WinDRM Docs – Release 1.0
WinDRM was developed from a relatively new broadcast standard called Digital Radio Mondiale. It is based on a proven robust technology called Coded Orthogonal Frequency Division Multiplexing or COFDM. This method of sending data transmits multiple signals simultaneously over a single path (USB carrier for WinDRM). Each one of these signals has its own unique frequency range which is modulated using Quadrature Amplitude Modulation for voice, text messages and images. COFDM spreads these carriers (WinDRM has up to 51) spaced apart at precise frequencies (thus FDM) across a bandwidth of 2.3 or 2.5 KHz. It is this spacing that makes them unique (i.e. Orthogonal, the O in OFDM) which keeps the demodulator (WinDRM’s receiver) from seeing frequencies other than its own. COFDM has close to a white noise spectrum which gives it “benign electromagnetic interference properties with respect to other signals.” WinDRM can not be used to decode commercial DRM transmissions. An open source receiver is available for this is at: http://drm.sourceforge.net/ For further info on COFDM go to: http://en.wikipedia.org/wiki/Orthogonal_frequency_division_modulation Other digital HF picture transfer programs such as Digtrx and HamPAL all share the core ham DRM standard and therefore are compatible.
The WinDRM GUI (graphic user interface)
5 Radio Buttons (left side) - (enabled under program control only) as follows:
Input/Output
IO – Enabled: Sound card is linked and passing data to the processor. Disabled: Indicates sound card is not compatible and/or PC’s processor is too slow. If not enabled, WinDRM will not function.
Frequency Acquisition
Freq – Enabled: The three frequency pilots (3 vertical lines in the waterfall display) have been found. This correlates with the DC Offset frequency (normally 350Hz) which is graphically shown as a blue vertical line (the start) in the “Display” spectrum.
Time Synchronization Acquisition
Time – Enabled: Timing acquisition is done. This indicates the search for the beginning of the OFDM symbol has been completed. Disabled: No synchronization, usually caused by poor SNR, distortion of the transmitted signal and/or receive band pass less than 2.5 KHz wide. Note: False indications (flickering) can be caused by AWGN (atmospheric noise) and generally, may be ignored.
Frame Synchronization
Frame - Enabled: Frame synchronization is done and indicates the start of a DRM frame (400ms) has been found. The Receiver is in synchronization with the WinDRM transmitting station. Disabled: Lost frequency synchronization due to poor SNR or change in frequency (avoid “tuning” for DRM!). Note: False indications (flickering) can be caused by AWGN (atmospheric noise) and generally, may be ignored.
Fast Access Channel
FAC – Enabled: Receiver (WinDRM) is in the tracking mode, has received a good Cyclic Redundancy Check (CRC) and is in synchronization with the WinDRM transmitting station. FAC is a separate logical channel and modulated with 4-Amplitude Quadrature Modulation (4QAM). FAC provides BW info (2.3/2.5khz), call sign and other DRM transmit parameters for the DRM receiver to quickly find this info so the signal can be demodulated. Disabled: Lost sync, bad data CRC as a result of poor SNR, distortion on the transmitted signal and/or change in frequency. See HB9TLK’s technical specs at: http://www.qslnet.de/member/hb9tlk/drm_h.html
Main Service Channel
MSC - Enabled: Indicates actual audio and data bits are being decoded for voice, text message and/or images. Like FAC, MSC enabled indicates the CRC has been acknowledged and good data has been received (Info data for MSC will be incremented after the CRC has been computed). Disabled: Disruptions and/or artifacts of voice, text message not received, or missed block/segment/packet image data. QRM/QSB/QRN and weak signals can cause MSC to fail or “flicker” during reception. An SNR reading of 7 or higher generally ensures MSC will remain enabled. Note: All these radio buttons must be enabled before WinDRM will begin decoding the received picture or voice data. This is all done automatically and is dependent upon the quality of the signal.
Files: (download from http://n1su.us/windrm/download.html)
The .wav files must be created using Digitrx or similar program. For docs on how to create these files, go to http://www.kiva.net/~djones/index.htm for instructions. Note: These wave files are not necessary to execute WinDRM. WinDRM stores files/pics with errors in the Corrupt folder. Good, error free Files/pics are stored in the Pictures folder. Mixer.bin contains data for your sound card’s mixer settings. Settings text file stores user settings such as com port, call sign, etc.
Other files are created by WinDRM include:
bsr.bin
bsr0.bin
bsrreq.bin
RX_Log.txt
startRX.bat (required for Windows 2000 only)
startTX.bat (required for Windows 2000 only)
startPIC.bat (required for Windows 2000 only, Picture mode)
Known specs and definitions:
Data rate
Transmit data rate may be derived during transmission from the 4 digit number found in the SNR box. This number is dependent upon selection made in the DRM TX settings. The default is 1070 (Mode box showing B/L/16/0). This number (1070) when multiplied by 2.5 equals the exact MSC bit rate (2.5 x 1070 = 2.675 Kbps). This is the actual MSC capacity (bits/frame). Currently, the codecs in use are Linear Predictive Coding and Speex at 2.4Kbps. It is possible to raise this codec rate to 3600 or higher but at the cost of lower protection rate schemes. For HF, with its propagation/noise/multi-path problems, the quality of speech would probably be unacceptable. However, for Data WinDRM offers a “Speed” mode which provides a higher bit rate of 4.362Kbps and a “Robust” mode of 1.567Kbps. By changing the DRM TX settingss for Mode, MSC protection, MSC Coding and Bandwidth bit rates may be carefully chosen to match the transceiver filters and band conditions. Future development may include other codecs.
