[Elecraft] OT a bit: K3 Ant Tuner

[David Gilbert]

It's not just a power issue.  A filter only achieves its design goals if 
the impedance feeding it and the load impedance it sees are as 
expected.  Most filters are going to want to be fed by 50 ohms and see a 
load of 50 ohms.  Most rigs (not sure about the K3) don't actually 
present a pure 50 ohm output impedance, so using the internal tuner in 
the K3 supposedly would assure that the filter sees the correct feed 
impedance, and for an operation like Field Day having a properly 
performing filter might be more important than a bit of power loss in 
the K3 tuner inductor.

On the other hand, I'm not sure that the SWR meter in the K3 is a 
perfect indicator of a match to a 50 ohm load.  I recently did some SWR 
measurements on a new antenna setup for five different bands (three 
different antennas) using four different indicators ... the SWR meter in 
the K3, an AEA HF-CIA, an Elecraft W2, and a new FA-VA5.  All four 
instruments were located in the same spot on the transmission line for 
each band (I swapped them in and out), and I plotted the SWR curves for 
frequencies across each band band.  The readings with the most deviation 
from the others came from the K3, and for certain cable lengths (I did 
readings with and without an additional 7 foot length of feedline 
inserted) it was significant.

73,
Dave  AB7E



On 7/5/2019 8:32 AM, Don Wilhelm wrote:
> Rich,
>
> Yes and no.  With 2 antenna tuners in-line, there will be a bit more 
> loss due to inductor winding resistance, but other than that, it 
> should do harm.
>
> Several bandpass filters indicate that they should be between the rig 
> and the tuner (so the bandpass filters are not run at a high SWR).
> If the power rating of the bandpass filter is marginal with respect to 
> the rig power, then I would observe that caution. Refer to the 
> bandpass filter specs.
>
> 73,
> Don W3FPR
>
> On 7/5/2019 10:57 AM, Rich wrote:
>> To minimize emails direct replies would be nice.  I searched the web 
>> and could not find an answer.   I know there are a ton of smart folks 
>> on this list so I thought I would ask.
>>
>> On Field Day at typical setup is :
>>
>> K3 (or any radio) - bandpass filter -  External Antenna Tuner  - Antenna
>>
>> So the antenna was tuned via the external tuner, but saw a guy then 
>> using the K3 ant tuner to touch up the SWR between the radio and the 
>> bandpass filter.  Is that an acceptable practice?
>>
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