[CQ-Contest] Coax Stubs for SO2R

Tue Jul 26 13:40:38 EDT 2016

On Tue,7/26/2016 7:02 AM, Rudy Bakalov via CQ-Contest wrote:
> For me the important lesson learned from this discussion is that stubs are not as easy as snip-snip you got yourself stubs. Deploying them takes planning and careful testing.

Yes.

> That is, takes a lot of time.

I spent about 6 hours on each set of double stubs -- one set to go on 
the 40M antenna, another for the 80M antenna for our CQP trailer.

> I did a very quick back of the envelope calculation. In order to achieve the same level of attenuation you need two sets of stubs. Right there you have roughly 800' of LMR400.

Now you lost me. First, LMR400 is not an ideal choice for stubs. Best is 
a good RG8 with a heavy copper braid shield and solid copper center.  As 
I showed in my applications note, a good RG8X is second best, and makes 
the stub rejection broader.

Second, I don't understand why you need 800 ft of coax to make two stubs 
with a matching section between them. Look at the table (by K2TR) from 
K1TTT's website, which I added to my tutorial on coax and stubs.  For 
80M, you need two 46 ft shorted stubs with a 23 ft matching section. For 
40M, divide those numbers by 2.  That's 176 ft of coax for the finished 
stubs, and, of course, we want to cut them long and trim them.  If I 
were buying new coax for this purpose, I'd  choose Davis RF Buryflex, 
which they will sell in just about any length you choose.

http://k9yc.com/Coax-Stubs.pdf

> A 1000' spool is $450. Then you probably have another $100 in connectors. $550 in materials alone. And we haven't even made the stubs yet.

I buy Amphenol 83-1SP connectors in lots of 100 so that I have them 
around. Often when I buy, I combine quantities with neighbor hams or 
with members of our local club, NCCC. Last time I bought I paid about 
$3.20 per connector.

For each double stub, we need six 83-1SPs, two coax Tees, and two coax 
barrels. I use only Amphenols, but I buy mine used at ham flea markets, 
which I typically pay a few bucks apiece. That comes to about $26 per 
set of double stubs for the cost of connectors.

> Add the time to cut, trim, and crimp the stubs. Add the time to properly position them along the feed line. I don't know how others value their time, but I would rather spend it with the family or operate the station than spend two weekends in a spiderweb of stubs and severed feed lines.

That's a reasonable choice that we all have to make. :)  Some of us 
enjoy building our stations more that others. Many of us are retired, so 
have more time than those still working.

> I also think proper stub placement is easier said than well done. Think about it- the SO2R remote switch is at the base of the tower and then the individual antenna feed lines go up the tower. You either have to find the ideal location up along the tower or coil tons of coax at the base.

Proper placement will, indeed, depend on everyone's individual 
installation. It certainly doesn't have to be a spiderweb of coax 
though. In the contest stations I've visited, the stubs are neatly 
bundled and hung either above the operating area, under it, or along 
feedlines at suitable locations. Here's what we did for W6GJB's CQP 
trailer. k9yc.com/7QP.pdf  See slides 18-21  My double stub for 40M is 
coiled outside my shack in the feedline just before it enters the 
grounding panel.

Also, we generally only need stubs for bands that are harmonically 
related -- 80/40, 40/20, 40/15, 20/10.  Double stubs are generally 
needed only for antennas that are very closely spaced.

> If you coil up all that coax at the base of the tower you need to build some sort of a structure to hold it.

Only if you have roving bands of copper thieves in your neighborhood. 
The double stubs outside my shack simply have all the connectors 
carefully weatherproofed.

> If you decide to have it up the tower then you add significant wind load surface to the tower. Not good.

There's no advantage to placing stubs closer to the antenna unless 
that's where your antenna switch is.

> Of course, I may be over-engineering things,

I hope this makes it seem a lot easier.

> but I prefer avoiding complexity.

I think many of us try to avoid complexity when we're in the middle of a 
contest, so we automate as much of our switching as we can, or as we 
have the time and money to do. Over the years, I've done that in my 
station, and it reduces the number of my screw-ups during the contest. 
:)  In W6GJB's contesting trailer, the stubs are simply patched in 
series with the dipoles for 80 and 40M. When you switch to those bands, 
the stubs are there -- you don't have to think about it.  Likewise with 
my 40M monoband wire Yagi that's a few feet below my SteppIR.

