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KX3 temporary high SWR on PTT with external Amplifier

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EA2BD

KX3 temporary high SWR on PTT with external Amplifier

Hello,
I want to check if anyone experiences the same behaviour when connecting the KX3 to an external amplifier.

- I receintly added an external amplifier to my KX3.
- I connected the PTT cable to the ACC2 port and to the amplifier.
- I set the Menu ACC2 on the KX3 to Active low, as specified.
- I verified if the cable works and it closes contact all right every time I key down.

The TROUBLE is:
Everytime I send a dit (CW) or start talking (Voice) the SWR indicator on the KX3 shows full reading (Hi SWR!) just briefly and it quickly relaxes down to normal reading (SWR 1:1) during the rest of transmission.

I believe there should be any kind of delay between the TX on the KX3 and the TX on the ampli, that causes the momentarily Hi SWR reading... But this is extrange because the PTT cable is in!

Does anyone have experienced similar phaenomena?
Any idea to overcome this?
Do you consider there will be a real overload on the finals due to this small transient time?

I drive with 2 watt out from the KX3 to get around 90W out from my Amplifier.

Wait for your feedback, many thanks!
73 de Ignacio EA2BD

Elecraft mailing list

Re: KX3 temporary high SWR on PTT with external Amplifier

Yes, the switching time in the amplifier is too slow, hence you need to consider sequencing the amp keying so that it keys first then the KX3. Sounds like the amp has a relay vs solid state switching.

Mel, K6KBE

From: EA2BD via Elecraft <[hidden email]>
To: [hidden email]
Sent: Thursday, September 29, 2016 9:06 AM
Subject: [Elecraft] KX3 temporary high SWR on PTT with external Amplifier

Hello,
I want to check if anyone experiences the same behaviour when connecting the
KX3 to an external amplifier.

- I receintly added an external amplifier to my KX3.
- I connected the PTT cable to the ACC2 port and to the amplifier.
- I set the Menu ACC2 on the KX3 to Active low, as specified.
- I verified if the cable works and it closes contact all right every time I
key down.

The TROUBLE is:
Everytime I send a dit (CW) or start talking (Voice) the SWR indicator on
the KX3 shows full reading (Hi SWR!) just briefly and it quickly relaxes
down to normal reading (SWR 1:1) during the rest of transmission.

I believe there should be any kind of delay between the TX on the KX3 and
the TX on the ampli, that causes the momentarily Hi SWR reading... But this
is extrange because the PTT cable is in!

Does anyone have experienced similar phaenomena?
Any idea to overcome this?
Do you consider there will be a real overload on the finals due to this
small transient time?

I drive with 2 watt out from the KX3 to get around 90W out from my
Amplifier.

Wait for your feedback, many thanks!
73 de Ignacio EA2BD

--
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Sent from the Elecraft mailing list archive at Nabble.com.
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Don Wilhelm

Re: KX3 temporary high SWR on PTT with external Amplifier

In reply to this post by EA2BD

Ignacio,

The amplifier is not switching to the transmit state within the time
between when the KX3 pulls PTT low and the time RF appears. I believe
that time is about 8 milliseconds.
Yes, your KX3 is working into an open load when that happens - hence the
high SWR.
That condition is known as "hot switching", and even if it does not
eventually damage the KX3 PA, the relay contacts in your amplifier T/R
changover will become pitted due to the arcing.

One solution is to modify your amplifier with a QSK T/R switch or
substitute fast vacuum relays.
Another solution is not to use QSK or VOX - connect a footswitch to the
KX3 PTT *input* (ACC2 jack's TIP connection) and set the ACC2 IO menu to
LO=PTT if the footswitch grounds the connection.
Then use the footswitch to put the KX3 into transmit before you operate
the paddles or speak into the microphone. In other words, do not turn
on VOX.
Another way to put the KX3 into transmit mode without the footswitch is
to use the XMIT button on the KX3.

