Elecraft

Why predistortion ?

Classic

List

Threaded

36 messages Options

JHRichards

Why predistortion ?

Why are so many ops obsessed with predistortion?

The Elecraft K-Line already produces some of the cleanest, purest
transmit signals around. Do we need predistortion ? If so, why, and
how much better is it than what we already have? Should I wait to buy a
new rig until that is available?

Thanks and Happy Trails to all. K8JHR
_________________________________
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

wayne burdick

Re: Why predistortion ?

Administrator

Hi JR,

Virtually all class-AB-biased amplifier stages have worst-case 3rd-order IMD in the range of -30 dBc (ARRL method) on some HF bands. This reflects a limitation in the state of the art. Even with adequate feedback and bias, an amplifier operated in the vicinity of its 1 dB compression point (where it is most efficient) will exhibit such characteristics.

To improve on this you either need to operate class A, which is highly inefficient, or use predistortion.

A small number of commercial transceivers are now providing predistortion, in some cases as an optional/experimental setting (that not everyone uses, or at least not all the time). There are constraints on predistortion power range imposed by the headroom limit of the amplifier stage itself. Go over that point and distortion will be worse than without predistortion.

Predistortion, correctly applied, can reduce interference between adjacent stations on a crowded band. This is a factor at least some fraction of the time during typical amateur radio use. Beyond that, the motivation for a “pure“ signal exemplifies the amateur spirit of cooperation, and is an example of keeping the hobby on the forefront of electrical design.

Wayne,
N6KR

----
elecraft.com

> On Sep 13, 2020, at 2:34 PM, JR <[hidden email]> wrote:
>
> Why are so many ops obsessed with predistortion?
>
> The Elecraft K-Line already produces some of the cleanest, purest transmit signals around. Do we need predistortion ? If so, why, and how much better is it than what we already have? Should I wait to buy a new rig until that is available?
>
> Thanks and Happy Trails to all. K8JHR
> _________________________________
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Edward H Russell

Re: Why predistortion ?

Well put.

TKS,
73 ED W2RF

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of Wayne Burdick
Sent: Sunday, September 13, 2020 6:03 PM
To: JR <[hidden email]>
Cc: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

Hi JR,

Virtually all class-AB-biased amplifier stages have worst-case 3rd-order IMD in the range of -30 dBc (ARRL method) on some HF bands. This reflects a limitation in the state of the art. Even with adequate feedback and bias, an amplifier operated in the vicinity of its 1 dB compression point (where it is most efficient) will exhibit such characteristics.

To improve on this you either need to operate class A, which is highly inefficient, or use predistortion.

A small number of commercial transceivers are now providing predistortion, in some cases as an optional/experimental setting (that not everyone uses, or at least not all the time). There are constraints on predistortion power range imposed by the headroom limit of the amplifier stage itself. Go over that point and distortion will be worse than without predistortion.

Predistortion, correctly applied, can reduce interference between adjacent stations on a crowded band. This is a factor at least some fraction of the time during typical amateur radio use. Beyond that, the motivation for a “pure“ signal exemplifies the amateur spirit of cooperation, and is an example of keeping the hobby on the forefront of electrical design.

Wayne,
N6KR

----
elecraft.com

> On Sep 13, 2020, at 2:34 PM, JR <[hidden email]> wrote:
>
> Why are so many ops obsessed with predistortion?
>
> The Elecraft K-Line already produces some of the cleanest, purest transmit signals around. Do we need predistortion ? If so, why, and how much better is it than what we already have? Should I wait to buy a new rig until that is available?
>
> Thanks and Happy Trails to all. K8JHR
> _________________________________
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net Please help support this email
> list: http://www.qsl.net/donate.html Message delivered to
> [hidden email]

Randy Farmer-2

Re: Why predistortion ?

