Hi everybody.
This is essentially a request for what I believe the scientific folks call "peer review"...
I continue to try to understand why none of my equipment has been receiving the ISS digipeater very well since the switch back to 2 meters, despite the fact that the same hardware does well on terrestrial packet and in the case of 145.825 in particular, I have even received packets from PSAT since re-configuring for VHF reception on my Raspberry Pi / RTL-SDR iGate. So, my point is that it isn't that NOTHING is working on 2-meter packet or 145.825 here. And as I've mentioned in the past, I hear from others with similar stories so we're not sharing hardware or location.
This evening there was a favorable pass here and I see on ariss.net that several stations were digipeated while the ISS was over the U.S. Great news!
I monitored that pass in receive-only mode with the same type of TXCO version-3 RTL-SDR that I use for my iGate. The results were very strange and I hope incorrect. I certainly would appreciate it if someone might repeat my test when time permits.
Here is an image showing my SDR tuned to the local NOAA Weather Radio on 162.475. By all appearances, my frequency display is accurate in the VHF band.
https://www.dropbox.com/s/w1dll06xwinteap/NOAA-Wx-Radio-on-freq.png?raw=1
... without changing any settings other than frequency, the following image shows a Spectra-Vue plot of my reception of the packet transmissions from the ISS on this evening's pass:
https://www.dropbox.com/s/s46o3pi87yk9t2h/spec-view.png?raw=1
... I took a ballpark stab at the center point of closest approach and unless I did something awfully wrong, it's roughly 5 KHz above the expected 145.825 frequency. If by any chance this is accurate, it explains why I've been seeing poor reception here.
(On the other hand, if my observations are completely wrong and flawed, this makes just over 1000 times that I've looked foolish!)
Anyway, if anyone is setup to make similar observations, I would imagine that we would all like to know if there is a frequency issue up there. If not, then of course I'm sorry to tie up the mailing list!
73!
-Scott, K4KDR Montpelier, VA USA
Scott,
I had a look at the two noted images. The first thing that I noticed was that the mode was set in both cases to wide band FM not narrow band FM. If you are trying to copy ISS packet using WBFM that might be the source of your problem. It could be that the new radio on the ISS has a somewhat lower deviation than the old radio. The second image (Spectravue) does indicate that your receive might be a bit high in frequency.
If you are not using your SDR to try and copy the ISS then perhaps you should state what equipment you are in fact using; I may have missed it from an earlier post. I have been having good luck copying the ISS using my FT-817. Sometimes I use a dual band VHF/UHF collinear vertical and sometimes a small yagi, the yagi works better but the vertical still works OK too. I don't adjust for doppler, I just set the FT-817 to 145.825. Doppler on 145.825 for a typical pass is about +/- 3.5 kHz at least according to GPredict.
cheers, Graham ve3gtc
On 2017-04-24 22:20, Scott wrote:
Hi everybody.
This is essentially a request for what I believe the scientific folks call "peer review"...
I continue to try to understand why none of my equipment has been receiving the ISS digipeater very well since the switch back to 2 meters, despite the fact that the same hardware does well on terrestrial packet and in the case of 145.825 in particular, I have even received packets from PSAT since re-configuring for VHF reception on my Raspberry Pi / RTL-SDR iGate. So, my point is that it isn't that NOTHING is working on 2-meter packet or 145.825 here. And as I've mentioned in the past, I hear from others with similar stories so we're not sharing hardware or location.
This evening there was a favorable pass here and I see on ariss.net that several stations were digipeated while the ISS was over the U.S. Great news!
I monitored that pass in receive-only mode with the same type of TXCO version-3 RTL-SDR that I use for my iGate. The results were very strange and I hope incorrect. I certainly would appreciate it if someone might repeat my test when time permits.
Here is an image showing my SDR tuned to the local NOAA Weather Radio on 162.475. By all appearances, my frequency display is accurate in the VHF band.
https://www.dropbox.com/s/w1dll06xwinteap/NOAA-Wx-Radio-on-freq.png?raw=1
... without changing any settings other than frequency, the following image shows a Spectra-Vue plot of my reception of the packet transmissions from the ISS on this evening's pass:
https://www.dropbox.com/s/s46o3pi87yk9t2h/spec-view.png?raw=1
... I took a ballpark stab at the center point of closest approach and unless I did something awfully wrong, it's roughly 5 KHz above the expected 145.825 frequency. If by any chance this is accurate, it explains why I've been seeing poor reception here.
