This is an excerpt from the news report from C21MM website dated Oct 18,
2024 (https://c21mm.mydx.de/?News):
"We erected two 22m Spiderbeam fiberglass poles for 160 and 80m
verticals with one elevated radial. For 40m and 30m we use (rhombic)
loops with 50 Ω impedance and on 60m we use another vertical with
one elevated radial. DL8LAS and DL6KAC installed a DHDL receiving
antenna. This helps against the very high atmospheric noise (up to
S9). Fortunately, we do not have a lot of manmade noise at both
QTHs. Regarding the lowbands, we are very satisfied with the antenna
performance from 80m to 30m. On 160m we didn’t hear any station
until now."
This feels like a long shot, but how sensitive is FT8 decoding to
receiver settings in a high tropical QRN environment? I don't operate
FT8 too much and I live in Southern California, so I really don't have
any experience using FT8 in the presence of strong random bursts of
noise. Does AGC pumping from static bursts clobber FT8? Is reducing RF
gain and increasing AF gain the right approach?
73, Mike W4EF........................
On 10/21/2024 1:34 PM, GEORGE WALLNER wrote:
Low band noise on DXpeditions:
It is easy tothink that going to a small island you will escape the
noise of modern "civilization". Far from it!
If the islandhas some population, they will be using generators, solar
panels, inverters and electronics of the cheapest kind, with zero or
verylittle filtering. In one place, the TX vertical was picking up the
noise of the solar plant of a village (pop.300) from 1.5 miles!
Elsewhere, the DXpedition brings its own noise sources: generators
(especially invertergenerators), computers, switch node wall-warts,
inverters and so on.
Unless they the station is very close to the water, grounding will be
difficult asmany islands have very poor ground (coral rubble and
sand). And unlike with a home station, there isn't enough time tohunt
down, filter and eliminate all the noise sources. If it is a tropical
island south of the equator, the TS noise fromthe Inter Tropical
Convergence Zone (ITCZ) and then after about 10:00 Z, the TS noise
emanating from Papua NewGuinea/Indonesia will add to the local noise.
At all our recent DXpeditions (VP6A, E51D, K8R, T32JV, FW7JV and N5J)
noise was the biggestissue on TB. We spent precious hours and days,
hunting down sources and filtering them. There are many things that
can be done,including placing the generators at a distance, grounding
them and filtering the power cables, etc. Grounding all thestation
equipment also helps. Installing clamp-on ferrites or pre-made common
chokes can reduce the noise radiated bycables and the noise carried to
the antenna on the outside of the coax shields. You can go on like
that ... until you find that theDXpedition is over and it is time go
pull it all apart... without the noise being completely eliminated.
What I've learned is that, apart from good basic noise reduction
practices at the station, a good RX antennaplaced at a substantial
distance is the best and the most "time-effective" way to improve
reception on TB. TheDXpedition that seriously wants to work CW on TB
(and most promise) should prepare in advance and carry all the
material needed toinstall an RX antenna on the second day. (On the
first day you are working the big guns... buteven then.) A flag at 500
to 1000 feet from the nearest antenna and the station, fed via a well
choked coax(check Jim, K9YC's excellent write up on chokes at
http://k9yc.com/2018Cookbook.pdf ) will be often sufficient. It will
be much better with a remote low-noise pre-amp. A DHDL will be even
better but it is a verylow gain antenna and a low noise remote pre-amp
at the antenna is a MUST! All that should be prepared in advance, not
jerry-rigged on site
from available bits and pieces.
If you do it right, you will get emails like this:
"...incredible ears on E5-N, this morning, at 1107 UTC, just before
local SR, I worked E51D QRP, using a "nothing special" Inv-L. "
It wasn't the ears, which are not what they used to be. It was a 50
foot long DHDL pointing NE with a low-noise pre-amp, at the end of
1000 feet of quad-shield coax with three chokes, grounded at two
points, feeding a Flex 6700 via the RX ANT port. That's all.
73,
George
On Mon, 21 Oct 2024 01:47:59-0700 Michael Tope wrote:
C21MM has been in solid for well over 1.5 hours on FT8 tonight and
it's stillearly. They were loud enough at times (at least on my end)
for a CW QSO, but they didn't decode my signal on FT8 untiltheir
signal peaked up to R=0, whereas on this end I was decoding solidly
down to R=-20. Clearly they have some receivechallenges. The DHDL
antenna that C21MM plans to use for receive has been employed by
AA7JV on some of his expeditions,so it's got a proven track record.
Perhaps there is a storm that is very close to them causing unusually
high QRN.
I need to go to bed, today is a work day 🙁
73, Mike W4EF.................
On 10/20/2024 6:13 PM, Wes Stewart via Topband wrote:
The realities aboutsome of these DXpedtions is that they are
organized by Europeans and favor working EU. Take the just concluded
(if theykept to schedule) PX0FF expedition. The ops were all
Europeans and >60% of their Qs were with EU and only 21%were with
NA. They didn't even operate 160 CW. They made 1046 FT8 QSOs on
160 out of >150,000 total.
8R7X was another one with EU 54% and NA 31%. Of course propagation
favored EU, but they were activelong enough that I worked them on
both 160 CW and FT8 as well as 22 other band/modes.Ditto A8OK that I
worked on 33 band/modes, none on topband. EU 64%, NA 19%.I'm not
trying to disparage our EU friends, I'm just pointing out the numbers.
C21MM will be QRV for at leastanother week. So far they haven't
made any topband CW contacts and only 6 with NA presumably on FT8.
Theyclaim to have installed an RX antenna, but have high noise. So
we shall see, but I'm not holding my breath. To their credit they
have worked about the same number of CW and FT8 Qs and a few on
RTTY, three of them mine.
AA7JV is a dedicated 160 man, who will put in the hours needed.
These other guys are not so motivated and want torun up their Q
count by working the most productive bands, or by turning on the FT8
robots.Wes N7WS
On Sunday, October 20, 2024 at 12:11:54 PMMST, Jim Brown
<jim@audiosystemsgroup.com> wrote: On 10/20/2024 11:14 AM, Steve
Harrison wrote:
If possible, please spend some timeattempting to work some North
American stations on *160 and/or 80m **CW*. A few minutes here and
there
is NOT enough; HOURS on the low bands are needed in order to catch the
propagation peaks all across the NA and SA continents.
YES! Veteran expeditionerAA7JV recognized that topband openings
tendedto happen on one or two nights of a multi-week activation, and
developednetworks to allow simultaneous operation on CW and FT8
during every hourthere's a possibility of propagation. One of the
most glaring failuresis abandoning the band at the first hint of
daylight, when propagationPEAKS over the next 45 minutes to an hour!
73, Jim K9YC
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