I agree,
If I have 5 bucks invested in my stubs I'd be amazed!
And as shown before for less than 5 bucks they seem to work awful well.
https://youtu.be/wgn_L_LUXcI
Joe WB9SBD
Sig
The Original Rolling Ball Clock
Idle Tyme
Idle-Tyme.com
http://www.idle-tyme.com
On 7/26/2016 9:37 AM, Jeff AC0C wrote:
I would guess most guys don't go to this much effort. New stuff and
optimized placement? Wow, that would be cool!
I built the stubs up on an as-needed basis with whatever I had laying
about; there's no LMR400 around here. It's all RG-11 or 213. 213 has
a bit better attenuation dip and is more rugged. All of the T
connectors were Chinese specials initially and later most were swapped
with AMP parts that I ran across at swaps and hamfests. Never blew up
a Chinese one though so can't say the 50 year old AMP are better.
The stubs are hanging off of the existing tower-based 2x6 antenna
switch which feeds a bunch of monobanders so no additional switching
was needed. I did not optimize the placement; had room for them and
it was easy to do so they went out there.
They live in a metal trash (no UV/mouse problems like plastic) can
which is staked to the ground (so it does not blow away in the big
winds we get). There is a foot of some sort of Styrofoam stuff at the
bottom so if the thing ever starts taking on water for some reason, it
won't leave them swimming. Although if you seal the stub ends, it's
not a problem either. I went with the metal after going out one time
to check how the stuff looked before fall and found my stubs tub half
full of water. I think that was a week or two after CQWW RTTY one
year... Got lucky nothing blew up there!
I measure the isolation with a vna at the shack. If I think I need
more attenuation, then I build another stub and grab a 1/8 wave (or
whatever is close) to space it away from the current one and turn my
single stub into a pair.
I don't hear my other radios at all except on the 40/20m combo. Added
another stub and the level did not drop which is a possible clue that
there may be something on my 40m 4-square that's generating it's own
harmonics when hit with some power (which if you have seen my 4-square
you can EASILY believe that...). I do have a set of 5b4agn filters in
the shack that run between the amps and the rigs which are
autoswitched. The filters do a decent job of cutting down on
interference and definitely keep the rigs protected, but the added
stubs take the situation from a "tolerable" case to a "I don't need to
worry where I am on the band" sort of thing, most of the time.
Like anything in radio, if perfection is not required, costs and time
invested can be scaled back quite a lot. Building a set of stubs and
finding the hardware is sort of a hassle. But it's something you do
one time and enjoy for a long run.
73/jeff/ac0c
www.ac0c.com
alpha-charlie-zero-charlie
-----Original Message----- From: Rudy Bakalov via CQ-Contest
Sent: Tuesday, July 26, 2016 10:02 PM
To: Joe
Cc: Jukka Klemola ; cq-contest
Subject: Re: [CQ-Contest] Coax Stubs for SO2R
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. That is, takes a lot of time.
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. 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.
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.
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.
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.
If you decide to have it up the tower then you add significant wind
load surface to the tower. Not good.
Of course, I may be over-engineering things, but I prefer avoiding
complexity.
Rudy N2WQ
Sent using a tiny keyboard. Please excuse brevity, typos, or
inappropriate autocorrect.
On Jul 26, 2016, at 9:12 AM, Joe <nss@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@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@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@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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