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K3: 630m amplifiers

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Edward R Cole

K3: 630m amplifiers

With the recent expansion of use to 630m for the K3s and upgraded K3
which only transmit at nom 1mw, a question arises:

Is there interest in a linear amplifier taking 1mw drive to produce
either 25w or 100w?

I pick those two power outputs because with typically inefficient
antennas on 630m 25w => 1w ERP and 100w => 5w ERP (approx). These
two ERP are mentioned in the WARC-12 band approval and FCC as
possible max allowed power levels. Currently the ARRL Experimental
Group is approved at 20w ERP but there are not many stations running
that in the group. I run 100w with 0.1mw drive from my K3 for approx
3w ERP. 1mw is typical output for mixers so the amp would be usable
by low-power transverters, as well.

I am wondering what kind of interest there would be for a linear amp
that could be driven by the K3s/K3? I would probably have an
optional Rx preamp in such a package. No idea of cost at this
juncture as its just in "maybe status". Wayne has stated to me that
Elecraft is not intending to build such due to the limited market.

73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[hidden email]

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Tom Azlin W7SUA

Re: K3: 630m amplifiers

Hi Ed.

I am more interested in a non-linear class C or higher amp for those
bands as was not thinking to run modes that need a linear amp. WSPR, a
WSJT mode, WSQ, and the like.

73, tom w7sua
Chino Valley AZ

On 7/26/2015 1:23 PM, Edward R Cole wrote:

> With the recent expansion of use to 630m for the K3s and upgraded K3
> which only transmit at nom 1mw, a question arises:
>
> Is there interest in a linear amplifier taking 1mw drive to produce
> either 25w or 100w?
>
> I pick those two power outputs because with typically inefficient
> antennas on 630m 25w => 1w ERP and 100w => 5w ERP (approx). These two
> ERP are mentioned in the WARC-12 band approval and FCC as possible max
> allowed power levels. Currently the ARRL Experimental Group is approved
> at 20w ERP but there are not many stations running that in the group. I
> run 100w with 0.1mw drive from my K3 for approx 3w ERP. 1mw is typical
> output for mixers so the amp would be usable by low-power transverters,
> as well.
>
> I am wondering what kind of interest there would be for a linear amp
> that could be driven by the K3s/K3? I would probably have an optional
> Rx preamp in such a package. No idea of cost at this juncture as its
> just in "maybe status". Wayne has stated to me that Elecraft is not
> intending to build such due to the limited market.
>
> 73, Ed - KL7UW
> http://www.kl7uw.com
> "Kits made by KL7UW"
> Dubus Mag business:
> [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
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>
>

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Don Wilhelm-4

Re: K3: 630m amplifiers

Tom,

Soundcard sourced digital modes are really SSB signals and need a linear
amplifier.

73,
Don W3FPR

On 7/26/2015 8:25 PM, Tom Azlin W7SUA wrote:

> Hi Ed.
>
> I am more interested in a non-linear class C or higher amp for those
> bands as was not thinking to run modes that need a linear amp. WSPR, a
> WSJT mode, WSQ, and the like.
>
> 73, tom w7sua
> Chino Valley AZ
>
> On 7/26/2015 1:23 PM, Edward R Cole wrote:
>> With the recent expansion of use to 630m for the K3s and upgraded K3
>> which only transmit at nom 1mw, a question arises:
>>
>> Is there interest in a linear amplifier taking 1mw drive to produce
>> either 25w or 100w?

Alan Bloom

Re: K3: 630m amplifiers

On 07/26/2015 05:32 PM, Don Wilhelm wrote:

> Soundcard sourced digital modes are really SSB signals and need a linear
> amplifier.

The one exception might be FSK. It is constant-amplitude so a class C
amplifier should be fine.

FSK modes include RTTY and I believe WSPR and WSJT.

