[CQ-Contest] Coax Stubs for SO2R

[Joe]

OK,
We all have here been discussing harmonics.

While I have heard harmonics, and these stubs help greatly with that 
problem.

I personally get more results from protection from ummm, wide band noise?

Maybe that isn't the right term, but say someone in on 40 CW and you are 
on 20 any mode,
You are not hearing the direct harmonic, but more of think a 2 meter 
repeater without duplexors. a either sucking of the band where each time 
the 40 station transmits, the 20 station looses it's sensitivity, like 
it's being desenced.

OR

not a de sensing, but an elevated noise floor pulsing with the 40 CW 
think 2 meters aurora contact.

Are the stubs really helping with these two wide signal problems ,, or 
am I dreaming that they are.

Joe WB9SBD
Sig
The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com
On 7/19/2016 4:04 AM, Jukka Klemola wrote:
>>> In case you really want to experiment, make the stub a little long.
>>>     -if you want to be precise, I would suggest to tune the stub to
>>> harmonic
>>> band lower edge
>>> Second, find a place where it attenuates the harmonic more than elsewhere.
>>>     -you will likely notice the maximum attenuation placement is not
>>> critical
>>>     -you will likely notice finding the spot where the attenuation is not
>>> too
>>> great is narrow
>>>
>> There is no need for "experimentation -- this is all well-settled science
>> that I learned in my university EE classes more than 50 years ago. The
>> resonant frequency of a quarter-wave  stub can easily be measured with even
>> the simplest of antenna analyzers. Connect the open-circuit stub to the
>> analyzer, then tune the analyzer frequency to find the lowest impedance (it
>> should be very near zero ohms).
>>
> In case a person wants to experiment, he can do some experimentation.
> My email was written so there is no complicated measuring equipment.
>
> That is, there is no need for antenna analyzers.
> You can use the station you have as the signal source and receiver on the
> harmonic band to evaluate the outcome.
> You can park the stub close enough to the band you want to attenuate using
> just two radios you have.
>
> You need your radio to analyze your system anyway to experiment the stub
> placement.
>
> You will notice the level of harmonic signal at the lower edge, in the
> center and at the upper edge of the band.
> Then decide what to do about the stub length. Shortening the stub will rise
> the attenuation frequency.
> I would suggest to leave it just a bit long .. I like CW more anyway.
>
>
> To do all that properly by scientific terms, you might need a bunch of
> Benjamins you can let go in return to a few boxes with some electronics
> inside.
>
> But as you have your station and want to experiment a little - it does not
> have to be any more complicated.
>
>
> Ward has the writing series about all technical matters .. this might be
> one tale to tell.
>
>
> 73,
> Jukka OH6LI
>
>
> PS.
> **Warning, scientific content:
> The stub length requirement along the feedline may get a small twist
> because of your system properties on the unwanted band .. in case there
> just happens to be s steep curve affecting the bands interaction, the
> antenna, the transmitter output or any other part of the system may
> attenuate the upper or lower part of the harmonic band by itself and you
> would need the stub more for the other part of the band.
>
> This is the weak connection between stub length and positioning ..the
> connection is not direct and is definitely not in any university books. You
> have to run into this phenomena and ponder a while what it is before you
> get the idea how it works.
>
> You do not have to notice this at all if you make and tune your stub when
> it is a part of your system with two or more radios and accessories you
> have.
>
> And, furthermore, if you make all analysis and pruning using lab
> instruments, you can easily forget the instruments output circuitry for
> sure have different output criteria than your transmitters' outputs.
> Same applies for the receivers' inputs. How they interact with the world
> that is outside the band they are on.
>
> This is precisely what harmonics are. They are a set of phenomena outside
> the intended use of the equipment and these phenomena do vary.
>
> Using lab equipment beyond a point will mislead you, will bring you
> extended work because you need to evaluate the outcome anyway with the real
> station, in addition to the lab equipment.
> For nearly any setup, the lab equipment will bring you to the ballpark ..
> but to really see how your station works, you must use the radios and other
> equipment at your station.
> The equipment have their characteristics and that is the real world where
> you need to be able to make the QSOs.
>
> The simplest example of this is connecting the stub to the RF testing
> equipment may differ a little from the way you connect it to your
> transmission system .. I have done that error and I hope also many others.
> I did that before I got a two port analyzer. Tuning a stub with one port
> tool, like the Autek RF-1 small black box, can bring you into a journey you
> will actually see real life phenomena through experimentation.
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