHF amplifier.
If you de rate it and use a pair to make a 200W PA you would have a very nice and clean signal. No cooling problems, super clean and fet will last for ever.

I think that fewer amplifier stages, "IMD" proven devices and avoiding ferrite where possible (in particular in the driver stages) is the way to go, to solve the IM3 and IM5 issues.

This fet has 25dB gain which means 316 milliwatt in is 100 Watt out.
VK4DD and VK4AKV have build a bullet proof 2m amp using this fet.
We expect that the same can be done for HF, but we haven't tried it yet.

Cost? A single fet is around $90.

Please try to focus on positive things in ham radio.

73 Ron VK4DD


« Last Edit: December 14, 2011, 02:08:14 AM by VK4DD » Logged
M0HCN
Member

Posts: 566




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« Reply #155 on: December 14, 2011, 06:57:10 AM »

Be a  little careful there, there is a guy on the EMRFD email list playing with the larger version of that part and having terrible trouble getting good behavior on HF.

Seems that 3rd harmonic was so high that a diplexer and significantly sized dump resistor was needed (Think third harmonic -6dBc!).
This one might be different, but just be aware that a data sheet that characterizes the part at a single frequency does NOT tell the whole story.

I am still not sure that I see the advantage over a pair of MRF150 (I don't see how the claimed 70% efficiency of the new part is possible in linear service).  The new part might save $20 give or take on the transistor, but you now have a bigger heat transfer headache, give me the pair of devices any day.

As to doing away with the ferrite, good luck with that, you need something to make the transformers, and air core is going to make for something electrically very long on 6M, with a huge amount of stray coupling.
I suppose a narrow band amp could do the L match thing with air cored coils, but that is usually good for much less then an octave bandwidth.

Yea, the new LDMOS parts are very high gain, but the good parts for linear HF service are not really any cheaper then they ever were, SD2933's for example, can make a perfectly satisfactory 400W or so from a pair, given the right surrounding circuits.

I would note that in the general case the rise in IMD occurs somewhat below rated output power with semiconductor amps, so you usually want to leave 25% or so of the device datasheet rating unused (Also good for reliability and the ease of getting the heat away). Running anything at balls out 100%  of its electrical and thermal rating is not good for reliability or signal quality.

Finally I would note that doing this improves the distortion into a modest mismatch of the high Z variety, as it means there is potentially some "spare" drain voltage to support the required drain voltage swing into 60 ohms rather then 50 at the output of the matching network.

It might be fine on HF, but until somebody tries, there is no way of knowing.

Regards, Dan.

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KB8E
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Posts: 50




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« Reply #156 on: December 14, 2011, 07:25:55 AM »

The MRF150 has a thermal resistance of about 0.6 C/W. The MRFE6VP6300H has to develop twice the power in about the same amount of space, but since its thermal resistance is about 0.2 C/W, the nod, cooling wise, goes to the MRFE6VP6300H. If the 3rd harmonic is really as high as only -6 dBc or so, I would be concerned that the form that a reflective filter takes could affect the efficiency significantly. Maybe that's why a dissipative filter had to be used. It's been a long time, 25 years or so, since I used an MRF150 (yeah its that old) so I'm a little rusty on its operation, but the newer part does look interesting.
Sam
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M0HCN
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Posts: 566




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« Reply #157 on: December 14, 2011, 09:43:30 AM »

Interesting sure, but until someone pulls off a HF broadband linear amp using one, do not get too excited.
Just be a little cautious of applying data sheet VHF measurements to top band is all, sometimes weird things happen.

At some point I might get one (they are relatively cheap) and try for maybe 200W from the thing, just to see how it pans out (Which is the only way to know).

I would add one further note, the narrow band design they used to measure the device, does NOT swamp the gate capacitance, where anything wideband will need to, so the gain in a wideband application will be lower because some of the drive power will be dumped into the gate swamping resistors.

I would love to know what is going so very wrong at HF with that KW class part, but even freescale (After hinting for a while about a HF app note to come), seem to have given up.

Regards, Dan.
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VK4DD
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Posts: 79




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« Reply #158 on: December 14, 2011, 12:02:22 PM »

I find this the most interesting part for Amateur radio because it is virtually bom proof.
Its like a tube you can abuse it and it keeps going. Most fets give a blue flash and you loose a 100 or 200 bugs. I have put this one in these situations and it kept going.
Not only me but Kev VK4AKV abused it and heard the same from a Kiwi.
Look it is possible to kill it if you bias it wrong or don't cool it properly, or drive it with way too much power, but in all other cases it has been very forgiving.. very.
So a highly recommended part. I used to put protection on solid state finals but with this fet I was so confident that I just left it out.

Dan your 200W is conservative and does make cooling easy. Dont forget to mount 6mm copper heat spreader. If you leave away the copper than the base of the heat sink needs to be much thicker, more than 10mm any way.