Alan N1AL
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Joe Subich, W4TV-4

Re: K3: 630m amplifiers

In reply to this post by Don Wilhelm-4

Don,

WSPR, JT65 and JT9 are (1 of N tone) FSK modes. They are no
different than conventional AFSK (1 of 2) in that the tones
are continuous phase, constant amplitude and can be amplified
by a class C amplifier without generating undue IMD or clicks.

I haven't seen the details of WSQ yet - if it is a multiple
simultaneous tone mode it would require a linear amplifier -
but the other listed "sound card" modes are fine with an
amplifier that operates in class C (or even a switch mode
amplifier so long as the bandpass filter is sufficient).

73,

... Joe, W4TV

On 2015-07-26 8:32 PM, Don Wilhelm wrote:

> Tom,
>
> Soundcard sourced digital modes are really SSB signals and need a linear
> amplifier.
>
> 73,
> Don W3FPR
>
> On 7/26/2015 8:25 PM, Tom Azlin W7SUA wrote:
>> Hi Ed.
>>
>> I am more interested in a non-linear class C or higher amp for those
>> bands as was not thinking to run modes that need a linear amp. WSPR, a
>> WSJT mode, WSQ, and the like.
>>
>> 73, tom w7sua
>> Chino Valley AZ
>>
>> On 7/26/2015 1:23 PM, Edward R Cole wrote:
>>> With the recent expansion of use to 630m for the K3s and upgraded K3
>>> which only transmit at nom 1mw, a question arises:
>>>
>>> Is there interest in a linear amplifier taking 1mw drive to produce
>>> either 25w or 100w?
>
> ______________________________________________________________
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Dave-7

Re: K3: 630m amplifiers

Do we run into the FCC external amplifier 15 dB gain limit here?

73 de dave
ab9ca/4

On 7/26/15 7:51 PM, Joe Subich, W4TV wrote:

>
> Don,
>
> WSPR, JT65 and JT9 are (1 of N tone) FSK modes. They are no
> different than conventional AFSK (1 of 2) in that the tones
> are continuous phase, constant amplitude and can be amplified
> by a class C amplifier without generating undue IMD or clicks.
>
> I haven't seen the details of WSQ yet - if it is a multiple
> simultaneous tone mode it would require a linear amplifier -
> but the other listed "sound card" modes are fine with an
> amplifier that operates in class C (or even a switch mode
> amplifier so long as the bandpass filter is sufficient).
>
> 73,
>
> ... Joe, W4TV
>
>
> On 2015-07-26 8:32 PM, Don Wilhelm wrote:
>> Tom,
>>
>> Soundcard sourced digital modes are really SSB signals and need a
>> linear
>> amplifier.
>>
>> 73,
>> Don W3FPR
>>
>> On 7/26/2015 8:25 PM, Tom Azlin W7SUA wrote:
>>> Hi Ed.
>>>
>>> I am more interested in a non-linear class C or higher amp for those
>>> bands as was not thinking to run modes that need a linear amp. WSPR, a
>>> WSJT mode, WSQ, and the like.
>>>
>>> 73, tom w7sua
>>> Chino Valley AZ
>>>
>>> On 7/26/2015 1:23 PM, Edward R Cole wrote:
>>>> With the recent expansion of use to 630m for the K3s and upgraded K3
>>>> which only transmit at nom 1mw, a question arises:
>>>>
>>>> Is there interest in a linear amplifier taking 1mw drive to produce
>>>> either 25w or 100w?
>>
>> ______________________________________________________________
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>>
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Tom Azlin W7SUA

Re: K3: 630m amplifiers

In reply to this post by Alan Bloom

Hi Don and Alan,

I was thinking one of the slow multi tone FSK modes that are a single
tone at a time. WSQ is in the same class.

http://www.qsl.net/zl1bpu/SOFT/WSQ.htm

CW would be another mode that would not need a linear amp I think.

On the other hand PSK31 would require a linear amp.

