[Elecraft] k3 SWR readings seem generous

[Stewart Baker]

This thread came at the right time. I have just finished 
re-calibrating my LP-100A. I did this after having used the unit 
for 6 months, however the calibration was very close to the 
original settings.

Then I thought that I would check my K3 SWR indication.
The results are not as good as I would expect.

I set the K3 with a tune power of 10W, representing  the level of 
power one might use to adjust an ATU.

The measurements I made were using 2 x 8 inch lengths of RG8U from 
the K3 into the LP-100A coupler, and then from the coupler into 
the dummy load.

The dummy load is a precision 100W one which I measured with a VNA 
and has a VSWR of <1.03 from 1 to 30 Mhz. To simulate a 2:1 VSWR
I used another dummy load (not quite as good) in parallel.

The K3 output was from ANT1 using the internal ATU. The ATU was 
automatically tuned to 1:1 on all bands.
The results I got for 2:1 VSWR are as follows:-

			LP-100			    K3
160         1.99                1.8
80           1.99                1.8
60           1.99                1.8
40           1.95                1.8
30           1.97                1.6
20           1.97                1.4
17           1.97                1.3
15           1.96                1.2
12           1.96                1.5
10           1.96                1.4  

As can be seen my K3 SWR indication constantly under reads.
However, it really gets bad on 20,17 & 15.

I will be interested in the results of others conducting similar 
tests.

73
Stewart G3RXQ             		
 
On Thu, 1 Jan 2009 17:47:04 -0800, Mike Scott wrote:
> I have been working on antennas today and have a puzzle. I am 
finding that
> the K3 SWR indications are unbelievable generous.
>
> With my 40M inverted V fed with RG8X (50 ohm) coax I see that 
the K3 seems
> generous in the SWR indication on tune with ATU bypassed. I have 
noticed a
> slight change in SWR with K3 power setting so the following was 
taken with
> K3 tune power set to 100 watts. If I set it to 10 watts the 
discrepancy is
> greater...
>              SWR     SWR     SWR
> Freq.         K3      VA1     Daiwa
> 7.00 MHz     1.3      1.92    2.0
> 7.05 MHz     1.2      1.92    1.9
> 7.1 MHz      1.2      1.98    1.95
> 7.15 MHz     1.3      2.26    2.1
> 7.2 MHz      1.9      2.60    2.3
> 7.25 MHz     1.5      2.88    2.6
> 7.3 MHz      1.6      3.32    2.7
>
> The Daiwa is the CN-101L cross needle meter. The VA1 is the 
Autek Rx Vector
> antenna analyzer.  The VA1 does not have a tuned input so it is 
possible
> that it can be fooled by local broadcast stations. I don't 
suspect this
> issue here as there aren't any close by broadcast stations that 
I am aware
> of. The Daiwa and the VA1 tend to agree pretty well anyway. The 
K3
> measurements are the outliers. This antenna on a "Tenna Dipper" 
shows
> minimal SWR at 7.040 MHz, just where I tuned it a few years ago. 
The LED
> does not extinguish indicating higher than 1:1 SWR at the 
minimum. If you
> look at the numbers, I guess I don't believe the K3, Do you 
think my antenna
> is below 1.6 to 1 across the entire 40M band?
>
>
> So now on to 20M dipole fed with RG58 (50 Ohm Coax)...
> The Tenna Dipper fully extinguishes at 13.805 MHz indicating 
that my antenna
> is bit too long but is close to 1:1 at that frequency.
>
> Freq        K3     VA1     Daiwa
> 13.81       --     1.12    --
> 14.0 MHz    1.1    1.24    1.31
> 14.1 MHz    1.1    1.30    1.70
> 14.2 MHz    1.1    1.55    1.85
> 14.3 MHz    1.2    1.69    1.85
>
> RG58 may have some losses on this band so perhaps all of the SWR 
indications
> are generous, some more than others. The dipole is a low one and 
probably
> isn't 72 ohms at the feed point.
>
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> K3-100 #508/ KX1  #1311
>
>
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