With Less ferrite, i was referring to use less stages, and if possible no transformers in particular in the drive train I was thinking about using MMIC or similar. Some have flat gain from DC to a few 300 or 400 Mhz and beyond that.
The cable amplifier modules are interesting (like BGY68) but they probably use transformers inside them. The BGY68 for instance goes for under $20.
I haven't tried the BGY68 but they are worth having a go at that price.
I don't like that they are specified to 5Mhz but may be they will go a little lower??

The MHW591 and 592 are produced any more and were ideal for this application.

Any way if tx chain of the driver has a nice and flat frequency response that that is a bonus too which make things easier.

To Sam, I would say have a play with these 6300H, you won't regret it.
I am distributing >>>> FREE PCB <<<<< for them on 2m (for as long as stock lasts.)

73 Ron.
« Last Edit: December 14, 2011, 01:30:44 PM by VK4DD » Logged
VK4DD
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Posts: 79




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« Reply #159 on: December 14, 2011, 12:26:59 PM »

Dan,

Hopefully we don't have to use pre-distortion to reduce the 3th harmonic Grin.

No seriously, if was going to use these MRFE6VP6300H on HF than I would probably parallel the gates and inputs and use it as if it is one fet. Off course you need two for a push pull.
My idea is to add some extra capacity just behind the drain to ground.
All that because these things whistle all the way up to 400 Mhz and I want to able to beep on high frequencies.
 
No need to say that this is experimental !!
Would love to hear if some one has tried them on HF because Freescale does show 1.8 Mhz in their data sheet.

The MRFE6VP6300H is the smallest of the whole series one is in MHO the most interesting one because it is very forgiving. Unlike the its bigger brothers this one is not pulse mismatch mismatch capability but no time limit (refer to data sheet). In other words good for hams because we stuff up more frequently  Wink

73 Ron.
« Last Edit: December 14, 2011, 02:11:26 PM by VK4DD » Logged
ZENKI
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Posts: 1648




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« Reply #160 on: December 15, 2011, 12:19:14 AM »

We should not become obsessed with pursuing high  IMD performance numbers just for the sake of it.  The root cause of most splatter is products greater than the 11th order. The easiest approach is just too follow the guidelines in the ITU regulations SM329. We should aim for a 3rd order figure of -36 for 3rd order and any IMD product above 8khz away should be suppressed 80db. IMD reduction should be optimized under voice conditions and not optimized for the best 2 tone numbers. All the work and standards have been done  for us by the ITU, there is no need for hams to  reinvent  the wheel. SM329 would be an excellent starting point for a ham standard, it  even mentions  ham transmitters however these regulation have never been enforced or adopted. The ITU wanted amateur transmitters to fall under these rules however amateur societies were largely against these rules. These days it would not make much for amateur to be compliant. Even modes like ESSB is covered under the ITU regulations because IMD product suppression is a function of bandwidth % which would ensure that even ESSB dont do as much damage as they do today.

Download standard SM329 from the ITU's web page it free once you register. Its an excellent technical reference document  for understanding out of band spurious emissions and how to go about measuring them.

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VE7RF
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Posts: 212




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« Reply #161 on: December 15, 2011, 08:07:54 AM »

We should not become obsessed with pursuing high  IMD performance numbers just for the sake of it.  The root cause of most splatter is products greater than the 11th order. The easiest approach is just too follow the guidelines in the ITU regulations SM329. We should aim for a 3rd order figure of -36 for 3rd order and any IMD product above 8khz away should be suppressed 80db. IMD reduction should be optimized under voice conditions and not optimized for the best 2 tone numbers. All the work and standards have been done  for us by the ITU, there is no need for hams to  reinvent  the wheel. SM329 would be an excellent starting point for a ham standard, it  even mentions  ham transmitters however these regulation have never been enforced or adopted. The ITU wanted amateur transmitters to fall under these rules however amateur societies were largely against these rules. These days it would not make much for amateur to be compliant. Even modes like ESSB is covered under the ITU regulations because IMD product suppression is a function of bandwidth % which would ensure that even ESSB don't do as much damage as they do today.

Download standard SM329 from the ITU's web page it free once you register. Its an excellent technical reference document  for understanding out of band spurious emissions and how to go about measuring them.



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

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


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


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


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

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

Later...Jim  VE7RF
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M0HCN
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« Reply #162 on: December 15, 2011, 04:58:36 PM »

Quote
What he fails to mention is that in order to produce an IMD product, you require the 2 x tones to be equal amplitude and also equal phase
Pretty sure you are wrong there, if they are different frequencies then BY DEFINITION the phase will constantly shift, phase is after all the integral dt of frequency.
Equal level is also in the general case NOT the worst scenario for IMD, you can generally make a rig behave much worse then the result from a standard two tone test with a little work with the level control on one of the generators.  Real speech and something like the 95th percentile on the energy spectrum would be interesting to see, together with the peak spectrum, but it is very hard to standardize that test. 

