Topband: C21MM

Mon Oct 21 16:34:11 EDT 2024

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 at 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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