Let's try to fix that awful formatting!Stoopid Yahoo Mail!
Hi, gang,
Need some expert advice.
I have been having trouble with getting my remote SGC autocoupler to "tune" my
inverted-L. It worked GREAT last season...but not this year...
After much farting around, the SG-231 now easily tunes a 50-foot inverted-L
wire on 80-10 (but not 160 as before. I suspect a bad relay or relay solder
joint), and a separate quarter-wave inverted-L wire for 160 has its own coaxial
feed line running back to the shack (no tuner, cuz the '231 still won't match
it on 160, even when it's resonant). Both antenna wires (separated by 6-10 feet
in the vertical run, with each "horizontal portion" trailing away from the feed
point in opposite directions) share a common radial field, 32, 45-foot-long
ground radials. Each coax run is 110-130 feet of RG-6, and each is terminated
at the antenna end in a choke made from 13 turns of RG-6 on FT-240-31 (or 43)
cores.
This makes for a quiet, good-performing low-band antenna on the cheap. Well, it
did until my present issues with the 160-m wire's SWR... I tested the coax run
from the tuner to the shack for line loss with a power meter and the VNA, and
the loss is low, especially at 160). I have used RG-6 for dozens of HF antennas
over the past 30 years with excellent results. This is the first oddity.
After installing the 160-m quarter-wave wire, I quickly brought my MiniVNA (and
its Android tablet) to the feed point to sweep for impedance and SWR. Instead
of having a normal, single-line trace, the SWR and impedance traces were
dynamic squiggles -- a lot like an AM modulation envelope on a scope. And
although the impedances looked good at 50-100 ohms, the "SWR squiggle" seemed
to suggest a low-SWR value of 3:1 or 4:1 at best, dipping at around 1.87 MHz. I
got similar results when using the VNA in the shack.
(Also, each time I run a sweep when the unit is connected to the antenna, the
traces change more than a little bit. I suspect something's weird, or that
external RF is getting into the unit.)
I have had issues with this VNA over the years and had to resolder an internal
connector at one time. I don't know if that issue has returned, or whether the
device is being bothered by a 10-kW AM transmitter 3 miles away (KOLM 1520). To
get another perspective I brought the KX3 to the antenna feed point (chilly at
15 F with a stiff breeze!), which produced results that are close to expected.
See listing below. But in the shack (on the far end of 110-130 feet of RG-6),
the high SWR readings persist and the values don't seem to track those taken
with the KX3 at the feed point.
FREQ Feed Point SWR SWR from Shack
1.725 3.8 3.2
1.750 2.8 3.2
1.775 2.3 3.1
1.800 1.9 3.0
1.825 1.6 2.9
1.850 1.6 2.8
1.875 1.8 2.7
1.900 2.2 2.7
1.925 2.7 2.9
1.950 3.2 3.0
1.975 4.0 3.1
2.000 4.6 3.1
The 2:1 SWR bandwidth seems a bit broad, even with the rig right at the feed
point, but there is a 50-foot wire and a couple trees nearby, so that's
probably why. But the SWR from inside the shack really seems suspect. The "dip"
is shallow and very broad...and it doesn't correlate well. I am going to
replace the shack-side coax connector and adapter to see if that changes
anything. Could be the cable, too. Just don't know...
Any ideas?
Thanks,
--Kirk in MN My book, "Stealth Amateur Radio," is now available from
www.stealthamateur.com and on the Amazon Kindle (soon)
On Friday, January 11, 2019 2:42 AM, Kirk Kleinschmidt via TowerTalk
<towertalk@contesting.com> wrote:
Hi, gang,
Need some expert advice.
I have been having trouble with getting my remote SGC autocoupler to "tune" my
inverted-L. It worked GREAT last season...but not this year...
After much farting around, the SG-231 now easily tunes a 50-foot inverted-L
wire on 80-10 (but not 160 as before. I suspect a bad relay or relay solder
joint), and a separate quarter-wave inverted-L wire for 160 has its own coaxial
feed line running back to the shack (no tuner, cuz the '231 still won't match
it on 160, even when it's resonant). Both antenna wires (separated by 6-10 feet
in the vertical run, with each "horizontal portion" trailing away from the feed
point in opposite directions) share a common radial field, 32, 45-foot-long
ground radials. Each coax run is 110-130 feet of RG-6, and each is terminated
at the antenna end in a choke made from 13 turns of RG-6 on FT-240-31 (or 43)
cores.
This makes for a quiet, good-performing low-band antenna on the cheap. Well, it
did until my present issues with the 160-m wire's SWR... I tested the coax run
from the tuner to the shack for line loss with a power meter and the VNA, and
the loss is low, especially at 160). I have used RG-6 for dozens of HF antennas
over the past 30 years with excellent results. This is the first oddity.
After installing the 160-m quarter-wave wire, I quickly brought my MiniVNA (and
its Android tablet) to the feed point to sweep for impedance and SWR. Instead
of having a normal, single-line trace, the SWR and impedance traces were
dynamic squiggles -- a lot like an AM modulation envelope on a scope. And
although the impedances looked good at 50-100 ohms, the "SWR squiggle" seemed
to suggest a low-SWR value of 3:1 or 4:1 at best, dipping at around 1.87 MHz. I
got similar results when using the VNA in the shack.
(Also, each time I run a sweep when the unit is connected to the antenna, the
traces change more than a little bit. I suspect something's weird, or that
external RF is getting into the unit.)
I have had issues with this VNA over the years and had to resolder an internal
connector at one time. I don't know if that issue has returned, or whether the
device is being bothered by a 10-kW AM transmitter 3 miles away (KOLM 1520). To
get another perspective I brought the KX3 to the antenna feed point (chilly at
15 F with a stiff breeze!), which produced results that are close to expected.
See listing below. But in the shack (on the far end of 110-130 feet of RG-6),
the high SWR readings persist and the values don't seem to track those taken
with the KX3 at the feed point.
FREQ Feed Point SWR SWR from Shack
1.725 3.8 3.21.750 2.8 3.21.775 2.3 3.1
1.800 1.9 3.01.825 1.6 2.91.850 1.6 2.81.875 1.8
2.71.900 2.2 2.71.925 2.7 2.91.950 3.2 3.01.975 4.0
3.12.000 4.6 3.1
The 2:1 SWR bandwidth seems a bit broad, even with the rig right at the feed
point, but there is a 50-foot wire and a couple trees nearby, so that's
probably why. But the SWR from inside the shack really seems suspect. The "dip"
is shallow and very broad...and it doesn't correlate well. I am going to
replace the shack-side coax connector and adapter to see if that changes
anything. Could be the cable, too. Just don't know...
Any ideas?
Thanks,
--Kirk in MN
My book, "Stealth Amateur Radio," is now available from www.stealthamateur.com
and on the Amazon Kindle (soon)
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