K3 6M SWR

[wb6rse1]

Antenna: M2inc 6M5X. I'm getting much higher SWR readings from an LP100 vs the K3. The LP100 shows a rather flat response across several hundred kc vs a typical curve over the same frequency range using the K3's internal SWR meter. The LP100 coupler is rated to 54 MHz.

Anyone else experience this?

TU - Steve WB6RSE
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[Don Wilhelm-4]

Steve,

How much higher is "much higher"?  And at what level?

Do you have the LP-100 in the line at the same time as the K3?  If that
is the situation, then your results are not surprising, even a short
length of coax can cause a vast difference in SWR readings - that effect
becomes more significant as the frequency is increased.

To do a valid test, connect the coax to the LP-100 and observe the SWR
reading.  Then disconnect the coax from the output of the LP-100 and
connect it directly to the K3.  How do the SWR readings compare?  If you
have calibrated the K3 wattmeter (see the manual), the readings should
be close to each other (an SWR difference of 0.2 is NOT significant
IMHO).  One of the most inaccurate instruments that hams use everyday is
the wattmeter - they are often in error by as much as 20% when measuring
power, but can be worse than that when measuring an SWR that is greater
than 1.0.  The only thing that can be said with certainty is that a
properly balanced wattmeter will indicate an SWR = 1.0 when the
reflected power is zero.

If a wattmeter is properly balanced, we can always know that zero
reflected power will produce a 1.0 SWR, but fr values away from 1.0,
inaccuracies can and will exist - that is just a fact of life, and the
LP-100 is better than most for accuracy in power, but I cannot speak for
its SWR accuracy.

So bottom line, be certain you are measuring SWR at the same point along
the feedline.  In theory, it should not make any difference, but in
practice it does.  The further away from an SWR of 1.0, the worse the
potential error.  Reacatance at the measurement point further
complicates the situation because one measurement technique will produce
a different result than another technique (even though they will be the
same at SWR = 1.0).  That is precisely why I use a known pure resistive
100 ohm load (SWR = 2.0)when setting the SWR indication on the
wattmeters in transceivers that I calibrate - that produces an SWR meter
that will be accurate at SWR = 1.0 and SWR = 2.0, but at values other
than those two points, I would not bet my lunch on exact readings.  All
bets are off when measuring an antenna for comparing two meters - better
instrumentation is needed for valid observations.

I now step down from my "wattmeter soapbox".

73,
Don W3FPR

[hidden email] wrote:
> Antenna: M2inc 6M5X. I'm getting much higher SWR readings from an LP100 vs the K3. The LP100 shows a rather flat response across several hundred kc vs a typical curve over the same frequency range using the K3's internal SWR meter. The LP100 coupler is rated to 54 MHz.
>
>
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