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Author Topic: Ham Xcvrs' and Amps', Transmit Spectral Purity, IMD Products, vs. comm/maritime  (Read 154157 times)
KA4WJA
Member

Posts: 1098




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« Reply #105 on: February 10, 2018, 05:56:02 PM »

Hello to all,

I suppose that since most never hear themselves on-the-air, and darn few ever hear what their own transmitter does on freqs +/- a few khz (or worse +/- 10 to 20khz), the actual transmit IMD and spectral purity of our signals tend to get over-looked...and that is a shame!

But, the simple fact is that the limiting factors in most of our HF receivers these days are:

a)  The transmit products (IMD for SSB and digital modes and wide-band noise/transmitter phase-noise, primarily effecting CW) of all the other stations on-the-air....

b)  Local noise levels / RFI (caused by all the misc RF radiating products around us these days)

The limiting factors are NOT how good the 3rd-order IMD spec is on your receiver...although in some very rare instances (probably < 0.1% of hams), this can be a factor, but even then not the only one...

I hope this info here helps some of my fellow hams understand what our modern HF rigs are doing to pollute the airwaves, even if they're operated with "good amateur practice", in accordance with the factory operations manual, etc...(now, if you crank-up the mic gain on most rigs, things will get worse....and many times, they'll get really bad....but, if you start with a bad rig, things get really bad very quickly...and if you start with a good rig, things might be "okay")


Almost 4 years since I started this thread, and after three years of inactivity, I'm sure there will be one or two hams here that will not appreciate bringing this thread back to life....but, there are a few reasons that I'm doing this.


1)  The basic reasons are:

a)  Tornado spawned by Hurricane Irma took down two of my 3 large trees (and a few smaller ones) and all my wire antennas supported there, as well as destroyed my rotor and damaged antennas on my tower (but I do have a new tower on the ground)...so I'm considering a station rebuild and was thinking about buying a new rig as well....

Updating my research....and then during some recent discussions with friends about transmit IMD, I found them repeating the oft-heard mantra of "high-voltage SSPA's have clean transmit signals", but here (like many things in life) this myth just persists.  Sad


b)  New radios on the market, many of them costing 1000's of $$$$, and only the Apache Labs (ANAN) software pre-distortion equipped SDR transceivers have significantly improved transmit IMD.  (sad, but true!)


c)  A clarification of sorts showing that 2-tone testing is actually very representative...and that white noise testing can make explaining results easier to laypersons, as the effects are easier to show on the analyzer screen, using white noise....(although, dynamic testing can show deficiencies of power supplies, etc. that static two-tone testing / white noise testing do not show, 2-tone testing DOES show what is happening!  and 3-tone tests from VHF/UHF TV-broadcast amplifiers that I've looked at years ago, also correlated well to 2-tone testing...)

From one of Rob Sherwood's papers, here is a 2-tone test overlaid with a white noise test (of his Icom IC-781)...
Have a look:



{BTW, during my discussions with friends, one asked why I didn't just post all the IMD specs of all the rigs???  Well, that's a LOT of data to sort thru, and I don't have the time for that...but then thought, I could do so (like I did for HF Amps) for at least a dozen or so rigs....Which ones??  I took suggestions, and also had some in mind that I might want to buy.}

For IMD comparisons of HF Amps, have a look here:
https://www.eham.net/ehamforum/smf/index.php/topic,100600.0.html


2)  Those that just want the brief nitty-gritty...here 'ya go:

a)  Even now in 2018, there is still no direct correlation that "12 volt PA's splatter, and hi-voltage PA's are clean"....yes, some hi-voltage PA rigs produce better IMD figures than some 12 volt PA rigs, but it is not a direct correlation...


b)  With the exception of the "pre-distortion" enabled Apache Labs ANAN rigs, the Icom M-802 HF Marine/Ham Transceiver still produces better IMD figures (by a significant amount) than ALL current HF ham rigs (or any made in the past 40+ years), and the Icom is a 12vdc rig, using a simple 12vdc PA!

http://www.eham.net/reviews/detail/6205

But, some minor improvements from Kenwood with their TS-590SG (at ~ $ 1400 USD) and for those with hefty wallets their TS-990S (at ~ $7000 USD), and those who want to take out a second mortgage to buy a rig might look at the IC7851 (at ~ $14,000 USD!!!)...these might allow some like me looking for "a real radio with knobs" to at least not pollute the airwaves too much....BUT..

I still wonder why Icom (and others) just won't make a decent transmitter and PA...heck the Icom M-802 sells for ~ $1800....but it appears that most hams are really getting shafted with crappy transmitters!


c)  This discussion is about transmit IMD and spectral purity, not about receivers....but many seem to be picking rigs based on their position on a list (assuming they can afford them)...I'm still surprised by the focus on "Sherwood's List"....now Rob Sherwood is a GREAT guy!!  A GREAT ham!  And, has done wonders for my favorite brand of HF radio, R.L. Drake!!  I love the guy! Smiley Smiley

But, geeze guys...."the list" isn't the "be all / end all" of how to judge HF rigs....and if you don't believe me, just read what Rob himself writes!!  Please remember that these "85 to 90db radios" are specified for serious CW operations/pileups/contesting...and for SSB operations, even in pileups and SSB contesting, receivers with 15 to 20db worse close-spaced IMD specs are adequate, and these other factors (mentioned in the quotes below) are important!



Quotes from Rob [I added some bold type for emphasis]:
{What level of performance do we need close-in on CW for a radio to perform well most of the time? I think 85 dB will suffice most of the time. Certainly one may want a 100 dB dynamic range radio, but other factors of a transceiver’s performance are very important, too. Ten-Tec receive audio is better (cleaner) than Elecraft K3 audio, for instance.

On SSB transmitted intermodulation products from QRM 3 to 5 kHz away is usually far above the LO phase noise (RMDR) of today’s top receivers.

Thus the “holy grail” of wanting a 100 dB radio is only a CW pile-up issue.

If every other feature or specification of a radio was top notch, it would seem logical to pick a 100 dB radio over an 85 or 90 dB radio, however this is rarely the case. With good firmware, Ten-Tec and Elecraft have made their DSP radios much less susceptible to having the AGC “load up” or “over react” to impulse noise (clicks, tick and pops). No Japan, Inc. radio at the moment has figured this out.........

