Here's the quick & dirty reply to the "get it in the right place along
the line" placement worry.
1. Build your stub and get it ready for install
2. Measure the amplitude of the 2nd harmonic on whatever the band you
are wanting to stick a stub in. Say it's 40m transmitting on rig 1 so
you would look at the 20m 2nd on rig 2. This is the baseline.
3. Now go out and stick that stub in whatever the MOST CONVENIENT PLACE
IS along the line. If you have a remote antenna switch, that's likely
the point where the feed line comes off the tower and hooks into that
switch. Don't sweat the location. Just stick it on.
4. Back in the shack, check the level of that 2nd harmonic. If it's
"good enough" - then you are done. If it's not good enough, then you
have more work to do.
I find the generic single stub, pretty much randomly placed, to be good
for say 15 dB or better. Maybe I'm just lucky. Or maybe I'm just that
good. ha ha. But if the stub measures 25 dB on the bench and I'm
getting 15 dB in actual use, and let's say I need a few more to reach
"good enough" - then I can add in some extra feed line and see if the
attenuation improves (because that "moves" the stub to a more favorable
point). Or I can whip up a double stub (which will have more
attenuation). Or do consider something else that would reduce the coupling.
My point is that building and using the stub is far more important and
worrying to death about line placement. You can always refine the line
placement later, if needed.
Stubs are a marvelous and wonderful thing!
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 2/22/20 7:27 PM, Jeff Blaine wrote:
Mike,
Good you are getting that filtering added. SO2r without filtering is
a recipe for frying front ends. Guess luck has been in your favor.
On the stub location, outside is fine. In fact all my stubs have been
located outside. There is some magic as to the optimal place along
the feedline to place stubs but I've never fine tuned to that point.
I load the stub at the base of the tower where the antenna stack
matches are and they work fine.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 2/22/20 3:52 PM, Mike Smith VE9AA wrote:
Is it reasonable to assume I could locate all my coax stubs 165' away
from
the shack outside at the antenna switch?
Currently I run SO2R with no band pass filters, nor coax stubs, but I
have a
'relatively' large lot (2.2ac) and "radio 2" has a single antenna
(horizontal ZS6BKW) located at the opposite end of the lot and the
primary
"radio 1" has a variety of verticals or vertical arrays, so it works.
Sometimes that's an advantage (speed of QSY's; not ever having to worry
about switching in stubs or filters) but sometimes there is a very small
amount of crossband QRM (self inflicted) and it always prevents
running on 2
bands with my 'best' antennas. For example, when I am running on
40m/80m I
have to choose one 4-Sq and always the horizontal antenna is parked on
"radio 2" (a ZS6BKW w/ 15m add-on element).
If I bought 2 sets of bandpass filters and made up 6 coax stubs that
I could
locate out at the antenna switch, I think it would be a small step up
for my
signal on some band combos. The relatively low ZS6' ain't exactly a
pileup
buster ;-)
Reason is, there is NO ROOM in the shack for stubs. Just none.
So, any downside to doing it this way?
Mike VE9AA "NB"
Mike, Coreen & Corey
Keswick Ridge, NB
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