Re: [HamSCI] Digest for hamsci@googlegroups.com - 2 updates in 1 topic
David Kazdan
- Eclipse experiments, Wednesday August 12th 2026 - 2 Updates
infotechcomms <infote...@googlemail.com>: Aug 05 09:56AM -0700
There is a partial solar eclipse over the UK on August 12th 2026 and the
RSGB’s Propagation Studies Committee in the UK would like your help with
some radio experiments.
The Sun’s obscuration will exceed 90% over most of the UK, but it will be a
total eclipse over Iceland, the Atlantic Ocean and eventually parts of
northern Portugal and Spain.
The total eclipse continues down into northern Portugal and Spain where it
passes over Valencia, and totality ends at 19:32hrs UTC. It will remain a
partial eclipse over Spain until after sunset.
As the eclipse progresses it will mean that F2/E-layer illumination of the
ionosphere is diminished. At the same time it will also mean that D-region
absorption may be reduced. This may affect propagation on the lower bands,
including medium wave (AM), 80 metres and perhaps even 40 metres.
RSGB would like you to run WSPR on 80m or 40m if possible during the
eclipse, from 17:00hrs UTC to 20:00hrs UTC. And repeat the exercise either
the day before or the day after so comparisons can be drawn.
RSGB has also organised two contests on 80m CW and 40m FT8, both to run
from 16:30hrs UTC to 19:30hrs UTC on August 12th. These are open to
non-RSGB members as well. For the FT8 contest, amateurs are asked to send
their locator rather than skip directly to a signal report.
We’re not sure whether low-band signals will cross the Atlantic during the
eclipse, but it is worth a try!
For more details see: *https://tinyurl.com/RSGBeclipse*
ENDS
Steve Nichols G0KYA
Chairman, RSGB Propagation Studies Committee
Tel +44 7899 992389
Francis Rowsell <francis....@ieee.org>: Aug 05 09:59PM +0100
A good initiative from RSGB.
I was thinking about the note published in the group about H-Mode maybe
someone should experiment with that if its ready to try?
Frank G8PQH
On Wed, Aug 5, 2026 at 5:56 PM 'infotechcomms' via HamSCI <
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Frank Sole
ghby...@k9trv.org
What you have observed is only true for hams in the US or its territories who are transmitting. It’s Okay for most other countries, and it’s Okay to receive.
If the spread spectrum signal is transmitted by, perhaps, the University of Valencia, in Europe or nearby. It’s legal.
73
George K9TRV
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Francis Rowsell
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Phil Karn
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Marco Lisi
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Phil Karn
I'm just stating my interpretation of the current US FCC rules: you can do whatever you want on HF if you keep it inside 2.8 kHz, ID and don't encrypt. It took many years of banging our heads against the wall to get even this far, as there was vociferous opposition from certain parties who seem to have not really noticed that, except during contests, the ham bands are often just not that busy.
I understand spread spectrum quite well (I worked at Qualcomm for 20 years) so while you are right that a carefully designed spread spectrum system need not cause harmful interference, this can be easier said than done. Non-spread forms of multiple access (eg, time and frequency division) are orthogonal, meaning that you can design a receiver that will pick up one time slot or frequency channel and completely reject all others, in theory at least.
Not so in spread spectrum; the price for an essentially unlimited set of spreading codes is that they're no longer perfectly orthogonal. In a direct sequence system, each signal looks like wideband noise. Interfering signals are suppressed only by the process gain: the ratio of the spread to unspread bandwidth. If that's 100:1, then the process gain is 20 dB. *IF* all the signals arrive with equal power, and *IF* strong error correction is used, this can work well, especially when you have a lot of users each irregularly generating traffic with a low average duty cycle, where the overhead of constantly reserving and releasing small amounts of channel capacity is intolerable (like every time you begin speaking through a variable bitrate codec). This was the principle behind Qualcomm IS-95 CDMA (which uses direct sequence) but it required user transmitters to be under tight closed-loop power control by the base station.
