Elecraft

KPA500 Minimum Drive?

Classic

List

Threaded

6 messages Options

James Bennett

KPA500 Minimum Drive?

I share my KPA500 with a K3 and a KX3. When I want to operate JT65 or JT9 I normally run about 25 watts out, using the KX3 to drive the amp. With the KX3 set to 1.8 watts out, the amp gives me 25; with 2.2 watts from the KX3, I get 30 watts out from the amp.

But, what if I want to run 20 watts? Or 15? When I back the KX3 power level below 1.8, the KPA500 shows zero on the LED power display. Does this mean it is no longer amplifying, or is it actually amplifying but not enough for the circuitry to determine how much?

Jim Bennett / W6JHB
Folsom, CA
______________________________________________________________
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]

Phil Wheeler-2

Re: KPA500 Minimum Drive?

Seems like if you want to run such low power
levels, you'd go barefoot and not use the amp, Jim.

Phil W7OX

On 6/15/16 4:54 PM, James Bennett wrote:
> I share my KPA500 with a K3 and a KX3. When I want to operate JT65 or JT9 I normally run about 25 watts out, using the KX3 to drive the amp. With the KX3 set to 1.8 watts out, the amp gives me 25; with 2.2 watts from the KX3, I get 30 watts out from the amp.
>
> But, what if I want to run 20 watts? Or 15? When I back the KX3 power level below 1.8, the KPA500 shows zero on the LED power display. Does this mean it is no longer amplifying, or is it actually amplifying but not enough for the circuitry to determine how much?
>
> Jim Bennett / W6JHB
> Folsom, CA

______________________________________________________________
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]

k6dgw

Re: KPA500 Minimum Drive?

In reply to this post by James Bennett

Hmmm ... I guess first question is, what's the problem? 25 W to 20W is
slightly less than 1 dB, 0.16 S-unit. Just run barefoot?

The LED Power display on the KPA500 is digital. It "measures the
power," and puts it into one of a number of bins. If something is in
the bin, it lights the LED. If the measured power isn't high enough for
the lowest bin, all the bins are empty, no LED's light up, although
there is still RF being made.

Measuring power with simple instruments is hard ... well, sort of
impossible. You can measure the voltage, but then you need to know the
impedance, a complex number, not easily measured with a DVM. You can
measure the current -- same problem. KPA500 is designed to emit 500W
with 25-30W input. I think you're pushing the envelope here and nothing
is wrong.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the Cal QSO Party 1-2 Oct 2016
- www.cqp.org

On 6/15/2016 4:54 PM, James Bennett wrote:

> I share my KPA500 with a K3 and a KX3. When I want to operate JT65 or
> JT9 I normally run about 25 watts out, using the KX3 to drive the
> amp. With the KX3 set to 1.8 watts out, the amp gives me 25; with 2.2
> watts from the KX3, I get 30 watts out from the amp.
>
> But, what if I want to run 20 watts? Or 15? When I back the KX3 power
> level below 1.8, the KPA500 shows zero on the LED power display. Does
> this mean it is no longer amplifying, or is it actually amplifying
> but not enough for the circuitry to determine how much?
>
> Jim Bennett / W6JHB Folsom, CA

______________________________________________________________
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]

Jack Brindle-2

Re: KPA500 Minimum Drive?

Fred’s assessment is correct - the output power resolution below 25 watts is pretty low. But it is still putting out power, at least to a point. There _is_ a lower limit to input power - it involves the ability of the frequency counter to do its job. If the counter cannot get an accurate count, it won’t be able to corroborate the frequency for the correct band selection. This level is in the neighborhood of 1 watt, giving you some range to play with.

Enjoy playing with your KPA500!

Jack, W6FB

> On Jun 15, 2016, at 7:15 PM, Fred Jensen <[hidden email]> wrote:
>
> Hmmm ... I guess first question is, what's the problem? 25 W to 20W is slightly less than 1 dB, 0.16 S-unit. Just run barefoot?
>
> The LED Power display on the KPA500 is digital. It "measures the power," and puts it into one of a number of bins. If something is in the bin, it lights the LED. If the measured power isn't high enough for the lowest bin, all the bins are empty, no LED's light up, although there is still RF being made.
>
> Measuring power with simple instruments is hard ... well, sort of impossible. You can measure the voltage, but then you need to know the impedance, a complex number, not easily measured with a DVM. You can measure the current -- same problem. KPA500 is designed to emit 500W with 25-30W input. I think you're pushing the envelope here and nothing is wrong.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the Cal QSO Party 1-2 Oct 2016
> - www.cqp.org
>
> On 6/15/2016 4:54 PM, James Bennett wrote:
>> I share my KPA500 with a K3 and a KX3. When I want to operate JT65 or
>> JT9 I normally run about 25 watts out, using the KX3 to drive the
>> amp. With the KX3 set to 1.8 watts out, the amp gives me 25; with 2.2
>> watts from the KX3, I get 30 watts out from the amp.
>>
>> But, what if I want to run 20 watts? Or 15? When I back the KX3 power
>> level below 1.8, the KPA500 shows zero on the LED power display. Does
>> this mean it is no longer amplifying, or is it actually amplifying
>> but not enough for the circuitry to determine how much?
>>
>> Jim Bennett / W6JHB Folsom, CA
> ______________________________________________________________
> 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]

James Bennett

Re: KPA500 Minimum Drive?

