Sound Card Packet  with AGWPE

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Most recent AGWPE version is:  2013.415  15 Apr 2013

Computer requirements
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Using the Tuning Aid

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Problems with Receiving

As you troubleshoot receive problems, remember that AGWPE provides you with some visual aids:

  • The Sound Card Tuning Aid screen is accessible from the AGWPE menu. It can be used to "see" the quality of received signals and, for HF packet particularly, help in tuning the radio to the correct frequency. Go to the Tuning Aid page to see examples of how good and packet signals should look.
  •  If AGWPE successfully decodes a packet on a radioport, then the green light on that radioport's modem icon will flash once .

Note: Please make sure you are using the latest version of AGWPE before troubleshooting problems. Your problem may have been fixed in the most recent version of AGWPE!

1. No Sine Wave in Oscilloscope
2. Oscilloscope Activity But No Decoding

1.  No Sine Wave in Oscilloscope

Tune to a busy packet channel and select the Sine Wave oscilloscope mode in the Sound Card Tuning Aid. If you do not see sine wave activity, look for a reason at one of five places along the RX audio path:

a. Radio/antenna

First confirm that audio signals -- preferably packets! --  are are being received at the radio. Disconnect the sound card interface temporarily and see if you can hear packets from the radio's speaker and/or see the radio's 'S' bars or the 'Busy" indicator light up.

  • If you don't see or hear packet activity:
    • is the squelch too high? Since AGWPE prefers no squelch for transmitting, it's best to leave the squelch off (even though AGWPE will still receive with the squelch on, providing the squelch is not set too high).
    • is tone squelch (CTCSS and DTSS) turned off?
    • if dual VFOs, is the correct VFO/band selected?
    • is the antenna connected?
    • is the radio tuned to the right frequency?
    • is the mode set for FM and not accidentally in CW, SSB or another mode?
    • can you hear packets by using a different antenna (more gain)? or by moving the antenna to another location (higher, away from possible EMI interference)?
    • can you hear packets using a different radio with a different antenna? with a different radio but the same antenna?
  • If you can't hear packets from the radio's speaker (internal or external):
    • Is the speaker volume knob set too low? Low speaker volume would only affect sound card receiving if your interface's RX cable connects to the radio's external speaker or microphone jack, not a data jack.
    • If your interface's RX audio connects to the radio's external speaker jack, is that radio jack known to work with speakers? Plug in a different speaker or use a meter to test the jack.

b. Radioport settings

Check the following in the Properties settings for the sound card:

  • Make sure you have selected the correct sound card device
  • Make sure you have selected the correct packet baud rate for the radioport channel

c. Volume Control settings

Use the Volume Control screen to check your sound card settings:

  • If you happen to have more than one sound card (i.e. mixer device), make sure you are working with Recording settings for the correct sound card. (Program Bug: if you have more than one sound card, AGWPE's Volume Control Screen can be used to set the first card but not a second card. To control the second card, you will need to use the Windows Volume Control Program.)

  • Make sure you are working with the Volume Control Recording settings, not the Playback settings.

  • Make sure you have selected the correct input jack -- LINE IN or MIC -- where your RX interface cable is attached.

  • Make sure the vertical volume sliders for the selected input jack is not at or near the bottom (about 1/3 up is fine). If you see Balance sliders, make sure they are centered.

  • If there are still no signals, try selecting the other input source -- Microphone or Line In. You may have the plug in the wrong jack. If this was the problem, move the plug back to the correct jack and reset the input source.

d. RX audio cable

See the RX audio cable page for wiring schematics and other hints.

  • Is the RX cable plugged in completely at the sound card jack? Make sure you haven't used the wrong sound card jack or haven't confused the RX cable with the TX or PTT cable. (Hint: put labels on the ends of all cables.)
    If you are using two sound cards, is the RX cable plugged into the right one?
  • Are you using a stereo jack at the sound card plug? You should use a stereo plug for most sound cards.
  • You can not interface two radios to the sound card using the microphone jack. The Microphone jack on sound cards is not stereo capable, so you will probably only receive audio from the port 1 (left channel) radio.  Use the LINE IN jack instead (see Rx audio page).
  • Test the cable:
    • Unplug it from the sound card jack and plugging it into a speaker (if the speaker has a plug and not a jack, use clips leads or an in-line coupler to join the two plugs). If you hear RX audio in the speaker, the RX cable is OK, or
    •  Use a multi-meter:
      • test for continuity and short circuits. Check your solder connections if you find a problem.
      • Is the RX audio line wired to the tip of the stereo plug? The ring of the stereo plug should be unwired, unless you are interfacing to two radios. The sleeve should be wired to the sound card ground.
    • Is the RX line securely soldered to the correct pin in the radio plug?
    • If the RX cable has an in-line isolation transformer, make sure it is a 1:1 transformer, unless you are using the radio's external speaker for RX audio. If you are using the external speaker, then you should be using a 1000:8 transformer and the 1000 Ohm primary coil of the transformer should be wired to the sound card side, not the radio side.
  • Try using another cable without a transformer.

e.  Sound card or driver

  • Does the sound card work with other Windows' sound generating programs? If not, in the Windows Control Panel under Sounds/Multimedia, make sure the sound card is installed and there are no conflicts with other devices.
  • Sound card suddenly stops working after a few minutes and always about the same number of minutes: This probably a power management issue; your computer or laptop is going into power saving mode and is turning off the sound card.
  • Driver: Make sure you have the latest driver for your version of Windows. You can the latest version from the sound card/chipset manufacturer's website (better source than the computer manufacturer).
  • Card: Some cards may not work with AGWPE even with the correct driver. See Compatible Sound Cards.