Image data transfer time
KA2HZO provides the following on-the-air transmission times calculated between the TX mouse click and the release of the transmitter’s PTT. This provides real throughput capability of WinDRM in the default, robust and speed modes.
File Size Kbytes Mode in Sec=Default Mode in Sec=Robust Mode in Sec =Speed
5 26 40 19
10 44 72 29
15 61 104 39
20 78 135 49
25 95 166 59
The “Speed” mode can provide better than 2.5 times faster throughput than the “Robust” mode and 1.5 times faster than the default DRM TX parameters. Chose wisely and you will be rewarded.
PC requirements
Windows OS, 2000 or XP. 700mHz minimum processor speed with 1.2gHz or higher to ensure smooth operation. Avoid executing other programs while WinDRM is decoding or transmitting unless you have a fast PC. For testing/experimenting, some PCs will allow two instances of WinDRM to be run in a back-to-back mode (connect sound card line out/speaker to line in/mic and carefully set levels). One instance may then be used to transmit pics to the other. For Windows 2000, see WinDRM “Help” info under “About.”
Status of received data in the Info box for images (Pics)
The expanded “Info” box during receive provides a status of the data being decoded as it is received. These counters are shown in three sets of one to three digits separated with a forward slash (/). The first set is the number of memory segments (size) in the file. The second set shows the number of good segments decoded. The last set shows the segment number of the last segment decoded.
The first set of numbers represents what WinDRM “knows about” at the start of the transmission and will change because the program begins assembling the data before the total is known. If a segment is received in error (CRC failure), a following instance can provide the opportunity to receive it again. If received ok, the counter will increment. After all the data is received, the segment counts will all agree indicating the file has been received error free (and if a pic, it will open up in a new window) on the desk top.
For example, after receiving a 10kbyte file, the Info box displays 100/100/100. The size of the file can be determined from the first three numbers since each segment is 100 bytes (100 multiplied x 100 equals the file size of 10kbytes). The next two sets of numbers show that 100 segments were decoded and the last segment decoded was segment number 100.
Status of received data in the info box for voice
While receiving voice, the Info block displays a two digit number representing the quality of the decoded data. The quality is determined by the number of good frames of data received versus bad since the last synchronization. 70 percent or higher number usually provides sufficient speech quality to understand what is being said for a QSO. With SNRs of 15 or higher, expect a quality number near 100 percent.
Status of transmitted data in the Info box for files (Pics)
After transmitting the lead in sync data, the Info box provides the status of the file (pic) as it is being sent. The counter consists of two sets of numbers separated by a forward slash (/). First set shows the instance being sent while the second set shows the percentage (1 to 100 percent) of the total segments sent. The number of instances the pic will be sent is shown in the “Select File” window. A choice of 1 to 3 may be selected but additional instances can be sent by adding the file for transmission in this Select File window more than once.
Status of transmitted data in the Info box for voice
No data is shown in the Info box during voice transmission except during the lead in sync period.
Info box during “lead in” transmission
In both pic and voice transmissions, lead in sync data is being sent to the receiving station to set up the timing and other OFDM carrier information. This lead in maybe lengthened to provide more set up (sync) time at the receive end by selecting long lead in under the Select Files window. During this time (several seconds), the Info box will show various data which has no meaning for the user other than to indicate this lead in data is being transmitted and the actual file data has not started. Some of this data also includes determining the size of the file and packetizing data prior to be sent.
Text Message data
Up to 60 ASCII characters (including spacing) may be transmitted. Greater than 60 will be truncated at the receive window. Text messages may not be sent with data (file/picture transmissions). Text messages may be added/changed during TX. The data rate is only 80bps, but the message is continuously transmitted during the voice transmission. On receive, the text message window remains open at the end of the transmission for further review. Message window may be closed at any time. Text messages may only be sent and received with Digital Voice transmissions.
