KPA1500 design

[Rick WA6NHC]

I've never designed an amp so I'm knowingly ignorant here.  But I was
wondering:

 

If one removed the power supply from a KPA500 and moved it to an external
box (adding regulation and a 13.8 VDC, 30 amp capable supply while you're
there) then;

Put FOUR of the (KPA500) PA modules together in the 'amp' box (two push, two
pull, AB class) and matched them into one output;

 

Would it feasible to have legal limit (loafing) output with 100 watts of
drive (limited on the input to meet the 15 db gain FCC spec)?

 

Or am I just being too ignorant?

 

Rick WA6NHC

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[Alan Bloom]

You could do it with four unmodified KPA500s and three hybrid combiners.

Alan N1AL

On Tue, 2012-02-21 at 15:52 -0800, Rick Bates wrote:

> I've never designed an amp so I'm knowingly ignorant here.  But I was
> wondering:
>
>  
>
> If one removed the power supply from a KPA500 and moved it to an external
> box (adding regulation and a 13.8 VDC, 30 amp capable supply while you're
> there) then;
>
> Put FOUR of the (KPA500) PA modules together in the 'amp' box (two push, two
> pull, AB class) and matched them into one output;
>
>  
>
> Would it feasible to have legal limit (loafing) output with 100 watts of
> drive (limited on the input to meet the 15 db gain FCC spec)?
>
>  
>
> Or am I just being too ignorant?
>
>  
>
> Rick WA6NHC
>
> ______

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[KD3RF]

Let's see...

That would only be $8,000, along with the attendant problems with power dividers and combiners and keeping the two modules balanced and in phase with each other, not only to mention keeping everything cool.

I ran a full K Line in the CW contest this past weekend and worked everyone I could here, most times on the first call.

500 Watts seems to work just fine for my needs.

My antenna is a 3 element Cubex cubical quad at 40 ft, which helps.

[David Gilbert]

Actually, a power ratio of 3 is almost 5 db, which is a huge difference
when you're talking signals near the noise level.  On most HF bands it
can literally be the difference between being Q5 versus not being
discernible at all.   If you think 5 db is no big deal, keep in mind
that the KPA500 offers only 2 db more than that (7 db total) over a
barefoot K3.

Dave   AB7E


On 2/21/2012 8:55 PM, Ron D'Eau Claire wrote:
> Congratulations Andy!
>
> I'm mindful that data does not change beliefs, the difference is power
> between a KPA500 and the legal limit is slightly over 1/2 of one S unit.
>
> But for those who want to have the biggest signal, it does take the legal
> limit **and** a big antenna.
>
> 73, Ron AC7AC
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[Geoffrey Downs-3]

Perhaps Elecraft could bring out a hybrid combiner/controller for those who
want to run more power than one KPA500 can give. A new product for Elecraft
and a boost to KPA500 sales. (Or maybe they already have it in mind).

No charge for this business consultancy ;-)

73 to all

Geoff
G3UCK

-----Original Message-----
From: Alan Bloom
Sent: Tuesday, February 21, 2012 11:58 PM
Subject: Re: [Elecraft] KPA1500 design

You could do it with four unmodified KPA500s and three hybrid combiners.

Alan N1AL


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[alsopb]

For those who don't believe Dave, here is some suggested reading material.

N6BT's new Antenna Book, Array of Light

He discusses the significant difference an extra 2db makes.

Yes he also sells antennas, but what he says rings true.

73 de Brian/K3KO



On 2/22/2012 07:54, David Gilbert wrote:

>
> Actually, a power ratio of 3 is almost 5 db, which is a huge difference
> when you're talking signals near the noise level.  On most HF bands it
> can literally be the difference between being Q5 versus not being
> discernible at all.   If you think 5 db is no big deal, keep in mind
> that the KPA500 offers only 2 db more than that (7 db total) over a
> barefoot K3.
>
> Dave   AB7E
>
>
> On 2/21/2012 8:55 PM, Ron D'Eau Claire wrote:
>> Congratulations Andy!
>>
>> I'm mindful that data does not change beliefs, the difference is power
>> between a KPA500 and the legal limit is slightly over 1/2 of one S unit.
>>
>> But for those who want to have the biggest signal, it does take the legal
>> limit **and** a big antenna.
>>
>> 73, Ron AC7AC
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[Geoffrey Mackenzie-Kennedy-3]

Hi Al,

Indeed one could combine amplifiers by using Hybrid Combiners.  However when
used for SSB and especially if driven by a typical amateur solid state
transceiver working from a 12V DC supply, a potential problem to be
considered is that the level of Odd Order IMD products as seen at the output
might become too high relative to PEP (or test tone).


Granted that this problem can also arise when using any other form of linear
amplifier when driven by a similar exciter, but when using
"Combined`Amplifiers" some (if not all) of the IMD products appearing at the
output of each amplifier can add when combined  i.e stronger IMD products
transmitted.  Lucky if they cancel :-)

73,

Geoff
LX2AO


On February 22, 2012 at 12:58 +0100, Alan Bloom wrote:


> You could do it with four unmodified KPA500s and three hybrid combiners.

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[David Gilbert]

And although I've posted this link before, here it is again for anyone
who missed it and wants to hear what a difference of 2 db makes.  
Actually, there are several audio files there that compare various CW
signal levels at or near the background noise level:

a.  six steps of signal strength in one db increments

b.  two competing signals either one db or two db apart

c.  the impact of CW speed on intelligibility of signals very near the
noise level

The methodology I used to generate the files is also described there,
but in a nutshell I used CW Player (written by F6DQM) to record CW of
known amplitudes and mixed them with band noise recorded from my K3.

http://www.ab7e.com/weak_signal/mdd.html

73,
Dave   AB7E



On 2/22/2012 5:30 AM, Brian Alsop wrote:

> For those who don't believe Dave, here is some suggested reading material.
>
> N6BT's new Antenna Book, Array of Light
>
> He discusses the significant difference an extra 2db makes.
>
> Yes he also sells antennas, but what he says rings true.
>
> 73 de Brian/K3KO
>
>
>
> On 2/22/2012 07:54, David Gilbert wrote:
>> Actually, a power ratio of 3 is almost 5 db, which is a huge difference
>> when you're talking signals near the noise level.  On most HF bands it
>> can literally be the difference between being Q5 versus not being
>> discernible at all.   If you think 5 db is no big deal, keep in mind
>> that the KPA500 offers only 2 db more than that (7 db total) over a
>> barefoot K3.
>>
>> Dave   AB7E
>>
>>
>> On 2/21/2012 8:55 PM, Ron D'Eau Claire wrote:
>>> Congratulations Andy!
>>>
>>> I'm mindful that data does not change beliefs, the difference is power
>>> between a KPA500 and the legal limit is slightly over 1/2 of one S unit.
>>>
>>> But for those who want to have the biggest signal, it does take the legal
>>> limit **and** a big antenna.
>>>
>>> 73, Ron AC7AC
>> ____

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