How a ham picks one transceiver over another is likely all over the map. For me if the ergonomics are poor, or if the receive audio is fatiguing to listen to, then that radio falls off my selection list. At the end of the day, hopefully whatever we buy we enjoy using.
I sold an expensive radio about 10 years ago that worked OK, but I just didn’t like it compared to my 15 year old radio of the same brand.
73, Rob, NC0B
(15-JUL-2014) }

{ DO NOT OVER-RATE DYNAMIC RANGE
One thing that I need to stress is [that] the amateur community has become obsessed with which radio has a close-in dynamic range a few dB higher than another.

Decades ago Tom Rauch W8JI and I were saying that a close-in dynamic range (DR3) of 80 dB would perform well most of the time. Back then with all the up-conversion radios on the market, most had a DR3 around 70, with some in the 60s.
The Orion I was the first commercial radio to go back to what we now call "down conversion" and it had a DR3 over 90 dB. The amateur community now has a good selection of radios that have a DR3 value in excess of 85 dB.

It is rare that an 85 dB radio will not be adequate in a CW pileup. [and from other papers/talks:  a ~ "70db radio" works well, in SSB service/pileups/contesting.]

All the T-T products except the Omni-VII are 90 dB or better, along with products from most of the other OEMs.
Once you have decided you want a 90 or better radio, for example, then there are lots of other important parameters to consider, such as:
• clean receive audio for low fatigue in a contest,
• a good AGC (which T-T has recently improved in respect to handling impulse noise),
• the ease of use (user interface),
• reliability,
• quality of service and long-term parts support,
• long term firmware support,
• lack of ALC overshoot, (a problem with the TS-590S and IC-7410 for example) when driving a linear.
• The list goes on.
You don't buy a car with one specification, like horse power. The 427 cubic inch Corvette from years ago had lots of horse power but didn't handle very well!
73, Rob, NC0B
(16-DEC-2013) }

{ THE BIG PICTURE:
With 10 or more radios with 85 to 105 dB DR3s at 2 kHz, it is time to look at the big picture:
 Clean receive audio,
clean transmitter IMD,
 a good AGC that doesn’t go nuts over an impulse click, tick or pop,
 a reliable radio that doesn’t beak all the time,
an ALC that doesn’t overshoot and fault your linear amplifier, or even worse blow your amp.
 And when service is needed, good and reasonably fast factory service.
 How about long term support of radios out of production, such as on-going firmware updates and parts availability. (Unfortunately there is only so much anOEM can do about supplying out-of-production chips, PA transistors, LCD screens, etc.)


At the end of the day, do you enjoy using your radio on the air?

I hate to tell you how many radios I have had the good fortune to borrow and use on the air in contests that I really would not want to have to use on a daily basis. I sold one very expensive radio that just wasn’t a good fit for me. I took the money and put up two more towers and Yagi antennas.
Hopefully when you turn off your rig after a contest, a DX contact or just a rag chew, you feel that “that was fun”. This is a hobby, and using your radio should be enjoyable.
73, Rob, NC0B
(21-DEC-2013) }



3)  Okay... Now, let's look at some modern rigs....and some of my favorites...

These are 3rd, 5th, 7th and 9th order transmit IMD figures, in db below PEP, with the rigs operated at the spec'd max output (typically 100 watts) unless otherwise noted.

{FYI, unless otherwise specifically notated, all of these Transmit 2-tone IMD test figures are from published ARRL Product Review Tests...in some circumstances they found an "outlier" (worst band) and also listed "typical" as well as this "worst case", and in those cases, this data is also included...(also note that some rigs may only have old spectral scans and/or data listed for 3rd and 5th order IMD, but every effort is made to provide as much real data as I can.) }


[Please note the asterisks, etc....as these are ones I have personally owned (***), have used extensively(**), used briefly and liked(*).....and/or interested in(+)....also please note I use italics to highlight comment/opinion, everything else is factual data.]


+  Apache Labs  ANAN-8000D [no ARRL test yet, so these figures are from Adam Farson, VA7OJ/AB4OJ, from Sept 2017]  (50vdc LDMOS PA)

33 / 40 / 54 / 60  (with NO pre-distortion) at 200 watts

67 / 70 / 70 / 70  (with pre-distortion) at 200 watts

Sorry, I cannot copy the analyzer spectrum scan of the ANAN-8000D, as this is proprietary data of Adam's....but you can have a look for yourself on page #33  of this page
http://www.ab4oj.com/sdr/apache/anan8000dle_notes.pdf




+  Apache Labs ANAN-100D  (12vdc PA)

29 / 35 / 39 / 44 (worst case,  NO pre-distortion)

38 / 38 / 44 / 52 (typical, NO pre-distortion)

49 / 56 / 59 / 60  (worst case, with pre-distortion)

52 / 54 / 60+ / 60+  (typical, with pre-distortion)



*** Icom M-802  (12vdc PA) {nice HF marine and ham rig...few "user" adjustments, but a real nice rig w/ GREAT transmit IMD!}

47 / 50 / 58 / 60  (at 150 watts)  {3 to 6db better at 100 watts}

Have a look:





*** Drake TR-7  (12vdc PA)  {although not the cleanest IMD, one of my favorite rigs of all time, sweet SSB audio xmt and rx, and no modern ALC issues....one of the best SSB receivers (and darn good CW as well) in a ham rig, ever!}

38 / 44 / 51 / 58 (at 100 watts)

33 / 38 / 45 / 50 (at factory spec'd 150 watts)


** Kenwood TS-830s  (vacuum tube PA, two 6146's) {sweet rig all-around, my 2nd favorite}

32 / 52 / 70 / 70+


Collins 32S-3  (vacuum tube PA, two 6146's)

42 / 53 / 65 / 76

Have a look:




** Icom IC-781  (28vdc PA) 150-watt out {not the cleanest IMD, but a great SSB rig, both xmt and rx}

37 / 39 / 47 / 50 (old ARRL test) at 150 watts out

35 / 43 / 49 / 54 (from Rob Sherwood's paper)

Have a look:




* Yaesu FT-102  (vacuum tube PA / three 6146b's)

40 / 40 / 50 / 60  (at 150 watts out)


** Icom IC-765  (12vdc PA)  {a great rig in it's day, and darn good even by 2018's standards...used the 765 and 761 for many hours each day for months on end, 6 - 7 days/wk, at MARS station in 1990/91...}

40 / 45 / 48 / 50


** Icom IC-761  (12vdc PA)  {a great rig in it's day, and darn good even by 2018's standards...used the 765 and 761 for many hours each day for months on end, 6 - 7 days/wk, at MARS station in 1990/91..}

31 / 45 / 48 / 50


* Icom IC-756ProII  (12vdc PA)

30 / 40 / 48 / 50


+  Kenwood TS-590SG  (12vdc PA)

31 / 38 / 48 / 55 (worst case)

42 / 38 / 48 / 58 (typical)


+  Kenwood TS-990  (50vdc PA)

31 / 46 / 52 / 57  (worst case)

39 / 46 / 54 / 56  (typical)

The rigs above are ones that I've used / been interested in...
Note the asterisks above, as these are ones I have personally owned (***), have used extensively(**), used briefly and liked(*).....and/or interested in(+)


The rest below were all suggested by some friends...and/or prominently discussed by many hams.


