Topband: C21MM

[Michael Tope]

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 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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