SWR safe levels question

[KD8NNU]

Getn's

I have been searching for the "safe" swr level for the k3.   The reason
that I ask this is because the SWR reading on the k3 is differnt than my
MFJ 259 and the meter levels on the front of my tuner.

My tuning procedure is to have a switch in the antenna lines so that I
first look at the mfj to dial in a very low SWR value.

Then I switch the radio back in line and use the tune feature at 15w to
check the settings.  Sometimes they are spot on with the 259 other times
they are not.

When I transmitt I also get the SWR bouncing on the amp meter and the k3
if I try to tune to the lowest number on the k3 instead of the meter on
the tuner.

So what is the correct thing to look at and is this normal

Setup is a barefoot k3 to a mfj 962d tuner.  Current antenna is an Alpha
Delta Trapped dipole.

I am not haveing any problem, just trying to understand what is
reallying happening in the system.

I think that I over think this way too much but if I could find a real
referenc for max swr for the k3 and understood what I am looking at it
could make me a better operator.

Thanks
~73
Don
KD8NNU
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[AC7AC]

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[k6dgw]

I worked my way through college on the engineering crew of the local
[only] TV station.  Twice a year, we had to do a Proof of Performance
and log it.  It included assuring that the HP frequency/modulation
monitors were correct.  The CE assigned the modulation monitors to me
and said, "You can't use any method that relies of the calibration of
any of our test equipment."

Very long story short, I finally discovered that if I fed the aural
transmitter a known audio frequency and slowly increased the amplitude
while monitoring the amplitude of the FM carrier, it would go to zero at
a known modulation index determined by the zero-order Bessel function of
the first kind.  I could get a known frequency audio signal from the
sync generator which was phase locked to the network which was phase
locked to the NBS standard.  And the key ... I could use my SX-28/VHF
converter with the narrow crystal filter to exclude the FM sidebands to
measure the amplitude on the S-meter ... but ONLY because I was looking
for zero on the meter.  That's the the key.  The meter is accurate and
requires no calibration at zero.  Elsewhere, it's anyone's guess.

And that's the key to your issue, Don.  SWR bridges are notoriously
inaccurate at all readings, except zero [i.e. 1:1].  When the bridge is
balanced [i.e. the load is 50+j0 ohms], it produces zero volts and all
meters are inherently accurate at zero.  At any other value, your guess
is as good as any of theirs.

Fred K6DGW
Auburn CA

On 8/28/2011 6:15 AM, [hidden email] wrote:
>
> Getn's
>
> I have been searching for the "safe" swr level for the k3.   The reason
> that I ask this is because the SWR reading on the k3 is differnt than my
> MFJ 259 and the meter levels on the front of my tuner.
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[Bob Cunnings NW8L]

If you're looking for a documented level, here's the change note
describing the SWR power rollback feature when it was introduced (MCU
1.87 / DSP 1.69 on 5-3-08):

  * POWER ROLLBACK BASED ON REFLECTED POWER:  Power rollback begins at about
    2.5:1 at 100 W (and of course much higher SWRs are tolerated at
lower power settings).
    Recovers to original target power level after mismatch is corrected.

When making antenna tuner adjustments I adopt the usual convention for
solid state finals: keep the SWR below 2:1. In the case of the K3 that
apparently puts me well below the foldback threshold at 100 W so I'm
content. It's the SWR indication on the K3 that I care about since
that's what's driving the K3's foldback feature.

Bob NW8L

>I have been searching for the "safe" swr level for the k3.
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[KD8NNU]

Thanks Bob,

This was the kind of information that I was looking for.

I am not haveing problems per say, I just wanted to know how good is
good or how closes is close.

When I get it close on the MFJ and then go to check with power, I desire
to have the meter on the tuner match the K3.  My goal is to get the
reflected power needle to be at zero if possible and also have the k3 at
1.1

Now with this information if the k3 is a little different I suspect it
is due to the antenna switch and the extra coax.

Thx
Don

~73
Don
KD8NNU


On Sun, Aug 28, 2011 at 1:37 PM, Bob Cunnings wrote:

> If you're looking for a documented level, here's the change note
> describing the SWR power rollback feature when it was introduced (MCU
> 1.87 / DSP 1.69 on 5-3-08):
>
>   * POWER ROLLBACK BASED ON REFLECTED POWER:  Power rollback begins at
> about
>     2.5:1 at 100 W (and of course much higher SWRs are tolerated at
> lower power settings).
>     Recovers to original target power level after mismatch is
> corrected.
>
> When making antenna tuner adjustments I adopt the usual convention for
> solid state finals: keep the SWR below 2:1. In the case of the K3 that
> apparently puts me well below the foldback threshold at 100 W so I'm
> content. It's the SWR indication on the K3 that I care about since
> that's what's driving the K3's foldback feature.
>
> Bob NW8L
>
>> I have been searching for the "safe" swr level for the k3.
> ______________________________________________________________
> 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

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