In reply to this post by wayne burdick

I can testify to the effectiveness of predistortion techniques from my 5
years or so as a CDMA Cellular Base Station engineer with Motorola. The
first generation of CDMA transmitters had a very specific "spectral
mask" that had to be certified. As I recall, the transmitter output that
met the Spectral Mask requirements of something like -60 dBc outside of
the channel bandwidth showed up with essentially vertical sides (and a
very flat top) on a spectrum analyzer. Obtaining this performance was
neither cheap nor easy, and the associated testing was pretty stringent
as well. Meeting the specs demanded very sophisticated predistortion
techniques. Be glad that conventional SSB and the fairly simple
waveforms used in amateur digital comms don't require too much dynamic
headroom. The first generation CDMA waveform had a roughly 10:1, or 20dB
peak-to-average power ratio. This meant that the transmitters we
designed to produce 20W average power were actually capable of 200W
continuous output power and still met the spectral mask IMD
requirements. Putting multiple carriers through the PA required either
higher power capability or derating the power output for each individual
carrier. I no longer work in the industry, so I don't know what the
current generation of signals requires, but with the greater bandwidths
and more complex modulation schemes used now you can bet the
requirements, and therefore the transmitter design challenge, didn't get
any easier.

73...
Randy, W8FN

On 9/13/2020 6:03 PM, Wayne Burdick wrote:

> Hi JR,
>
> Virtually all class-AB-biased amplifier stages have worst-case 3rd-order IMD in the range of -30 dBc (ARRL method) on some HF bands. This reflects a limitation in the state of the art. Even with adequate feedback and bias, an amplifier operated in the vicinity of its 1 dB compression point (where it is most efficient) will exhibit such characteristics.
>
> To improve on this you either need to operate class A, which is highly inefficient, or use predistortion.
>
> A small number of commercial transceivers are now providing predistortion, in some cases as an optional/experimental setting (that not everyone uses, or at least not all the time). There are constraints on predistortion power range imposed by the headroom limit of the amplifier stage itself. Go over that point and distortion will be worse than without predistortion.
>
> Predistortion, correctly applied, can reduce interference between adjacent stations on a crowded band. This is a factor at least some fraction of the time during typical amateur radio use. Beyond that, the motivation for a “pure“ signal exemplifies the amateur spirit of cooperation, and is an example of keeping the hobby on the forefront of electrical design.
>
> Wayne,
> N6KR
>
> ----
> elecraft.com

Wes Stewart-2

Re: Why predistortion ?

In reply to this post by JHRichards

You're kidding, right?

Wes N7WS

On 9/13/2020 2:32 PM, JR wrote:
> The Elecraft K-Line already produces some of the cleanest, purest transmit
> signals around....
>
> Thanks and Happy Trails to all. K8JHR

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

W2xj

Re: Why predistortion ?

In reply to this post by wayne burdick

wayne,

After you have the K4 fully put to bed, for your next project you might want to consider an amp that is directly driven by an I/Q stream. The amplifier will be much more efficient (less power consumption) and you start out with less IMD before any pre-distortion.

Sent from my iPad

> On Sep 13, 2020, at 6:05 PM, Wayne Burdick <[hidden email]> wrote:
>
> Hi JR,
>
> Virtually all class-AB-biased amplifier stages have worst-case 3rd-order IMD in the range of -30 dBc (ARRL method) on some HF bands. This reflects a limitation in the state of the art. Even with adequate feedback and bias, an amplifier operated in the vicinity of its 1 dB compression point (where it is most efficient) will exhibit such characteristics.
>
> To improve on this you either need to operate class A, which is highly inefficient, or use predistortion.
>
> A small number of commercial transceivers are now providing predistortion, in some cases as an optional/experimental setting (that not everyone uses, or at least not all the time). There are constraints on predistortion power range imposed by the headroom limit of the amplifier stage itself. Go over that point and distortion will be worse than without predistortion.
>
> Predistortion, correctly applied, can reduce interference between adjacent stations on a crowded band. This is a factor at least some fraction of the time during typical amateur radio use. Beyond that, the motivation for a “pure“ signal exemplifies the amateur spirit of cooperation, and is an example of keeping the hobby on the forefront of electrical design.
>
> Wayne,
> N6KR
>
> ----
> elecraft.com
>
>> On Sep 13, 2020, at 2:34 PM, JR <[hidden email]> wrote:
>>
>> Why are so many ops obsessed with predistortion?
>>
>> The Elecraft K-Line already produces some of the cleanest, purest transmit signals around. Do we need predistortion ? If so, why, and how much better is it than what we already have? Should I wait to buy a new rig until that is available?
>>
>> Thanks and Happy Trails to all. K8JHR
>> _________________________________
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

David Gilbert-2

Re: Why predistortion ?