    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. 

SignaLink USB Interface user?  See the AGWPE-Signalink USB page on this web site for troubleshooting suggestions.

2.  Oscilloscope Activity But No Decoding

If AGWPE is receiving signals but is not decoding them, look at these possibilities:

f.  "Recording" Volume Settings

AGWPE is very tolerant of RX audio volume levels, but your volume settings may still be too loud or too soft.

  • Too soft/muted: try raising the receive volume sliders until you see more deflection (peaks and valleys) in the Tuning Aid's Sine Wave. If the sliders don't change the wave significantly, try turning up the volume at the radio.
    If the RX audio from the radio is still too low:

    • make sure you are pulling audio from the correct radio pin/plug. Some radios have different RX audio pins/plugs for different modes or packet baud rates. Make sure you are using the one for your packet baud rate. (Example: the Yaesu FT-847 has a Data In/Out stereo plug jack for HF modes and a 6 pin mini-DIN jack for packet. Audio from the HF jack will be too weak for packet. If you buy a sound card interface, you may get only the Data In/Out plug and not the 6-pin mini-DIN plug.)

    • remove any attenuation circuit you may have in the RX line

    • try plugging the RX audio line into the MIC jack instead of the LINE IN

    • install an audio pre-amplifier in the RX line.

  • Too loud: If the sine pattern has very thick and tall waves (nearly fill the scope top to bottom), try lowering the volume settings. (If the sliders don't change the wave, try turning down the volume at the radio.)

  • 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?
  • Is the mode set for FM and not accidentally in CW, SSB or another mode?
  • 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. When it transmits, 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.
  • Note that distorted packet signals simply cannot be decoded. For example, if you have mountains (or tall buildings) near you, then signals may be reflected by the mountains (or buildings) and result in multipath (or phase) errors. You can try using a small beam antenna to overcome the problem. Align the antenna with the boom parallel to the mountains.

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. And computer (laptop) noise can get into radios (particularly HTs) and antenna if they are too close to the computer.

Note: "noise" from other components in the computer can get into the sound card and create insurmountable difficulties for AGWPE, particularly on decoding. There may be no solution for this, other than using a second, external sound card.

Here are some external sources of noise that you might be able to do something about:

  • Power noise: Especially on laptops, noise can enter the sound card from the power supply. Try disconnecting the power supply and run on battery only. If your radio is connected to a poor quality power supply or if it's connected to a battery charged by a poor quality power supply, you may also have problems. See
  • 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 if you:
    • 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 snap-on core on the monitor cable, close to the computer and another close to the monitor
    • re-locate either the device or your interface cables
    • use shielded interface cables
    • use ferrite cores (split or toroids) on the interface cables.
    • use shielding on the radiating device
    • move mag-mount or HT antennas away from the computer


  • RFI, radio frequency interference, can be reduced if you:
    • limit the length of your interface cable
    • use interface cables with shielding
    • use 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 link.

    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 as your radio, so they share the same electrical ground.

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 some manufactured interfaces may not provide isolation on all three cables (For example, the West Mountain NOMIC used to not provide isolation for a RX cable). You can verify if the interface does by visual inspection: look for a small transformer in audio line circuit; or ask the manufacturer.

Buxcomm (and perhaps other vendors) offer a simple add-on audio isolation cable if you don't want to build your own. You simply plug in the isolation cable between your sound card jacks and your audio in and your audio out lines. The Buxcomm item is called a ISOL8R at

Below are screen shots from the Tuning Aid's Sine Wave scope showing a ground loop:


EMI or RFI on Your Receive Audio Cable?

You can use the Sound Card Tuning Aid to "see" if you have interference or some other problem affecting your RX audio cable. Here is a way to hear it:

  • Tune your radio to a busy frequency.

  • Temporarily remove your interfaces TX audio plug from the LINE OUT jack of the soundcard and instead plug in your computer speakers. Leave the RX audio plug from the interface in the LINE IN (or MIC) jack.

  • If you can't hear the radio's RX audio in your computer speakers, increase the RX volume sliders in AGWPE's Soundcard Volume Settings screen.