The subtle part is that in the general case we are not dealing with only two tones, but with a large number closely spaced, and you can generate a huge number of even first order products when you have a complex sound like speech even in communications bandwidth, ESSB just makes the potential spacing wider, and increases the potential for higher energy levels further from the carrier.

Now I don't have strong views on ESSB, there is usually enough space on most bands for everyone to play at any reasonable bandwidth, and if things get madly busy, I would hope everyone would narrow the modulation bandwidth on their rigs to play nice (I have been known to perpetrate AM when experimenting with class E and switching drain supplies on a quiet band).

Regards, Dan.
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VE7RF
Member

Posts: 212




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« Reply #163 on: December 16, 2011, 02:09:31 AM »

Dan,

Hopefully we don't have to use pre-distortion to reduce the 3th harmonic Grin.

No seriously, if was going to use these MRFE6VP6300H on HF than I would probably parallel the gates and inputs and use it as if it is one fet. Off course you need two for a push pull.
My idea is to add some extra capacity just behind the drain to ground.
All that because these things whistle all the way up to 400 Mhz and I want to able to beep on high frequencies.
 
No need to say that this is experimental !!
Would love to hear if some one has tried them on HF because Freescale does show 1.8 Mhz in their data sheet.

The MRFE6VP6300H is the smallest of the whole series one is in MHO the most interesting one because it is very forgiving. Unlike the its bigger brothers this one is not pulse mismatch mismatch capability but no time limit (refer to data sheet). In other words good for hams because we stuff up more frequently  Wink

73 Ron.


##  what's wrong with it's bigger brother's ?   They make those in 600w..and also 1200w.  And both are good for linear service on HF.   Any of the 3 x versions, with the idle current cranked up a bit..and  the devices run at 1/3 rated power, would make for a clean, low imd amp.  If the xfmrs  were optimized for the lower po, it would be eff as well.  Aside from 2M, [I assume FM] have these devices been tried on HF ssb ? [ linear service?]

later... JIm  VE7RF
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VE7RF
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Posts: 212




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« Reply #164 on: December 16, 2011, 05:24:05 AM »

Quote
What he fails to mention is that in order to produce an IMD product, you require the 2 x tones to be equal amplitude and also equal phase
Pretty sure you are wrong there, if they are different frequencies then BY DEFINITION the phase will constantly shift, phase is after all the integral dt of frequency.
Equal level is also in the general case NOT the worst scenario for IMD, you can generally make a rig behave much worse then the result from a standard two tone test with a little work with the level control on one of the generators.  Real speech and something like the 95th percentile on the energy spectrum would be interesting to see, together with the peak spectrum, but it is very hard to standardize that test. 

The subtle part is that in the general case we are not dealing with only two tones, but with a large number closely spaced, and you can generate a huge number of even first order products when you have a complex sound like speech even in communications bandwidth, ESSB just makes the potential spacing wider, and increases the potential for higher energy levels further from the carrier.

Now I don't have strong views on ESSB, there is usually enough space on most bands for everyone to play at any reasonable bandwidth, and if things get madly busy, I would hope everyone would narrow the modulation bandwidth on their rigs to play nice (I have been known to perpetrate AM when experimenting with class E and switching drain supplies on a quiet band).

Regards, Dan.

##  You can easily have the upper and lower tones in or out of phase ..with each other.  That's why spectral phase refractors [ all pass filters] are used for audio processing chains.  with loads of audio processing gear, the bass freqs will lag behind the upper freqs.  To 'time align' them, an all pass filter is used, to put it all back in phase. they usually start around 150 hz..and as you slowly progress  higher and higher in freq, you get more and more delay.   You can't speed stuff up in the analog or digital domain, you can only slow stuff down..to a common denominator.  But that's a moot point anyway. The point was, using 2 x extremely wide spaced tones will skew the results.

##  did you see Zenki's comments  about the ITU insisting that ham gear meet ITU specs ??  Apparently, the worlds member societies, like RSGB/ARRL, etc, etc, were all dead against it. What does that tell you?  It tells me there is an obvious lack of leadership, and short sighted thinking.  They had their chance...and blew it big time.  IF it had been invoked, then  gradually the imd problem would have been  eventually resolved. Real simple. All equipment made after a certain date must meet min specs.   Heck, they could have all at least  agreed on a cut down version..and all agreed on a bare min IMD spec.  Since there is NO rules or spec..the result is the mess we have today, with $12K yaesu's, that are rated for 400w pep out...and are -22db pep.

## remember all the thousands of yaesu 1000/D's and also  1000-MP's..and also  1000-MK-V's...that all had [and still have] key clix??  A simple ITU spec or at least an agreement could have been made to nip that in the bud.  yaesu's answer, don't even acknowledge the problem even exist.  All my service manuals brag abt the superb keying waveforms on CW, and the excellent rc shaping networks they installed.  Yaesu should have had a mass recall on all of em. If a min spec had been in place on this crap, they would never have got past the factory gates.

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

Later...Jim  VE7RF
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