A recent look into my own signal quality on PSK made me take a search on the net for information on PSK signal quality.
I came upon this web site (link) which is a site concerned with
"This site is devoted to promoting RSQ as an improved signal reporting system for narrow band digital modes and to demonstrating its application to the popular PSK31 mode."
To this end, they recommend and point out that Regions 1 and 3 have adopted the following
Readability (% of text)
R5 95%+ Perfectly readable
R4 80% Practically no difficulty, occasional missed characters
R3 40% Considerable difficulty, many missed characters
R2 20% Occasional words distinguishable
R1 0% Undecipherable
Strength
S9 Very strong trace
S7 Strong trace
S5 Moderate trace
S3 Weak trace
S1 Barely perceptible trace
Quality
Q9 Clean signal, no visible sidebar pairs
Q7 One barely visible pair
Q5 One easily visible pair
Q3 Multiple visible pairs
Q1 Splatter over much of the spectrum
Seems very reasonable to me and will become part of my operating practices.
Showing posts with label PSK. Show all posts
Showing posts with label PSK. Show all posts
Sunday, March 1, 2009
PSK Splatter solved
While operating PSK on 20m this morning I received a report that I was splattering across the band. With this in mind I though I should look into this.
I was not operating outside my normal situation.
FT2000D
30W - 80W depending on the QSO
Signallink USB
HP PC
only have 1 antenna, the Windom
Let the experiment begin.
Not knowing how bad the problem was, I went up to 18.1MHz to find a quiet place to poke around.
The only station I saw on the band was a fellow operator here in Ottawa, VE3OIJ. We transmitted back and forth a bit and found nothing remarkable. Leading me to think nothing is seriously broken.
I wanted to see my own signal, so I used the IC7000 to receive the tx output of the FT2000D
Rig
TRX - FT2000D
Freq - 18.1MHZ
Tx Power - 50W (by the FT2000D meter)
PSK Tones - 600Hz
SignalLink
Tx - 3/10
Measurements - HRD on IC7000
Signal S9+20 (input to IC7000 grounded at antenna switch)
IMD - 19dB
SNR - 19dB
Fundamentals 600Hz @ -20dB
Spurs @ 1800Hz @ -70dB 3rd Harmonic
"Image" @ 2900Hz @ -80dB 5th Harmonic
Spurs @ 3300Hz @ -80dB ??
At 6dB/S-unit, if my fundamental was received at his station at S9, then this "splatter" would be received at -S2, i.e. 2 S-units below, S0, these cannot possibly be the splatter my fellow operator saw.
VE3OIJ was able to see these terms, but we are less than 10km apart. It may make sense to follow these terms a bit more. The plot below shows my signal from 1W to 150W into my dummy load. In all cases the relative size of the "splatter" remained fixed. This tells me that these terms are not being generated by the radio's linearity ans regardless of my transmit power would not be a problem to any one but an operator in my city.
How to get gid of these? Don't know.
Next step was to try back on frequency, in case it was RF feedback into the shack that only happens on 20m.
Rig
TRX - FT2000D
Freq - 14.070MHZ
Tx Power - 50W (by the FT2000D meter)
PSK Tones - 600Hz
SignalLink
Tx - 3/10
Measurements - HRD on IC7000
Signal S9+20 (input to IC7000 grounded at antenna switch)
IMD - 19dB
SNR - 19dB
Fundamentals 600Hz @ -20dB
Spurs @ 1800Hz @ -70dB 3rd Harmonic
"Image" @ 2900Hz @ -80dB 5th Harmonic
Spurs @ 3300Hz @ -80dB ??
Identical results.
Below is a typical waterfall on 20m, "strong" signals are 30dB above the noise floor. If anyone else had terms like the ones above in their transmit signals there is no way I would ever see or be concerned with them.
Summary
I cannot improve the relative power in these terms by adjusting my TX power, as they go dB for dB with my fundamental signal.
Only someone in my local area will see these signals as significant, and the operator who indicated I was splattering did not leave his call so I can not tell. I should has asked, but I did not, a short QSO may have been a better idea.
For now I'll assume every thing is ok and go back to having fun.
Update:
Here is another plot of my tx signal.
