Bob, Thanks for bringing that up. I had forgotten about that effect, mostly because I don't do radio near the equator. =!8^} Here is a pdf discussing VHF/UHF atmospheric losses due to weather. Lots of math.https://www.itu.int/dms_pubrec/itu-r/rec/p/R-REC-P.370-7-199510-W!!PDF-E.pdf
--- Ciao baby, catch you on the flip side. GEO
Time flies like an arrow, fruit flies like a banana.
On Thursday, May 9, 2019, 10:14:13 AM PDT, Bob via AMSAT-BB [email protected] wrote:
Taiwan lies within the northern edge of the Equatorial Scintillation Zone which is an area near the magnetic equator that suffers significant signal attenuation even at VHF (and more so at UHF an up). It is more pronounced during periods of high solar activity. In the past couple of weeks we have been having some mild geomagnetic disturbances caused by coronal holes, and more recently an earth-effective sunspot. Normally we think in terms of HF impacts, but it will have big impact on space communication if you are on one side of that scintillation zone and the satellite is on the other -- forcing the signal to cross through that area. Best I've read indicates you can anticipate another 20 dB of signal loss on 70 cm. That might be the difference between a signal that sounds great and one that is below the noise level.
As many others have stated you also have weather influences, especially on the 70 cm band, that will happen due to what is going on in the Troposphere.
73, Bob, WB4SON
On Thu, May 9, 2019 at 4:03 AM Hans BX2ABT via AMSAT-BB [email protected] wrote:
Well, I know VHF/UHF propagation and I know satellites are line-of-sight, but how about signals from outer space trying to traverse the ionosphere and atmosphere? Es makes terrestrial signals bounce back, but does it also make space signals bounce back into space? Or at least degrade them? You say "think horizontal" but space communications are also partly horizontal if you take low elevation into consideration. I feel there is more to this, but so far haven't found any info on this.
73 de Hans
BX2ABT
On 05/09/2019 05:53 AM, GEO Badger wrote:
Hans,
What I believe you are really asking is what effects VHF/UHF propagation. Lighting up a bird is a line of sight connection, not propagation in the classic sense of bouncing off the ionosphere and ground like in HF comms. But, there are atmospheric phenoms that can effect VHF/UHF comms. Tropo ducting, but that is normally for terrestrial comms. Same for sporadic E, which is bouncing signals off of ionized clouds similar to the ionosphere propagation..Think horizontal.
Then there is weather. Whether or not you have nice weather. Rain, snow, clouds and dust are a few of the things that can effect sat comms.
Ciao baby, catch you on the flip side. GEO
Time flies like an arrow, fruit flies like a banana.
On Wednesday, May 8, 2019, 7:12:57 AM PDT, Hans BX2ABT via AMSAT-BB [email protected] wrote:
The last couple of days the Fox birds haven't been coming in as well as before. Signal strengths are down, fading has increased and it is almost impossible for me to open them. Now the sporadic E season also has kicked off in the last few days, with increased activity here in east Asia. Is this a coincidence or do the two have a connection? And are there other factors that influence LEO propagation? I know satellite tumbling is one factor that causes fades, but are there also ionospheric or atmospheric influences? Thanks for the insight. 73 de Hans (BX2ABT) _______________________________________________ Sent via [email protected]. mailto:[email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite
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Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb
_______________________________________________ Sent via [email protected]. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb