[Elecraft] How accurate is the K3 SWR meter

[Don Wilhelm]

Robert,

I will not answer your question, but may offer some things to 
contemplate.  If I had to make a guess, I would say that the K3 SWR 
readings should be accurate.

Now, while saying that, if you are adjusting for a 1:1 SWR, the exact 
calibration of the wattmeter will not be any issue, just adjust for 
minimum reverse power and operate - that will be the correct setting.

You have the same problem as the man with two watches and never knows 
what time it is.
I really cannot answer your question because I do not haqve enough data.

The measurement of SWR with easy to connect SWR meters is not going to 
give you great and reliable results.  My advice is to trust none of them 
unless they have been calibrated and proven their worth.

If you want to do some tests with 2:1 SWR loads, I suggest you look at 
the Caddock Thick Film Power resistors.  Two 50 ohm resistors in series 
will give you a precision 100 ohm (SWR = 2.0) dummy load, while 2 of the 
50 ohm resistors in parallel will give you a 25 ohm (SWR = 2.0) 
precision load.

Of course, these resistors must be mounted on a heatsink to yield there 
advertized power rating, but  a heat sink salvaged from a computer CPU 
application will do a great job.

This are the loads I use when calibrating the SWR on wattmeters.  I 
cannot project accuracy beyond the SWR=2.0 point, but I do understand my 
measurement limitations.  Good engineering requires that I understand 
and reveal my measurement limits and the accuracy (1% in this case) of 
the measurement.

73,
Don W3FPR

On 3/19/2012 9:42 PM, Robert G. Strickland wrote:
> I am pretty new to the K3 world and just getting acquainted with the
> radio. I have a Vectronics Vector 500 antenna tuner with a cross needle
> swr meter. I notice a disparity between the swr readings on the K3 and
> on the antenna tuner. So, how accurate is the K3 swr reading? I can
> imagine that the Vector cross needle reading is not particularly
> accurate, but I don't know that for fact. I don't have access to a high
> quality swr bridge, so I'm trying to figure out which reading to trust.
> Any comments are much appreciated.
>
> ...robert