K2/100 Problem with Hi Reflected Power driving amp

[John WA6YSY]

Hi all. I have a K2 with the KPA100 installed. I'm using the K2/100 to drive
a tube amplifier through a tuner. The K2-100 keeps tripping off with the
HiRefl message showing not every time, but often enough that a QSO is
impossible. The K2/100 doesn't 'reset' (has no output) when rekeyed unless I
rotate the power setting knob ever so slightly.

What am I doing wrong? Any way to increase the delay before the High
Reflected power takes effect as I suspect it's transient? I also have the
t-r rel

Any assistance will be greatly appreciated.
73, John  WA6YSY

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[Don Wilhelm-4]

John,

Just how high is the reflected power (do a TUNE and it will be
displayed).  The KPA100 throttles back power if the SWR is greater than
2.0-1.

There are several possibilities, and only some have to do with the
K2/100.  One is a bad coax, another is a PL-259 that is not properly
tightened to the KPA100 (or anywhere else in the system).  What happens
when you transmit into a dummy load?

Your problem may be in the input of the amplifier and not the K2.  If
the amplifier drive impedance changes when it sees RF, then it may not
be usable without modification.  Is there any chance that the input
circuit to the amp is not fully switched and the bias stable within the
15 ms. period after the K2 key is closed?
Does the problem show up only on CW or do you get the same result when
operating SSB with PTT?  If that is the problem, you will have to
speed-up the relay in the amp (or replace it with a faster relay).

If this is a recently constructed KPA100, I have a different set of
questions?  Do you find the same result on all bands or only one or
two?  Does the Hi Refl message appear when working the KPA100 into a
dummy load?

73,
Don W3FPR

John wrote:

> Hi all. I have a K2 with the KPA100 installed. I'm using the K2/100 to drive
> a tube amplifier through a tuner. The K2-100 keeps tripping off with the
> HiRefl message showing not every time, but often enough that a QSO is
> impossible. The K2/100 doesn't 'reset' (has no output) when rekeyed unless I
> rotate the power setting knob ever so slightly.
>
> What am I doing wrong? Any way to increase the delay before the High
> Reflected power takes effect as I suspect it's transient? I also have the
> t-r rel
>
> Any assistance will be greatly appreciated.
> 73, John  WA6YSY
>  
>

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[Doug Joyce]

John / Don:  I don't have a K2 (just got my new K3/10 operational
yesterday), but I wonder why you need a tuner between the K2/100 and the
tube amplifier.  Shouldn't the tuner be put in bypass mode or does the
amplifier not have a tuned input on the various ham bands?

73, Doug  VE3MV

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: <[hidden email]>
Cc: <[hidden email]>
Sent: Saturday, January 10, 2009 12:53 PM
Subject: Re: [Elecraft] K2/100 Problem with Hi Reflected Power driving amp

> John,
>
> Just how high is the reflected power (do a TUNE and it will be
> displayed).  The KPA100 throttles back power if the SWR is greater than
> 2.0-1.
>
> There are several possibilities, and only some have to do with the
> K2/100.  One is a bad coax, another is a PL-259 that is not properly
> tightened to the KPA100 (or anywhere else in the system).  What happens
> when you transmit into a dummy load?
>
> Your problem may be in the input of the amplifier and not the K2.  If
> the amplifier drive impedance changes when it sees RF, then it may not
> be usable without modification.  Is there any chance that the input
> circuit to the amp is not fully switched and the bias stable within the
> 15 ms. period after the K2 key is closed?
> Does the problem show up only on CW or do you get the same result when
> operating SSB with PTT?  If that is the problem, you will have to
> speed-up the relay in the amp (or replace it with a faster relay).
>
> If this is a recently constructed KPA100, I have a different set of
> questions?  Do you find the same result on all bands or only one or
> two?  Does the Hi Refl message appear when working the KPA100 into a
> dummy load?
>
> 73,
> Don W3FPR
>
> John wrote:
> > Hi all. I have a K2 with the KPA100 installed. I'm using the K2/100 to

drive
> > a tube amplifier through a tuner. The K2-100 keeps tripping off with the
> > HiRefl message showing not every time, but often enough that a QSO is
> > impossible. The K2/100 doesn't 'reset' (has no output) when rekeyed
unless I
> > rotate the power setting knob ever so slightly.
> >
> > What am I doing wrong? Any way to increase the delay before the High
> > Reflected power takes effect as I suspect it's transient? I also have
the

> > t-r rel
> >
> > Any assistance will be greatly appreciated.
> > 73, John  WA6YSY
> >
> >
> _______________________________________________
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> You must be a subscriber to post to the list.
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[Stephen W. Kercel]

John:

As another poster noted, why do you use a tuner between the K2 and the
amp unless the amp has an untuned input?

Are you sure that the tuner is actually adjusted to present a 50 ohm
load to the K2?

Echoing some of Don's points:

Is there something wrong with the timing of the keying sequence?
Specifically, is the amp being switched in slightly after the K2 comes
on? One theory of your problem is that when you key the K2 it comes up
to full power, and then the relay that cuts the amp into the circuit
closes a moment later, and while the relay is moving from one position
to another the fully powered K2 is looking into an open circuit.

Assuming that timing is not the problem, as Don has noted, perhaps your
amplifier input impedance is changing as it moves from no power to full
power. The protective circuitry of the K2 can be very touchy; mine gives
the Hi Refl warning and starts to roll back power if my SWR exceeds 1.7.

Assuming that the amplifier does not require the full 100 Watts drive to
operate properly (most do fine with 65-80 Watts drive) one way to deal
with varying load impedance (provided it does not vary too much) is to
put a 1 dB 50 ohm 25 Watt fixed attenuator between the K2 and the
amplifier input. That would attenuate your 100 Watt output to only 80
Watts drive, however, it would significantly dampen the variation in
impedance that the K2 sees.

Fixed high power attenuators are not that common in ham radio, but are
very common in professional situations. Brand new ones can be quite
expensive, but you can get pretty good deals on them on eBay. There are
various brands; NARDA is one of the better choices.

I am currently in the process of refurbishing an old Dentron GLA-1000B
(tuned input) to use with my K2/100. For that reason, I am very
interested in hearing your progress in solving your problem. I am just
about to start building the QSK switch that AD5X (a regular poster on
this list) published in the February 2008 QST.

I really hope you get this solved.

73,

Steve Kercel
AA4AK


John wrote:

> Hi all. I have a K2 with the KPA100 installed. I'm using the K2/100 to drive
> a tube amplifier through a tuner. The K2-100 keeps tripping off with the
> HiRefl message showing not every time, but often enough that a QSO is
> impossible. The K2/100 doesn't 'reset' (has no output) when rekeyed unless I
> rotate the power setting knob ever so slightly.
>
> What am I doing wrong? Any way to increase the delay before the High
> Reflected power takes effect as I suspect it's transient? I also have the
> t-r rel
>
> Any assistance will be greatly appreciated.
> 73, John  WA6YSY
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft   
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>  

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