Elecraft K3  (12vdc PA)

33 / 40 / 48 / 50

Have a look:



Elecraft K3s  (12vdc PA)

30 / 38 / 41 / 48  (typical)

35 / 36 / 48 / 62 (specially tuned transmitter and PA, by Elecraft engineering dept, after the above disappointing results were reported, prior to publication, see Nov 2016, QST, page 50, for details)



Icom IC-7300  (12vdc PA)

30 / 37 / 44 / 58


Icom IC-7851  (50vdc PA)

29 / 40 / 48 / 70  (worst case)

36 / 52 / 49 / 61  (typical)


Icom IC-7800  (50vdc PA)

32 / 49 / 52 / 52


Icom IC-7600  (12vdc PA)

31 / 35 / 41 / 48


Hilberling PT-8000A  (50vdc PA)

29 / 41 / 50 / 52  (worse case)

35 / 48 / 54 / 59  (typical)


Icom IC-706  (12vdc PA)

33 / 31 / 38 / 44


Icom IC-706mkIIG  (12vdc PA)

30 / 33 / 37 / 43


Yaesu FT-857  (12vdc PA)  {from Aug '03 QST}

25 / 40 / 50 / 52

Yaesu FT-857D  (12vdc PA)  {from Nov '04 QST}

21 / 32  (3rd and 5th order IMD was all that was reported)


Yaesu FT-897  (12vdc PA)

23 / 37 / 47 / 50


Icom IC-735  (12vdc PA)

33 / 39 / 43 / 47


Yaesu FTdx-5000  (50-vdc PA)

30 / 48 / 46 / 47  (class B)

43 / 64 / 68 / 72  (class A)  [but, you must NOT have any ALC, just like the older FT-1000MP MkV, otherwise you're almost defeating the advantage of Class A operation]

Have a look at how the ALC screws things up, zero ALC vs. half-scale ALC:



Yaesu FT-dx-3000  (12vdc PA)

27 / 40 / 42 / 52  (worse case)

31 / 40 / 45 / 52  (typical)


Yaesu FT-991  (12vdc PA)

22 / 32 / 39 / 45  (worse case)

26 / 37 / 41 / 46  (typical)


Yaesu FTdx-1200  (12vdc PA)

32 / 35 / 42 / 50  (worse case)

37 / 38 / 44 / 50  (typical)


Kenwood TS-590S  (12vdc PA)  (un-modified units suffer from serious ALC-overshoot and other ALC issues)

29 / 32 / 42 / 52


Flex-5000  (12vdc PA)

34 / 40 / 48 / 54


Flex-6500  (12vdc PA)

32 / 43 / 48 / 51  (worse case)

39 / 42 / 49 / 55  (typical)


Flex-6700  (12vdc PA)

32 / 40 / 44 / 55


Ten Tec Orion  (12vdc PA)

32 / 42 / 52 / 58


Ten Tec Orion II  (12vdc PA)

28 / 42 / 44 / 52


Ten Tec Omin VI+  (12vdc PA)

26 / 43 / 45 / 54


And, a few 10-watt QRP rigs:

Elecraft K2  (12vdc PA) 10-watt QRP

29 / 40 / 50 / 62


Elecraft  KX3  (12vdc PA) 10-watt QRP

30 / 40 / 51 / 55


Ten Tec Argonaut (12vdc PA)  10-watt QRP

30 / 36 / 47 / 51  (worse case)

37 / 42 / 58 / 59  (typical)


Flex-1500  (12vdc PA)  10-watt QRP

22 / 38 / 48 / 48


I hope this helps some understand what our modern HF rigs are doing to pollute the airwaves, even if they're operated with "good amateur practice", in accordance with the factory operations manual, etc...(now, if you crank-up the mic gain on most rigs, things will get worse....and many times, they'll get really bad....but, if you start with a bad rig, it's bad no matter what and things get really bad very quickly...and if you start with a good rig, things are better from the start and might be "okay")


The 40-odd radios above represent most of the popular HF rigs on the ham bands today and sold in the past 30 - 40 years, as well as a few that are very new (and some so obscenely expensive that few hams will ever operate one)....oh, and 25 of the above 40 rigs, also find themselves in the top 30 of the rigs listed by "narrow-spaced (2khz) 3rd-order rec IMD" on Rob Sherwood's list, maybe now some will see the red herring that buying a rig from a "list" can be? Smiley


73,

John,  KA4WJA

« Last Edit: February 10, 2018, 06:16:41 PM by KA4WJA » Logged
KA4WJA
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Posts: 1098




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« Reply #106 on: February 10, 2018, 07:09:49 PM »

I wanted to edit/clarify something above, but unable to do so after 30 minutes???  So, here's a very brief post. ")

In case you want to look specifically at this "12vdc PA myth", please have a look:


1)  The TS-590SG and TS-990S are the same brand, made in the same factory, of similar vintage, etc....and if you compare their respected transmit IMD, the "50vdc PA" is not the panacea the myth states. Smiley

Kenwood TS-590SG  (12vdc PA)  31 / 38 / 48 / 55 (worst case)
                                                       42 / 38 / 48 / 58 (typical)

Kenwood TS-990  (50vdc PA)      31 / 46 / 52 / 57  (worst case)
                                                     39 / 46 / 54 / 56  (typical)

[Remember the > $7000 cost of 990S is FIVE times the price of the 590SG of ~ $1400]



2)  And, what about Icom?

Well, the IC-7300, IC-7800, and IC-7851, are the same brand, made in the same factory, of similar vintage, etc....and if you compare their respected transmit IMD, here again the "50vdc PA" is not the panacea the myth states. Smiley

Icom IC-7300  (12vdc PA)   30 / 37 / 44 / 58

Icom IC-7851  (50vdc PA)   29 / 40 / 48 / 70  (worst case)
                                            36 / 52 / 49 / 61  (typical)

Icom IC-7800  (50vdc PA)   32 / 49 / 52 / 52

Of course there is also the Icom M-802.

