Topband: 3B9/M0CFW on 160

[Olof Lundberg]

This is an interesting discussion. I can not add much to the physics behind the scene but when working US on topband from 3B8 and 3B9 with decent signals while EU signals are absent it looks indeed obvious that some ducting must be involved and not textbook multihop with inherent losses. US and EU are more or less in the same direction NW.

LP to US is easy on 40 and fairly easy on 80 but very challenging on 160. The LP window at our sunset is very narrow and rare on 160, some minutes on 80 and much wider on 40.

Top band and 80 open up slowly at sunset while our sunrise is much more productive. I presume this is due to lingering daytime attenuation in the evening? Then of course the activity to the east of us is very low.

We have over the years been experimenting with RX antennas. Over our saltwater ground we have no space for beverages and bogs have never worked. I’d like to try some array of short active verticals but have assumed that they would be trouble in a tight M/M environment. Some years ago I brought one of those big DXE phasing boxes to 3B9 but I had to choose between making QSOs or fiddling the controls. Last year we tried a K9AY out on a rock in the lagoon which might have just marginally improved reception on 80 and 160. It appears that our local noise is OK provided we localise and turn off some offending led lights and other stuff. The transmit verticals on 80 and 160 almost always seem to be OK for RX. Tropical QRN is a limitation. This year we have just narrowly escaped a cyclone with associated localised thunderstorms and we can hear the crackle.

The first couple of hours in this year’s CQWWCW (our sunrise at 3B8 is 01:21UT) yielded just 8 qsos on 160 and 73 on 80. On 80 we worked a few US.

VOACAP is making a valiant and decent attempt to predict 80m propagation but is silent on 160. I assume we are always below MUF so it is attenuation that is the dominating factor. If I were young and with some time on my hand I would try to correlate the Big Data we can collect nowadays with RBN, WSPR and such and look deeper into the complex factors in the sun-earth environment that influence the attenuation and the variability thereof. But then again it is of course the unpredictability that makes for some of the fun?

73 Olof G0CKV 3B8M 3B9HA 3B8HA

> On 22 Nov 2024, at 08:16, Eric Scace K3NA <eric at k3na.org> wrote:
> 
> Hi Ron —
> 
>   See attached image of the twilight zones at 00:40Z today. You will see that 3B9 is in the middle (nautical) twilight zone band… and the twilight zones cross North America.
> 
>   Having worked this path myself from 3B9, I can testify to how cool it is. Ducting explains part of why the signal was so loud when you heard them — ducts are very low loss conduits for signals at the ducting frequency range. But escaping from a duct requires the signal to encounter some less-ionized part of the floor of the duct, so that the signal can continue down toward the earth’s surface. And the exit point still has some refraction, so the signal may exit the duct at a very shallow angle and travel a long way before it reaches the surface.
> 
> These thin spots are indeed spotty, transient, and move around.
> 
>   When I was on 3B9, clumps of geographically-adjacent stations would get worked — a spot corresponding to a weak spot in the duct. Some clumps were clearly connected to each other by an added ionospheric hop in the normal way. We could plot this clumps over time and see them move along with the terminator… but eventually (minutes or tens of minutes) a particular “leak” would close up. Maybe we had several “leaks” at one time, working different spots in North America… and sometimes no leaks at all.
> 
>   So yes — spotlight propagation.
> 
>   This emphasizes why it’s important for a DXpedition to be on top band every night. Some nights will have no ducts. Others with have leaky ducts — but the leaks will only illuminate certain patches of North America (in this case)… and on another night different patches of North America. To give everyone a chance, one has to be on every night. And for the person chasing the DX, one has to be listening every night until a leak/spot favors that person’s location.
> 
>   And then, as you experienced, it’s super easy to work each other through that low-loss path.
> 
> — Eric K3NA
> 
> 
>> On Nov 21, 2024, at 19:37, Ron Spencer via Topband <topband at contesting.com> wrote:
>> 
>> Tonight (11/21) around 0040Z I saw a signal pop up on the panadapter. Tuned to it and its 3B9/M0CFW calling CQ. 15dB or more above my noise floor. I couldn't believe how solid and loud they were. After amp came on line I called and worked them. During the wait time I did a quick internet search to see if is indeed a real station. Yep.
>> 
>> What amazed me, and still does, is absolutely NO rbn or packet spots during the at least 5 minutes they were on. And no other callers. Even after I spotted them on packet and the kst chat page.
>> 
>> I have no explanation for this. Why no rbn spots? Why no other callers when they were very solid for almost the  whole time they were calling CQ? Was this an example of very small spot light prop? There were others on so its not like no one was tuning the band. Baffling.
>> 
>> Below is a screen shot of their signal. they are in the red area. Received on my homebrew 8 antenna circle array with no preamp.  
>> 
>> Perhaps someone out there has an explanation.
>> 
>> Ron
>> 
>> N4XD
>> Sent using https://www.zoho.com/mail/
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