Update #2
I was in a QSO with a Spanish station and received a 575 report, so again I thought something must be wrong. A plot of my transmit signal is below.
This time I recognized that the "regrowth" was at N times 120Hz, pointing me to a power problem. Also, I though I'd take a look at my CW output as a means to remove the PSK hardware and software from the equation. Below is my CW plot, this was for 10W output.
In my shack I power my table from two power bars. One regular power bar for all the ordinary stuff, PC, lamp, monitors, and a filtered power bar for the FT2000D, DMU2000, and the Kenwood PS-53 for the IC-7000 and / or TS-850. Both power bars are powered from the same wall outlet which has a dedicated 15A circuit for the sta
I can see in the plot above, that the same N*120Hz side tones are present, the first pair are only 35dB down.
Below is a plot of the same CW transmission when the FT2000D + DMU2000 and Kenwood PS-53 supply are on the same power bar as the rest of the shack. (avoiding the MFJ power
I can see in the plot below, that only the first 120Hz side tones are present, but now are 60dB down, a 25dB improvement. The MFJ-1164B power bar will need some further investigation.
In the meantime, returning to PSK mode, below shows a much improved transmit signal.
Rig
TRX - FT2000D
Freq - 18.10MHZ
Tx Power - 130W (by the FT2000D meter, just for testing)
Excellent.
Now I think I have a very good idea of how clean the PSK signal should be from my radio and will keep an eye.
Summary:
1) If you have an extra radio and Signallink you can run 2 copies of DM780 and see your own transmit signal. Grounding the second rig's antenna input will enable enough signal in to be detected.
2) Your AC supply should be suspected if you have N*120Hz sidebands
3) Read an understand how volume controls should be set for your software and PSK interface hardware
4) Looking at your CW output can help isolate the problem
5) a good transmit signal will have better than 25dB IMD, better than 25dB SNR and 60 to 70dB spurious free range.
All for now.
I was not operating outside my normal situation.
FT2000D
30W - 80W depending on the QSO
Signallink USB
HP PC
only have 1 antenna, the Windom
Let the experiment begin.
Not knowing how bad the problem was, I went up to 18.1MHz to find a quiet place to poke around.
The only station I saw on the band was a fellow operator here in Ottawa, VE3OIJ. We transmitted back and forth a bit and found nothing remarkable. Leading me to think nothing is seriously broken.
I wanted to see my own signal, so I used the IC7000 to receive the tx output of the FT2000D
Rig
TRX - FT2000D
Freq - 18.1MHZ
Tx Power - 50W (by the FT2000D meter)
PSK Tones - 600Hz
SignalLink
Tx - 3/10
Measurements - HRD on IC7000
Signal S9+20 (input to IC7000 grounded at antenna switch)
IMD - 19dB
SNR - 19dB
Fundamentals 600Hz @ -20dB
Spurs @ 1800Hz @ -70dB 3rd Harmonic
"Image" @ 2900Hz @ -80dB 5th Harmonic
Spurs @ 3300Hz @ -80dB ??
At 6dB/S-unit, if my fundamental was received at his station at S9, then this "splatter" would be received at -S2, i.e. 2 S-units below, S0, these cannot possibly be the splatter my fellow operator saw.
VE3OIJ was able to see these terms, but we are less than 10km apart. It may make sense to follow these terms a bit more. The plot below shows my signal from 1W to 150W into my dummy load. In all cases the relative size of the "splatter" remained fixed. This tells me that these terms are not being generated by the radio's linearity ans regardless of my transmit power would not be a problem to any one but an operator in my city.
How to get gid of these? Don't know.
Next step was to try back on frequency, in case it was RF feedback into the shack that only happens on 20m.
Rig
TRX - FT2000D
Freq - 14.070MHZ
Tx Power - 50W (by the FT2000D meter)
PSK Tones - 600Hz
SignalLink
Tx - 3/10
Measurements - HRD on IC7000
Signal S9+20 (input to IC7000 grounded at antenna switch)
IMD - 19dB
SNR - 19dB
Fundamentals 600Hz @ -20dB
Spurs @ 1800Hz @ -70dB 3rd Harmonic
"Image" @ 2900Hz @ -80dB 5th Harmonic
Spurs @ 3300Hz @ -80dB ??