73, Jim K9YC
>
> Rudy N2WQ
>
> Sent using a tiny keyboard.  Please excuse brevity, typos, or inappropriate autocorrect.
>
>
>> On Jul 26, 2016, at 9:12 AM, Joe <nss at mwt.net> wrote:
>>
>> Really? 200+ Euros? And coax made homebrew stubs are not much cheaper? HUH?
>>
>> Joe WB9SBD
>> <CLEAN-IDLE-TYME-LOGO-120x96.jpg>
>> The Original Rolling Ball Clock
>> Idle Tyme
>> Idle-Tyme.com
>> http://www.idle-tyme.com
>>> On 7/25/2016 4:53 PM, Rudy Bakalov wrote:
>>> Jukka, Jim, and Steve,
>>>
>>> Thank you for taking the time to go into details. What's clear to me that the non liner AB type of amps contributes significantly to harmonics along with improper amp         loading/tuning.
>>>
>>> As I mentioned earlier I already have BPFs so now I am left with the mechanical challenge of stubs. Specifically, will have to follow Jukka's advice on adding coax between the remote SO2R switch and the antennas.
>>>
>>> Honestly, I even wonder if the hassle of building and placing two sets of stubs (it seems the opinion is that two are needed) is really that much cheaper compared to buying high power BPFs. Between Remo's filters and the link below there are affordable alternatives to Ranko's BPFs:
>>>
>>> http://www.antennas-amplifiers.com/Band-Pass-Filter
>>>
>>> For €1200 one can have plug and play filtering (although I may run into components' thermal properties when the filters are outside by the tower) that is not critical with respect to placement along the feed line.
>>>
>>> Who sad ham radio is a hobby; feels like serious engineering work to me :-)
>>>
>>> Thank you all for your patience.
>>>
>>> Rudy N2WQ
>>>
>>> Sent using a tiny keyboard.  Please excuse brevity, typos, or inappropriate autocorrect.
>>>
>>>
>>> On Jul 25, 2016, at 4:41 PM, Jukka Klemola <jpklemola at gmail.com> wrote:
>>>
>>>> Hi,
>>>> I try give simplified answers ...
>>>>
>>>> This should answer also Rudy's question.
>>>>
>>>>
>>>> 2016-07-25 15:47 GMT+03:00 Joe <nss at mwt.net>:
>>>>
>>>>> This also puzzles me.
>>>>> OK if an amp because of it's tuned matching circuits, block out of band
>>>>> energies
>>>>
>>>> Amplifier circuits attenuate unwanted band energy.
>>>> But to a limit.
>>>> A Pi filter attenuates to some level, Pi-L attenuates more.
>>>> If that is not enough, we need additional attenuating, that is additional
>>>> filtering like a stub
>>>>
>>>>
>>>> The why do we have these energies at all in the first place?
>>>>
>>>> When amplifying a signal in an amateur amplifier, the plate current when
>>>> only PTT is activated is less than a quarter of plate current with maximum
>>>> specified signal that is amplified.
>>>> It means there is plate current through most of the sine wave signal cycle,
>>>> but not all of it.
>>>> It means there is a sharp corner in the output signal .. it is not a clean
>>>> sine wave.
>>>> Such signal with such corners has harmonic energy.
>>>> This energy propagates towards the antenna connector.
>>>> It travels through the output circuit; most often Pi or Pi-L.
>>>> On an oscilloscope, the signal looks pretty much like a sine wave but it
>>>> contains harmonic energy.
>>>>
>>>> Sorry, but this gets more complex when digging deeper.
>>>> Next step would require you to read some books or at least web sites.
>>>>
>>>> Easy to understand information packages are ARRL hand book and Orr/W6SAI
>>>> Radio Handbook.
>>>>
>>>> ARRL handbook is easy to find and purchase.
>>>> I would suggest to try and find also a paper book:
>>>> http://www.eham.net/reviews/detail/3963
>>>>
>>>> W2VJN book is a must if you want to understand more about RF filtering
>>>> needs at a multi radio station.
>>>>
>>>>
>>>> ** Encouragement, keep it simple message:
>>>> As we are hams, we can use ready made recipes for stubs, among many other
>>>> things.
>>>> That is allowed for us and us hams, we can just accept many things as given
>>>> facts.
>>>>
>>>>
