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#qsx #lpf #lpf #qsx

Juan Rubio
 

Last week I received the 10w PA for QSX. I have assembled it according to the clear manual.
I have tested it and it works  as the manual say.
And I tested itiwith a little more input until the output was 20 watts and 3A of consume. I think it is all right for CW and SSB but maybe to hot for Digi modes. 
The low pass filter can support the 20 watts in CW?
And in the design of the QSX is it possible to put a little more gain in the exciter to get to 20 exit watts?

ajparent1/KB1GMX
 

At 20W out and 3A DC current (assume 13.8V) your putting 41watts of DC
in and seeing about 48% efficiency or 21W of pure heat and at that
voltage fully distorted.

Best power without distortion at 13.8 is about 13.5W some might see 14
but that -1db compression point and more is definitely dirty for SSB.

To run at that power without distortion the Voltage has to be 20V or more.
At that power level its, going to be hot, about 65C/150F so a fan would help.
Ran for a hour at 10W power out as stress test.  For higher voltage and
sustained power the heat sink would have to be  three times the width 
for the same length.

It was not rated for 100% at extreme overdrive.  100% at 10W and tested there.
If you crank up the power 20W is only 3DB and your doing that for little gain
and greater distortion and harmonics.  Also running at that power using
higher voltages does give up tolerance to abuse (bad swr, overdrive and all).

If anything turn it down to 4-5W and drive an external linear to the 30-50W level.
The operating rule is anything less than 4x power increase (1 S unit) is pointless.
Generally going for 10X (about 50W) is the next useful level of power increase
that the other guy will notice.

Allison

Juan Rubio
 

Thanks Allison for interesting explanation.

EA3CWT, Juan

El sáb., 12 ene. 2019 22:19, ajparent1/KB1GMX <kb1gmx@...> escribió:
At 20W out and 3A DC current (assume 13.8V) your putting 41watts of DC
in and seeing about 48% efficiency or 21W of pure heat and at that
voltage fully distorted.

Best power without distortion at 13.8 is about 13.5W some might see 14
but that -1db compression point and more is definitely dirty for SSB.

To run at that power without distortion the Voltage has to be 20V or more.
At that power level its, going to be hot, about 65C/150F so a fan would help.
Ran for a hour at 10W power out as stress test.  For higher voltage and
sustained power the heat sink would have to be  three times the width 
for the same length.

It was not rated for 100% at extreme overdrive.  100% at 10W and tested there.
If you crank up the power 20W is only 3DB and your doing that for little gain
and greater distortion and harmonics.  Also running at that power using
higher voltages does give up tolerance to abuse (bad swr, overdrive and all).

If anything turn it down to 4-5W and drive an external linear to the 30-50W level.
The operating rule is anything less than 4x power increase (1 S unit) is pointless.
Generally going for 10X (about 50W) is the next useful level of power increase
that the other guy will notice.

Allison

geoff M0ORE
 

In my instruction manual which I read many times before getting the soldering iron hot,

Instruction manual page 34, note 5 refers.

Did you monitor the distortion of your 20 watts?  SSB and Digimodes need the same purity of signal and Allison has said that the PA can be used at full rating, 100% duty-cycle for 1 hour. I don't think even FT8 transmits for that long. ( see page 34, note 9)

Geoff

On 1/12/2019 8:54 PM, Juan Rubio wrote:
Last week I received the 10w PA for QSX. I have assembled it according to the clear manual.
I have tested it and it works  as the manual say.
And I tested itiwith a little more input until the output was 20 watts and 3A of consume. I think it is all right for CW and SSB but maybe to hot for Digi modes. 
The low pass filter can support the 20 watts in CW?
And in the design of the QSX is it possible to put a little more gain in the exciter to get to 20 exit watts?

geoff M0ORE
 

Sorry Allison, I replied to original post before reading your excellent response. My amp started to show distortion at 10.8 Watts, 13.8 Volt supply, using two tone test. Not tested at higher supply voltage as 10 Watts is plenty for QRP.

Geoff

On 1/12/2019 9:19 PM, ajparent1/KB1GMX wrote:
At 20W out and 3A DC current (assume 13.8V) your putting 41watts of DC
in and seeing about 48% efficiency or 21W of pure heat and at that
voltage fully distorted.

Best power without distortion at 13.8 is about 13.5W some might see 14
but that -1db compression point and more is definitely dirty for SSB.

To run at that power without distortion the Voltage has to be 20V or more.
At that power level its, going to be hot, about 65C/150F so a fan would help.
Ran for a hour at 10W power out as stress test.  For higher voltage and
sustained power the heat sink would have to be  three times the width 
for the same length.

