Problems with Receiving
2. Oscilloscope Activity But No Decoding
Card: Some cards may not work with AGWPE even with the correct driver.
(Read the section on Compatible Sound Cards on the More About AGWPE page on this site.)
If the problem appears to be your sound card, consider replacing the card or adding another. New cards are fairly inexpensive or you may find a
"used" sound card at a hamfest/computer show or in a discarded computer. PCMCIA and USB sound cards are also available. A second sound card dedicated only to ham programs may actually be very useful.
Your first card then be used for Windows and other programs.
Note: If receiving works for a while but then stops, your computer's power management settings may be turning off the sound card.
MIC input: If you are using Microphone input, note that most sound cards expect a maximum input voltage on the microphone line of about 200 mV, which is much less than most radio's maximum output, e.g. 500 mV. For this reason, you should probably use a voltage attenuation circuit in a microphone RX cable. The ideal attenuation will depend on the sound card's input and radio's output specifications. You can try to use the volume sliders to find an ideal spot, but the setting is likely to be very delicate without the attenuation circuit.
In addition, check that your are not using the Microphone Boost or the 20dB option on our sound card, if available. This option is not found in the AGWPE Volume settings, but it may be found as a button in the Windows' Recording Volume Setting window under the Microphone slider (you may need to use the Option: Advanced menu option to have it display). This option will increase the MIC input by 100 times, which could distort your packet even more.
g. AGWPE Settings
Baud Rate: Make sure you have selected the correct packet baud rate in the Sound Card Setup screen
Ports: If you are only using one port, set AGWPE for Single Port (not Dual Port) on the Properties screen
h. Poor Signal quality:
1200 baud packet: To successfully decode a packet, you need about an S3 signal at minimum.
9600 baud packet: To successfully decode a packet, you need nearly an S9 signal. (see 9600 Packet Operations on the Baud Rates and Modes page.
for additional advice about 9600 baud packet operations.)
300 baud packet (HF SSB): Use the Sound Card Tuning Aid's Waterfall Scope to accurately tune the signal. (see HF Packet Operations on the Baud Rates and Modes page. for additional advice about HF packet operations.
Are you tuned to the correct frequency exactly? Do you have tone squelch on? Do you have manual squelch on?
Is the radio's squelch set too high and blocking many signals. (The squelch should not be operating when using AGWPE. For transmitting, AGWPE needs to hear the frequency at all times.)
Packet collisions -- two or more transmitting stations send packets at the same time, making both unintelligible. This is a common problem on busy frequencies, e.g. APRS. No real solution is available although network members could experiment with traffic reduction and collision avoidance schemes and settings, such as slotting.
The other station's packets are too distant, faint, or noisy:
Increase your radio knob's volume control if the radio knob controls RX audio volume; or increase your RX Volume Setting for LINE IN (or MIC, if you are using that).
Poor radio signal path: You may be experiencing multi-path refraction/ reflection problems (signal waves arriving out of phase) or a Fresnel null (part of the signal wave is blocked) because of the antenna's poor position. Try moving your antenna.
Use a better antenna (more height, more gain, more separation from noise or interference sources).
Ask the other station to increase power.
Ask the other station to try a different antenna or a different antenna location.
Consider an antenna feed-line problem at your station if there is any other evidence of weakened signals, e.g. moving the antenna doesn't help and you experience low audio and static on your RX signal compared to the signal someone nearby is receiving.
The packets the other station is sending are are poorly formed:
The sending station sent the packet without sufficient TX delay.
Its radio didn't have sufficient time to power up or switch from receive to transmit. As a result, the beginning of the packet was lost. Ask the sending station to increase TX delay in his station's TNC or sound card.
The sending station's TNC or sound card was over-driving the radio (sending packet tones that were too loud) and his radio had to "clip" the signal (reduce the deviation). This results in a poorly formed packets at the receiving end (low tone is louder than high tone). Ask the sending station to reduce his station's TNC drive level.
Some radios offer a bass boost function that will distort a packet signal. Make sure the sending station is not using this feature.
Are you using the MIC jack on the sound card instead of the LINE In jack?
Then you probably should have an attenuation circuit in the RX cable. See the RX audio cable Help page for such a circuit.
i. Interference
Signal interference from EMI, RFI, and ground loops can distort received packet signals so much that they can not be decoded. Radios such as the Yaesu FT-290 are known for being susceptible to computer noise interference.
EMI, electro-magnetic interference, can come from any nearby AC- powered source, such as your monitor. Turn off the monitor temporarily and then turn it on to see if your packet program recorded any signal when it was off. You may be able to reduce EMI by:
change the monitor scan rates or screen size or combinations of both in:
Windows Desktop > Right Click > Setting Tab > Monitor --- etc....
replace outdated or incorrect monitor driver software
place a ferrite slug on the monitor cable, close to the computer and another close to the monitor
re-locating either the device or your interface cables using shielded interface cables
using ferrite cores (split or toroids) on the interface cables.
using shielding on the radiating device
RFI, radio frequency interference, can be reduced by limiting the length of your interface cable using interface cables with shielding
using ferrite cores (split or toroids) on cables.
Ground loops can result when DC current flows between your computer and your radio. Normally, DC current should not flow between the devices, but it will if there is a voltage potential difference between the devices.
Unfortunately, a sound card interface can become that direct connection.
If you have your computer and radio plugged in to a different branch of the AC wiring in your house you may have problems. Plug your computer in to the same AC outlet strip as your radio so they share the same electrical ground. For laptops, which use an AC-to-DC transformer, you may be more likely to have problems.
To break the ground loop, you should use isolation transformers on your RX and TX audio cables, plus a phototransistor, or optocoupler, in the PTT line (a simple transistor in the PTT line does not does provide isolation). You must isolate all three connecting cables. Note that manufactured interfaces may or may not provide isolation on all three cables (For example, the West Mountain NOMIC does not provide isolation for a RX cable). You'll need to verify if they do by visual inspection or by contacting the manufacturer.
Below are screen shots from the Tuning Aid's Sine Wave scope showing a ground loop: