Official Position on Adaptive Predistortion

W2PP

Gerald:
   I'm still hoping you will comment on my post above regarding the orphan problems????
Peter

N8SDR

Actually John running radios below there rated power output can at times cause the IMD to be worse than if run at or near full power.

David Decoons, wo2x

I tend to notice the single LDMOS amps are pretty bad with IMD as you start running near rated output. The SPE 1.3 & 1.5k, Acom 1200s for example. Simon Brown (Ham Radio Deluxe fame,) sent his 1200s back since it was bad with IMD. I think Acom has made some changes since. The dual LDMOS amps (Flex PGXL, KPA1500, German kit amp) are a lot cleaner due to the headroom. The 6600 running with low cut at 100 and Power Genius XL is very acceptable. Not APD clean but well within acceptable limits. Based on reports I get on IMD levels, I would rather Flex continue with development of features to improve my enjoyment of using the radio. Dave wo2x

Bill -VA3WTB

The radios has many under the hood tweeks done since that old test that effect IMD performances. Most Flexes I see now can have an IMD as low as -40

Bill -VA3WTB

That is true Dave, If Flex were in trouble with IMD performance. They would not have put APD on the back burner.

Gene - K3GC

The Question, IMO, isn't whether Flex is in trouble without APD (I feel definitely that Flex is quite healthy).

The main question is how much market would Flex gain with APD?  Also, a cleaner signal is good Ham citizenship.

Bill -VA3WTB

Two things come to mind.
First, I don't think they have lost a lot of market share,,Flex radios offer so much that they sell because of what they do,,and what they can do in the future. Flex has things no other company has.
And the same question can be asked about all ham radio companies, Icom for instance has two SDR radios out without APD and are doing just fine without it. And they don't seem to plan on it ever.

Secondly, Flex radios are very good ham citizens because they are one of the cleanest radios on the market. -40 is really good, so bothering others is not an issue,,unless the radio is setup poorly.

And considering the engineering put into the Flex amp to make it really clean shows their commitment to clean signals.

Nigel

I think out of band transmissions is mandated by everyone not just the FCC. or has the licence changed that much?

WQ2H - Jim Poulette

I see Wayne's point, the present numerical standards do present a fairly low bar. And while it really sounds cool from a philosophical perspective - it reminds me of that old idiom of "gilding the lily".

CFR Part 47 §97.307 (a-e) (Emission Standards) do however stipulate emissions limit criteria for radio apparatus put in service after 1 JAN 2003. It's definitely worth at least looking over: http://www.arrl.org/files/file/Regulatory/March%208,%202018.pdf

73
Jim, WQ2H

Rick Peterson

Howard, KY6LA

For an example of the benefits of APD for an amateur digital mode, see:

http://www.qsl.net/wa6nut/PureSignal

This link shows the FreeDV+ signal before and after activating PureSignal (FreeDV plus Video is a multimedia HF mode combining digital voice and video, employing 66 subcarriers total).

Without APD, this mode would produce unacceptable splatter on adjacent frequencies.  So APD is being applied to amateur digital modes with great benefit.

I'm looking forward to FlexRadio's implementation of APD.

Regards, Rick, WA6NUT

AC9S

The latest QST has an excellent article by Rob Sherwood that should be a call to action on predistortion.  Hopefully the market will respond to this the way it did to Rob and the ARRL's focus on receiver performance over the last 10 - 15 years or so.  Some SSB signals I see during major contests look like the pyramids of Giza on the waterfall.  I know it will take a while to cycle all the old poor performing transmitters out of use once good ones begin to appear, but we will never get better if we don't start.  I would think predistortion would be a competitive advantage.

Keith - AC9S

Stan VA7NF

Some contesting stations (CW and SSB) intentionally produce dirty signals - because it keeps other stations away from "their" frequency resulting in better reception.
As long as there is an advantage of dirty signals taking "poor performing transmitters out of use" will not happen.  On CW it also makes a more noticeable signal, and in many cases more readable.

AC9S

Yeah - I know.  It is a really poor practice and I suppose if we were to be true to principle we would avoid working those guys - at least in S&P.

HCampbell WB4IVF

According to Flex noise mitigation and pre-distortion are #1 and #2 customer priorities, per Flex’s comments on the customer priority survey results: 

 “…. the survey was very helpful in revealing the relative importance of noise mitigation and pre-distortion. We have heard these messages loud and clear and have already begun discussions on next steps to make improvements in these areas of performance.”

 So there is light at the end of the tunnel for those of us who would like to see progress in these areas, although I’m still a bit disappointed that Automatic AGC-T in some form didn’t make the cut. 

Howard

Mark K1LSB

What "survey"?  I was never aware of any survey..

Bill -VA3WTB

Were have you been Mark, that is all people talked about for weeks on here. The survey Flex invited us to fill out?

Mark K1LSB

Let me repeat, what "survey"?  I received no invitation (or any notice at all, for that matter) from Flex or anyone else.

HCampbell WB4IVF

https://community.flexradio.com/flexradio/topics/did-you-take-the-flex-survey

Mark Erbaugh

I think contest organizers should recognize this practice and penalize this kind of behavior. Until they do, if a dirty signal gives a station an advantage, why wouldn’t a competitor have a dirty signal? After all, if your goal is to “win,” why wouldn’t you do everything within the rules (and even slightly beyond so long as you don’t get caught) to give yourself an edge?

TomWA1MBA

It has been quite a while (years) since activity on this topic, and I am reading it in late 2022. I feel like I'm missing something. So here are some questions to help me fill in my noobie gaps. 

1) Isn't there a difference between Pre Distortion and Adaptive Pre DIstortion? 

If the amplifier is known in advance, it seems like all transfer function parameters are internal and can be known except the changes due to output load.

2) Is output load variability the one and only (complex) variable that requires the "A" in APD? 

3) And, can't match be detected during tuning (at least in a fully Flex system) ? 

4) If so, then although the matrix becomes large, can't the amplifier characteristics be entirely formulated in advance (output vs. input IQ, DC biases, load, temperature) ? 

5) Are people miss-using APD to mean PD? 

6) Do people want the radio to somehow learn an added non-Flex amplifier?  (therefore to Adapt)

7) Do any 6000 series radios employ PD for their internal 100W PAs now? (from what I've read, the possibility to implement APD is designed in but not implemented. Fine. What abiut PD?)

7a) if No, then are they so linear as to be comparatively acceptable if not superior to other 100W radios on the market)

8) Does the Power Genius Amplifier, when connected to a 6000 series employ PD? (I have seen a mention of an "IMD Pre-corrector" in a review, and I'm aware of the harmonic diplexer load). I have not seen a specification of 2-tone IMD for the Power Genius.

And finally a comment rather than a question. Problematic IMD is so obvious on the waterfall. And when I hear /see it it's always (so far) been a solid state power amplifier. And in general not noticed on tube amplifiers unless the station is having ALC problems. Not seen on a 100W barefoot rig. Now that is just my observation. If I am at least 50% right, then it seems that a solid state Flex power amplifier should have IMD reduction circuits. And PD is a way to do it very well indeed.

Thanks for your attention.

AC9S

ICOM is stepping up. Isn't about time for Flex?

IC-7610 | Products | Icom Inc. (icomjapan.com)

Keith - AC9S

Mr Radio

More about IC 7610:

https://forums.qrz.com/index.php?threads/icom-ic-7610-adds-digital-pre-distortion.878480/

John K3MA

Gerald's first post in this thread was in January 2015. Almost 9 years ago. Think about it. 9 years of development and it still has not made the released software. Several of the Flex radios that were around then and he indicated were capable of implementing APD have now gone end of life.

Rob N4GA

Think about THIS 9 years later - nobody needs APD.

The radios themselves FAR exceed the distortion performance metrics. And if you can't design an amplifier that does as well, APD is not going to bale you out.

73

What amazing things have you accomplished in the last 9 years?

N4GA

Mark K1LSB

"Think about THIS 9 years later - nobody needs APD."

Guess again. Every operator who's running a strong signal adjacent to another QSO needs APD. Rob Sherwood himself has lamented lately that all of the Big Name manufacturers brag about how amazing their receivers are, yet none of them appear to give a hoot about the sorry state of their transmitters.

"The radios themselves FAR exceed the distortion performance metrics."

Exceed what 'distortion performance metrics', exactly? The cleanest transmitter Rob Sherwood has ever tested, an ancient Collins 32S-3, measured -39dB IMD3, and nothing built today can even match that...nothing, that is, except a transmitter running APD, which can easily beat the 32S-3 by at least an extra 20dB.

"And if you can't design an amplifier that does as well, APD is not going to bale you out."

Wrong again. My radio can easily correct for the distortion of any contemporary linear amplifier by simply using an RF sampler (available anywhere) to capture the amplifier's output and feed it back into the APD circuit in the radio.

Not meaning to be argumentative, just correcting a bunch of mis-statements.

Mark

Rob N4GA

No problem Mark, we'll just disagree.

First, this is Amateur Radio communication here. Most commonly SSB over HF, which by any real audio quality standard is garbage.

Knowing this, the FCC has NO spec for IMD, they instead suggest an acceptable bandwidth (3kHz). They however, do have an actual emission standard for harmonic distortion and this is -43dB from the fundamental.

So back to IMD - as long as your audio is not noticably distorted, AND your entire signal (all the IMDs) are inside the target BW (3kHz), that's all that is needed. You're officially not bleeding outside your BW.

And you can obtain this easily with the equipment that is currently on the market.

If you're overdriving your amp, using a really messy amp, or a really messy TX, then this is operator error.

Ever since APD was moved into the Amateur Radio arena by Apache Labs / Anan, that small group of users has taken on APD like a religion. Mostly because they were the only ones to have this so-called holy grail and nobody else did. Usually those people also have what they think are studio quality audio setups - all for really bad SSB audio quality. Pretty entertaining.

73

Rob

www.n4ga.com

W2PP

Well ICOM thinks APD is worth the effort as it will be included in their new linear amplifier. The amplifier is designed to work with the IC 7610.

Peter

David Decoons, wo2x

If the PW2 is like the PW1 then it REALLY needs APD. PW1 was a "dirty" amp, as were most of the MRF150 x 8 amps of the day. I've owned the PW-1, Yaesu Quadra, ALS1300.

Take a Yaesu FTdx-3000 and pair it with the Quadra. You wouldn't want to be receiving next to that with it running rated power out.

I find the Flex 6700 @ 14.6 volts and the PG XL run clean. Not APD clean but a lot cleaner than other compos of radios and amps on the market.

I had both the Anan 8000dle and original blue face 7000dle. Both were not clean without APD. Maybe choice of output devices or bias not set for optimal IMD? The 7000dle could not make rated power out (100 watts) on 12 meters. Max was 89 watts and power scale was not linear. I understand the newer Thetis software allows for better power calibration at multiple levels per band.

So, my take on APD is it is good to have to be a courteous neighbor but if you have a good radio and amp, plus have them set up correctly APD is not really necessary.

W2PP

I agree with you. I was just pointing out that ICOM is apparently going to use it.

Peter

David Decoons, wo2x

Well competition is good for the consumer.

I know the PW2 has been announced for a while. I bet they are in the same boat as other manufacturers with procuring parts.

73

Dave wo2x