Posted by
Iain MacDonnell - N6ML-2 on
Nov 04, 2009; 7:28pm
URL: http://elecraft.85.s1.nabble.com/K3-SWR-Accuracy-reprise-tp3943810p3947558.html
I've been noticing some apparently anomalies in this area too, for example...
I have two dummy loads - one is a 2kW rated PalStar, which doesn't
appear to be exactly 50ohms (but close enough for usual purposes), and
a Bird Termaline, which is mil-spec 50ohms (and shows as such on a
sweep analyser), 150W rated.
With 100W at 3520kHz, into the Bird, my LP-100A shows 1.00:1, and the
K3 shows 1.0:1.
Into the PalStar, the LP-100A shows 1.20:1, but the K3 still shows 1.0:1.
I'm using the same feedline arrangement in both cases (i.e. I unplug
the cable from one load and plug it into the other), and I do NOT have
the KAT3 installed. I've tried different feedline arrangements too
(including a short one between the K3 and the LP-100A coupler), and
the results seem to be consistent.
~Iain / N6ML
On Wed, Nov 4, 2009 at 9:53 AM, Eric Swartz - WA6HHQ, Elecraft
<
[hidden email]> wrote:
> How long is the coax between the LP100 sensor and the K3? This can have
> a significant impedance transformation impact as you go to higher
> frequencies, leading to a different indicated SWR at each end.
>
> 73, Eric
>
>
> Stewart wrote:
>> Hi,
>> Now traffic on the new K3 Macro functions has somewhat died down,
>> I would like to raise again the issue of the K3's SWR measurement
>> accuracy.
>>
>> I did some tests using dummy loads and a LP-100 meter as follows.
>>
>> 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 consistently under reads.
>> However, it really gets bad on 20,17 & 15.
>>
>> From previous replies I understand that this under reading would
>> be compensated for in the firmware, sometime in the future .
>>
>> Is this still on the list of problems to be addressed ?
>>
>> 73
>> Stewart G3RXQ
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