These days when the space news feeds go away are trying.
The CME that was expected to hit early on the 25th (that is, as I'm typing now) actually hit about 12 hours early, 1437 UTC, or 9:37 ET. The K index shot up to 8 in the 1500 to 1800 chart. As Spaceweather.com reported it:
CME IMPACT SPARKS SEVERE GEOMAGNETIC STORM: Arriving hours earlier than expected, a CME struck Earth's magnetic field on March 24th at 1437 UT. The impact opened a crack in our planet's magnetosphere and sparked a severe G4-class geomagnetic storm--the strongest since Sept. 2017.
The storm has been subsiding since then, with the K index down to 4 at the
0000 UT update for March 25 - as you can see in their plot. The conditions on
the radio have been disrupted. In the 1900 hour (UTC - 3PM ET), as the
storm started to settle there was a ton of activity on the VHF 6 meter band,
with strong signals from as far south as the Falkland Islands, but they
gradually went away over the course of the next few hours and by 2200 UT, I
could watch chunks of the band for long periods and not see signs of one
signal.
Speaking of that, my station modification to allow monitoring more of the 6m band all of the time that I've posted about a few times is currently working much better. I had talked about the problem back on the 10th and then added an important update last Sunday. In that second post, I mentioned a work around with a very lucky find at the Orlando hamfest: a $5 used amplifier to replace the $55 kit I built (and that sells for $88 as a ready-to-use module). I added one more thing to this, an attenuator (which everyone calls a pad). I just didn't know exactly what value pad to use, so I got this set and experimented a bit. The pad goes between the output of the SDR Switch and the 2-way splitter. Judging by watching the broadband noise in the software display of the 50.0 to 50.4 MHz portion, 13 dB is a good value, but I should probably look at 16 a bit more and compare on different days.
This clip from the block diagram I've published shows the 13 dB pad in the red highlight box.
The problem I was trying to fix with the new LNA was that while the mod was
great in that 50.0 to 50.4 MHz frequency range, it ruined my station at lower
frequencies. It has been said that "engineering is the art of
compromise" because there are rarely ideal solutions that work everywhere for
everything. If there were, there would be no need to design things -
everyone would build the same circuits. This amplifier has a higher NF than
the original one, which might hurt 6m performance, but it completely fixes the
radio's HF coverage.
As, usual it's not completely "Done done," but it's working well enough to try
more things.
I limit my use of LNAs to VHF or above, mostly receiving aircraft traffic or at one point weather satellites.
ReplyDeleteThere was so much noise at the last house, I gave up on HF. Even after eliminating the sources in the house, the neighborhood RF noise still killed most bands. The Kenwood become a upscale AM broadcast receiver.
So I'm mostly working mobile from the park nowadays when work and family schedules allow.
QRN like that is always going to be specific to your location and sometimes very specific, like block by block or house by house, but it's always the case the higher you go in frequency the more important LNAs become. Just like it's always better to put the LNA and PA at the antenna feedpoint to minimize losses in the coax, but for lower frequencies you need to figure out if the improvement is worth the cost to you - both in the hardware prices and inconvenience.
DeleteThe LNA I started out with had a 0.5 dB NF, which is actually lower than you'll need at 50 MHz, while the replacement amp is specified at 4.2 dB. I have a few tenths loss before that so I'm probably looking at about a 5 dB system NF. I'm not sure it really matters, but I'm trying to figure out how to tell without some really expensive test equipment.
The weak signal digital modes are very efficient at extracting signals from the noise, and I think that's a big reason for their popularity. I know there are people who say "it's not real radio" but the industries that use HF for a living use modes like that. Also, it has been proven in multiple tests that skilled CW operators can copy CW that's below the audio noise floor - their hearing has been trained to be a narrowband filter.
I have a friend in the SF Bay area who transmits CW but due to the noise levels of Silicon Valley, he can't receive. Instead he rents time on a remote SDR located on the coast in a relatively radio quiet area. Where there's a will, there's a way.
DeleteSometimes ya gotta beat the problem to death, SiG...
ReplyDelete