ISS Packet Frequency?
Since I have been using both a Kenwood TH-D72A and other less-than-optimal gear for packet and APRS over the last several years, I decided to do a side-by-side packet decoding test this afternoon during a 38 degree ISS pass at 2048 UTC. Both ground stations were connected via a splitter to the same antenna (an old analog TV antenna at 0 degree elevation and covering all 360 degrees azimuth). Both ground stations also shared the same Pentium dual-core laptop computer for software.
The less-than-optimal station included the following: Icom IC-02AT HT Unified Microsystems SCI-6 Sound Card Interface AGWPE UI-View32
The Kenwood TH-D72A was in packet mode and decoding through the latest version of Yet Another APRS Client (YAAC).
Both stations were tested prior to the pass on terrestrial APRS with almost identical decoding results. Tuning during the pass was done in 5 kHz increments on both stations (145.830 MHz, 145.825 MHz, 145.820 MHz). Reception during the ISS pass was less than stellar due to local noise, but both stations decoded the same number of packets (13), although they didn't always decode the exact same packets.
So even with the non-linear frequency shift noted previously by K4KDR and myself, there does not seem to be any appreciable difference between my ISS packet decoding ability now and any point in the past, even with non-packet hardware. Perhaps a couple of other stations could share their experience in this regard.
Todd AL0I
Stupid question time: Do you have the sound card and audio processing sample rates set the same (identical)?
Norm n3ykf
On Wed, Apr 26, 2017 at 5:51 PM, Stewart Todd Morgan morgan_st@bellsouth.net wrote:
Since I have been using both a Kenwood TH-D72A and other less-than-optimal gear for packet and APRS over the last several years, I decided to do a side-by-side packet decoding test this afternoon during a 38 degree ISS pass at 2048 UTC. Both ground stations were connected via a splitter to the same antenna (an old analog TV antenna at 0 degree elevation and covering all 360 degrees azimuth). Both ground stations also shared the same Pentium dual-core laptop computer for software.
The less-than-optimal station included the following: Icom IC-02AT HT Unified Microsystems SCI-6 Sound Card Interface AGWPE UI-View32
The Kenwood TH-D72A was in packet mode and decoding through the latest version of Yet Another APRS Client (YAAC).
Both stations were tested prior to the pass on terrestrial APRS with almost identical decoding results. Tuning during the pass was done in 5 kHz increments on both stations (145.830 MHz, 145.825 MHz, 145.820 MHz). Reception during the ISS pass was less than stellar due to local noise, but both stations decoded the same number of packets (13), although they didn't always decode the exact same packets.
So even with the non-linear frequency shift noted previously by K4KDR and myself, there does not seem to be any appreciable difference between my ISS packet decoding ability now and any point in the past, even with non-packet hardware. Perhaps a couple of other stations could share their experience in this regard.
Todd AL0I
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The sound card is set for "2 channel 16-bit, 48000 Hz (DVD Quality)." I am not aware that AGWPE lets you set a sample rate for that application.
I have a vague recollection of changing the sound card sample rate from 44100 Hz to 48000 Hz in order accommodate my Alinco DJ-X11T, but I don't recall any sample rate change affecting AGWPE performance on this laptop.
Todd AL0I
On 4/27/2017 7:40 AM, Norm n3ykf wrote:
Stupid question time: Do you have the sound card and audio processing sample rates set the same (identical)?
Norm n3ykf
It's merely on the short list of things that I check when these sort of symptoms show up. Next would be changing the output/input sound level settings. Low/lower early in the chain.
I use direwolf. It gives a signal strength report with a received signal. Software manual has optimal window. Also can do bit flipping to recover unrecoverable packets. (corrupted data retrieved by compting the checksum).
Can you record the RF on an SDR and make multiple tries decoding?
Neatest thing is that RF becomes digital. Store record forward reverse fold spindle and mutilate.
Norm n3ykf
On Thu, Apr 27, 2017 at 8:57 AM, Stewart Todd Morgan morgan_st@bellsouth.net wrote:
The sound card is set for "2 channel 16-bit, 48000 Hz (DVD Quality)." I am not aware that AGWPE lets you set a sample rate for that application.
I have a vague recollection of changing the sound card sample rate from 44100 Hz to 48000 Hz in order accommodate my Alinco DJ-X11T, but I don't recall any sample rate change affecting AGWPE performance on this laptop.
Todd AL0I
On 4/27/2017 7:40 AM, Norm n3ykf wrote:
Stupid question time: Do you have the sound card and audio processing sample rates set the same (identical)?
Norm n3ykf
Yes, I can, but I'm not complaining about performance. The point of the TH-D72A vs. IC-02AT test was to see if evidence existed to support the notion that there might be some anomaly with the new ISS APRS system that might explain why some operators (Scott, K4KDR and others apparently) are unable to decode packets now when they could previously, either on 70 cm or 2 m. If my comparison test had come up, say, 13 to 2 packets decoded in favor of the TH-D72A, that would lend credence to the notion that such an anomaly might exist but is masked by the better performance of purpose-built (i.e. designed for packet/APRS) equipment like Kenwood and Yaesu transceivers.
When you have a measure of experience with something like ISS APRS reception, it's easy to brush off reports like Scott's and just chalk them up to operator ignorance, operator incompetence, simply forgetting a step or two in a setup process, etc. But Scott is asking for some help (a sanity check), and I was just trying to perform a few independent tests. There are plenty of other operators who could do the same thing.
So now the question would seem to turn to things like:
What do Scott's station and the others have in common (if anything)? Are they all SDR type stations? If they are SDR stations, are typical SDR stumbling blocks handled properly (offset, center spike at 0 Hz offset, etc.) Are the station components and transmission lines well shielded? Have local interference sources come into existence on or near 145.825 MHz since the ISS was previously on that frequency?
Todd AL0I
On 4/27/2017 9:18 AM, Norm n3ykf wrote:
Can you record the RF on an SDR and make multiple tries decoding?
Norm n3ykf
participants (2)
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Norm n3ykf -
Stewart Todd Morgan