One reason to use the internal ATU with an external tuner is so the
transmitter can see a low SWR over a range of frequencies, without
retuning the external filter. Also, if the external tuner can only get
down to, say 2:1, the internal ATU will get it down to 1:1, and the
transmitter will be happier.
73,
Scott K9MA
On 7/5/2019 13:20, Mark Goldberg wrote:
I stand corrected.
I made an assumption, probably incorrectly, that the reason they had a
second tuner was that the first did not successfully tune the antenna. They
just decided to put the bandpass filter between the two tuners, which would
have provided a mismatch at both the filter input and output. I just used a
mismatch at the output as an example. I just provided an example of filter
performance degradation with even what would be considered a reasonable SWR.
I prefer Jack's solution of bypassing the internal K3 tuner. I do have a
situation where my antenna tuner can't tune my antenna on 160. Rather than
try to use two tuners in series with the requisite losses, I added a shunt
inductor on a big ferrite core to provide most of the required inductance
for a match. It gets hot.
73,
Mark
W7MLG
On Fri, Jul 5, 2019 at 10:57 AM David Gilbert <xda...@cis-broadband.com>
wrote:
I think you misread the situation. The question isn't whether to put a
single antenna tuner between the antenna and filter versus putting it
between the rig and the filter. The question is whether putting an
ADDITIONAL tuner (the one internal to the K3) at the input of the filter
is a good idea. And to me it seems the answer is yes.
I think we all agree that the right feed impedance and load impedance
for a filter is important. And as I pointed out, not just for power
handling, but also for the filter to actually filter as it was intended.
73,
Dave AB7E
On 7/5/2019 10:18 AM, Mark Goldberg wrote:
I could not let this go. I've done a lot of work with bandpass filters.
The
mismatch will degrade the filter.
For an example, I used Elsie, which is a filter calculator. Using the
example 20 Meter bandpass filter, the passband loss is about .25 dB with
matched 50 ohms in and out. Changing the output impedance to 38+j12 (38
ohms plus 135 nH inductor at 14.15 MHz, about 1.5:1 SWR), the passband
losses increase to about 0.4 - .44 dB and vary more over the band.
Here are the schematics and plots, anyone is welcome to check my
calculations, as I do make mistakes!
https://drive.google.com/file/d/1kj31IL_px6nVyRadW4nOi_c6FLgyaRyk/view?usp=sharing
The loss in the filter will almost double. For 100W in, the loss goes
from
about 6W to about 10W. So, it is not a good idea. A worse match will
result
in even more losses, perhaps overheating and destroying the filter.
73,
Mark
W7MLG
On Fri, Jul 5, 2019 at 8:32 AM Don Wilhelm <donw...@embarqmail.com>
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?
--
Scott K9MA
k...@sdellington.us
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