[Elecraft] Can I measure antenna impedance with K2?

[Per-Tore Aasestrand]

Hi Don,

I still doubt that this is correct.

The L/C values given by the tuner, are the values as seen from the tx side.
It is the values that will make the tx happy. It does not say much about
the impedance at the rig end of the feeder.

In order to change the VSWR on the feeder itself, one has to put the
matching network (tuner) between the antenna and the feeder.

BTW, the tx is probably not conjugate matched by the tuner. Conjugate
matching does not apply to transmitters or power amplifiers. But I realize
there is a huge dissension in this area too. ;-)

Per-Tore / LA7NO



On 31 July 2014 22:42, Don Wilhelm <w3fpr at embarqmail.com> wrote:

> Per-Tore,
>
> Yes it is correct.  He stated that it is the impedance at the rig end of
> the feedline.
> That will not likely be the feedpoint impedance of the antenna. That
> impedance can be found if you do the calculations for the impedance
> transformation of the feedline (for which the length of the feedline must
> be known).
>
> 73,
> Don W3FPR
>
>
> On 7/31/2014 4:23 PM, Per-Tore Aasestrand wrote:
>
>> Hi Matt,
>>
>>  Of course you realise that the output impedance of the ATU will be the
>>> complex conjugate of the impedance at the rig end of your feedline.
>>>
>> I wonder if this is correct
>>
>> IMO, the task of the tuner is to make the tx happy, so it can look into
>> the
>> load it is designed for. Thus, it will translate the impedance as seen
>> from
>> the antenna connector into something as close to 50 ohm as possible. The
>> tuner will not change anything on the feeder. With or without the tuner,
>> the feeder will have the same VSWR.
>>
>> Per-Tore / LA7NO
>>
>>
>>
>>
>> On 31 July 2014 22:02, Matt VK2RQ <matt.vk2rq at gmail.com> wrote:
>>
>>  Of course you realise that the output impedance of the ATU will be the
>>> complex conjugate of the impedance at the rig end of your feedline.
>>> However, if you want to know the impedance of your antenna, you need to
>>> realise that the feedline is acting as an impedance transformer, and you
>>> need to take into account factors such as length of feedline, frequency
>>> of
>>> operation characteristic impedance and velocity factor of the feedline,
>>> etc..
>>>
>>> 73, Matt VK2RQ
>>>
>>>  On 1 Aug 2014, at 1:02 am, TF3KX <kristinn1 at gmail.com> wrote:
>>>>
>>>> Thanks. Yes, I can determine the tuner settings (L/C-values, etc.) and
>>>>
>>> from
>>>
>>>> the network equations derive the impedance these settings match into. It
>>>> would be neat if the K2 had enough CPU power and memory to carry these
>>>> calculations out for me and just display the R+jX. Perhaps a good
>>>> project
>>>> for a small program or an app...
>>>>
>>>> 73 - Kristinn, TF3KX
>>>>
>>>>
>>>>
>>>> --
>>>> View this message in context:
>>>>
>>> http://elecraft.365791.n2.nabble.com/Can-I-measure-
>>> antenna-impedance-with-K2-tp7591798p7591803.html
>>>
>>>> Sent from the Elecraft mailing list archive at Nabble.com.
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