>>>> Does not a Radio have the equivalent of an "Exciter" ( the ummm low level
>>>>> driver )
>>>>
>>>>> And the "AMP"  ( the final output amplifying system )
>>>>> So, if all this filtering is happening why do we have spurious out of the
>>>>> radio, but not an amp?
>>>> There are a lot more signals in the radio than the mains input and RF
>>>> connector with RXinput / TX output.
>>>> To start with, the radio's oscillator is not on your actual output
>>>> frequency.
>>>> There are other oscillators, mixers, filters, amplifier circuits, more
>>>> filters and so on inside your transmitter before the antenna connector.
>>>> All those are creating or limiting spurious signals and we need to engineer
>>>> the radios so the radios do not emit unnecessary signals and we engineer
>>>> our radios so they do not input unnecessary signals or at least the radio
>>>> does not care about the unnecessary/unwanted signals.
>>>> Emissions are emissions; intended or spurious.
>>>> The receiving side phenomena are under words immunity or susceptibility.
>>>> Together they are electromagnetic compatibility EMC.
>>>>
>>>> These spurious signals propagating from device to another device can be as
>>>> bad as K1EA described about the radios they used.
>>>> The radio2radio signal propagation happened on a set of phenomena caused by
>>>> some radio internal signalling leaking through radio wiring and propagating
>>>> to another radio so the receiver of the other radio heard the transmitting
>>>> radio signal regardless the frequencies the radios were on,
>>>> That is a really puzzling situation and typically difficult to overcome.
>>>> Most likely the leaking and injecting mechanism was through antennas
>>>> connected to radios but not necessarily. That kind of electromagnetic
>>>> incompatibility should be rare, though.
>>>>
>>>> After Ken K1EA et al added RF and maybe also other filtering, the radios
>>>> stopped hearing each other that badly.
>>>>
>>>> Other filtering are for example ferrites we place on DC power cords, mains
>>>> wires and other .. PTT / band data and any other wiring you have at your
>>>> station. We attenuate unwanted signals until they do not bother us.
>>>> You can find a lot of information about different kinds of filtering in the
>>>> internet.
>>>>
>>>> All cases are different.
>>>>
>>>> Some hands-on information here:
>>>> http://wiki.k1ttt.net/Default.aspx?Page=2008%20Maintenance%20and%20Upgrade%20Blog&NS=&AspxAutoDetectCookieSupport=1
>>>>
>>>> Look for words
>>>>   -harmonic
>>>>   -power
>>>>
>>>>
>>>>
>>>>> Joe WB9SBD
>>>>
>>>> 73,
>>>> Jukka OH6LI
>>>>
>>>>
>>>>> Sig
>>>>> The Original Rolling Ball Clock
>>>>> Idle Tyme
>>>>> Idle-Tyme.com
>>>>> http://www.idle-tyme.com
>>>>>> On 7/25/2016 5:48 AM, Rudy Bakalov via CQ-Contest wrote:
>>>>>> Jukka,
>>>>>> It is the statement below that really puzzles me. All amp people I know,
>>>>>> including those that manufacture commercial amps, categorically state that
>>>>>> amps do not generate harmonics on their own. That is, amps merely amplify
>>>>>> them.
>>>>>> To me this seemingly minor difference is huge. If amps only amplify but
>>>>>> do not generate harmonics then there is no scientific reason for filtering
>>>>>> after the amp assuming the same amount of filtering is applied before the
>>>>>> amp. In practical terms, this would mean that low power BPFs before the amp
>>>>>> are as effective as high power BPFs after the amp.
>>>>>> The key point here is GENERATE vs AMPLIFY harmonics. Can the average
>>>>>> commercial, well stabilized amp generate harmonics?
>>>>>> Rudy N2WQ
>>>>>> Sent using a tiny keyboard.  Please excuse brevity, typos, or
>>>>>> inappropriate autocorrect.
>>>>>> On Jul 24, 2016, at 5:14 PM, Jukka Klemola <jpklemola at gmail.com> wrote:
>>>>>>> In case you do that, you still need stubs after the amp.
>>>>>>> Amplifier creates harmonics out of the fundamental frequency.
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