Identical results.
Below is a typical waterfall on 20m, "strong" signals are 30dB above the noise floor. If anyone else had terms like the ones above in their transmit signals there is no way I would ever see or be concerned with them.
Summary
I cannot improve the relative power in these terms by adjusting my TX power, as they go dB for dB with my fundamental signal.
Only someone in my local area will see these signals as significant, and the operator who indicated I was splattering did not leave his call so I can not tell. I should has asked, but I did not, a short QSO may have been a better idea.
For now I'll assume every thing is ok and go back to having fun.
Update:
Here is another plot of my tx signal.
Update #2
I was in a QSO with a Spanish station and received a 575 report, so again I thought something must be wrong. A plot of my transmit signal is below.
This time I recognized that the "regrowth" was at N times 120Hz, pointing me to a power problem. Also, I though I'd take a look at my CW output as a means to remove the PSK hardware and software from the equation. Below is my CW plot, this was for 10W output.
In my shack I power my table from two power bars. One regular power bar for all the ordinary stuff, PC, lamp, monitors, and a filtered power bar for the FT2000D, DMU2000, and the Kenwood PS-53 for the IC-7000 and / or TS-850. Both power bars are powered from the same wall outlet which has a dedicated 15A circuit for the sta
I can see in the plot above, that the same N*120Hz side tones are present, the first pair are only 35dB down.
Below is a plot of the same CW transmission when the FT2000D + DMU2000 and Kenwood PS-53 supply are on the same power bar as the rest of the shack. (avoiding the MFJ power
I can see in the plot below, that only the first 120Hz side tones are present, but now are 60dB down, a 25dB improvement. The MFJ-1164B power bar will need some further investigation.
In the meantime, returning to PSK mode, below shows a much improved transmit signal.
Rig
TRX - FT2000D
Freq - 18.10MHZ
Tx Power - 130W (by the FT2000D meter, just for testing)
Excellent.
Now I think I have a very good idea of how clean the PSK signal should be from my radio and will keep an eye.
Summary:
1) If you have an extra radio and Signallink you can run 2 copies of DM780 and see your own transmit signal. Grounding the second rig's antenna input will enable enough signal in to be detected.
2) Your AC supply should be suspected if you have N*120Hz sidebands
3) Read an understand how volume controls should be set for your software and PSK interface hardware
4) Looking at your CW output can help isolate the problem
5) a good transmit signal will have better than 25dB IMD, better than 25dB SNR and 60 to 70dB spurious free range.
All for now.
Tuesday, November 25, 2008
Operating Digital Mode
Over the past six months I have been predominately operating PSK31 mode. PSK31 is a half-duplex digital phase shift keying modulation mode with a signal bandwidth of 31.25Hz. Its uses a varicode to represent ASCII characters and the net speed is about 50 words per minute. PSK31 has a low power requirement because if it's compact bandwidth and low snr requirements.
A bit error rate of 1 in a 100 is achieved at a signal to noise ratio of about 5dB. After propagation loss, if 50W PSK transmission achieves a workable 5dB SNR then a 50W SSB trnasmission with 100 times the bandwidth (3kHz) would achieve a dissapointing -15dB SNR. This simple example serves to present why PSK is well suited for DX operation without the need for significent kWatt transmit powers and beam antennas.
Within the 3kHz pass band of the audio signal, there is enough "space" for up to 40 parallel QSO's. Although this density would be quite uncommon, I have easly worked 20M band conditions where there have been >20 with no difficulty. The program running on the PC will copy all the QSO's and hilight callsigns and CQ calls. Without touching the rig's VFO you can monitor all 20 QSO, and move between them for transmission.
PSK31 was developed by Peter Martinez G3PLX.
Rig and Hardware
Software
Setup
The setup is quite straightforward, The radio is connected to the Signalink USB with a connector providing audio input and output signals as well as a PTT control to key the transmitter. Connection to the PS cannot be simpler than the single necessary USB cable.
