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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