73,
Don W3FPR

On 9/29/2016 12:06 PM, EA2BD via Elecraft wrote:

> Hello,
> I want to check if anyone experiences the same behaviour when connecting the
> KX3 to an external amplifier.
>
> - I receintly added an external amplifier to my KX3.
> - I connected the PTT cable to the ACC2 port and to the amplifier.
> - I set the Menu ACC2 on the KX3 to Active low, as specified.
> - I verified if the cable works and it closes contact all right every time I
> key down.
>
> The TROUBLE is:
> Everytime I send a dit (CW) or start talking (Voice) the SWR indicator on
> the KX3 shows full reading (Hi SWR!) just briefly and it quickly relaxes
> down to normal reading (SWR 1:1) during the rest of transmission.
>
> I believe there should be any kind of delay between the TX on the KX3 and
> the TX on the ampli, that causes the momentarily Hi SWR reading... But this
> is extrange because the PTT cable is in!
>
> Does anyone have experienced similar phaenomena?
> Any idea to overcome this?
> Do you consider there will be a real overload on the finals due to this
> small transient time?
>
> I drive with 2 watt out from the KX3 to get around 90W out from my
> Amplifier.
>
> Wait for your feedback, many thanks!
> 73 de Ignacio EA2BD
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/KX3-temporary-high-SWR-on-PTT-with-external-Amplifier-tp7622916.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> 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]
>

Bill K9YEQ

Re: KX3 temporary high SWR on PTT with external Amplifier

Not a cheap solution, but Heil produces a foot switch that sequences the key
line. Of course this requires some wiring.

Bill
K9YEQ

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of Don
Wilhelm
Sent: Thursday, September 29, 2016 1:08 PM
To: EA2BD <[hidden email]>; [hidden email]
Subject: Re: [Elecraft] KX3 temporary high SWR on PTT with external
Amplifier

Ignacio,

The amplifier is not switching to the transmit state within the time between
when the KX3 pulls PTT low and the time RF appears. I believe that time is
about 8 milliseconds.
Yes, your KX3 is working into an open load when that happens - hence the
high SWR.
That condition is known as "hot switching", and even if it does not
eventually damage the KX3 PA, the relay contacts in your amplifier T/R
changover will become pitted due to the arcing.

One solution is to modify your amplifier with a QSK T/R switch or substitute
fast vacuum relays.
Another solution is not to use QSK or VOX - connect a footswitch to the
KX3 PTT *input* (ACC2 jack's TIP connection) and set the ACC2 IO menu to
LO=PTT if the footswitch grounds the connection.
Then use the footswitch to put the KX3 into transmit before you operate the
paddles or speak into the microphone. In other words, do not turn on VOX.
Another way to put the KX3 into transmit mode without the footswitch is to
use the XMIT button on the KX3.

73,
Don W3FPR

On 9/29/2016 12:06 PM, EA2BD via Elecraft wrote:

> Hello,
> I want to check if anyone experiences the same behaviour when
> connecting the
> KX3 to an external amplifier.
>
> - I receintly added an external amplifier to my KX3.
> - I connected the PTT cable to the ACC2 port and to the amplifier.
> - I set the Menu ACC2 on the KX3 to Active low, as specified.
> - I verified if the cable works and it closes contact all right every
> time I key down.
>
> The TROUBLE is:
> Everytime I send a dit (CW) or start talking (Voice) the SWR indicator
> on the KX3 shows full reading (Hi SWR!) just briefly and it quickly
> relaxes down to normal reading (SWR 1:1) during the rest of transmission.
>
> I believe there should be any kind of delay between the TX on the KX3
> and the TX on the ampli, that causes the momentarily Hi SWR reading...
> But this is extrange because the PTT cable is in!
>
> Does anyone have experienced similar phaenomena?
> Any idea to overcome this?
> Do you consider there will be a real overload on the finals due to
> this small transient time?
>
> I drive with 2 watt out from the KX3 to get around 90W out from my
> Amplifier.
>
> Wait for your feedback, many thanks!
> 73 de Ignacio EA2BD
>
>
>
> --
> View this message in context:
> http://elecraft.365791.n2.nabble.com/KX3-temporary-high-SWR-on-PTT-wit
> h-external-Amplifier-tp7622916.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> 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]
______________________________________________________________
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Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

EA2BD

Re: KX3 temporary high SWR on PTT with external Amplifier

Hello,

thanks for all your comments. Okay, that's what I supposed it was going on.
I'll try to find a way to get out of this and make the amp switches earlier.

Take care, 73
Ignacio