In reply to this post by JHRichards

I don't know where you got the idea that the K-Line produces the
cleanest signals. As several people have pointed out, because of the 12
volt finals the transmit IMD performance of the existing K-line is
relatively poor.

Dave   AB7E

On 9/13/2020 2:32 PM, JR wrote:
> Why are so many ops obsessed with predistortion?
>
> The Elecraft K-Line already produces some of the cleanest, purest
> transmit signals around.   Do we need predistortion ? If so, why, and
> how much better is it than what we already have? Should I wait to buy
> a new rig until that is available?
>
> Thanks and Happy Trails to all.   K8JHR

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Bill Frantz

Re: Why predistortion ?

In reply to this post by wayne burdick

Wayne is right, it's the right thing to do. And we amateurs try
to produce the best signals we can. (Ignore the wide CW signals
during contests. :-) )

But the value will also show up during multi-op situations like
running 14A during field day. Field day is much more fun if
everyone gets a chance to operate.

73 Bill AE6JV

On 9/13/20 at 6:03 PM, [hidden email] (Wayne Burdick) wrote:

>Predistortion, correctly applied, can reduce interference
>between adjacent stations on a crowded band. This is a factor
>at least some fraction of the time during typical amateur radio
>use. Beyond that, the motivation for a “pure“ signal
>exemplifies the amateur spirit of cooperation, and is an
>example of keeping the hobby on the forefront of electrical design.

-----------------------------------------------------------------------
Bill Frantz | Privacy is dead, get over | Periwinkle
(408)348-7900 | it. | 150 Rivermead
Rd #235
www.pwpconsult.com | - Scott McNealy (1999) | Peterborough,
NH 03458

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

wayne burdick

Re: Why predistortion ?

Administrator

In reply to this post by David Gilbert-2

12 volts is a severe constraint for MOSFET PAs. But, like a lot of other manufacturers, we accept this constraint so the equipment can be used in a wide variety of portable/emergency power situations. As a result we have IMD numbers in exactly the same range as other products that are subject to this constraint.

On the other hand, our transceivers are best in class in terms of transmitted keying bandwidth. See paper by K9YC for example. Perhaps that's what JR was thinking of.

73,
Wayne
N6KR

> On Sep 13, 2020, at 6:50 PM, David Gilbert <[hidden email]> wrote:
>
>
> I don't know where you got the idea that the K-Line produces the cleanest signals. As several people have pointed out, because of the 12 volt finals the transmit IMD performance of the existing K-line is relatively poor.
>
> Dave AB7E
>
>
> On 9/13/2020 2:32 PM, JR wrote:
>> Why are so many ops obsessed with predistortion?
>>
>> The Elecraft K-Line already produces some of the cleanest, purest transmit signals around. Do we need predistortion ? If so, why, and how much better is it than what we already have? Should I wait to buy a new rig until that is available?
>>
>> Thanks and Happy Trails to all. K8JHR
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]

Charlie T, K3ICH

Re: Why predistortion ?

In reply to this post by David Gilbert-2

According to Rob Sherwood, the Collins 32S-3 produces the cleanest SSB signal on the air of any commercial amateur radio transmitters.

73, Charlie k3ICH

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of David Gilbert
Sent: Sunday, September 13, 2020 9:51 PM
To: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

I don't know where you got the idea that the K-Line produces the cleanest signals. As several people have pointed out, because of the 12 volt finals the transmit IMD performance of the existing K-line is relatively poor.

Dave AB7E

On 9/13/2020 2:32 PM, JR wrote:
> Why are so many ops obsessed with predistortion?
>
> The Elecraft K-Line already produces some of the cleanest, purest
> transmit signals around. Do we need predistortion ? If so, why, and
> how much better is it than what we already have? Should I wait to buy
> a new rig until that is available?
>
> Thanks and Happy Trails to all. K8JHR

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html Message delivered to [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Jim Brown-10

Re: Why predistortion ?

In reply to this post by JHRichards

On 9/13/2020 2:32 PM, JR wrote:
> The Elecraft K-Line already produces some of the cleanest, purest
> transmit signals around. Do we need predistortion ?