It also works well in GPS (which is also direct sequence with roughly the same bandwidth) because the satellites in medium earth orbit are all roughly equidistant from everyone on earth; GPS wouldn't work so well if you're in a spacecraft that's approaching one of the satellites and hearing a much louder signal from it than all the others.
Direct sequence spread spectrum would probably work very well on the HF ham bands with physically remote transmitters running low power: an ocean buoy, for example. It's an experiment I would like to try, probably under STA. It wouldn't get close enough to anyone to bother anybody. But I don't see how I could transmit much power spread across the entire 20m band without bothering some of the nearby locals in San Diego.
This is not to say that we can't apply the *principles* of spread spectrum to HF while staying within the 2.8 kHz FCC limit. Spreading is relative; even 2.8 kHz could be a "spread" signal if it is carrying a very low user data rate (think WSPR or FT8). Frequency hopping has a lot of merit here. I've long thought about a "frequency hopped" version of FT8 where instead of keeping your tones within just a few Hz of each other in an oft-futile attempt to avoid QRM, they'd randomly hop around the entire 2.8 kHz segment for the entire 15 seconds. Sure, two stations would occasionally transmit directly on top of each other for a few hundred milliseconds, but as long as it didn't happen too often the strong FEC would fix it. The tones otherwise remain orthogonal so you can still coexist with the other hams in town as long as you don't use so much power that your transmitted phase noise blankets everybody. (This is already a problem because most people run far too much power on FT8; they don't realize that if you can be heard by ear, you're already too strong.)
Hopping on every symbol couldn't be compatible with standard FT8. But we could make a compatible change that would provide some of the same benefits as full blown frequency hopping: hop to a new random frequency with each 15 sec transmission. FT8 receivers already decode everything they hear within the receiver's passband; my FT4/FT8 skimmers bundled with ka9q-radio already listen to much wider segments, especially on 20m. There's simply no need to stay on the same frequency where you might collide repeatedly with someone else who has chosen the same frequency and time slot. You can't prevent occasional collisions but by randomizing you can keep them from becoming pathological.
So there are definitely useful applications of spread spectrum principles we could try on HF without having to spread across an entire ham band. And as long as we stay inside 2.8 kHz, it wouldn't *legally* be "spread spectrum".
Phil
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Marco Lisi
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Phil Karn
Right now (0300Z, 2000 local) I'm seeing a noise spectral density (N0) on 20m of -124 dBm/Hz from my W6LVP loop, WB6CXC filter/preamp and RX888.
Because there's some net gain in the path, that probably overstates the actual noise level at the antenna. The CCIR models give a noise level of about -133 dBm/Hz at 14 MHz in a typical suburban environment. If that's valid for my location, it implies my antenna has a net gain of about 9 dB, which is entirely reasonable.
Let's say you transmit just 1 W (+30 dBm) of direct sequence spread over the 350 kHz of the 20m ham band. That's -25 dBm/Hz, a transmitted power spectral density 100-110 dB above the receiver noise.
How far would the transmit and receive antennas have to be from each other to have 100 dB of path loss on 14 MHz? For line of sight between two 0 dBi gain antennas, the answer is 170 km. Sure, it would be less in reality because of scatter, reflections and absorption but I seriously doubt the minimum separation could be brought down to, say 1 km -- and some hams are closer to me than that.
See the problem? And that's just 1 W.
So while I might try this in a free-floating buoy in the middle of the Pacific, I don't want to try it at home here in San Diego. I think I'd find pins in my coax very quickly.
Again I think it makes perfect sense to experiment with spread spectrum techniques on HF in a 2.8 kHz bandwidth. That's already wide enough to benefit from some frequency diversity, since it often exceeds the coherence bandwidth while ordinary WSPR and FT8 do not. For the user data rates in WSPR and FT8, 2.8 kHz actually represents a healthy spreading ratio.
You wouldn't use more of the band than one SSB transmission, and you could share that 2.8 kHz with other users of the same scheme, especially if you use frequency hopping instead of direct sequence to mitigate the near-far problem. With frequency hopping it doesn't matter how strong the jammer is (within reason) as long as you don't collide more often than the error correcting code can handle. I think this could be a very reasonable starting point for a next generation of a FT8-like protocol.
Phil
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