73, tom w7sua

On 7/26/2015 5:43 PM, Alan wrote:

> On 07/26/2015 05:32 PM, Don Wilhelm wrote:
>
>> Soundcard sourced digital modes are really SSB signals and need a linear
>> amplifier.
>
> The one exception might be FSK. It is constant-amplitude so a class C
> amplifier should be fine.
>
> FSK modes include RTTY and I believe WSPR and WSJT.
>
> Alan N1AL
> ______________________________________________________________
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>

Tom Azlin W7SUA

Re: K3: 630m amplifiers

In reply to this post by Dave-7

Not if you build your own is my understanding!

73, tom w7sua

On 7/26/2015 5:56 PM, dave wrote:

>
> Do we run into the FCC external amplifier 15 dB gain limit here?
>
> 73 de dave
> ab9ca/4
>
>
>
> On 7/26/15 7:51 PM, Joe Subich, W4TV wrote:
>>
>> Don,
>>
>> WSPR, JT65 and JT9 are (1 of N tone) FSK modes. They are no
>> different than conventional AFSK (1 of 2) in that the tones
>> are continuous phase, constant amplitude and can be amplified
>> by a class C amplifier without generating undue IMD or clicks.
>>
>> I haven't seen the details of WSQ yet - if it is a multiple
>> simultaneous tone mode it would require a linear amplifier -
>> but the other listed "sound card" modes are fine with an
>> amplifier that operates in class C (or even a switch mode
>> amplifier so long as the bandpass filter is sufficient).
>>
>> 73,
>>
>> ... Joe, W4TV
>>
>>
>> On 2015-07-26 8:32 PM, Don Wilhelm wrote:
>>> Tom,
>>>
>>> Soundcard sourced digital modes are really SSB signals and need a
>>> linear
>>> amplifier.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> On 7/26/2015 8:25 PM, Tom Azlin W7SUA wrote:
>>>> Hi Ed.
>>>>
>>>> I am more interested in a non-linear class C or higher amp for those
>>>> bands as was not thinking to run modes that need a linear amp. WSPR, a
>>>> WSJT mode, WSQ, and the like.
>>>>
>>>> 73, tom w7sua
>>>> Chino Valley AZ
>>>>
>>>> On 7/26/2015 1:23 PM, Edward R Cole wrote:
>>>>> With the recent expansion of use to 630m for the K3s and upgraded K3
>>>>> which only transmit at nom 1mw, a question arises:
>>>>>
>>>>> Is there interest in a linear amplifier taking 1mw drive to produce
>>>>> either 25w or 100w?
>>>
>>> ______________________________________________________________
>>> Elecraft mailing list
>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>> Help: http://mailman.qth.net/mmfaq.htm
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>>> Please help support this email list: http://www.qsl.net/donate.html
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>>>
>> ______________________________________________________________
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Jim Brown-10

Re: K3: 630m amplifiers

In reply to this post by Tom Azlin W7SUA

Hi Tom,

It's convenient to think that, but it's wrong. The problem is that
neither of those signals are continuous -- both are changed to convey
information. Mother nature recognizes a keyed CW waveform as a square
wave modulating a carrier. Any waveform more complicated than a
continuous carrier has multiple components, and in the case of a square
wave or impulse, an infinite number of them. If that waveform is passed
through a non-linear amplifier, distortion will be produced. There will
be both harmonic and intermodulation distortion.

Take a look at slides 13 and 15 in http://k9yc.com/FTDX5000_Report.pdf.
Slide 13 is a continuous carrier. The sidebands at -48dBC are probably
hum. Now look at Slide 15, which is the same radio transmitting a series
of dits.

I haven't measured an un-keyed K3 yet, but I suspect it's cleaner,
especially with the new synth board. I may get to that this week.

Several years ago, some of the serious engineers running RTTY noticed
that the K3 running FSK wasn't as clean as when running AFSK. Wayne and
the crew did some serious work on the firmware and it's now better.