If you care about a clean signal, YES! If you don't mind being a bad
neighbor, no.

73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Jim Brown-10

Re: Why predistortion ?

In reply to this post by wayne burdick

On 9/13/2020 3:03 PM, Wayne Burdick wrote:
> Virtually all class-AB-biased amplifier stages have worst-case 3rd-order IMD in the range of -30 dBc (ARRL method) on some HF bands. This reflects a limitation in the state of the art.

I hope that this feature will be implemented for CW as well. CW is 100%
AM of a carrier by rectangular pulses, so any distortion in the transmit
chain results in clicks. Elecraft pioneered very clean keying waveforms;
it would be unfortunate for that to be lost with IMD in the power stages.

73, Jim K9YC
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

David Gilbert-2

Re: Why predistortion ?

In reply to this post by wayne burdick

Of course, but that's a conscious choice by Elecraft and it does not
result in the "cleanest, purest signals around." I give Elecraft tons
of credit for the other measures they have take to produce good signals,
which is why I own and will keep my upgraded K3 probably forever, but
K8JHR simply was incorrect in his comment and it makes a difference when
considering the expanding focus by folks like Sherwood and others to
clean up the bands. When it comes to IMD, Elecraft is not one of the
better players. The fact that that's by choice doesn't change
anything. I suspect that 95+% of K3 rigs are used in portable/emergency
situations less than 5% of the time.

73,
Dave AB7E

On 9/13/2020 7:14 PM, Wayne Burdick wrote:

> 12 volts is a severe constraint for MOSFET PAs. But, like a lot of other manufacturers, we accept this constraint so the equipment can be used in a wide variety of portable/emergency power situations. As a result we have IMD numbers in exactly the same range as other products that are subject to this constraint.
>
> On the other hand, our transceivers are best in class in terms of transmitted keying bandwidth. See paper by K9YC for example. Perhaps that's what JR was thinking of.
>
> 73,
> Wayne
> N6KR
>
>
>
>> On Sep 13, 2020, at 6:50 PM, David Gilbert <[hidden email]> wrote:
>>
>>
>> I don't know where you got the idea that the K-Line produces the cleanest signals. As several people have pointed out, because of the 12 volt finals the transmit IMD performance of the existing K-line is relatively poor.
>>
>> Dave AB7E
>>
>>
>> On 9/13/2020 2:32 PM, JR wrote:
>>> Why are so many ops obsessed with predistortion?
>>>
>>> The Elecraft K-Line already produces some of the cleanest, purest transmit signals around. Do we need predistortion ? If so, why, and how much better is it than what we already have? Should I wait to buy a new rig until that is available?
>>>
>>> Thanks and Happy Trails to all. K8JHR
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [hidden email]

Charlie T, K3ICH

Re: Why predistortion ?

Maybe I'm missing something here, but it would seem to me that if an FET linear amplifier running from 50 V or higher is considerably cleaner than one running from 12 V, that, for a high end rig, a simple step-up switching supply could solve the problem. But, that obviously adds to the cost so it IS somewhat of a conundrum.

However, implementing the pre-distortion function IS probably a better long-term solution.

73, Charlie k3ICH

-----Original Message-----
From: [hidden email] <[hidden email]> On Behalf Of David Gilbert
Sent: Monday, September 14, 2020 12:43 AM
To: Elecraft Reflector <[hidden email]>
Subject: Re: [Elecraft] Why predistortion ?

Of course, but that's a conscious choice by Elecraft and it does not result in the "cleanest, purest signals around." I give Elecraft tons of credit for the other measures they have take to produce good signals, which is why I own and will keep my upgraded K3 probably forever, but K8JHR simply was incorrect in his comment and it makes a difference when considering the expanding focus by folks like Sherwood and others to clean up the bands. When it comes to IMD, Elecraft is not one of the better players. The fact that that's by choice doesn't change anything. I suspect that 95+% of K3 rigs are used in portable/emergency situations less than 5% of the time.