Operating
A quiet 40M band example
The image below is of the program DM780 which is part of the Ham Radio Deluxe package. This screen shot shows;
Operation of this digital mode is relatively straightforward and is very rewarding from a DX perspective because of its key properties. Bands can get very busy at times and there are no shortage of new calls. I have had spent as much time calling CQ or QRZ and driving long strings of QSO's as well as looking around and answering calls from others. South America, Africa, all of Europe, the Middle East and Russia are all within reach from my wire dipole. I'd suggest this mode to anyone who thinks that they might enjoy it.
- Compact spectrum controlled through cosine pulse shaping and modest linearity requirements.
- The baud rate of 31.25Hz is conveniently related to the popular 8kHz sample rate of basic sound card circuits.
- The Varicode used supports the entire 127 cahracter set of the ASCII code.
A bit error rate of 1 in a 100 is achieved at a signal to noise ratio of about 5dB. After propagation loss, if 50W PSK transmission achieves a workable 5dB SNR then a 50W SSB trnasmission with 100 times the bandwidth (3kHz) would achieve a dissapointing -15dB SNR. This simple example serves to present why PSK is well suited for DX operation without the need for significent kWatt transmit powers and beam antennas.
Within the 3kHz pass band of the audio signal, there is enough "space" for up to 40 parallel QSO's. Although this density would be quite uncommon, I have easly worked 20M band conditions where there have been >20 with no difficulty. The program running on the PC will copy all the QSO's and hilight callsigns and CQ calls. Without touching the rig's VFO you can monitor all 20 QSO, and move between them for transmission.
PSK31 was developed by Peter Martinez G3PLX.
Rig and Hardware
- FT2000D or IC-7000, Well yes you need a transceiver. The transceiver needs to be set in USB mode, regardless of the band you are operating. Also, because linearity considerations, it is important that compression be disabled. Usually on the IC7000 I can run 50W PEP comfortably, the FT2000D can easily double this but is not usual operation.
- SignalLink USB, the USB to Analog converter, provides interface between the rig and the PC. In this case, the adapter provides the analog converter, and PTT control. This device also provides isolation from Rig to PC. Transmit drive level is easily adjustable during QSO withe the front panel control. This is especially handy when you want to reduce power or give that 459 a bit of a boost.
- HP Pavilion Slimline PC, PC used for Ham Radio Deluxe and USB
Software
- Ham Radio Deluxe, Is the heart of the PSK31 modem.
Setup
The setup is quite straightforward, The radio is connected to the Signalink USB with a connector providing audio input and output signals as well as a PTT control to key the transmitter. Connection to the PS cannot be simpler than the single necessary USB cable.
Operating
- Frequencies
160m - 1838.150 kHz
80m - 3580.15o kHz
40m - 7035.15 kHz
30m - 10142.150 kHz
20m - 14070.150 kHz
17m - 18100.150 kHz
15m - 21080.150 kHz
12m - 24920.150 kHz
10m - 28120.150 kHz
80m - 3580.15o kHz
40m - 7035.15 kHz
30m - 10142.150 kHz
20m - 14070.150 kHz
17m - 18100.150 kHz
15m - 21080.150 kHz
12m - 24920.150 kHz
10m - 28120.150 kHz
- QSO's and Macros
A quiet 40M band example
The image below is of the program DM780 which is part of the Ham Radio Deluxe package. This screen shot shows;
- Vertical window on the left which shows QRZ info for the call sign which was identified.
- Horizontal window across the bottom which is a representation of the 3kHz audio signal from the rig. PSK transmissions show as vertical traces, after a while you can learn to recognize the characteristic shape, as well as those of other digital modes. Clicking on any one of these will set the receiver to that frequency and if a transmission is made it will be on that half duplex frequency.
- The horizontal window on the top is a copy window in which the decoded PSK ASCII will appear.
- The horizontal window below it, is the outgoing message window, This is where you can enter the CQ CQ CQ or the reply you wish to send.
- Logging is very slick because it is a one click operation, and information from QRZ is automatically inserted if you are on line.
Operation of this digital mode is relatively straightforward and is very rewarding from a DX perspective because of its key properties. Bands can get very busy at times and there are no shortage of new calls. I have had spent as much time calling CQ or QRZ and driving long strings of QSO's as well as looking around and answering calls from others. South America, Africa, all of Europe, the Middle East and Russia are all within reach from my wire dipole. I'd suggest this mode to anyone who thinks that they might enjoy it.
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