73, Jim K9YC

On Sun,7/26/2015 6:57 PM, Tom Azlin W7SUA wrote:
> I was thinking one of the slow multi tone FSK modes that are a single
> tone at a time. WSQ is in the same class.
>
> http://www.qsl.net/zl1bpu/SOFT/WSQ.htm
>
> CW would be another mode that would not need a linear amp I think.

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Alan Bloom

Re: K3: 630m amplifiers

In reply to this post by Tom Azlin W7SUA

> CW would be another mode that would not need a linear amp I think.

No, CW requires a linear amplifier. CW is not constant-amplitude - the
amplitude changes every time you open or close the key. A class-C
amplifier would mess up the key shaping, causing key clicks.

Any true FSK or MSK signal should not be bothered by a non-linear
amplifier. The only caveat I can think of is that the amplitude of an
AFSK signal may have some ripple on it to the extent that the passband
of the transmit crystal filter is not flat. But I doubt that's a
significant issue.

Alan N1AL

On 07/26/2015 06:57 PM, Tom Azlin W7SUA wrote:

> Hi Don and Alan,
>
> I was thinking one of the slow multi tone FSK modes that are a single
> tone at a time. WSQ is in the same class.
>
> http://www.qsl.net/zl1bpu/SOFT/WSQ.htm
>
> CW would be another mode that would not need a linear amp I think.
>
> On the other hand PSK31 would require a linear amp.
>
> 73, tom w7sua
>
> On 7/26/2015 5:43 PM, Alan wrote:
>> On 07/26/2015 05:32 PM, Don Wilhelm wrote:
>>
>>> Soundcard sourced digital modes are really SSB signals and need a linear
>>> amplifier.
>>
>> The one exception might be FSK. It is constant-amplitude so a class C
>> amplifier should be fine.
>>
>> FSK modes include RTTY and I believe WSPR and WSJT.
>>
>> Alan N1AL
>> ______________________________________________________________
>> Elecraft mailing list
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>>
>>
>
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wayne burdick

Re: K3: 630m amplifiers

Administrator

CW also requires a highly stable ALC system, without unwanted dynamics, to preserve ideal envelope shaping. This is lacking on some all-mode rigs that pay little attention to CW.

Wayne
N6KR

On Jul 26, 2015, at 9:32 PM, Alan <[hidden email]> wrote:

>
> > CW would be another mode that would not need a linear amp I think.
>
> No, CW requires a linear amplifier. CW is not constant-amplitude - the amplitude changes every time you open or close the key. A class-C amplifier would mess up the key shaping, causing key clicks.
>
> Any true FSK or MSK signal should not be bothered by a non-linear amplifier. The only caveat I can think of is that the amplitude of an AFSK signal may have some ripple on it to the extent that the passband of the transmit crystal filter is not flat. But I doubt that's a significant issue.
>
> Alan N1AL
>
>
>
> On 07/26/2015 06:57 PM, Tom Azlin W7SUA wrote:
>> Hi Don and Alan,
>>
>> I was thinking one of the slow multi tone FSK modes that are a single
>> tone at a time. WSQ is in the same class.
>>
>> http://www.qsl.net/zl1bpu/SOFT/WSQ.htm
>>
>> CW would be another mode that would not need a linear amp I think.
>>
>> On the other hand PSK31 would require a linear amp.
>>
>> 73, tom w7sua
>>
>> On 7/26/2015 5:43 PM, Alan wrote:
>>> On 07/26/2015 05:32 PM, Don Wilhelm wrote:
>>>
>>>> Soundcard sourced digital modes are really SSB signals and need a linear
>>>> amplifier.
>>>
>>> The one exception might be FSK. It is constant-amplitude so a class C
>>> amplifier should be fine.
>>>
>>> FSK modes include RTTY and I believe WSPR and WSJT.
>>>
>>> Alan N1AL
>>> ______________________________________________________________
>>> 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]
>>>
>>>
>>
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Fausto Coletti