73,
Dave AB7E

On 9/13/2020 7:14 PM, Wayne Burdick wrote:

> 12 volts is a severe constraint for MOSFET PAs. But, like a lot of other manufacturers, we accept this constraint so the equipment can be used in a wide variety of portable/emergency power situations. As a result we have IMD numbers in exactly the same range as other products that are subject to this constraint.
>
> On the other hand, our transceivers are best in class in terms of transmitted keying bandwidth. See paper by K9YC for example. Perhaps that's what JR was thinking of.
>
> 73,
> Wayne
> N6KR
>
>
>
>> On Sep 13, 2020, at 6:50 PM, David Gilbert <[hidden email]> wrote:
>>
>>
>> I don't know where you got the idea that the K-Line produces the cleanest signals. As several people have pointed out, because of the 12 volt finals the transmit IMD performance of the existing K-line is relatively poor.
>>
>> Dave AB7E
>>
>>
>> On 9/13/2020 2:32 PM, JR wrote:
>>> Why are so many ops obsessed with predistortion?
>>>
>>> The Elecraft K-Line already produces some of the cleanest, purest transmit signals around. Do we need predistortion ? If so, why, and how much better is it than what we already have? Should I wait to buy a new rig until that is available?
>>>
>>> Thanks and Happy Trails to all. K8JHR
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net Please help support this
>> email list: http://www.qsl.net/donate.html Message delivered to
>> [hidden email]

Dr. William J. Schmidt, II

Re: Why predistortion ?

In reply to this post by Charlie T, K3ICH

6AU6 - 6CL6 - 6146A trio is a very and associated circuitry produces some of
the lowest distortion products when run at the right conditions (voltages,
etc). Note at 75 watts the 6146 is in its sweet spot.

Dr. William J. Schmidt - K9HZ

email: [hidden email]

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Charlie T
Sent: Sunday, September 13, 2020 9:42 PM
To: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

According to Rob Sherwood, the Collins 32S-3 produces the cleanest SSB
signal on the air of any commercial amateur radio transmitters.

73, Charlie k3ICH

-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of David Gilbert
Sent: Sunday, September 13, 2020 9:51 PM
To: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

I don't know where you got the idea that the K-Line produces the cleanest
signals. As several people have pointed out, because of the 12 volt finals
the transmit IMD performance of the existing K-line is relatively poor.

Dave AB7E

On 9/13/2020 2:32 PM, JR wrote:
> Why are so many ops obsessed with predistortion?
>
> The Elecraft K-Line already produces some of the cleanest, purest
> transmit signals around. Do we need predistortion ? If so, why, and
> how much better is it than what we already have? Should I wait to buy
> a new rig until that is available?
>
> Thanks and Happy Trails to all. K8JHR

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html Message
delivered to [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html Message
delivered to [hidden email]

--
This email has been checked for viruses by AVG.
https://www.avg.com

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Dr. William J. Schmidt, II

Re: Why predistortion ?

In reply to this post by Charlie T, K3ICH

Always tradeoffs to be made. Boosting 12V volts to 50V means some sort of
converter that can add its own distortion products, plus expense and
additional complexity (read that "reliability") and efficiency. There's no
free lunch here.

Dr. William J. Schmidt - K9HZ J68HZ

email: [hidden email]

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Charlie T
Sent: Monday, September 14, 2020 6:30 AM
To: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

Maybe I'm missing something here, but it would seem to me that if an FET
linear amplifier running from 50 V or higher is considerably cleaner than
one running from 12 V, that, for a high end rig, a simple step-up switching
supply could solve the problem. But, that obviously adds to the cost so it
IS somewhat of a conundrum.

However, implementing the pre-distortion function IS probably a better
long-term solution.

73, Charlie k3ICH

-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of David Gilbert
Sent: Monday, September 14, 2020 12:43 AM
To: Elecraft Reflector <[hidden email]>
Subject: Re: [Elecraft] Why predistortion ?

Of course, but that's a conscious choice by Elecraft and it does not result
in the "cleanest, purest signals around." I give Elecraft tons of credit
for the other measures they have take to produce good signals, which is why
I own and will keep my upgraded K3 probably forever, but K8JHR simply was
incorrect in his comment and it makes a difference when considering the
expanding focus by folks like Sherwood and others to clean up the bands.
When it comes to IMD, Elecraft is not one of the better players. The fact
that that's by choice doesn't change anything. I suspect that 95+% of K3
rigs are used in portable/emergency situations less than 5% of the time.

73,
Dave AB7E

On 9/13/2020 7:14 PM, Wayne Burdick wrote:
> 12 volts is a severe constraint for MOSFET PAs. But, like a lot of other
manufacturers, we accept this constraint so the equipment can be used in a
wide variety of portable/emergency power situations. As a result we have IMD
numbers in exactly the same range as other products that are subject to this
constraint.
>
> On the other hand, our transceivers are best in class in terms of
transmitted keying bandwidth. See paper by K9YC for example. Perhaps that's
what JR was thinking of.

>
> 73,
> Wayne
> N6KR
>
>
>
>> On Sep 13, 2020, at 6:50 PM, David Gilbert <[hidden email]> wrote:
>>
>>
>> I don't know where you got the idea that the K-Line produces the cleanest

signals. As several people have pointed out, because of the 12 volt finals
the transmit IMD performance of the existing K-line is relatively poor.
>>
>> Dave AB7E
>>
>>
>> On 9/13/2020 2:32 PM, JR wrote:
>>> Why are so many ops obsessed with predistortion?
>>>
>>> The Elecraft K-Line already produces some of the cleanest, purest
transmit signals around. Do we need predistortion ? If so, why, and how
much better is it than what we already have? Should I wait to buy a new rig
until that is available?

>>>
>>> Thanks and Happy Trails to all. K8JHR
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net Please help support this
>> email list: http://www.qsl.net/donate.html Message delivered to
>> [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html Message
delivered to [hidden email]

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html Message
delivered to [hidden email]

--
This email has been checked for viruses by AVG.
https://www.avg.com

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Joe Subich, W4TV-4

Re: Why predistortion ?

In reply to this post by Charlie T, K3ICH

On 2020-09-14 7:29 AM, Charlie T wrote:
>
> However, implementing the pre-distortion function IS probably a
> better long-term solution.

Pre-distortion on a 12V rig only hides the problem. Any "home
station" rig should have 28/50 V finals *and* then one can make
it even cleaner with pre-distortion. If necessary, use 50V
capable finals at 50W maximum output for 12V operation and
150-200 W output when a 48V supply is available.

73,

... Joe, W4TV

On 2020-09-14 7:29 AM, Charlie T wrote:

> Maybe I'm missing something here, but it would seem to me that if an FET linear amplifier running from 50 V or higher is considerably cleaner than one running from 12 V, that, for a high end rig, a simple step-up switching supply could solve the problem. But, that obviously adds to the cost so it IS somewhat of a conundrum.
>
> However, implementing the pre-distortion function IS probably a better long-term solution.
>
> 73, Charlie k3ICH
>
>
>
>
> -----Original Message-----
> From: [hidden email] <[hidden email]> On Behalf Of David Gilbert
> Sent: Monday, September 14, 2020 12:43 AM
> To: Elecraft Reflector <[hidden email]>
> Subject: Re: [Elecraft] Why predistortion ?
>
>
>
> Of course, but that's a conscious choice by Elecraft and it does not result in the "cleanest, purest signals around." I give Elecraft tons of credit for the other measures they have take to produce good signals, which is why I own and will keep my upgraded K3 probably forever, but K8JHR simply was incorrect in his comment and it makes a difference when considering the expanding focus by folks like Sherwood and others to clean up the bands. When it comes to IMD, Elecraft is not one of the better players. The fact that that's by choice doesn't change anything. I suspect that 95+% of K3 rigs are used in portable/emergency situations less than 5% of the time.
>
> 73,
> Dave AB7E
>
>
>
> On 9/13/2020 7:14 PM, Wayne Burdick wrote:
>> 12 volts is a severe constraint for MOSFET PAs. But, like a lot of other manufacturers, we accept this constraint so the equipment can be used in a wide variety of portable/emergency power situations. As a result we have IMD numbers in exactly the same range as other products that are subject to this constraint.
>>
>> On the other hand, our transceivers are best in class in terms of transmitted keying bandwidth. See paper by K9YC for example. Perhaps that's what JR was thinking of.
>>
>> 73,
>> Wayne
>> N6KR
>>
>>
>>
>>> On Sep 13, 2020, at 6:50 PM, David Gilbert <[hidden email]> wrote:
>>>
>>>
>>> I don't know where you got the idea that the K-Line produces the cleanest signals. As several people have pointed out, because of the 12 volt finals the transmit IMD performance of the existing K-line is relatively poor.
>>>
>>> Dave AB7E
>>>
>>>
>>> On 9/13/2020 2:32 PM, JR wrote:
>>>> Why are so many ops obsessed with predistortion?
>>>>
>>>> The Elecraft K-Line already produces some of the cleanest, purest transmit signals around. Do we need predistortion ? If so, why, and how much better is it than what we already have? Should I wait to buy a new rig until that is available?
>>>>
>>>> Thanks and Happy Trails to all. K8JHR

