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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