Icom M-802  (12vdc PA)    47 / 50 / 58 / 60  (at 150 watts)  {3 to 6db better at 100 watts}

[The price of the 7300 (~ $1300) is ONE TENTH the cost of the 7851 (~ $12,500)...with the M-802 at ~ $1850...]



3)  Unfortunately, Yaesu hasn't had many rigs with even "acceptable" transmit IMD, unless run them in Class A (and without any ALC), and of course they aren't cheap radios...



73,

John,  KA4WJA

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KB2TIS
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« Reply #107 on: February 11, 2018, 09:21:42 AM »

> Icom M-802  (12vdc PA)    47 / 50 / 58 / 60  (at 150 watts)  {3 to 6db better at 100 watts}

Has anyone actually measured these kind of values in real life, not just what is claimed in a filing somewhere?

https://www.eham.net/ehamforum/smf/index.php/topic,100634.msg815777.html#msg815777

Seems to show that those numbers are a dream even at 100W.
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KM1H
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« Reply #108 on: February 11, 2018, 09:44:39 AM »

Well, since you just had to resurrect this antique thread while also starting a new one to add to the confusion here are a few of my comments.

1. Limit ALL ham rigs to no more than 5-6dB of compression/limiting, no more than rated output (which includes internal power controls), and restrict the maximum amount of the audio gain by software sampling the RF output level.
Minimal added engineering required and even opened up still acceptable specs/performance on marine and other commercial channels.

2. White noise IMD testing goes back over 50 years from my own personal experience with military products and their acceptance testing including HF amps in the 1-10KW range....using tetrodes.

Quote
Kenwood TS-590SG  (12vdc PA)  31 / 38 / 48 / 55 (worst case)

Please specify the testing method; those look like ARRL cherry picked Watts to me and not what any respectable marine or military multi channel amp would accept.
                                                     

Carl
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KA4WJA
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« Reply #109 on: February 11, 2018, 05:39:43 PM »

Carl,
Sorry about the misspelling.  Smiley


1)  As for what the testing method is....and "cherry picked watts"??
First allow me to include all the TS-590SG data, from yesterday:
Kenwood TS-590SG  (12vdc PA)  31 / 38 / 48 / 55 (worst case)
                                                       42 / 38 / 48 / 58 (typical)
Quote
Kenwood TS-590SG  (12vdc PA)  31 / 38 / 48 / 55 (worst case)

Please specify the testing method; those look like ARRL cherry picked Watts to me and not what any respectable marine or military multi channel amp would accept.

2)  Now, as to what the testing method is...
As I wrote above, these are the published ARRL Product Test results, as printed in QST magazine...(in the case of the TS-590SG, that you partially quoted, you'll find them on page 49, of July 2015 issue)

Here is what I wrote yesterday:
These are 3rd, 5th, 7th and 9th order transmit IMD figures, in db below PEP, with the rigs operated at the spec'd max output (typically 100 watts) unless otherwise noted.

{FYI, unless otherwise specifically notated, all of these Transmit 2-tone IMD test figures are from published ARRL Product Review Tests...in some circumstances they found an "outlier" (worst band) and also listed "typical" as well as this "worst case", and in those cases, this data is also included...(also note that some rigs may only have old spectral scans and/or data listed for 3rd and 5th order IMD, but every effort is made to provide as much real data as I can.) }

For the detailed test procedure, I thought we covered this a couple years ago, but here 'ya go.

The ARRL product test product test procedures are all detailed here:

http://www.arrl.org/test-procedures-manual

If you look at pages 17 thru 19, you will see the details of the two-tone IMD test procedures.


Here they are (without the diagram):

Quote
4.5 TWO-TONE TRANSMIT IMD TEST

4.5.1 The purpose of the Two-Tone Transmit Test is to measure the intermodulation-distortion (IMD) products present in the RF output of the DUT transmitter. The transmitter will be operated in the SSB mode at 3.900 MHz and14.250 MHz initially and then on all other available bands subsequently. A two-tone audio input at frequencies of 700 and 1900 Hz, within the manufacturer's amplitude specifications, will be used.


4.5.2 Test hook-up (See Fig. 4-5)
  

        NOTE: If proceeding in the test series, only the two-tone generator, shown within the dotted      line, must be added to the previous Spectral Purity Test hook-up for the IMD Test.


    4.5.2.1 With all power switches in the OFF position and the transceiver in the receive mode,             connect the following:

Connection                                             Connectors                               Cable Type
DUT RF OUT To Wattmeter IN           As Required To Type N             50-Ohm Coax
Wattmeter OUT To PWR Attn IN        Type N To Type N                      50-Ohm Coax
PWR Attn OUT To Step Attn              Type N To BNC                          50-Ohm Coax

Connection                                                  Connectors                               Cable Type
Step Attn OUT To Spectrum Analyzer IN     BNC To BNC                       50 Ohm Coax
--------------------------------------------------------------------------------------------------------------------------
Two-Tone Generator OUT To DUT MIC IN    BNC To As Required                  Coax
--------------------------------------------------------------------------------------------------------------------------
Power to DUT                                                As Required                              As Required


4.5.3 Test Procedure

                            Fig. 4-5 ── Two-Tone Transmit IMD Test Hook-up


4.5.3.1 Turn on the DUT, RF wattmeter and spectrum analyzer and set the following controls:

Instrument                                                Control                                     Position
DUT                                                          Mode                                          LSB
                                                               Band Selector                            80 Meters
                                                               Frequency                                  3.900 00 MHz

                        
                                                                     XMIT/RCV                                RECEIVE
                                                             DRIVE or RF LEVEL                        Minimum
                                                                Microphone                                    Minimum

Two-Tone Generator                                     TONE A (700 Hz)                               OFF
                                                                   TONE B (1900 Hz)                             OFF
                                                                   HI-Z/LO-Z                                      As Required
                                                                   BALANCE                                          Center
                                                                       LEVEL                                           Full CCW
                                                                   Attenuator                                         –30 dB

RF Wattmeter                                               Mode Select                                           “T”

Step Attn                                                      Attenuator                                           –40 dB


Spectrum Analyzer                           CENTER FREQ (FREQUENCY)        03.89870 MHz
(Menu in Parentheses)                                     SPAN (SPAN)                          20 kHz
                                                                REF LEV (AMPLITUDE)                 –40 dBm
                                                                   ATTEN (AMPLITUDE)                    20 dB

                                                                   RES BW (BW)                                 100 Hz
                                                                   VIDEO BW (BW)                              10 kHz
                                                                  THRESHOLD (DISPLAY)               –110 dBm
                                                                  SWP TIME (SWEEP)                          AUTO


4.5.3.2   NOTE: If proceeding from the previous tests, this paragraph may be skipped.

Receiver hiss should be heard; adjust the volume to the desired level. Allow all equipment at least 10 minutes warm-up time before proceeding to step 4.5.3.3.