In reply to this post by k6dgw

Yes, if I wanted 12 watts (which is the same as 15 for all intents and purposes) I could run barefoot. However, why stress the KX3 by running it as hard as possible, key down, for long digital transmissions like PSK31?

I never said there was a problem or that something was wrong. I simply am curious if the designers of the amp who monitor this reflector know what it does with less RF input than what gives an LCD indication of power. That's all.

Jim / W6JHB

> On Jun 15, 2016, at 19:15, Fred Jensen <[hidden email]> wrote:
>
> Hmmm ... I guess first question is, what's the problem? 25 W to 20W is slightly less than 1 dB, 0.16 S-unit. Just run barefoot?
>
> The LED Power display on the KPA500 is digital. It "measures the power," and puts it into one of a number of bins. If something is in the bin, it lights the LED. If the measured power isn't high enough for the lowest bin, all the bins are empty, no LED's light up, although there is still RF being made.
>
> Measuring power with simple instruments is hard ... well, sort of impossible. You can measure the voltage, but then you need to know the impedance, a complex number, not easily measured with a DVM. You can measure the current -- same problem. KPA500 is designed to emit 500W with 25-30W input. I think you're pushing the envelope here and nothing is wrong.
>
> 73,
>
> Fred K6DGW
> - Northern California Contest Club
> - CU in the Cal QSO Party 1-2 Oct 2016
> - www.cqp.org
>
>> On 6/15/2016 4:54 PM, James Bennett wrote:
>> I share my KPA500 with a K3 and a KX3. When I want to operate JT65 or
>> JT9 I normally run about 25 watts out, using the KX3 to drive the
>> amp. With the KX3 set to 1.8 watts out, the amp gives me 25; with 2.2
>> watts from the KX3, I get 30 watts out from the amp.
>>
>> But, what if I want to run 20 watts? Or 15? When I back the KX3 power
>> level below 1.8, the KPA500 shows zero on the LED power display. Does
>> this mean it is no longer amplifying, or is it actually amplifying
>> but not enough for the circuitry to determine how much?
>>
>> Jim Bennett / W6JHB Folsom, CA
> ______________________________________________________________
> 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]

Gary Gregory-2

Re: KPA500 Minimum Drive?

In reply to this post by Jack Brindle-2

or Tap the PWR button the kpa500 and watch the digital display on the
amplifier.
Gary

On 16 June 2016 at 13:50, Jack Brindle <[hidden email]> wrote:

> Fred’s assessment is correct - the output power resolution below 25 watts
> is pretty low. But it is still putting out power, at least to a point.
> There _is_ a lower limit to input power - it involves the ability of the
> frequency counter to do its job. If the counter cannot get an accurate
> count, it won’t be able to corroborate the frequency for the correct band
> selection. This level is in the neighborhood of 1 watt, giving you some
> range to play with.
>
> Enjoy playing with your KPA500!
>
> Jack, W6FB
>
>
> > On Jun 15, 2016, at 7:15 PM, Fred Jensen <[hidden email]> wrote:
> >
> > Hmmm ... I guess first question is, what's the problem? 25 W to 20W is
> slightly less than 1 dB, 0.16 S-unit. Just run barefoot?
> >
> > The LED Power display on the KPA500 is digital. It "measures the
> power," and puts it into one of a number of bins. If something is in the
> bin, it lights the LED. If the measured power isn't high enough for the
> lowest bin, all the bins are empty, no LED's light up, although there is
> still RF being made.
> >
> > Measuring power with simple instruments is hard ... well, sort of
> impossible. You can measure the voltage, but then you need to know the
> impedance, a complex number, not easily measured with a DVM. You can
> measure the current -- same problem. KPA500 is designed to emit 500W with
> 25-30W input. I think you're pushing the envelope here and nothing is
> wrong.
> >
> > 73,
> >
> > Fred K6DGW
> > - Northern California Contest Club
> > - CU in the Cal QSO Party 1-2 Oct 2016
> > - www.cqp.org
> >
> > On 6/15/2016 4:54 PM, James Bennett wrote:
> >> I share my KPA500 with a K3 and a KX3. When I want to operate JT65 or
> >> JT9 I normally run about 25 watts out, using the KX3 to drive the
> >> amp. With the KX3 set to 1.8 watts out, the amp gives me 25; with 2.2
> >> watts from the KX3, I get 30 watts out from the amp.
> >>
> >> But, what if I want to run 20 watts? Or 15? When I back the KX3 power
> >> level below 1.8, the KPA500 shows zero on the LED power display. Does
> >> this mean it is no longer amplifying, or is it actually amplifying
> >> but not enough for the circuitry to determine how much?
> >>
> >> Jim Bennett / W6JHB Folsom, CA
> > ______________________________________________________________
> > 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]
>

--

*Gary - VK1ZZ, K3NHLSkype: Gary.VK1ZZhttp://www.qsl.net/vk1zz
<http://www.qsl.net/vk1zz>Motorhome Portable*
*Miss Behavin'*

*Elecraft K3KPA500FT #18KAT500FT #007*
______________________________________________________________
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]