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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