4.5.3.3  Tune the DUT per the operator's manual for the test frequency of 3.900 MHz. Turn on the two-tone generator and set both tone switches to ON. With the DUT in the LSB mode, set the generator LEVEL and ATTENUATOR controls for the maximum audio input as specified by the manufacturer. If the manufacturer does not list a specification for this figure, adjust the 2-tone generator’s amplitude for maximum rated RF output of the transmitter with the transmitter’s microphone gain near maximum. Observe the transmitter power as shown by the wattmeter. Ensure that the output power of the DUT is not greater than the manufacture's maximum power output rating. Unkey the transmitter and set the step attenuators for approximately -46 dBm input to the spectrum analyzer.

              CAUTION: The input to the spectrum analyzer at no time should exceed 0 dBm.


4.5.3.4   Place the DUT in the VOX mode and verify operation with the signal generator. Note on data sheet if VOX does not function correctly. Return the DUT to the PTT mode and key the transmitter. Set the BALANCE control on the generator for equal tone amplitude as shown on the display. Adjust the CENTER FREQ, if necessary, so that the display center is half-way between the two pips. The IMD-distortion products should now be visible.


4.5.3.5   Adjust the REF LEVEL control (and step attenuators, if necessary) for the peak of the two pips to be at –6 dB. The spectrum analyzer is now calibrated. The amplitude of each IMD distortion product may now be read in dB PEP (dB below the peak envelope power) directly from the display.


4.5.3.6   Manipulate, if necessary, the two-tone generator audio LEVEL and the transmitter audio gain and drive control to obtain the lowest possible IMD products. If this is done, the spectrum analyzer REF LEVEL control (and possibly the step attenuators) may need to be reset for tone pips of –6 dB.


4.5.3.7  Set the SWP TIME (in the SWEEP menu) for 6 seconds. Take a single sweep by depressing the SGL SWEEP button. Record all info on data sheet. Print and save to an appropriate file name.


4.5.3.8  Set and tune the transmitter for USB at a frequency of 14.250 MHz. Set the CENTER FREQ for 14.25130 MHz. and return the SWP TIME back to AUTO. Repeat paragraphs 4.5.3.3 to 4.5.3.7 for this frequency.


4.5.3.9  Repeat step 4.5.3.8 for the following frequencies (if applicable to the DUT): 1.850 MHz, 7.250 MHz, 10.120 MHz, 18.120 MHz, 21.250 MHz, 24.950 MHz, 28.350 MHz, 50.200 MHz, 144.200 MHz and 432.200 MHz.  

These are not "cherry-picked" watts (or tones), as the tone levels are adjusted until the rig is outputting its rated max PEP output, and then the step attenuators are adjusted so the signal peaks are 6 dB below the reference level on the spectrum analyzer. as we all know that the analyzer IS showing the combined tones at PEP....I explained this in some detail a few years ago, but don't have the time tonight, so I'll just quote an article. Smiley
From Keith Barkley in June 2001 RF Design Magazine:
Quote
[Remember that] PEP is the maximum instantaneous power of the combination of the two signals. A two-tone signal looks  similar to an AM modulated tone. The envelope of the RF signal varies as a sinusoidal with a frequency of Δf. When the voltages of f1 and f2 are out of phase, they cancel and the envelope is at a null.  When the two voltages are in-phase, they  add, and the voltage at the instantaneous peak is twice that of either tone. Because power is equal to the square of the voltage divided by the resistance, when the voltage increases by a factor of two, the power increases by a factor of 2 squared, or four.

Therefore, the PEP is four times the per-tone power and twice the average.

....If a peak reading power meter is used [as in the ARRL testing] to measure the PEP directly, that fact should be noted with the results...

Whether someone wishes to report the results directly off the analyzer screen referenced from one-tone (and list them as "dbc") or report the results directly off the analyzer screen, referenced from the "reference level"/PEP level (and list them as "db PEP"), the difference is 6db...
Anyone can add or subtract 6db as needed to allow you to have the numbers you like to see, but the IMD level is exactly the same!  It's just written differently, and there is no "cherry picking" here.  Smiley


As for the "tones"....use of non-harmonically-related audio tones (between 300hz and 3000hz), spaced at least 1000hz apart, for IMD testing of communications equipment was established by Bell Labs many years before I was born...(and I think even decades before Carl was born..Smiley
I don't think the ARRL is doing anything other than what has been accepted engineering practice for many years (decades!!)


FYI, mini-circuits, HP, Motorola, Tek, Agilent, etc. all have similar tech notes and will provide detailed test procedures for anyone interested in their equipment...I just happen to have RF Design article handy to quote from...



3)  As for "compression", "limiting", etc..
In my opinion, this is kind of a red herring in this post, since we're talking about test procedures where no compression/processing/limiting is engaged.......hence I won't dwell on it...
But, assuming you're talking about operating and not "testing", who is gonna write these rules?? Smiley
Not to mention that properly done, speech processing/compression can actually improve things...and nowadays it's done in DSP and (as long as the level isn't too high) does NOT adversely effect transmit IMD, so I agree with you here...but, again, who's gonna write those rules?  Smiley
1. Limit ALL ham rigs to no more than 5-6dB of compression/limiting, no more than rated output (which includes internal power controls), and restrict the maximum amount of the audio gain by software sampling the RF output level.
Minimal added engineering required and even opened up still acceptable specs/performance on marine and other commercial channels.

2. White noise IMD testing goes back over 50 years from my own personal experience with military products and their acceptance testing including HF amps in the 1-10KW range....using tetrodes.

Carl
 Yeah, white noise has been used for a long time....but two-tone testing has as well!!



Hope this clarifies things for all of you. Smiley
Gotta go!

 73,
John,  KA4WJA
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KA4WJA
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« Reply #110 on: February 11, 2018, 08:28:51 PM »

Brian,
We did cover that in that other thread you linked to.
And, I don't feel like rehashing it here. Smiley

In a nutshell, I cannot fathom a company like Icom (or the lab they hired) forging FCC application docs....and I have friends that work in EMC compliance labs, let me assure you the FCC is there all the frigging time!  (our tax dollars at work)

So, while others might not have found the results that were submitted to the FCC, I don't doubt that it did meet those numbers....
(parts changes, minor circuit changes, etc. can all be a cause of these disparate results)

But, whatever the case, fact is most of our modern ham rigs are significantly worse in regards to transmit IMD than they need to be, and it will not cost a lot to do it!  Smiley
(heck, just look at the TS-590SG...it's not perfect, but a fair sight better than many of the others these days, and it's not a wicked expensive rig...)


Not sure this clarifies things, but have a look at that thread...
 


73,
John,  KA4WJA
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« Reply #111 on: February 12, 2018, 02:57:56 AM »

So all you guy's are telling me that decades ago when I sat my license is no longer valid. I now have to conform to spectrum purity because the test gear has been now affordable to to armchair critics makes my license useless ? Can't you guy's get the true nature of HAM radio? If the guy's wide tell him, if he is splattering everywhere tell him. Oh that's right, some of us have just become users and cant fix problems. So we all have to be dumb down and everything produced just perfect.

In my shack I have so much test gear I could find fault with just about anything. If somebody makes a crap AMP then the market will judge and not buy. If a Ham makes a crap Amp then the few of us left will help get it right for them. This goes for all radio equipment, we are here to help not condemn. Oh bring back the days of knowing the nets started 10KHz up, spill over to other bands, looking for the fundamental signal, don't you guy's miss that? AM (DSB) were the days, agree? Relax, in the real world of HAM most the criticism come from bored tech's. BTW where are you? the HF bands are open, I have 10m contacts every other day and all the bands below are open every day sometime. Give me a call. analyze me, like to check you also.

Relax, it's not a knowledge contest, it just fun, cul.

ZL4IV


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« Reply #112 on: February 12, 2018, 05:23:48 AM »

Why would anyone expect standards or knowledge to remain static in the face of technology changes and more widely accessible data?  To do so would reduce support for ham radio's continued existence - and that reduced support would be justified. Ignorance is not bliss, and life in a comfortable fog is no way to live.

I don't agree that the market alone will sort things out.  A "watt is not a watt" (to paraphrase) and, indeed, some people do buy rubbish radios that an operator with standards would be ashamed to put on the air. It's all about taking personal responsibility and using the available data, gleaned either from tests we do ourselves using increasingly accessible RF test equipment, or from the work of others.

I commend John (KA4WJA) for posting the data.  They'll always be recalcitrants for whom no amount of engineering science is convincing but let's not be disheartened by that: if it makes thoughtful, objective operators think twice at the time of their next purchase, that's progress. It's perfectly reasonable to insist that your next transmitter be cleaner than your last.  In my case I'll have no hesitation in declaring a new SDR/LMOS amp combination a failure if it can't outdo my TS-590 or TS-830 or, more interestingly, my 50 year old Collins S-line/30L-1.

73, Peter.
« Last Edit: February 12, 2018, 05:42:22 AM by VK6HP » Logged
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« Reply #113 on: February 12, 2018, 05:13:54 PM »

Quote
Hope this clarifies things for all of you. Smiley
Gotta go!

 73,
John,  KA4WJA

About 2-3 sentences were all that was needed to determine the method you used which is the ARRL's version which results in a 6dB improvement versus the long established professional way of measuring which is against a single tone.

It has also been known for decades that the ARRL cherry picks the two tones for the best results.The ARRL caters to their advertisers who use the same fraudulent method and does not want uneducated hams to see how bad some of the crap on the market really is. I believe we have been thru this before.

Here is a quick paper on what you and everyone else should be measuring, the rest is pure garbage IMO.

Carl
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« Reply #114 on: February 15, 2018, 11:03:14 AM »

Hello again,

I got a couple e-mails asking some things that I've been hesitant to add here, as I don't wish to turn anyone off by "info overload" Smiley

Then thought, more knowledge is a good thing, so maybe I should try again to lay out some facts that many hams will find helpful??  Please remember that I'm not some random yahoo ranting on the internet (such as "Zenki"), I've been a ham 75% of my life, and there is some helpful info here, that I hope will not get lost in an argument.  Smiley

But, what to actually do??  How to get the facts out there, without the controversy?? Hmmm??

How about expressing some (common?) opinions first, and then hopefully we can get to the facts?  So here goes.


1)  I've been a member of the ARRL since 1974 (except for a one-year lapse), and while I do NOT agree with a good deal of their political (FCC) posture, nor do I appreciate their "editorializing" facts, or "factualizing" editorial comment (means they portray their opinions as facts), I'm still a member....mostly for the resources and to show the gov't that there are quite a few hams that are active (so we don't lose more of our spectrum!)

In my opinion ARRL HQ staff are just people who want to keep their job, and nobody wants to rock the boat...I suspect few have any real "love" for radio...(you know "amateur" comes from the "ama" / "amo", the latin root-word for love)

The factualizing of opinion is disturbingly insulting to me, and the lack of attention to real-world use of the airwaves is very disillusioning!  

I find their minimal attention to transmit IMD to be frustrating, but their two-faced attitude where they pay lip-service to the desire for good transmit IMD in a sentence or two of text, and then show fancy color graphics with 3rd order IMD ranges from -20db(PEP) to -35db(PEP), with -30db(PEP) showing "good", and rigs that test out with just a -23db(PEP)  to - 25db(PEP), with only a casual 3 word comment, while raving about the visual appearance / ease of use...Well this is truly sad!!!  Sad Sad

Further, we all know that static two-tone (or static white noise) transmit IMD testing, shows the best performance the transmitter or amplifier will generally have...but they never mention that!  
{Dynamic testing, where two-tones are dithered by a third tone, can show power supply deficiencies and circuit anomalies, that result in worse IMD....these tests are highly recommended today for external amps, to show their design and power supply issues, but the ARRL never talks about this!}

I'm also frustrated by ARRL HQ's lack of concern with real every-day hams, but somehow if you're a big contester or dx'er, you and your agenda gets instant and lengthy attention??

Oh, and don't get me started regarding their support of the no-code HF license!  I mean really??  Even I learned CW well enough to pass the test....but, truth-be-told, I couldn't copy 20wpm now to save my life!

I suppose the list of gripes about the ARRL could go on and on, but I think you see the point! Smiley  
Just, because the ARRL isn't perfect (what is?) and just because they frustrate me, etc., in MY OPINION, these are not reasons to discount all of their efforts....so let's look at what they do that is good, in regards to this discussion here.  Smiley

They use professionally accepted test methods (EIA/ECIA, Bell Labs, Motorola, etc.), many of which were designed and perfected over many decades...

No, even these are not perfect, I mean yeah a static two-tone isn't the best test, but it IS the data that we have for dozens of amps, and dozens & dozens of rigs, over the last 50 years, with transmit IMD all tested using the same method...so why not simply use this data to compare various radios and amps, compare and contrast various designs, etc., and learn what some rigs and amps are doing to pollute our airwaves, and to make purchase decisions??

Any ham that can't subtract 6db (or add 6db) to a spec if trying to compare to a result from a different test method, probably will not have sufficient knowledge of Inter-Modulation Distortion and Occupied Bandwidth, that would allow them to understand the importance of what we're discussing here.....so, I don't think this should be an issue.  Smiley

So, why not just use the info??

We can still gripe about some other issues with the ARRL, but why not use the data and resources they provide to improve ham radio??  

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 of you who bought 90db to 100db dynamic range radios, to actually get close to being able to use much of that potential).

So again, I ask...why not use the test data we have (from ARRL) and expertise of many experienced engineers (from Bell Labs, Motorola, HP, R&S, etc. etc.), to both learn about these topics and improve our on-air signals??


2)  Yep, static two-tone testing isn't the best.....But, the ARRL does use the standard, professionally accepted tones in transmit IMD testing....these are not "cherry picked" tones...

The use of two non-harmonically-related audio tones, between 300hz and 3400hz (spaced 1000hz apart), for SSB IMD testing, was established by "the phone company" (Bell Labs) in the 1930's (no, that's not a typo, the 1930's) for use in their multiplexed telephone network (in the late 1940's thru the late 80's this expanded to multiplexed radio / microwave telephone transmissions...and multiplexed baseband FDM Satcom telephony)  Their original tones were 800hz and 1800hz, I believe.

Parallel to this (from the 30's thru the 80's) were RCA, Westinghouse, GE, Motorola, etc....and harris, rockwell, etc. etc., all experimenting with radio comms and incorporating SSB experimentation, etc.

At some point (1950's I think) as more capacity was needed and technology improved, and as radio comms was coming into the forefront, most SSB baseband was reduced to 300hz to 3000hz...(it wasn't until the early 80's that this change was officially made in the world of HF maritime comms, when the int'l freq assignments were changed)

With wider spacing of the tones, the wider the occupied bandwidth is, the choice of increasing spacing of IMD test tones, for communications equipment, to 1200hz was made, with tones of 700hz and 1900hz, to better replicate the IMD results of the average male voice...and these 700hz and 1900hz tones were chosen by most RF engineering departments involved in radio comms...(there are some testers that use 400hz and 1800hz, and yes these show somewhat wider occupied bandwidth, as the wider spacing of the tones does widen-out the transmitter bandwidth)

The earliest use I had of these was in High School in the 1970's....and while I assume the ARRL was also using these tones as early as SSB was in in its infancy on the ham bands / the 1950's, (before I was born).....the earliest I have actual ARRL transmit IMD specs from is the 1970's.  Smiley

So, there is no tone cherry-picking going on here by the ARRL.  Smiley


3)  So what about this mumbo-jumbo about ARRL numbers being 6db better??

Well, the numbers are 6db better, but the actual figures are the same!!

How can that be, you ask??

Well, for SSB transmitters a 3rd order IMD spec of -30dbc IS the same as -36db(PEP)....so the ARRL reported IMD (referenced to PEP) is -36db, does "look" like 6db better than -30dbc....but one is -36db(PEP) and the other is -30dbc...and in actual fact they are the same!!!

Earlier / above, I detailed the reasons why the analyzer display shows what it does, with the 2 -tones representing the radio operating at its rated max PEP output (typically 100watts)...



(this example image is an IC-781 at 150 watts PEP)

Quote
[Remember that] PEP is the maximum instantaneous power of the combination of the two signals. A two-tone signal looks  similar to an AM modulated tone. The envelope of the RF signal varies as a sinusoidal with a frequency of Δf. When the voltages of f1 and f2 are out of phase, they cancel and the envelope is at a null.  When the two voltages are in-phase, they  add, and the voltage at the instantaneous peak is twice that of either tone. Because power is equal to the square of the voltage divided by the resistance, when the voltage increases by a factor of two, the power increases by a factor of 2 squared, or four.

Therefore, the PEP is four times the per-tone power and twice the average.

....If a peak reading power meter is used [as in the ARRL testing] to measure the PEP directly, that fact should be noted with the results...


But, it seems more / different writings on this are needed here??

So, from the 1980's, from the late Helge Granberg, Motorola RF engineer:


Quote
Figure 1

Figure1 shows a low distortion, two-tone envelope displayed on
an Oscilloscope screen.


Figure 2

Figure 2 shows on a spectrum analyzer screen the same
signal displays as two discrete frequencies separated by the
difference of the audio frequency or frequencies.

The display represents the rate at which peak power
occurs when the two frequencies are in phase and the
voltages add. Thus, one peak contains one-fourth (-- 6 dB)
of the peak envelope power (PEP). An average reading
power meter would read the combined power of the tones,
or half the PEP, assuming the envelope distortion is
negligible. The third order distortion products (d3), fifth order
(d5), etc., can be seen on each side of the tones. The actual
power (PEP) of each distortion product can be obtained by
deducting the number of decibels indicated by the analyzer.


Now that the actual display is understood, let's get back to this myth that the ARRL numbers are fudged?? Or overly generous??  Of course they are not fudged!  And, they are not generous....you just need to look at the qualifier "(PEP)"  vs.  "c".

As I wrote above -30dbc is the same as -36db(PEP)...

The "dbc" figure is the older, so-called "mil-standard" and the "db(PEP)" is the newer, EIA/ECIA standard (from the 1970's/80's), and this EIA standard was also used by the FCC (and ITU) for many communications specs...the "dbc" figure is the IMD referenced to the the level of the tones on the analyzer (and the tones display at 6db below PEP)...the "db(PEP)" figure is the IMD referenced to PEP...


Now, if you want a more official statement on this....here 'ya go:
Again, quoted from the late Helge Granberg:
Quote
"In one method, the military standard (1131 A-2204B), the distortion products are referenced to one of the two tones of the test signal.....in the second method, (the EIA/ECIA standard), the amplitude of the distortion products is referenced to the peak envelope power, which is 6 dB higher in power than that represented by one of the two tones.

