A question about the KXPA100.

[Elecraft mailing list]

I would like to drive the amp with a tx  that shows the PTT Out line to be 250mA at 30 V (max).  Do I need to modify current and voltage from the transmitter to the KXPA100?
The Key In pin for the amp wants 5V at 1 mA.

AJ4YA
Grady

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[Jim Rhodes-2]

The KXPA100 has 5v on the key line and is activated by a closure to ground.
Current upon closure is only about 1ma. You seem to make it sound like your
radio has a voltage on the key out port, this would be unusual in modern
rigs. Most rigs provide a closure to ground to key the amp. It seems likely
to me that your radio is rated to handle up to 30v on the key port and a
current of up to 250ma. This would mean that the rig would have no problem
handling the 5v at 1ma from the KXPA100. However if the rig truly measures
30v (or actually any voltage) on the key port you would need some kind of
relay or other switching circuit to provide the closure to ground to key
the KXPA100.

On Wed, Jun 14, 2017 at 7:06 PM, Grady Harper via Elecraft <
[hidden email]> wrote:

> I would like to drive the amp with a tx  that shows the PTT Out line to be
> 250mA at 30 V (max).  Do I need to modify current and voltage from the
> transmitter to the KXPA100?
> The Key In pin for the amp wants 5V at 1 mA.
>
> AJ4YA
> Grady
>
> Sent from my iPad
> ______________________________________________________________
> 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]
>

--
Jim K0XU
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[Don Wilhelm]

Grady,

Is that "250mA at 30 V (max)" the listing in the rig's specifications?
If so, it says that the rig's rating for its KEYOUT (or PTT Out) is the
maximum it can tolerate without damage.  It normally would be a closure
to ground (either through a saturated transistor or FET or relay
points), and source no voltage of its own.

You can easily check that by putting your DMM probe between the PTT Out
jack and ground.  First set your DMM to read voltage and do a quick
transmit.  If my guess is right, your DMM will read zero volts when in
either receive or transmit - proof that the rig does not source voltage
on its PTT Out jack.  That spec rating is only the maximum voltage and
current that it can handle from an external device.

If all that is true, then set the DMM to read ohms, and then put it in
transmit.  The DMM is expected to indicate very nearly zero ohms.

If those things check out as expected you are "good to go".  The KXPA100
will source 5 volts with a current of 1mA when the KEYIN jack is
shorted.  That does not exceed either the voltage nor the maximum
current rating for your rig.

Nothing is needed other than the connecting cable.

73,
Don W3FPR

On 6/14/2017 8:06 PM, Grady Harper via Elecraft wrote:
> I would like to drive the amp with a tx  that shows the PTT Out line to be 250mA at 30 V (max).  Do I need to modify current and voltage from the transmitter to the KXPA100?
> The Key In pin for the amp wants 5V at 1 mA.
>
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