(On the other hand, if my observations are completely wrong and flawed, this makes just over 1000 times that I've looked foolish!)
Anyway, if anyone is setup to make similar observations, I would imagine that we would all like to know if there is a frequency issue up there. If not, then of course I'm sorry to tie up the mailing list!
73!
-Scott, K4KDR Montpelier, VA USA
Thanks for the feedback, Graham!
I wasn't concerned with demod or decoding packets on this particular night; but rather to run a wide-band capture with no doppler correction to allow the transmitted signal to paint the doppler curve on my display to identify the center crossing at closest approach. That does a number of things for me like identify the transmitted frequency (at least as received by my hardware), verify my TLE's, and to get a visualization of how much doppler shift is occurring between AOS & LOS.
It does interest me quite a bit to try to characterize differences between those who are seeing better performance -vs- those who are not, so you're right on to mention hardware. We can't generalize, but I see "some" evidence since the freq change that the group having better luck might be those with equipment like the FT-817 and the folks using the excellent Kenwood HT's. But it goes without saying that with such a large sample group, a VERY large number of people could step forward with minimal equipment reporting good success as well. From my own testing I can observe that I decode way more packets with an SDRPLay than with a cheap mobile rig or generic RTL-SDR. I know that sounds obvious (that superior hardware gives superior results) but that's not my point... rather that it just "feels" like that wasn't so much the case with the previous 2-meter setup.
I could easily be wrong but when it seems like some experimentation might provide some useful info to improve everyone's enjoyment of the resource, I have a hard time leaving it alone!
============================
On Mon, Apr 24, 2017 at 8:33 PM, Graham planophore@aei.ca wrote:
Scott,
I had a look at the two noted images. The first thing that I noticed was that the mode was set in both cases to wide band FM not narrow band FM. If you are trying to copy ISS packet using WBFM that might be the source of your problem. It could be that the new radio on the ISS has a somewhat lower deviation than the old radio. The second image (Spectravue) does indicate that your receive might be a bit high in frequency.
If you are not using your SDR to try and copy the ISS then perhaps you should state what equipment you are in fact using; I may have missed it from an earlier post. I have been having good luck copying the ISS using my FT-817. Sometimes I use a dual band VHF/UHF collinear vertical and sometimes a small yagi, the yagi works better but the vertical still works OK too. I don't adjust for doppler, I just set the FT-817 to 145.825. Doppler on 145.825 for a typical pass is about +/- 3.5 kHz at least according to GPredict.
cheers, Graham ve3gtc
===========================================
On 2017-04-24 22:20, Scott wrote:
Hi everybody.
This is essentially a request for what I believe the scientific folks call "peer review"...
I continue to try to understand why none of my equipment has been receiving the ISS digipeater very well since the switch back to 2 meters, despite the fact that the same hardware does well on terrestrial packet and in the case of 145.825 in particular, I have even received packets from PSAT since re-configuring for VHF reception on my Raspberry Pi / RTL-SDR iGate. So, my point is that it isn't that NOTHING is working on 2-meter packet or 145.825 here. And as I've mentioned in the past, I hear from others with similar stories so we're not sharing hardware or location.
This evening there was a favorable pass here and I see on ariss.net that several stations were digipeated while the ISS was over the U.S. Great news!
I monitored that pass in receive-only mode with the same type of TXCO version-3 RTL-SDR that I use for my iGate. The results were very strange and I hope incorrect. I certainly would appreciate it if someone might repeat my test when time permits.
Here is an image showing my SDR tuned to the local NOAA Weather Radio on 162.475. By all appearances, my frequency display is accurate in the VHF band.
https://www.dropbox.com/s/w1dll06xwinteap/NOAA-Wx-Radio-on-freq.png?raw=1
... without changing any settings other than frequency, the following image shows a Spectra-Vue plot of my reception of the packet transmissions from the ISS on this evening's pass:
https://www.dropbox.com/s/s46o3pi87yk9t2h/spec-view.png?raw=1
... I took a ballpark stab at the center point of closest approach and unless I did something awfully wrong, it's roughly 5 KHz above the expected 145.825 frequency. If by any chance this is accurate, it explains why I've been seeing poor reception here.
(On the other hand, if my observations are completely wrong and flawed, this makes just over 1000 times that I've looked foolish!)
Anyway, if anyone is setup to make similar observations, I would imagine that we would all like to know if there is a frequency issue up there. If not, then of course I'm sorry to tie up the mailing list!
73!
-Scott, K4KDR Montpelier, VA USA
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Scott