  • When you can hear RX radio audio in the speakers, tune the radio to a quiet frequency and lower the AGWPE RX volume slider to its minimum (you may need to also turn down the radio' speaker volume dial if you get RX audio from the radio's mic or speaker jack. )

  • Now increase the AGWPE TX Playback volume controls (WAVE & TX Master) to maximum.

  • You should hear no radio signals or radio noise. If you hear any Hummmmmm or Hissssssss it should  be very, very slight. If it very distinct, you probably have a RFI, EMI or ground loop noise coming through your RX audio cable. Just to be sure, compare the sounds from your computer speakers with the sounds from your radio's speaker to see if the sounds are the same as the radio's (no problem) or different ( a problem).


j. Sound Card Clock

  • Each sound card has a reference "clock" that is supposed to oscillate at a sampling rate of approximately 11025 Hz. Many of the low-cost sound cards that come standard with a computer, particularly "on board" sound chips, may oscillate at a rate significantly lower or higher than this standard, and this can create a problem for AGWPE, particularly on decoding received packets.

    To attempt to correct for inaccurate clocks,  AGWPE has a user-selectable sound card clock adjustment. It doesn't really adjust the sound card clock rate; it just adds in a mathematical adjustment to the AGWPE decoding algorithm.

    If you are experiencing decoding problems, you can try adjusting the sound card clock from the Sound Card Modem Setup screen. AGWPE's default adjustment setting is "4", which is no adjustment.

    Screen shot  <-- Click for larger image

    Using trial-and-error, you can try to find an adjustment that results in better packet decoding. I do not know in absolute terms how much change in Hz there is for each setting, but Stephen WA8LMF found that a lower adjustment (1, 2 or 3) is needed for clocks that operate below the standard rate. NOTE: Clock adjustments are NOT applied immediately by AGWPE. To apply a new clock adjustment, you must restart AGWPE.

    As reported by Stephen WA8LMF, here's an even more powerful way to change the clock adjustment. Using the CheckSR program found at flDigi download sites, he discovered his clock rate was only 10800 Hz, well below the 11025 standard. He then discovered that ... 

    .. you can hand-edit the AGWPE configuration files and enter any value from 1 to 20 to more closely fine-tune the clock rate adjustment value. In the main AGWpe folder, you will find the files "port0.ini" and "port1.ini".   These files contain the settings specific to a particular AGWPE radioport (i.e. baud rate, whether it is a sound card or a physical COM port, the label you see in the ports list, etc).   The first part of a port.ini file looks like this:

    <-- Sample rate correction 1-20
    SOUNDCARD=Realtek AC97 Audio

    The line "SENS_THRESHOLD=" is rather misleadingly labeled.   It DOES NOT adjust the sensitivity (i.e. input audio gain).   It is actually a sample rate correction factor done with a crude relative scale of integers from 1 to 20.  The default value is  4 .   

    I discovered that entering the value "
    1" here made my lousy motherboard sound system start working with AGWpe on receive.  It still wouldn't decode some of the more screwed up, out-of-spec on-air transmissions that the iMic would, but it DID copy everything from a correctly-set local digipeater.  

    Bottom Line: Experiment with values for this variable in the .ini file until you get the best decode performance possible.

    While experimenting, it's best to test with the reception of a weak station (less than S8)

    Interestingly, you may find the best adjustment setting may change with the seasons if your hardware is outdoors or exposed to heat fluctuations.

    At what rate does my sound card clock oscillate?

    AGWPE does not come with a method for measuring your sound card's clock rate, but other programs do.

    For example, the flDigi download sites offer a stand-alone program called CheckSR.exe. Specify a sample rate of 11025, press Start, let the program run for a minute or two, and then press Stop. It should then tell give you the exact rate of your clock. Try this site for checksr.exe:

    MMSSTV also has a procedure for gauging the clock rate. It's more complex and is  described in the MMSSTV help. (The MMSSTV download site is at )

    Perhaps  with a measurement of your clock speed and the information above, you can make an educated guess about how much of an adjustment to enter into AGWPE.


k. Radio Settings

  • If your radio has signal processing settings, turn them off. For example, some Yaesus have a "bass boost" function. Others radios such as the ICOM IC-706MKIIG, have a "DSP" setting. These settings should be turned off/disabled.
  • Make sure you are using the correct RX data output source on the radio. For example, on a Yaesu FT-8500, AGWPE can not decode 1200 bps through the data port , only through the speaker-out jack. The "problem" with the data port is that it has no de-emphasis circuitry and so the packet tones are skewed by at least 6 dB. (To fix that, "You would need to add the right value capacitor." Sorry I can't help much beyond that.)
  • Hand-held radio often have a "battery saver' or "power saver" setting that turns off the radio's receiver circuit for a few seconds or parts of a second. It that setting is on, you may be missing the first part of packets.

If your problem is not resolved by the problem solving pages on this website, join the AGWPE Yahoo Group to ask a question or search the archives for previous postings that may relate to your problem:

Other troubleshooting page on this web site:
    Program Behavior

Last Updated:

by Ralph Milnes NM5RM


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