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Author Topic: Ham Xcvrs' and Amps', Transmit Spectral Purity, IMD Products, vs. comm/maritime  (Read 152718 times)
K6AER
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« Reply #270 on: September 25, 2018, 02:25:32 PM »

I thought L-band was from 1-2 GHz.
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KA4WJA
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« Reply #271 on: September 25, 2018, 02:35:31 PM »

Mile,
You are correct...
I thought L-band was from 1-2 GHz.
That's why it is so staggering that we are seeing increased terrestrial background noise being received by satellites with their antennas point at the earth...
INMARSAT and Iridium use L-band (actually their uplink/downlink bands are adjacent / straddle each other....from 1525mhz thru 1660mhz)....
And, in addition to their engineering groups, they're in contact with ITU working groups, etc. to assess how-to reduce the hoards of un-certified (or just self-certified / BS'ed paperwork) consumer electronics populating the world, causing the rise in our background noise!!  Sad

Now, if we hams want to help ourselves....well, then that is up to us... Smiley


73,
John,  KA4WJA


P.S.  Of course their is also, Globalstar [sic], and Thurya, on L-Band...as well as other regional (and global) mobile satellite communications systems, some using VHF and some using S-Band....
« Last Edit: September 25, 2018, 02:38:32 PM by KA4WJA » Logged
G3RZP
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« Reply #272 on: September 26, 2018, 02:06:23 AM »

A little ironic that Iridium is having problems - it was spurious emissions from Iridium satellites interfering with Radio Astronomy on 1420 MHz that led way back in 1993 to the WRC charging ITU-R Study Group 1  with setting up what became Task Group 1/5 to revise Recommendation SM329 on Spurious Emissions.
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KM1H
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« Reply #273 on: September 26, 2018, 08:39:13 AM »

A little ironic that Iridium is having problems - it was spurious emissions from Iridium satellites interfering with Radio Astronomy on 1420 MHz that led way back in 1993 to the WRC charging ITU-R Study Group 1  with setting up what became Task Group 1/5 to revise Recommendation SM329 on Spurious Emissions.

And the circle of unintended consequences continues Roll Eyes
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SWLER1965
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« Reply #274 on: October 01, 2018, 12:35:45 PM »

With the kids out of the house I hope to have the time to learn but wow I've got a long road ahead.   Thank goodness for Google

Thx to u all
Jon
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KA4WJA
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« Reply #275 on: October 15, 2018, 04:45:47 PM »

FYI, here are some updated / corrected transmit IMD figures for the Apache Labs ANAN-8000DLE (form Nov 2018, QST)

As for the ANAN-8000DLE....it's a nice rig (just wish it had "knobs"!)...

In any case, I looked closely at Adam Farson, VA7OJ/AB4OJ's, detailed test of the ANAN 8000DLE, last summer...

Here are the transmit IMD test results that he published (at 14.1mhz):
-33 / -40 / -54 / -60  (with NO pre-distortion) at 200 watts
-67 / -70 / -70 / -70  (with pre-distortion) at 200 watts

FYI, the ARRL testers had some difficulty getting the pre-distortion to work well, and they found only 3db to 5db improvement in transmit IMD with it turned on, versus off....
The ARRL updated their review of the ANAN-8000DLE, stating that after their original IMD tests, they sent their unit to Apache Labs service center / Doug Wigley, W5WC (in Arkansas), where Doug quickly determined that the RF Coupler output was too high and caused the "pure signal" pre-distortion to become overloaded and seriously effected its functionality because of this overload distortion...
He changed some resistor values, which solved the problem!  (and Apache Labs has also changed these in production models)
He returned this unit to ARRL and they (ARRL) re-did their transmit IND tests and in Nov 2018 issue of QST, published the updated / corrected IMD test results of the ANAN-8000DLE...see pages 63 and 64...



John,  KA4WJA

The ARRL updated their review of the ANAN-8000DLE, stating that after their original IMD tests, they sent their unit to Apache Labs service center / Doug Wigley, W5WC (in Arkansas), where Doug quickly determined that the RF Coupler output was too high and caused the "pure signal" pre-distortion to become overloaded and seriously effected its functionality because of this overload distortion...
He changed some resistor values, which solved the problem! (and Apache Labs has also changed these in production models)

He returned this unit to ARRL and they (ARRL) re-did their transmit IND tests and in Nov 2018 issue of QST, published the updated / corrected IMD test results of the ANAN-8000DLE...see pages 63 and 64...


Here are their results (at 200 watts PEP):




Comparing Adam Farson, VA7OJ/AB4OJ's tests with the new ARRL tests...

ARRL Tests (typical)
-30 / -38 / -47 / -54  (with NO pre-distortion) at 200 watts
-32 / -43 / -54 / -59  (with pre-distortion) at 200 watts, old/defective results
-54 / -64 / -60 / -60  (with pre-distortion) at 200 watts, Updated Results (from 20m for comparison to Adam Farson, VA7OJ/AB4OJ's tests on 20m, but check out the 40m and 80m results which are really nice!)

Adam Farson, VA7OJ/AB4OJ's tests on 20m:
-33 / -40 / -54 / -60  (with NO pre-distortion) at 200 watts
-67 / -70 / -70 / -70  (with pre-distortion) at 200 watts

Comparing Adam Farson, VA7OJ/AB4OJ's tests with the ARRL tests (both their original results and their updated test results)...clearly shows that pre-distortion does work....BUT...

But, in my opinion, this also shows that this is not an "off-the-shelf" / mass-producable feature...yet!!
And, is also shows (again, in my opinion) why Flex and Icom have decided to not incorporate pre-distortion into their units (nothing like marketing a feature, that doesn't work out-of-the-box, to ruin your reputation)...

Just wanted to update / clarify these results for all... Smiley


Fair winds...
73,
John,  KA4WJA
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VK6HP
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« Reply #276 on: October 15, 2018, 06:40:47 PM »

John

I saw the QST update and concluded that there's a part of the ANAN pre-distortion implementation story missing and, while it could be said to be no-one's business but their own, it does impact the path to conclusions such as the one you've drawn.  For example, if the problem originated in simple manufacturing variations of the coupler, and if the production line testing was inadequate, that's a fixable situation, especially by (e.g.) large Japanese manufacturers.  On the other hand, if the parameter sensitivity in implementing the technique is so high that it's impossible for the average amateur to set up, that's a different story.  

I don't own an ANAN but am hanging out for a new exciter with pre-distortion capability to drive my KPA1500 (which has the coupler built in). Based on my investigation to date, and my reading of the ANAN-related material, I think the predistortion implementation is tractably simple to set up.  However, it looks as though there might be a case for more robust level (and perhaps other) parameter monitoring.  In saying that, I'm aware that there's a swag of people who have trouble with even proper mic gain and compressor settings via ALC monitoring but I guess it's interesting to ask if, in overall transmitter output terms, poor pre-distortion is any worse than none at all.  On the basis of the ARRL experience, apparently not.  But I'd still be wanting to take a close look at the wideband output before coming to that conclusion. It might be also worth bearing in mind that that the level issue was presumably not a gross maladjustment, and extrapolations from that situation are undoubtedly dangerous.

Pre-distortion in a radio with knobs is a deal maker for me, and I'd personally be delighted if ICOM implemented it tomorrow. Meanwhile, the 32S-3 keeps its best IMD ranking in my modest shack. I just keep reminding people of that because, 50 years after the Collins was built, it does not seem unreasonable to demand a mainstream amateur transmitter with better IMD performance.

73, Peter.

 

« Last Edit: October 15, 2018, 06:43:46 PM by VK6HP » Logged
G3RZP
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« Reply #277 on: October 16, 2018, 12:24:53 AM »

One cannot get around the fact that the last generation of tube PA transceivers (using the 6146 family) were significantly better on IMD, especially the higher orders (which cause more splatter QRM), than the solid state rigs that followed them.

Not that this should be surprise when you consider the transfer characteristics of the solid state devices. It is however somewhat interesting that no manufacturer of amateur equipment ever went down the route of Cartesian feedback, which was used in VHF land mobile equipment.
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KA4WJA
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« Reply #278 on: October 16, 2018, 05:09:38 AM »

Peter,
I had similar thoughts when I read the original ARRL test reports earlier this year (after seeing Adam's excellent results last year)...
And while I don't have an ANAN either (nor any SDR rig), when I then saw one Youtube video of an ANAN rig and its set-up, and its band-by-band "gain" settings, etc. (that were not explained well) I became concerned that there must be some "art" to actually setting-up the pre-distortion?

And, now with the updated ARRL tests and their explanation of needing the rig modified by the ANAN service center, I'm left wondering if (as you questioned) there are in fact two issues at work here??

Perhaps the user settings are easy to do?? and/or not critical??  But, when combined with a production error / QC issue from the factory, it can be a problem??

Or, is there in fact critical user settings that need more precise adjustments than we are led to believe and/or some critical hardware values that need to be better understood by the manufacturer so that they can actually mass-produce a quality product (or perhaps better final assembly / testing / adjustments... i.e. "Quality Control")??

I don't know the answer to these questions, but the real issue here, in my opinion, is:
In order for this rig (or any well-performing pre-distortion-equipped SDR) to become a major-seller in the market (such as the IC-7300 is becoming), it simply cannot have these issues out-of-the-box...
{and, I do hope Apache Labs is reading this, and addresses these issues/concerns!}
Again, that's just my opinion... Smiley
 
John

I saw the QST update and concluded that there's a part of the ANAN pre-distortion implementation story missing and, while it could be said to be no-one's business but their own, it does impact the path to conclusions such as the one you've drawn.  For example, if the problem originated in simple manufacturing variations of the coupler, and if the production line testing was inadequate, that's a fixable situation, especially by (e.g.) large Japanese manufacturers.  On the other hand, if the parameter sensitivity in implementing the technique is so high that it's impossible for the average amateur to set up, that's a different story.
 





If Icom could actually implement a workable, off-the-shelf, pre-distortion system, that would be great!!
And, yes, I'd be looking to buy a well-performing pre-distortion-equipped SDR with knobs, too!! Smiley

But, in my brief talks with Flex (last year) and my readings on the ANAN, as well as my understanding of Icom (from years of dealing with them in the maritime industry), I'm not holding my breath... Smiley

Maybe we  will see a rig that you and I will quickly spend our $$$$ on, in 2019?? Maybe in 2020??
There are some small / niche manufacturers working on them, but I suspect (just my opinion) it will be Flex or Icom that will be first?
 
I don't own an ANAN but am hanging out for a new exciter with pre-distortion capability to drive my KPA1500 (which has the coupler built in). Based on my investigation to date, and my reading of the ANAN-related material, I think the predistortion implementation is tractably simple to set up.  However, it looks as though there might be a case for more robust level (and perhaps other) parameter monitoring.  In saying that, I'm aware that there's a swag of people who have trouble with even proper mic gain and compressor settings via ALC monitoring but I guess it's interesting to ask if, in overall transmitter output terms, poor pre-distortion is any worse than none at all.  On the basis of the ARRL experience, apparently not.  But I'd still be wanting to take a close look at the wideband output before coming to that conclusion. It might be also worth bearing in mind that that the level issue was presumably not a gross maladjustment, and extrapolations from that situation are undoubtedly dangerous.





Peter, when I read this sentence of yours: "I just keep reminding people of that because, 50 years after the Collins was built, it does not seem unreasonable to demand a mainstream amateur transmitter with better IMD performance.", I smiled wide!!
Because, this was one of the main reasons I started this thread / quest a few years ago!
Pre-distortion in a radio with knobs is a deal maker for me, and I'd personally be delighted if ICOM implemented it tomorrow. Meanwhile, the 32S-3 keeps its best IMD ranking in my modest shack. I just keep reminding people of that because, 50 years after the Collins was built, it does not seem unreasonable to demand a mainstream amateur transmitter with better IMD performance.

73, Peter.
60 years since the 32S-3 came to the market, and 40 some years since the first mass-produced SSPA HF ham rigs, and we have gone backwards in regards to transmit cleanliness!!  And, this is during the time that "everyone" is drooling over the prospect of "100db dynamic range receivers"??
With few hams willing to stand up and say that "the emperor has no clothes" (you cannot use a "100 db receiver", because our transmitters suck!!!) We got what we asked for... Sad

If some read the words of the same folks that worked so hard to bring us improved receivers...(NC0B, W8JI, W3LR, etc.)
https://www.eham.net/ehamforum/smf/index.php/topic,97093.msg1053647.html#msg1053647
And, then we all actually demand cleaner transmitters, maybe we will actually be able to use some of the capabilities of all those modern/expensive receivers??

But, as I wrote right up front...back in February:
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!
So, we got what most asked for...just that most didn't know any better... Sad


73,
John,  KA4WJA
 
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KA4WJA
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« Reply #279 on: October 16, 2018, 05:50:19 AM »

Ironically, as I was composing this message I received the Nov issue of QST, and read the updated tests of the ANAN-8000DLE....
So, even if this might seem to be a digression, I do want to post this as well...
Here goes..

~~~~~~~~~


Recently, in another thread I mentioned the "ease" and "inexpense" of actually producing a "clean" HF transceiver....and I didn't want anyone to get the idea that I believe the average ham can grab some misc parts out of their junk box and in a few hours have a clean 100-watt HF SSPA...

Further, I wanted everyone to be clear that while availability of more affordable test equipment has made it capable for more hams to do some more testing, it isn't as easy as it sounds, especially when dealing with many modern HF ham transceivers which have significantly worse real-world IMD results than a two-tone test shows, due to ALC issues, etc...

How to do that, and not start arguments?   I figured maybe I should just quote someone else?  So....

About a dozen years ago, when discussing transmitter linearity testing, SM5BSZ looked at several modern amateur HF rigs (and I though some of his thoughts/results might be interesting to some here....and his words might be easier to grasp than my ramblings?? So, I'm going to quote some of this paper below).

For clarification, in these quotes (when looking at static two-tone testing, as well as discussing 2-tone versus voice testing procedures), he was referring to the transmit IMD of the legacy FT-1000D transceiver, and the ALC issues of the IC-706 series as well as the FT-1000D, and other high-end transceivers:

Quote
"This particular interference [in the FT-1000D] is generated by the cross-over distortion in the power amplifier and/or driver stages as will be shown below. The purpose of transmitter testing is to find the weak spots of each transmitter and to characterize them, so that users can minimize the problems and manufacturers will be able to improve the equipment."
  (from SM5BSZ, in 2004)

[SM5BSZ, in regards to testing]
Quote
"In SSB mode the important information comes from the peak hold spectra, because the average power spectra are difficult to obtain in SSB mode on a sweeping analyser. It is not so easy to keep producing the worst splatter level by voice for the long time of a single sweep at a video bandwidth of 30 Hz."


And, when generically discussing our poor performing amateur transmitters and their ALC issues, and testing procedures, SM5BSZ wrote:

Quote
[Other than the poor PA designs] "One of the main problems in modern transmitters is the ALC, a servo system that is designed to keep the output power below a certain threshold. Any servo system can have stability problems and the ALC system of a transmitter is no exception. The interference generated can be horrible – but a standardized two-tone test will not show anything at all. It is becoming well known that the simple two-tone test does not reveal much of the real performance of a SSB transmitter. With two constant tones that are separated by 1 kHz, exactly the same maximum power is reached 1000 times each second. With the fast attack, slow release ALC characteristic of a typical SSB transceiver, the ALC control voltage will be very close to a DC voltage with just a small saw-tooth like component superimposed on it. Likewise the power supplies will be operating under nearly constant load, and their dynamic regulation is not being tested at all. Consequently the two-tone test will not show many of the problems that may occur during normal usage with voice modulation. It only shows the fundamental linearity of the final amplifier, not the rig as a whole.

Using ALC to provide voice compression on SSB is a bad habit from old times. It was not a good idea back then and it is really stupid in modern equipment. The ALC causes a lot of terrible splatter for no good reason at all. I have been told that amateurs want to watch the ALC meter to be sure the rig operates at full power. It would be much better to remove the control function and instead detect the drive level and show that on the meter."
{BTW, there are "mods" posted on the internet that take a well-performing ALC design that is not used as a voce compressor / does not adversely effect the transmitter's IMD products at all, and turns it into a splatter-producing ALC, in order to "give your rig more audio 'punch'!"..Huh  There is one fairly easy mod (just changing some cap values) from a European ham, for the Drake TR-7 that does just this...so, while there are some SS HF rigs that don't ALC issues, unfortunately there are hams that create these issues themselves...}



Also, from 2004:
Quote
"If the linearity of the power amplifiers is typically good enough. The results obtained in two-tone tests do not correlate at all with the splatter generated. The intermodulation products are typically far below the ALC sidebands with real voice signals. In a two-tone test, the peak power is reached with a repetition rate of about 1 kHz, causing the saw-tooth waveform of the ALC to have a frequency of 1 kHz with very low amplitude. Therefore the two-tone test essentially shows the power amplifier linearity. But testing with a real voice into the microphone shows what signals other band users really will have to cope with – and that is often something quite different and much worse.

The simple test, just measure the emitted spectrum while modulating the transmitter as if it was on the air, has a practical problem: professional spectrum analysers are not good enough! The sideband noise levels of the oscillators in the spectrum analyser (a multiple-conversion superhet) need to be substantially lower than those in the transmitter under test, or else you are measuring the test equipment, not the transmitter. The ones I have access to have sideband noise levels of about –100 dBc/Hz at 20 kHz, and the best performance I know of in a commercial instrument is –125 dBc/Hz at a frequency separation of 10 kHz (Rohde & Schwarz FSU series). This problem arises from the need to make professional test equipment broadband from near-DC to perhaps several GHz; but for testing amateur equipment we do not need broadband coverage, and therefore high-quality measurements are not so difficult, as will be shown below.

There is another problem, however, a more fundamental one that requires some discussion. The interference caused by a transmitter, be it noise sidebands, splatter or keying clicks, occupies a large bandwidth. The level one will see on a spectrum analyser depends strongly on the bandwidth, the sweep speed and the detector used. To produce a good characterisation of the interference it will be necessary to make two measurements – one that uses a peak-hold detector in SSB bandwidth and another that uses a detector for the average power in a narrow bandwidth. The two measurements are discussed in detail below."


And further in regard to testing procedures, SM5BSZ wrote:
Quote
"Testing transmitters is a far more complicated task than testing receivers. It is complicated in the sense that it is very difficult to set up a standardised test that has a chance to be generally accepted, and that would be relevant as a figure of merit for the spectral purity of a modulated transmitter.

Personally I think that excessive high order intermodulation is a direct consequence of the standardised two-tone test, because of the unbalanced emphasis that it gives to the lower (3rd and 5th) orders. The relatively low level of the third order intermodulation visible in the standardised two-tone test may well be a consequence of design engineers tweaking the bias current of the PA and perhaps the driver stages for optimum 3rd and 5th order performance, without regard to any other consequences. The normal 3rd order intermodulation can be described as loss of gain at maximum power, as the envelope is flattened slightly at the maximum power. By deliberately setting too low a bias current to create a loss of gain at the zero crossings as well, one can add another 3rd order intermodulation component that is in antiphase and thus reduces the total 3rd order intermodulation. Such techniques are well known, and often used to take advantage of rigid type acceptance test protocols – but the adverse consequences for wideband splatter are visible as increased levels of higher order intermodulation, even in the standard two-tone test. If the FT1000D had been designed to produce good results in the peak hold spectrum, the bias current would have been just a little higher. The third order intermodulation in the two-tone test would have been a little higher too, but the higher order components would have been much lower... and that is what matters most to other band users. I have been told that the FT1000D is known to produce very clean SSB signals on the bands – “one of the best rigs”. Knowing about the cross-over distortion, amplifier noise and ALC modulation from which it suffers, and how easy it could have been to eliminate all these problems at the development stage, the conclusion is that the current state of the art in amateur radio transmitters is highly unsatisfactory. Bad design is not limited to careless keying."



Again, I just wanted to be clear that while I stand behind my words that it isn't too expensive for most radio manufacturers to do (probably < $50 - $100, extra) nor is it too difficult (as many of these engineering departments already have these designs in their files, and some have 'em in production, and/or at least these RF engineers should already understand the intricacies of designing/building a clean SS PA!), making a clean 100-watt, 12vdc SSPA ham transceiver, isn't as simple as breadboarding a few parts together and isn't going to be done by the average ham in an evening... Smiley

Nor is the average ham able to adequately test the actual real-world transmit IMD of their rig...

So, we rely on the manufactures to produce good, clean transmitters with fairly linear PA's and without ALC issues (which for the most part, they fail to do)...
And, many of us rely on the ARRL to actually test these rigs and hold the manufacturers feet to the fire (which for the most part, they also fail to do)...

So, while cranking up the mic gain (and pegging out the ALC) usually produces some seriously crappy signals (wide and with quite high IMD products), many of our modern rigs are just not very good in the transmit spectral purity department (poor IMD) even when operated properly....and some that are "assumed" to be great (such as the Yaesu rigs when operated in Class A) are in reality pretty crappy with even a slight amount of ALC / when set as proscribed by the manufacturer!

So, if we do desire cleaner transmitters and less interference on-the-air....and desire to actually be able to use some of the great capabilities of our receivers...well then, it is up to us (my fellow hams) to do a few things:

a)  vote with our wallets and not buy rigs that have poor transmit IMD and/or have wide SSB occupied bandwidths....and only buy rigs that have good transmit IMD and fairly narrow SSB occupied bandwidths..

b)  try to teach our fellow hams about transmit IMD, and why it is important, even if we don't have a "perfect" way to test, the ARRL two-tone tests can be used to compare...

c)  teach our fellow hams how to better use/operate their radios to improve the transmit signal and interfere less with others...even if they bought a rig that tests well, it is up to the operator to understand how to actually use the radio properly (even if that means NOT following the manufacturers' recommendations)..


Hope this helps some.
Of course, none of this is a matter of life-n-death, but certainly important for many SSB operators!

73,
John,  KA4WJA

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G3RZP
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« Reply #280 on: October 16, 2018, 08:24:12 AM »

John,

ALC issues have been with us for many years. I still haven't managed to fix the power overshoot on my FT102 because Yaesu insisted on using ALC for power control. However, I can honestly hold my hand up and say that I NEVER put ALC into any of my professional designs! Admittedly, for maritime use when we had to have compatible AM or reduced carrier SSB (-16dB rel PEP), ALC would be a major PITA, so it was easier not to have it at all.....a VOGAD (long release time constant AF compressor) is another  matter.
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I4LEC
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« Reply #281 on: October 17, 2018, 07:27:29 AM »

As a PowerSDR mRX PS user, the Open Software that implements the so called Pure Signal (PS) feature (aka pre-distortion), I would like to bring up my experience.

PowerSDR mRX PS and its PS built in feature can be used in association with different hardware platforms, as long as you re-address the feedback, at a proper level, out of your PA down stream coupler back to the RX input while on transmit.

Matter of fact this is commonly performed on my Hermes board (main board for the ANAN 10, 100 series) as well as on the ANAN 200 series or even Red Pitaya, these don’t have a built in coupler, when operated W/O an Amp, the feedback is taken mostly form an internal leakage, up to the bands that provide enough leakage level.

The new ANAN series (7/8000 DLE) evidently implements a built in coupler, this way, even W/O an external one, at least the transceiver can reliably take fully advantage (on all bands) of PowerSDR mRX PS available feature.

My understanding is that on the 8000, while at full power, the built in coupler output resulted too high in level to the point that the voltage divider circuit had to be re-worked  for a proper level, according to my experience, this must have been really too high as the SW also implements an automatic attenuator up to 31dB that corrects the feedback level to the optimal one, no operation is required, once you select the PS option and allow the automatic correction, it just work.

In my layout, I placed the home made coupler, a very simple strip line designed for -45dB on 10m, at the end of the Amps chain, which consist of a 200W SS PA followed occasionally by a ceramic triode tube.

This way, even if the level difference out of the coupler is 20dB (from 10m to 160m) as the strip line is designed for the higher frequency (-45db to -65dB), the internal auto attenuator can compensate it, I just add an extra 6dB pad for a total of -51dB on 10m, a setup like this allows a range of power from 200W to 2KW, useful for both, the SS alone or paired with the tube one.

Based on my observations, the optimum feedback level resulted to be around 7dB below saturation of the input level, on 10m @200W the ATT shows 20dB and 30dB @2KW, whereas on 160m it will range from 0dB to 10dB, thus covering the expected range and always maintaining the optimal feedback.

As far as I am concern, I consider it a perfect functioning feature that I have been using it for the past four years, improved along the years in many aspects, a voltage divider on the built it 8000 coupler that required a slight mod (more attenuation), to my opinion cannot invalidate it at all. Smiley

73, Clay
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DL8OV
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« Reply #282 on: October 17, 2018, 10:38:17 AM »

ALC would be a major PITA, so it was easier not to have it at all.....a VOGAD (long release time constant AF compressor) is another  matter.

Sorry Peter, please could you clarify this? I thought that a VOGAD was a good thing as it replaces the microphone gain control and enables everything from a whisper to a shout to correctly modulate the TX.

Peter DL8OV
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KA4WJA
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« Reply #283 on: October 17, 2018, 11:32:40 AM »

Okay to both Peter and Peter....
It's always good to hear from you...both of you!  hi hi

I was going to ask a clarification as well... Smiley

ALC would be a major PITA, so it was easier not to have it at all.....a VOGAD (long release time constant AF compressor) is another  matter.

Sorry Peter, please could you clarify this? I thought that a VOGAD was a good thing as it replaces the microphone gain control and enables everything from a whisper to a shout to correctly modulate the TX.

Peter DL8OV

Specific to why I'm looking for clarity here is:

A while back I bought an accessory synthesized remote VFO for my Drake TR-7, but haven't used it (yet)....a Noble Radio NRV-7....and included in it is a "sound card interface", etc., and a VOGAD speech compressor .

Their description of their Speech Compressor is:

Quote
A VOGAD (Voice Operated Gain Adjusting Device) is also included for SSB operation.  This is an AGC controlled speech amplifier that keeps the audio level from the microphone relatively constant over a wide input level range and greatly increases the average talk power with little distortion.

The VOGAD (Voice Operated Gain Adjusting Device) speech compressor is adjustable from the front panel gain control.
It is basically a mic amplifier with an AGC system to increase the gain on lower input levels and
reduce the gain for higher mic input levels. This tends to keep the average microphone input level to the transmitter at a relatively constant level and provides a higher average output power
level with very low distortion. With proper setting of the compressor you should see a noticeable difference in average output power with the compressor on and off.

I assume this works well in quiet environments / when close-talking a mic, as is normal in commercial SSB comms....but, maybe not so good in today's ham shacks with background noise??
Please help me understand this a bit better...


FYI, I actually didn't give it much thought, as I never found a need for speech processing with my TR-7, but also I do have the Drake SP-7 external Speech Processor (an audio in/out unit that I believe takes mic audio in, and up-converts to 455khz, then does RF clipping/filtering then demods down to audio and inputs this to the rig...)  But, have never used it either...

So, if can comment on the VOGAD for SSB operation, that would be great....any pluses / minuses??  And, any thoughts on the late 70's technology Drake SP-7, please share as well...

Thanks.

73,
John,  KA4WJA

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KA4WJA
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« Reply #284 on: October 17, 2018, 12:19:46 PM »

Clay,
Thank You!!
Thank you so much for posting this info!!

This is exactly what we all need to know...

I am curious though, is there some reason (other than cost $$) that a wide-band flat-response directional coupler cannot be used??
Then there would be no need to set/adjust things band-by-band, either by hand or via software...
And, this would also give the end user a more seamless path to getting the rig (and the PureSignal pre-distortion) properly set-up??

{I have a really cheap coupler in the other room that is flat (+/- .5db or better) from 1mhz thru about 1500mhz....and I used to have a few others that were even better....and I've got a Bird "sampling slug" somewhere (a -50db sample) that is as flat as any ham would need across the HF range, etc..}
 
Those hams that are "software guys" or IT professionals, etc. might not have much of a learning curve, but for those of us who come from the RF side of things, we generally prefer radios with knobs, and it's gonna take a really great "computer-controlled-rig" to get us to budge....
And, one main reason for this (aside from being entrenched old farts) is the "problems" that are so often spoken of on the air and/or on-line these days...as opposed to the good facts (like Clay write of, here) that are usually unknown except to those who join a yahoo group, or are some fanboy for a product, etc...

(You know what they say, 100 good reviews and everyone just say "oh, ok"....but one or two bad reviews and everyone says "what a piece of crap", etc...)

Clay, thanks again for posting your experiences and giving us all some much needed info on how this all works and most probably how/why the ANAN-8000 that the ARRL tested, needed to have some circuitry changes...



Finally, for everyone...
In my personal opinion, this (pre-distortion) is a great feature that we have all been discussing here for half a decade....but, the way it is working / the way it is being implemented into our ham rigs (as of today, Oct 2018...Apache Labs is the only one with a full-power, pre-distortion-enabled, HF-SDR rig), is not quite "ready for the mass market"...

Again, in my opinion, it might be "mature technology" in the lab, and/or in the hands of software guys/It pros, but in the hands of even seasoned hams, problems still exist....and it's not quite ready for prime time, so-to-speak...

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


Further, this whole explanation / discussion about pre-distortion shows how smart the guys at Icom (and even at Flex) are... Smiley
Yes, I know some of you will think I'm being sarcastic, but I'm serious....they decided to not worry about pre-distortion and concentrate on what works and what features their customers wanted, at least to some extent....

But, it also shows how really super smart the Apache Lab, and PowerSDR, guys are!!!
They are leading the way forward in amateur radio SDR....and if they can get some of the RF things sorted-out and get the bugs out of the software, they will be leading the way....well leading the way, right behind Icom... Smiley
'Cuz as well all know, the 800lb Gorilla will eventually be considered the leader, even if the little guy (Apache Labs) is really the fore-runner... Smiley


Thanks again Clay!

73,
John,  KA4WJA
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