Leroy

Re: Why predistortion ?

In reply to this post by Dr. William J. Schmidt, II

DC to DC is used in video and RF frequency, over 50 years I know of,all the
time to get away from 60hz and other design nonlinearities.

Retired NIST DC to 18GHz lab tech

AB7CE Roy

-----Original Message-----
From: Dr. William J. Schmidt
Sent: Monday, September 14, 2020 10:05 AM
To: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

Always tradeoffs to be made. Boosting 12V volts to 50V means some sort of
converter that can add its own distortion products, plus expense and
additional complexity (read that "reliability") and efficiency. There's no
free lunch here.

Dr. William J. Schmidt - K9HZ J68HZ

email: [hidden email]

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Charlie T
Sent: Monday, September 14, 2020 6:30 AM
To: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

Maybe I'm missing something here, but it would seem to me that if an FET
linear amplifier running from 50 V or higher is considerably cleaner than
one running from 12 V, that, for a high end rig, a simple step-up switching
supply could solve the problem. But, that obviously adds to the cost so it
IS somewhat of a conundrum.

However, implementing the pre-distortion function IS probably a better
long-term solution.

73, Charlie k3ICH

-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of David Gilbert
Sent: Monday, September 14, 2020 12:43 AM
To: Elecraft Reflector <[hidden email]>
Subject: Re: [Elecraft] Why predistortion ?

Of course, but that's a conscious choice by Elecraft and it does not result
in the "cleanest, purest signals around." I give Elecraft tons of credit
for the other measures they have take to produce good signals, which is why
I own and will keep my upgraded K3 probably forever, but K8JHR simply was
incorrect in his comment and it makes a difference when considering the
expanding focus by folks like Sherwood and others to clean up the bands.
When it comes to IMD, Elecraft is not one of the better players. The fact
that that's by choice doesn't change anything. I suspect that 95+% of K3
rigs are used in portable/emergency situations less than 5% of the time.

73,
Dave AB7E

On 9/13/2020 7:14 PM, Wayne Burdick wrote:
> 12 volts is a severe constraint for MOSFET PAs. But, like a lot of other
manufacturers, we accept this constraint so the equipment can be used in a
wide variety of portable/emergency power situations. As a result we have IMD
numbers in exactly the same range as other products that are subject to this
constraint.
>
> On the other hand, our transceivers are best in class in terms of
transmitted keying bandwidth. See paper by K9YC for example. Perhaps that's
what JR was thinking of.

>
> 73,
> Wayne
> N6KR
>
>
>
>> On Sep 13, 2020, at 6:50 PM, David Gilbert <[hidden email]> wrote:
>>
>>
>> I don't know where you got the idea that the K-Line produces the cleanest

Elecraft mailing list

Re: Why predistortion ?

In reply to this post by JHRichards

Pre-distortion is often used in modern cellular base-station
transmiters, and perhaps digital broadcast systems where they have to
handle multiple carriers simultaneously, "at power".

It dramatically reduces transmitted intermodulation to very low levels,
allowing such multi carrier systems to co-exist very close to each
other, improving the reception of the base station by the mobile/handset
device. (Lower Bit Error Rate numbers.) Without spending mega bucks
for a PA system grossly over rated and inefficient, just to stay in it's
very linear region, well below the 1dB compression point! (As was
common not that long ago.)

As mobile phones these days are also almost all SDR in nature, even they
may apply pre-distortion to their TX signal, for the same reason.
Smaller lower cost and lower power consumption PA, but keeping it clean.