It was not rated for 100% at extreme overdrive.  100% at 10W and tested there.
If you crank up the power 20W is only 3DB and your doing that for little gain
and greater distortion and harmonics.  Also running at that power using
higher voltages does give up tolerance to abuse (bad swr, overdrive and all).

If anything turn it down to 4-5W and drive an external linear to the 30-50W level.
The operating rule is anything less than 4x power increase (1 S unit) is pointless.
Generally going for 10X (about 50W) is the next useful level of power increase
that the other guy will notice.

Allison

ajparent1/KB1GMX
 

Geoff,

For two tone that sounds about right.  For single tone its higher but not 20W!

Its a classic case of yes you can drive it harder and make the meter move
but linear, no.  I'd bet the output waveform at that power was nearly square.
 
Bump up the supply to 20V or change the electrolytics and go for 28V
then the output numbers get biger but then the output transformer is not
optimum.    I have a different amp that can easily get 50w out of a pair
of IRF510s but that with 28V supply and a 4"x8" with 1.25" fins heat sink.
But it does not have gain flatness to 30mhz either.  The output ferrite
BN61-7051 is nearly bigger than QSX amp.

It was designed for 10W and does that if you push for more your going to be 
outside spec, on your own and blind experimenting.

Allison

Jerry Gaffke
 

Safest is to settle for 10W @ 12V and spend your time improving the antenna.
Pushing that QSX amp to 20W @ 20V is apparently doable, but getting risky..
Going further will be an adventure, BS170 dissipation is yet another limiting factor:
    https://groups.io/g/QRPLabs/message/27731
    https://groups.io/g/QRPLabs/message/27757

One possible strategy:  Push it till is smokes, then back off 10%.  ;-)
A new QSX amp is only $26.

Jerry, KE7ER


On Sat, Jan 12, 2019 at 04:12 PM, ajparent1/KB1GMX wrote:
Its a classic case of yes you can drive it harder and make the meter move
but linear, no.  I'd bet the output waveform at that power was nearly square.
 
Bump up the supply to 20V or change the electrolytics and go for 28V
then the output numbers get biger but then the output transformer is not
optimum.    I have a different amp that can easily get 50w out of a pair
of IRF510s but that with 28V supply and a 4"x8" with 1.25" fins heat sink.
But it does not have gain flatness to 30mhz either.  The output ferrite
BN61-7051 is nearly bigger than QSX amp.

It was designed for 10W and does that if you push for more your going to be 
outside spec, on your own and blind experimenting.
 

ajparent1/KB1GMX
 

Jerry,

Testing to 20V was can we fry/damage this thing testing!  I did a lot of things to
try and force it to take off and oscillate or just plain die.  It didn't.  Doesn't mean
its efficient or suggests that 20W at 20V was a way to go.  Anyone saying they
get more than 14-15W at 13.8 is measuring a highly distorted power out.

However it is simpler than that as it was designed to be a very good 10W amp. 
If that is not enough don't force it, use a outboard amp of decent proportions
say 50, 100 watts or more.  Or use your QRO rig.

If you push it for more and the results are poor send all complaints to: 
dev_nul@...

That and fix your antenna.  Yes just a bit of snark.  But after hearing but
I want 20W and run on a small battery,  like say what, why?

Allison

Bill Cromwell
 

Hi Allison,

From time to time I have to wait a while until I can find civilized, polite, politically correct words to reply to some of the posts. By that time, somebody else has given the civilized reply and maybe another has giving the biting comments.

Are you saying there may be unpleasant consequences when trying to force 20 pounds of balogna into a 10 pound sack? Just a fresh point of view. Maybe not so fresh. I delivered that concept in a corporate report a decade of more ago in a file aptly named "five.pound.sack" :)

73,

Bill KU8H

On 1/13/19 12:28 PM, ajparent1/KB1GMX wrote:
Jerry,
Testing to 20V was can we fry/damage this thing testing!  I did a lot of things to
try and force it to take off and oscillate or just plain die.  It didn't.  Doesn't mean
its efficient or suggests that 20W at 20V was a way to go.  Anyone saying they
get more than 14-15W at 13.8 is measuring a highly distorted power out.
However it is simpler than that as it was designed to be a very good 10W amp.
If that is not enough don't force it, use a outboard amp of decent proportions
say 50, 100 watts or more.  Or use your QRO rig.
If you push it for more and the results are poor send all complaints to:
dev_nul@...
That and fix your antenna.  Yes just a bit of snark.  But after hearing but
I want 20W and run on a small battery,  like say what, why?
Allison
--
bark less - wag more

Jerry Gaffke
 

Allison,

We're on the same page.

My post was in response to somebody giving suggestions on goosing the power:
>> Bump up the supply to 20V or change the electrolytics and go for 28V
>>  then the output numbers get biger but then the output transformer is not optimum

And my advice is still:
> Safest is to settle for 10W @ 12V and spend your time improving the antenna.