Re: K3: 630m amplifiers

In reply to this post by Edward R Cole

It depends on how you made the amplifier.
I produce some models of amplifiers, of different powers, all in switching
operation.
Here an image of the DK7FC grabber, you can see at 472.1 KHz the
spectrogram of
a German station that use a class D amplifier, at 472.5 an Italian station
that use a 400W
tube linear amplifier and at 473.3 there is my signal with my QRO+ switching
PA.

https://www.dropbox.com/s/oziocm3vshfftgl/19012015.JPG?dl=0

I can assure that I often find local stations operating at 250-300 Hz from
my frequency
that are not minimally disturbed
I do not think that a linear amplifier is so better.
I also made a 100W output amplifier specifically designed for the K3.
This amplifier runs at 12 volt.
All my PA need an input signal (adjustable) from -10dBm to + 20 dBm

https://www.dropbox.com/s/u2yjp0ltv0kbsy5/K3%20and%20Pa.jpg?dl=0

73, Fausto IK4NMF

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Vic Rosenthal

Re: K3: 630m amplifiers

In reply to this post by Alan Bloom

A CW amplifier can be designed to run class-C but to be keyed in such a
way as to pass through the linear portion of the amplifying device's
curve when a CW element is starting or ending, in order to preserve the
shaping.

A simple example is the tube-type amplifier that has just enough fixed
bias applied to allow a small amount of plate current to flow (class
AB), with a grid resistor that provides the rest of the bias as a result
of rectified grid current as the drive ramps up. At full power the tube
is running class C with bias way beyond cutoff.

Good 1950's technology that can be made a little more sophisticated and
applied today!

73,
Vic, 4X6GP/K2VCO
Rehovot, Israel
http://www.qsl.net/k2vco/

On 27 Jul 2015 07:32, Alan wrote:

Fausto Coletti

Re: K3: 630m amplifiers

In reply to this post by Alan Bloom

Hi Alan,

In fact, the spectrogram that I posted shows strong key clicks of Class D
amplifier on the signal to 472.1 kHz.
Also the linear amplifier at 472.5 KHz in the spectrogram shows key clicks
but lower.
On the other hand you can see that my signal at 473.3 is very clean without
key clicks.
Many hams have asked me how it is possible that with a switching amplifier
there are no key clicks.
The answer is that I have taken a different approach by the schemes that are
on web and the result
you can see yourself.
It is very important to dampen all transients during switching from
interdiction to conduction and vice versa.
I had to work a lot but at the end I got a very clean TX.

73, Fausto IK4NMF

----- Original Message -----
From: "Alan" <[hidden email]>
To: "Fausto Coletti" <[hidden email]>
Sent: Monday, July 27, 2015 5:21 PM
Subject: Re: [Elecraft] K3: 630m amplifiers