"Docherty Amplifier" systems are also often used in other cases, where a
clean low power class A amp in effect "corrects" the output of a much
more powerful, more efficient but not as linear (class B) amplifier by
means of a combiner, dynamically adding or subtracting "signal" as
needed in analogue real-time. (Crude over simplification!)

The techniques are as yet not common in Amateur circles, but are
becoming widely used in several commercial scenarios, so it is only a
matter of time... As more and more mainstream radio transceivers adopt
SDR principles in both RX and TX paths, the cost savings at the high
power stages become significant, once the software is developed and
fully engineered.

73.

Dave G0WBX.

On 14/09/2020 17:00, [hidden email] wrote:
> Re: [Elecraft] Why predistortion ?

--
Created on and sent from a Unix like PC running and using free and open source software:

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Dr. William J. Schmidt, II

Re: Why predistortion ?

In reply to this post by Leroy

I don't think anyone said it can't be done or hasn't been done before. It
has. But you can't ignore the cost, reliability/ complexity, efficiency
(power and signal) of the changes. For those of us that have actually had
to design and implement circuit changes like this at the commercial level,
it sounds trivial but that is simply not reality.

Dr. William J. Schmidt - K9HZ J68HZ

email: [hidden email]

-----Original Message-----
From: lmarion [mailto:[hidden email]]
Sent: Monday, September 14, 2020 11:32 AM
To: Dr. William J. Schmidt <[hidden email]>; [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

DC to DC is used in video and RF frequency, over 50 years I know of,all the
time to get away from 60hz and other design nonlinearities.

Retired NIST DC to 18GHz lab tech

AB7CE Roy

-----Original Message-----
From: Dr. William J. Schmidt
Sent: Monday, September 14, 2020 10:05 AM
To: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

Always tradeoffs to be made. Boosting 12V volts to 50V means some sort of
converter that can add its own distortion products, plus expense and
additional complexity (read that "reliability") and efficiency. There's no
free lunch here.

Dr. William J. Schmidt - K9HZ J68HZ

email: [hidden email]

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Charlie T
Sent: Monday, September 14, 2020 6:30 AM
To: [hidden email]
Subject: Re: [Elecraft] Why predistortion ?

Maybe I'm missing something here, but it would seem to me that if an FET
linear amplifier running from 50 V or higher is considerably cleaner than
one running from 12 V, that, for a high end rig, a simple step-up switching
supply could solve the problem. But, that obviously adds to the cost so it
IS somewhat of a conundrum.

However, implementing the pre-distortion function IS probably a better
long-term solution.

73, Charlie k3ICH

-----Original Message-----
From: [hidden email] <[hidden email]> On
Behalf Of David Gilbert
Sent: Monday, September 14, 2020 12:43 AM
To: Elecraft Reflector <[hidden email]>
Subject: Re: [Elecraft] Why predistortion ?

Of course, but that's a conscious choice by Elecraft and it does not result
in the "cleanest, purest signals around." I give Elecraft tons of credit
for the other measures they have take to produce good signals, which is why
I own and will keep my upgraded K3 probably forever, but K8JHR simply was
incorrect in his comment and it makes a difference when considering the
expanding focus by folks like Sherwood and others to clean up the bands.
When it comes to IMD, Elecraft is not one of the better players. The fact
that that's by choice doesn't change anything. I suspect that 95+% of K3
rigs are used in portable/emergency situations less than 5% of the time.

73,
Dave AB7E

On 9/13/2020 7:14 PM, Wayne Burdick wrote:
> 12 volts is a severe constraint for MOSFET PAs. But, like a lot of
> other
manufacturers, we accept this constraint so the equipment can be used in a
wide variety of portable/emergency power situations. As a result we have IMD
numbers in exactly the same range as other products that are subject to this
constraint.
>
> On the other hand, our transceivers are best in class in terms of
transmitted keying bandwidth. See paper by K9YC for example. Perhaps that's
what JR was thinking of.

>
> 73,
> Wayne
> N6KR
>
>
>
>> On Sep 13, 2020, at 6:50 PM, David Gilbert <[hidden email]> wrote:
>>
>>
>> I don't know where you got the idea that the K-Line produces the
>> cleanest