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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