I have two Arrow 2 antennas and have been using them since 2013 on FM satellites. I use a Kenwood TH-D72 radio which is full duplex, so I can hear myself very well when I get into the bird. I am wondering about a phenomenon that I experience and why it happens.
It is much easier for me to hit the bird (and I have a much louder signal) when the bird is just about on the horizon than when it is directly overhead, or at a very high altitude. This should not be the case, as overhead it is only 400 miles away, but on the horizon, it is 2,000 miles away. But I am so much louder at the horizon. I "boom" into the bird. Does anyone have any answer to why this is? Brad KC9UQR
On 2019-07-26 16:15, Brad Smith via AMSAT-BB wrote:
I have two Arrow 2 antennas and have been using them since 2013 on FM satellites. I use a Kenwood TH-D72 radio which is full duplex, so I can hear myself very well when I get into the bird. I am wondering about a phenomenon that I experience and why it happens.
It is much easier for me to hit the bird (and I have a much louder signal) when the bird is just about on the horizon than when it is directly overhead, or at a very high altitude. This should not be the case, as overhead it is only 400 miles away, but on the horizon, it is 2,000 miles away. But I am so much louder at the horizon. I "boom" into the bird. Does anyone have any answer to why this is?
Hello Brad,
"Louder" is more S-meter bars, or audibly louder?
The received RF power should be greater overhead (twist your antenna a bit to change polarization and check). This results in more S-meter bars.
Is the horizon, for you, over a relatively unpopulated area? Do you live in a more populated area?
Demodulated audio may be quieter due to the myriad of people trying to cram into one channel and the uplink FM receiver PLL tracking the resulting chaos. This is my guess, as I haven't done analysis on the effect.
--- Zach N0ZGO
Zach Metzinger via AMSAT-BB wrote:
On 2019-07-26 16:15, Brad Smith via AMSAT-BB wrote:
I have two Arrow 2 antennas and have been using them since 2013 on FM satellites. I use a Kenwood TH-D72 radio which is full duplex, so I can hear myself very well when I get into the bird. I am wondering about a phenomenon that I experience and why it happens.
It is much easier for me to hit the bird (and I have a much louder signal) when the bird is just about on the horizon than when it is directly overhead, or at a very high altitude. This should not be the case, as overhead it is only 400 miles away, but on the horizon, it is 2,000 miles away. But I am so much louder at the horizon. I "boom" into the bird. Does anyone have any answer to why this is?
Hello Brad,
"Louder" is more S-meter bars, or audibly louder?
The received RF power should be greater overhead (twist your antenna a bit to change polarization and check). This results in more S-meter bars.
Is the horizon, for you, over a relatively unpopulated area? Do you live in a more populated area?
Demodulated audio may be quieter due to the myriad of people trying to cram into one channel and the uplink FM receiver PLL tracking the resulting chaos. This is my guess, as I haven't done analysis on the effect.
--- Zach N0ZGO
There is also the effect of the reflection off the Earth that can add 3db to your received signal on low passes. I believe this is well used by EME operators. But I don't think that fully makes up for the distance penalty. There is also the effect that the satellite's radiation pattern isn't necessarily equal in all directions, and other than the ISS, most are tumbling somewhat at random. That, I think, could be the main cause of the different signal reports.
Greg KO6TH
On 2019-07-26 17:04, Greg D wrote:
There is also the effect of the reflection off the Earth that can add 3db to your received signal on low passes. I believe this is well used by EME operators. But I don't think that fully makes up for the distance penalty. There is also the effect that the satellite's radiation pattern isn't necessarily equal in all directions, and other than the ISS, most are tumbling somewhat at random. That, I think, could be the main cause of the different signal reports.
Hello Greg,
Using the calculator over at pasternack.com for 70cm:
2000 mile Free Space Path Loss: 155.4 dB 400 mile Free Space Path Loss: 141.4 dB
I suspect he's referring to audio loudness, since the FM threshold effect would be in play once the CNR was > 8dB (assuming narrowband FM).
--- Zach N0ZGO
participants (3)
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Brad Smith -
Greg D -
Zach Metzinger