[Elecraft] KAT100 and external watt meter question

[John Buck]

Tom, I believe a clarification is in order.
As you correctly state, the KAT-100 does not change the impedance at the 
output of the KAT 100.  Since the impedance at that point is not 50 ohms 
unless a dummy load or matched antenna are used, and most SWR meters and 
Power meters including the DAIWA read correctly only if at a 50 ohm 
node, the meter will not indicate SWR or Power accurately unless the 
load is 50 ohms.  I know that the FWD and Rev power reading will not be 
accurate.  Is it possible that the SWR indicated by the ratio is correct 
  even if the load impedance is way off from 50 ohms?  Certainly the 
forward power and is not accurate.

Glen, your observations are probably correct.  You will get a good match 
on those frequencies where your antenna is close to 50 ohms and you will 
get false readings on those bands that are not 50 ohms.  If you put the 
watt meter between the KPA-100 and the KAT-100 you will be operating at 
a 50 ohm node and seeing accurate results. Placing a good 50 ohm meter 
on the unmatched node is not usually a good idea.  The voltages can get 
very high on some antennas.

Aloha,
John KH7T

Tom Hammond wrote:
> Glenn:
> 
>> I have a question as to what is the best way to use an external watt 
>> meter?
>> I have a DAIWA CN-101L external watt meter. I originally had the K2100 RF
>> out going to RF IN on the KAT 100 and ANT1 on the KAT100 going to 
>> connector
>> labeled  TR  on the external watt meter and then the antenna connected to
>> the connector labeled ANT on the external watt meter. I was getting a 
>> good match according to the K2100 display and the KAT100 LED's. The 
>> external watt meter however was showing high SWR on some bands especially 30 meters. 
>> On 40 meters and 20 meters the external watt meter, KAT100 and K2100 SWR 
>> displays all agree. On other bands the external watt meter showed very high 
>> SWR. I am
>> using a Carolina 40 Windom antenna by Radio works.
> 
> 
> The KAT100 _ONLY_ changes the impedance of the load it's being presented 
> between its ANT1 jack and the K2!!! Even though the ATU has done its 
> job, by providing an acceptable SWR to the K2, it has NOT changed the 
> load impedance of the antenna or its feedline.
> 
> As a result, the external wattmeter will always indicate the REAL SWR 
> being presented to the KAT100, and the KAT100 will indicate the 'TUNED' 
> SWR being presented to the K2.
> 
>> I re-arranged the configuration of the watt meter by connecting the RF 
>> out
>> from the K2100 to the TR connector on the external watt meter. Then 
>> the ANT
>> connector on the external watt meter goes to RF in on the KAT100. Then I
>> connected the antenna to the ANT1 on the KAT100. I then went through the
>> bands. The KAT100 re-adjusted the settings on all bands. Now the external
>> watt meter shows matched power out readings compared to the K2100 
>> display.
>> The SWR is low on all the bands according to the external watt meter, 
>> KAT100
>> and K2100. Is this the best way to have an external watt meter connected?
> 
> 
> It all depends upon what it is you want the DIAWA meter to indicate.
> 
> If you want it to duplicate the reading of the KAT100, then you have it 
> configured properly right now.
> 
> However, if you want to use the DIAWA to indicate actual SWR _ON_ the 
> feedline going to the antenna, then you should put it on the OUTPUT of 
> the KAT100, so it 'sees' what the antenna and feedline are doing.
> 
> 73,
> 
> Tom  N0SS
> 
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