[Elecraft] K3 6M SWR

[Don Wilhelm]

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

wb6rse1 at mac.com 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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