> Hi Fausto,
>
> The term "class D" can mean many different things. As long as a class-D
> amplifier uses some means to preserve the modulation envelope (the shape
> of the amplitude) then it would work fine for CW. But if the input CW
> signal is hard-limited then the wave shaping will be lost and key clicks
> will result.
>
> It's not an issue for FSK digital modes, because the amplitude is
> constant, so hard-limiting has no effect. But CW is actually a form of
> amplitude modulation so it needs a linear amplifier.
>
> 73,
>
> Alan N1AL
>
>
> On 07/27/2015 12:30 AM, Fausto Coletti wrote:
>> It depends on how you made the amplifier.
>> I produce some models of amplifiers, of different powers, all in
>> switching operation.
>> Attached an image of the DK7FC grabber, you can see at 472.1 KHz the
>> spectrogram of
>> a German station that use a class D amplifier, at 472.5 an Italian
>> station that use a 400W
>> tube linear amplifier and at 473.3 there is my signal with my QRO+
>> switching PA.
>> I can assure that I often find local stations operating at 250-300 Hz
>> from my frequency
>> that are not minimally disturbed
>> I do not think that a linear amplifier is so better.
>> I also made a 100W output amplifier specifically designed for the K3.
>> This amplifier runs at 12 volt.
>> All my PA need an input signal (adjustable) from -10dBm to + 20 dBm
>>
>> 73, Fausto IK4NMF
>>
>>
>>
>>
>> ----- Original Message ----- From: "Alan" <[hidden email]>
>> To: <[hidden email]>
>> Sent: Monday, July 27, 2015 6:32 AM
>> Subject: Re: [Elecraft] K3: 630m amplifiers
>>
>>
>>>
>>> > CW would be another mode that would not need a linear amp I think.
>>>
>>> No, CW requires a linear amplifier. CW is not constant-amplitude -
>>> the amplitude changes every time you open or close the key. A class-C
>>> amplifier would mess up the key shaping, causing key clicks.
>>>
>>> Any true FSK or MSK signal should not be bothered by a non-linear
>>> amplifier. The only caveat I can think of is that the amplitude of an
>>> AFSK signal may have some ripple on it to the extent that the passband
>>> of the transmit crystal filter is not flat. But I doubt that's a
>>> significant issue.
>>>
>>> Alan N1AL
>>>
>
>
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Edward R Cole

Re: K3: 630m amplifiers

In reply to this post by Edward R Cole

To catch up on the comments I address all that I have so far:

Re: linear vs class-C is really a moot point as its easy enough to
build a linear at 500-KHz. CW, JT65, FSK all do fine with class-C,
of course. And its true that any modulation of a continuous carrier
will impart some bandwidth. Its not likely that wide-band digital
modes will be approved in a band that is only 7-KHz wide so probably
those approved would work with a class-C amp. I think its just
simpler to provide class-AB then its a non-issue.

Re: 15-dB HF linear amp gain limit. If that is applied to 630m amps
then either I sell a kit or partial kit.
1mw in to 1w out is 30-dB and 100w out is 50-dB. I would have to
research the regs to see if the limit is for a certain level of input
(like 5w). Also the regs allow hams to sell amps to other hams
without this restriction (but at what quantity per year?).

First off I am not proposing to go into competition with MFJ. This
is just a home business building one at a time. If the FCC is going
to make this a small (tiny) business killer than its just not worth
the bother. If I say more than this it will get political and that is OT.

73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[hidden email]

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Jim Brown-10

Re: K3: 630m amplifiers

On Mon,7/27/2015 10:43 AM, Edward R Cole wrote:
> CW, JT65, FSK all do fine with class-C, of course.

Ed,

I suggest that you drive a Class C amp with a K3 transmitting CW and
look at the spectra with a P3 both at the output of the rig and at the
output of the amp. Set the P3 display for 5 kHz.

73, Jim K9YC
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Phil Wheeler-2

Re: K3: 630m amplifiers

I'd have to dig out my old circuit diagrams, but
it seems like when we used Class C amps "back in
the day" (1950's and 60s) we keyed the output
stage, not only the driver as with linear amps --
and we modulated the output stage in the AM days, too.

73, Phil W7OX

On 7/27/15 11:42 AM, Jim Brown wrote:

> On Mon,7/27/2015 10:43 AM, Edward R Cole wrote:
>> CW, JT65, FSK all do fine with class-C, of course.
>
> Ed,
>
> I suggest that you drive a Class C amp with a K3
> transmitting CW and look at the spectra with a
> P3 both at the output of the rig and at the
> output of the amp. Set the P3 display for 5 kHz.
>
> 73, Jim K9YC

Don Wilhelm-4

Re: K3: 630m amplifiers

Phil,

That is correct, and the keying of that output stage was shaped in many
cases.
Grid-block keying was all the rage for help in shaping the keying envelope.
Cathode keying was used too, but usually not with keying. You had to be
careful the key did not "bite" from the voltage on it.

