[Elecraft] OT a bit: K3 Ant Tuner

[K9MA]

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 <xdavid at 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 <donwilh at 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

k9ma at sdellington.us