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Ideal input voltage for TX on KXPA100?

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David Orman

Ideal input voltage for TX on KXPA100?

Hi,

In order to maximize TX quality and cleanliness from the KXPA100, what
should I aim for regarding input voltage on 100W keydown as seen by the KX3
display option PS? I've got an adjustable Astron VS-70M, but would like to
power other equipment, so am trying to find to sweet spot for the radio
before figuring out solutions for the other devices.

I do intend to eventually move to a K* device, wishful thinking/fingers
crossed we will see it at Dayton and it'll have a 200W output. ;) For now,
though, I just want to make sure I'm running my KX3/KXPA100 optimally and
being a good radio citizen on TX. Thank you in advance!

David / K5DJO
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Don Wilhelm

Re: Ideal input voltage for TX on KXPA100?

David,

Turn it up until you see at least 13.8 on the KX3 when idle, then check
the voltage during transmit. You really can go up to 14.5 volts with
no harm. If the voltage drops by more than 1 volt, you have too much
resistance (too many connections) in the power cord run from the power
supply.
Connect the power cable to the KXPA100 directly to the power supply
terminals. With a 15 amp draw there will be a substantial voltage drop
across a device like a Rigrunner.

73,
Don W3FPR

On 5/14/2017 2:43 PM, David Orman wrote:
> Hi,
>
> In order to maximize TX quality and cleanliness from the KXPA100, what
> should I aim for regarding input voltage on 100W keydown as seen by the KX3
> display option PS? I've got an adjustable Astron VS-70M, but would like to
> power other equipment, so am trying to find to sweet spot for the radio
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David Orman

Re: Ideal input voltage for TX on KXPA100?

Hi Don,

Thank you for the reply. Is there an ideal voltage under TX/ load? 13.8V
under load is easy, so is 14.5+. If there's advantage to running higher
voltages, I can, but if there is no advantage I'll just target 13.8 under
load and call it a day and not worry about dropping voltage for other
components.

David

On Sun, May 14, 2017, 14:11 Don Wilhelm <[hidden email]> wrote:

> David,
>
> Turn it up until you see at least 13.8 on the KX3 when idle, then check
> the voltage during transmit. You really can go up to 14.5 volts with
> no harm. If the voltage drops by more than 1 volt, you have too much
> resistance (too many connections) in the power cord run from the power
> supply.
> Connect the power cable to the KXPA100 directly to the power supply
> terminals. With a 15 amp draw there will be a substantial voltage drop
> across a device like a Rigrunner.
>
> 73,
> Don W3FPR
>
> On 5/14/2017 2:43 PM, David Orman wrote:
> > Hi,
> >
> > In order to maximize TX quality and cleanliness from the KXPA100, what
> > should I aim for regarding input voltage on 100W keydown as seen by the
> KX3
> > display option PS? I've got an adjustable Astron VS-70M, but would like
> to
> > power other equipment, so am trying to find to sweet spot for the radio
>

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Don Wilhelm

Re: Ideal input voltage for TX on KXPA100?

David,

Be careful about checking for 13.8 under load because you don't yet know
how much voltage drop you have in the power cable.
Check the difference between load and idle at whatever voltage you have
right now.
You MUST keep the maximum supply voltage to less than 15 volts.

What I am saying is that if you have significant voltage drop in the
power cable, then setting the voltage under load to 13.8 *may* result in
greater than 15 volts no load.

If you have significant voltage drop in the power supply to KXPA100
power routing, fix that first.

73,
Don W3FPR

On 5/14/2017 3:42 PM, David Orman wrote:

>
> Hi Don,
>
> Thank you for the reply. Is there an ideal voltage under TX/ load?
> 13.8V under load is easy, so is 14.5+. If there's advantage to running
> higher voltages, I can, but if there is no advantage I'll just target
> 13.8 under load and call it a day and not worry about dropping voltage
> for other components.
>
>

David Orman

Re: Ideal input voltage for TX on KXPA100?

Hi Don,

I'm making sure not to exceed idle voltages like this. If I set the power
supply to 14.2V no load, it's 13.8V under load (100W out tune on 80M). I
use 10 gauge cable, so I have relatively small voltage drop even with the
distribution block and fuses involved. I'm just trying to find out what the
optimal voltage under load is for TX cleanliness. Is that 13.8V? Is higher
voltage than this better? I appreciate the input; I'm truly just trying to
find out what 'ideal' looks like under load.

David

On Sun, May 14, 2017 at 3:50 PM, Don Wilhelm <[hidden email]> wrote:

> David,
>
> Be careful about checking for 13.8 under load because you don't yet know
> how much voltage drop you have in the power cable.
> Check the difference between load and idle at whatever voltage you have
> right now.
> You MUST keep the maximum supply voltage to less than 15 volts.
>
> What I am saying is that if you have significant voltage drop in the power
> cable, then setting the voltage under load to 13.8 *may* result in greater
> than 15 volts no load.
>
> If you have significant voltage drop in the power supply to KXPA100 power
> routing, fix that first.
>
> 73,
> Don W3FPR
>
>
> On 5/14/2017 3:42 PM, David Orman wrote:
>
>>
>> Hi Don,
>>
>> Thank you for the reply. Is there an ideal voltage under TX/ load? 13.8V
>> under load is easy, so is 14.5+. If there's advantage to running higher
>> voltages, I can, but if there is no advantage I'll just target 13.8 under
>> load and call it a day and not worry about dropping voltage for other
>> components.
>>
>>
>>
>

Don Wilhelm

Re: Ideal input voltage for TX on KXPA100?

David,

There is no specific voltage, except that "higher is better".

A fused distribution block will add 6 connector junctions and you can
expect .001 ohms from each one.
At 15 amps draw, that alone contributes about 0.1 volt drop.

73,
Don W3FPR

On 5/14/2017 6:42 PM, David Orman wrote:

> Hi Don,
>
> I'm making sure not to exceed idle voltages like this. If I set the
> power supply to 14.2V no load, it's 13.8V under load (100W out tune on
> 80M). I use 10 gauge cable, so I have relatively small voltage drop
> even with the distribution block and fuses involved. I'm just trying
> to find out what the optimal voltage under load is for TX cleanliness.
> Is that 13.8V? Is higher voltage than this better? I appreciate the
> input; I'm truly just trying to find out what 'ideal' looks like under
> load.
>