73,
Don W3FPR

On 7/27/2015 4:27 PM, Phil Wheeler wrote:
> I'd have to dig out my old circuit diagrams, but it seems like when we
> used Class C amps "back in the day" (1950's and 60s) we keyed the
> output stage, not only the driver as with linear amps -- and we
> modulated the output stage in the AM days, too.
>
> 73, Phil W7OX
>

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Alan Bloom

Re: K3: 630m amplifiers

In reply to this post by Jim Brown-10

The need for linear amplifiers with CW has been known for many years.
Quoting from the 1964 ARRL Handbook:

When key clicks introduced by the addition of an amplifier stage
are found only near the transmitter frequency, amplifier "clipping"
is indicated. It is quite common when fixed bias is used on the
amplifier and the bias is well past the "cut-off" value.

[In other words, a class C amplifier. Similar to a bipolar transistor
amplifier with no base bias.]

A linear amplifier (Class AB1, AB2 or B) will amplify the
excitation without adding any clicks, and if clicks show up, a
low-frequency parasitic oscillation is probably the reason.

Alan N1AL

On 07/27/2015 11:42 AM, Jim Brown wrote:

> On Mon,7/27/2015 10:43 AM, Edward R Cole wrote:
>> CW, JT65, FSK all do fine with class-C, of course.
>
> Ed,
>
> I suggest that you drive a Class C amp with a K3 transmitting CW and
> look at the spectra with a P3 both at the output of the rig and at the
> output of the amp. Set the P3 display for 5 kHz.
>
> 73, Jim K9YC

Tom Azlin W7SUA-2

Re: K3: 630m amplifiers

In reply to this post by Alan Bloom

Interesting discussion, but I'm now confused.

In all the old handbooks the discussion of amplifier design says ( page
76, 1941) "In amateur transmitters, and r.f. amplifier is invariably
operated Class C ( see Chaptr 3)." I though the final tuned circuit was
simply "pulsed" at the RF freq and then the output filtering knocked off
harmonics leaving a clean CW note. And in the article on construction of
a 100-175 watt CW transmitter ( page 155-157) the 6L6 crystal oscillator
was cathode keyed with a bit of RC shaping. Rest of stages powered up
when in transmit.

And I thought these days some AM broadcast transmitters operated Class
E. Clearly not linear.

73, tom w7sua

On 7/26/2015 9:32 PM, Alan wrote:

>
> > CW would be another mode that would not need a linear amp I think.
>
> No, CW requires a linear amplifier. CW is not constant-amplitude - the
> amplitude changes every time you open or close the key. A class-C
> amplifier would mess up the key shaping, causing key clicks.
>
> Any true FSK or MSK signal should not be bothered by a non-linear
> amplifier. The only caveat I can think of is that the amplitude of an
> AFSK signal may have some ripple on it to the extent that the passband
> of the transmit crystal filter is not flat. But I doubt that's a
> significant issue.
>
> Alan N1AL
>
>
>
> On 07/26/2015 06:57 PM, Tom Azlin W7SUA wrote:
>> Hi Don and Alan,
>>
>> I was thinking one of the slow multi tone FSK modes that are a single
>> tone at a time. WSQ is in the same class.
>>
>> http://www.qsl.net/zl1bpu/SOFT/WSQ.htm
>>
>> CW would be another mode that would not need a linear amp I think.
>>
>> On the other hand PSK31 would require a linear amp.
>>
>> 73, tom w7sua
>>
>> On 7/26/2015 5:43 PM, Alan wrote:
>>> On 07/26/2015 05:32 PM, Don Wilhelm wrote:
>>>
>>>> Soundcard sourced digital modes are really SSB signals and need a
>>>> linear
>>>> amplifier.
>>>
>>> The one exception might be FSK. It is constant-amplitude so a class C
>>> amplifier should be fine.
>>>
>>> FSK modes include RTTY and I believe WSPR and WSJT.
>>>
>>> Alan N1AL
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