An amplifier or device indicating a maximum distortion level of -30 dB in first method (Mil Standard) represents -36 dB with the second method (EIA/ECIA standard). Conversely, a -30 dB reading with ElA’/ECIA's PEP reference would be -24 dB when measured with the more conservative military method.

In practical measurements, the two tones can be adjusted [by the analyzer's internal, or an external, input attenuator or reference level adjustment] 6 dB down from the zero dB line, and direct IMD readings can be obtained on the calibrated scale of the analyzer.
Alternatively, the tone peaks can be set to the zero dB level and 6 dB deducted from the actual reading."

So, the "db(PEP)" numbers are not inflated, they are just 6db higher than the "dbc" numbers, but they represent the exact same level....

If a 100-watt (+50dbm) PEP radio's 3rd order IMD product is say -30db(PEP), that means that specific product is 1/10 of a watt (+20dbm), which is the same as -24dbc, as the "c" is already displayed 6db below PEP...


4)   Finally, some may wish to argue about solid-state vs. vacuum tube, or 50vdc vs. 13.8vdc solid-state PA's...but don't get too wrapped up in that, as there is even more to this...some have e-mailed and asked about the variations in transmit IMD, from similar / same transistors or tubes???

PA circuit design and construction plays a role here, but also so does the exact biasing and tuning of that particular PA.....usually, biasing an amplifier more toward class B will cause the lower order distortion products to go down, and the amplitudes of the higher order products to increase, and this is one way some manufacturers claim (and actually attain) a somewhat acceptable 3rd order spec, that they can advertise, but this is at the expense of increased higher order IMD...heavier biasing in AB (closer to A), can usually reduce the higher order products, but of course at the expense of efficiency, etc. (and sometimes an increase in lower order products).
In some designs, there is also a bias point where the 3rd order and 5th order products can be equal...

You may find it interesting to learn how can one 100-watt radio can have such different IMD specs from another (or how can one HF amp have varying IMD specs than another amp), when many of them use the same or similar devices (transistors, tubes, etc.)...have a look at the different results of lower-order and higher-order IMD products of the Elecraft K3s, depending on the PA circuit tuning and biasing...(please know I'm not picking on Elecraft, they're a great bunch of guys! It's just that the K3s is only rig that I have ARRL test results for, for different PA tuning/adjustments...so that's the example above I'm referring you to Smiley )


I know there is a lot here, and as I wrote up front I don't wish to overwhelm anyone, but do wish to better inform.  Hope I've done that??  Smiley


73,

John,  KA4WJA


« Last Edit: February 15, 2018, 11:11:49 AM by KA4WJA » Logged
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« Reply #115 on: February 15, 2018, 11:31:35 AM »

In May 1992 I published a 5 watt class A amp using the MRF 137.  The 3rd order products were -32 dB relative to each tone and the 5ths were -55 dB relative to each tone.  A couple of amps were built for lab use.  I also built a version using the MRF 138, which I used to replace the final in a Drake TR-7 to get a rave review from an audiophile that worked at ARRL HQ at the time--my audio sounded exactly like me while I was running a pileup on 75M in the Phone Sweepstakes.  With just 4 watts to a full wave loop.  Grin

It generated a letter to the editor how they shouldn't publish stuff that needed a 28 volt power supply.  He was only interested in designs that ran off of 12 volts.

I never did much more than that concerning the issue of transmit IMD--I was living it what may have been the cheapest single bedroom apartment in Newington at $220 a month. It didn't have enough AC to run a 100 watt rig without lights blinking, much less run high power.  Instead, I figured out how to get to the best VHF+ contest location within 4 hours of Newington and proceeded to amass a collection of grid and contest awards over the next six years.  I built a 50MHz to 10 GHz portable station--good enough to get grid awards on six microwave bands.  I have 902MHz quarter century grid award #25.  In 1995 I was awarded the John T. Chambers award for my outstanding contributions to VHF and UHF amateur radio by the Central States VHF Society.

Zak W1VT
« Last Edit: February 15, 2018, 11:47:47 AM by W1VT » Logged
KA4WJA
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« Reply #116 on: February 15, 2018, 12:18:57 PM »

Zack,
Awesome!

Many years ago, I built a 28-vdc PA for my 2m tranvtr.
I used a VMP-4..
It had decent IMD (3rd => -40 /  5th=> -50db) at 7 to 10 watts out (more than I needed, and all my 28-volt supply would allow for 100% duty-cycle), but I found an out-of-band spur (down about 40db, but still...)
Frustrated, but found no spur at 4 watts out, or below...
(ended up only needing 2 to 3 watts out, to drive a SS IPA and then to pair of 8874's, so it worked great for EME....no spurs and no IMD issues)


BTW, I went to school up your way...Worcester Poly Tech...although that was quite a while ago.
Still remember our station, W1YK, nice towers on top of a big 5/6-story building, on top of a big hill!


73,
John,  KA4WJA
« Last Edit: February 15, 2018, 12:24:30 PM by KA4WJA » Logged
AA2UK
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« Reply #117 on: February 15, 2018, 03:19:16 PM »

Zak, I was looking at some of your QSL's for working you on the Microwave bands in the mid to late 1990's. I just pulled out one from 1997 where we worked on 10gHz you were potable in FN42bl Mt. Wachusett and when you were in FN33kd on Mt Equinox. I also worked you when you were KH6CP/1 also on Equinox on 2304. I was at my home station for all these Q's from Sweetwater, NJ FM29qo.
Boy do I miss that location.
73, Bill AA2UK
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K6AER
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« Reply #118 on: February 15, 2018, 07:41:51 PM »

As long as mic. compression and mic, gain are adjustable on the radios the whole IMD discussion is a mote point. Every day I see terrible signals on the band. Worrying about IMD that is -30  or -40 dB on the third and fifth is a waist of time with the all knobs-to-the-right crowd.
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AC2RY
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« Reply #119 on: February 15, 2018, 08:09:53 PM »

As long as mic. compression and mic, gain are adjustable on the radios the whole IMD discussion is a mote point. Every day I see terrible signals on the band. Worrying about IMD that is -30  or -40 dB on the third and fifth is a waist of time with the all knobs-to-the-right crowd.

Audio signal compression should not be a problem in radio where SSB signal is synthesized digitally. Resulting signal can be digitally filtered to eliminate anything beyond passband before upconverting to carrier frequency. Even better can be done in direct sampling radios - where you can implement brickwall filtering directly at carrier frequency right before DAC. And there is usually no significant IMD caused by low power analog circuits.
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