[CQ-Contest] Coax Stubs for SO2R

Tue Jul 19 01:29:06 EDT 2016

Hello

have anyone tried making stubs from RG11 coax?

I determine i have some good lengths in stock and  I have always used
RG213 for stubs.

73s LB3RE Rag

Den tir, juli 19, 2016, 00:10 skrev Jim Brown:
> On Mon,7/18/2016 12:08 PM, Kenneth Wolff wrote:
>> Jim right of course -- the exception being the old Alphas with Pi-L
>> outputs.
>
> There are many amps with Pi-L outputs.  There's a table of those I've
> been able to learn about (with help from friends) at this link
> http://k9yc.com/Coax-Stubs.pdf
>
>
>> At the the old K1AR M2 we ran from my house we used a lot of stubs
>> because
>> we only had two towers.
>>
>> Stubs made with hard line have less loss and are deeper,  but narrower
>> nulls.
>
> Yes, and they can be TOO narrow, locking you into a narrow range of
> operating frequencies.
>
>>   Fixing 40 into 15 is a little trickier because it as a third
>> harmonic. I used an open 1/4 stub on 15m with a compensation stub to
>> tune
>> out the imaginary part of the leftover conductance on 40.
>>
>> Double and even triple stubs slightly offset across the band can be used
>> to
>> make a broader null.
>
> Yes.
>
>> The most important thing to do is to measure the coupling from each
>> transmit antenna into each other antenna using 10w transmit and either a
>> 50
>> ohm scope or a calibrated receiver.
>
> Yes, a very good move. But when we're talking stubs for harmonic
> suppression, we must measure that coupling at the frequency of the
> harmonic.
>
>> I made a spreadsheet of all the coupling (transcontuce) between antennas
>> to
>> plan my defense between bands. Some bands needed only a receive filer.
>> 1500W on 160m used to couple over 50W into the 80m vertical array. You
>> can
>> smoke receivers if you don't watch out!
>
> Great advice.  A vector network analyzer or a calibrated spectrum
> analyzer and signal generator can also do this well.
>
> 73, Jim K9YC
>>
>> - Ken K1EA
>>
>> On Mon, Jul 18, 2016 at 12:04 PM, Jim Brown <k9yc at audiosystemsgroup.com>
>> wrote:
>>
>>> Your logic is exactly backwards, Jukka, and it applies ONLY to
>>> optimizing
>>> the relationship between the stub and the power amp. When the output
>>> circuit element is a capacitor, the stub should be 1/4 wavelength from
>>> the
>>> amplifier at the harmonic it is intended to suppress. When the output
>>> circuit element is an inductor, the stub should be directly at the
>>> amplifier output, OR a halfwave up the line at the harmonic.
>>>
>>> But the relationship between the antenna and the stub also matters a
>>> LOT.
>>> A stub works by shorting the line at the frequency of the harmonic, and
>>> will be most effective when applied at a HIGH Z point on the line AT
>>> THE
>>> HARMONIC FREQUENCY. Most single-band antennas present a HIGH Z at the
>>> second harmonic, so the stub should be some multiple of half waves from
>>> the
>>> antenna.
>>>
>>> Note also the advantage of double stubs in portable setups where length
>>> of
>>> the line between antenna and stub cannot easily be controlled. Even if
>>> the
>>> first stub (nearest the antenna) is poorly placed, the second stub, a
>>> quarter-wave nearer the transmitter, provides its full attenuation.
>>>
>>> All of this is covered in the applications note for which I posted a
>>> link
>>> last night.
>>>
>>> http://k9yc.com/LocatingStubs.pdf
>>>
>>> The next link shows how we implement stubs in the trailer that W6GJB
>>> put
>>> together for or CQP and 7QP expeditions.  Note how close the 80 and 40
>>> antennas were to each other in the last setup, and the 40M dipole and
>>> C3SS
>>> were to each other in the daytime setups. At 600W from an Elecraft
>>> KPA500,
>>> we had zero problems with harmonics with CW stations on both bands.
>>>
>>> http://k9yc.com/7QP.pdf
>>>
>>> 73, Jim K9YC
>>>
>>> On Sun,7/17/2016 10:37 AM, Jukka Klemola wrote:
>>>
>>>> Placing a stub at output connector helps a tad in case your output
>>>> circuit
>>>> that shows a low impedance to ground at the harmonic. That is typical
>>>> for
>>>> nearly all our equipment that have a low pass circuit with a capacitor
>>>> going to ground as the last component of the output circuitry; a Pi
>>>> circuit
>>>> output.
>>>>
>>>
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Best Regards Stein-Roar "Rag"