But you know that roughly half of forum members are thinking this:
>   Push it till is smokes, then back off 10%.

Jerry



On Sun, Jan 13, 2019 at 09:28 AM, ajparent1/KB1GMX wrote:
Jerry,

Testing to 20V was can we fry/damage this thing testing! 

Martin
 

Hi all,

maybe it has been said somewhere else but why is the QSX having an output of 10 W disqualifying it for QRP contest activities?

I would prefer 5 W and then if needed for SSB use a PA

Martin DK3UW

Hans Summers
 

Hi Martin


  • Power output: 10W from 13.8V supply (power output is adjustable by the firmware)
Power is variable. You can set it to 5W if you wish. Or 1W for 1W contests. However you wish. 

73 Hans G0UPL

On Thu, Feb 28, 2019 at 6:08 PM Martin <m.sellschopp@...> wrote:
Hi all,

maybe it has been said somewhere else but why is the QSX having an output of 10 W disqualifying it for QRP contest activities?

I would prefer 5 W and then if needed for SSB use a PA

Martin DK3UW

ajparent1/KB1GMX
 

Martin,
For QRP contests you want 10W PEP  (SSB), an amp that only does 5W single tone
can't do that.  So for a full legal QRP SSB contest power you need a bit more robust
amp like this that can do 10W cleanly.  Least that is the logic.

The QSX has the option as Hans said for lower power.  Its nice to know the amp is
not straining or flat topping.

Allison

Martin
 

Hi Hnas & Allison,

isn't it necessary to have a rig doing max 5 w to qualify for QRP in a contest? If I remember well it is not accepted to just declare using only 5 W out from a transmitter capable of doing more.

Martin DK3UW

Alan G4ZFQ
 

l it is not accepted to just declare using only 5 W out from a transmitter capable of doing more.
Martin,

So pushing a 2.5 watt rated transmitter up to 5 watts is allowed?
What do the rules actually say?
If it is a homebrew rig who is to know how it has been setup or what voltage PSU is used.

73 Alan G4ZFQ

Hans Summers
 

Hi Martin

I am not an expert on contest rules but if you wish, you may configure your QSX as a 5W radio rather than a 10W radio. You can set it up to calibrate itself and limit itself to never any more than 5W. 

73 Hans G0UPL

On Thu, Feb 28, 2019 at 6:56 PM Martin <m.sellschopp@...> wrote:
Hi Hnas & Allison,

isn't it necessary to have a rig doing max 5 w to qualify for QRP in a contest? If I remember well it is not accepted to just declare using only 5 W out from a transmitter capable of doing more.

Martin DK3UW

ajparent1/KB1GMX
 

Martin.
Your correct and missing the example.  For SSB its 10W PEP.

To produce a 10W PEP signal you need an amp that can put 5W into
each of two tones.

So yes of course you turn it down but if you using a peak reading meter 
rather than averaging SSB peaks must be 10W Peak or less and CW 5W peak or less.

Its not cheating unless the odd contest says 5 W PEP SSB and few I know of do that.

Allison

ajparent1/KB1GMX
 

Alan,

What do the rules say?  Depends on the contest.  The rules are usually very clear.

ARRL contests its 5W CW and 10W PEP SSB.

If its mixed mode CW/SSB/DIGIi ts likely tthat and I'm certain of different than
pure CW.  Also for CW its much easier to be exact about 5W as I can use my
FT817 at full power (official 5W radio) and get 5W CW but more than that using
a peak reading meter under SSB.

Of course there are QRpp contests for not more than 1 milligallon (1W),
and  memory says there is one that 100mW is the limit.

Allison

Alan G4ZFQ
 

ARRL contests its 5W CW and 10W PEP SSB.
Allison,

Yes, but the question I am asking is whether contests have rules that say that rigs capable of more than the specified power are banned?

73 Alan G4ZFQ

Walter Keen
 

The QSX looks like a very versatile unit, I'm anxiously waiting to be able to order one


On Thu, Feb 28, 2019 at 8:26 AM Hans Summers <hans.summers@...> wrote:
Hi Martin

I am not an expert on contest rules but if you wish, you may configure your QSX as a 5W radio rather than a 10W radio. You can set it up to calibrate itself and limit itself to never any more than 5W. 

73 Hans G0UPL

On Thu, Feb 28, 2019 at 6:56 PM Martin <m.sellschopp@...> wrote:
Hi Hnas & Allison,

isn't it necessary to have a rig doing max 5 w to qualify for QRP in a contest? If I remember well it is not accepted to just declare using only 5 W out from a transmitter capable of doing more.

Martin DK3UW