Transmit and Receive parameters
The golden rule for reception can be summed up in just a few words. The OFDM data must all fit within the band pass of the receiver. The DC Offset of the transmitter’s default of 350Hz was chosen to ensure the 2.5Khz wide OFDM signal is inside both the transmit and receive audio band pass. The 350Hz is an offset from DC (0 hertz) and is the where the carriers of the OFDM “start”. The timing (OFDM searches for this) locks on and starts all it’s shifting from here for all the 51 carriers. WinDRM does this based on what ever the DC offset is set. This offset can be changed but it must fit within the band pass. The problem for most HF rigs is this: If the DC is changed too much from 350, not all the OFDM carriers may fit within the band pass. It is not important to be within a few hertz (or use the waterfall to exactly line up with the received pilot frequencies). Thirty to fifty hertz should be close enough unless a lower SNR is noted. Low SNR is may be caused by carriers outside the receiver’s band pass, however experience has found (on HF), low SNR is usually caused by improper audio levels, QSB, QRN, multi-path or just “weak signals”. If any “tuning” of the USB frequency is made during reception of the OFDM (DRM) signal, the demodulated data is phase shifted and attenuated. But even more serious, the orthogonality of the ORDM symbols are destroyed and that causes ICI (inter-carrier-interference). Click on “Reset” to re-sync the data if any tuning must be done to ensure all carriers are within the band pass of the receiver. When the WinDRM users talk on SSB, carefully tune them in on USB. This will ensure you are on “their” frequency. Be sure the receiver’s band pass is at least set to at least 2.4 kHz, no compression (or audio processing) and Fast AGC. For transmit, minimize distortion by avoiding any ALC action. For 100 watt rigs, set power to approximately 15 watts average power. Remember, this mode works best with very linear transmitters including high power amplifiers. OFDM has a rather high crest factor (peak power is much higher than the average power as read on your wattmeter). For a detailed explanation of how and why –not- to exceed the power limits of your rig, go to: http://www.tima.com/~djones/DRM_power.htm
CODEC
Selected under DRM TX Settings, “Codec” or “DATA” (for pics) being transmitted will be displayed. Under program control, the receiving station will automatically decode and display the type of transmission being sent (LPC, SPEEX or Data). Data is the default.
SNR
Signal-to-Noise-Ratio is an estimated value that indicates the quality/strength of the received signal. Experience has found, near error free data may be decoded with a level of approximately 7.0 dB. The higher the number, the better the signal is being received. An SNR of 10 or better usually ensures error free copy. QRN, QRM, transmit distortion and propagation problems caused by multi-path cancellation lower the SNR. Under “ideal” band conditions with signals over S-9, SNR may rise to 25db or greater. SNR is adversely affected if the transmitted or received signal’s COFDM carriers are attenuated because of bandpass filters that are too narrow for the BW being used.
DC
Refers to the frequency offset from 0 Hz to the start of OFDM carriers. Default is set at 350Hz. This is an arbitrary number set in an attempt to ensure both the 2.3 or 2.5 kHz signal BW “fits” with minimum attenuation inside the bandpass of the receiving station. This may be confirmed by observing the shifted PSD, transfer function displays or the moving waterfall displays. The accuracy of the receiving station’s tuning for the COFDM signal is dependent upon this factor which may allow up to 50Hz tuning error without degrading the decoding process. It is important to note however, that once sync is obtained, no further “tuning” of the signal should be attempted. A blue vertical line indicates the location of DC offset in the spectrum display. Values of 50 to 5000 Hz are valid entries but 350 Hz is normally used by all.
Mode
Displays the DRM TX settings. The default is:
B (DRM Mode B) S (Short Interleave) 16 (Main Service Channel 16 Quadrature Amplitude Modulation) 2.5 (2.5 kHz Bandwidth). Most stations use 2.5kHz since additional carriers are available with this wider BW for better receive performance. Note: The initial bandwidth setting is 2.3 kHz. The “Default” button will always set the bandwidth to 2.5 kHz.
Setup
PTT Port
Any com port 1 through 8 may be selected for control of the transmitter’s PTT using conventional RS232C data terminal ready (DTR) line. For most applications, a standard RS232C cable is used to connect the PC’s com port to the sound card interface (RIGblaster or equivalent). In addition, the DTR and ready to send (RTS) line may be used to mute the receiver’s speaker while receiving data. Implementation of this feature may be found at KB4YZ’s web site. (http://www.kiva.net/~djones/index.htm )
Setup
Call sign
Up to 8 number/letters may be entered. Properly entered, this provides a valid ID for all transmissions. This meets FCC requirements for station ID. “Hamdream” is the default.
Setup
Display
Receive Spectrum
The Spectrum’s display is approximately 2.5 kHz wide in the horizontal while the vertical shows the amplitude in dB (no scales are shown for any of the displays). The shape of the signal is rectangular and represents the band width of the received signal which may be either 2.3 or 2.5 kHz. This really does not serve much purpose other than to note the received signal should display a rectangular shape (if it doesn’t – something is wrong!) More importantly, however, it may be used to set the audio input level of the sound card. Too much input will over-drive the sound card (Line Input should always be used when available) and may cause distortion and low SNR/no decoded data. Carefully adjust the Mixer and the Receiver audio until the top of the OFDM spectrum averages approximately half way up in the display window. Although there is normally good dynamic range in most sound cards, the goal is obtain the highest SNR reading. After sync has been obtained, a blue vertical line will appear in the spectrum. This blue line shows where the timing for acquiring the OFDM signal has started (the DC offset frequency) which is normally 350Hz. This may pop up intermittently as it will “false” on random noise and may be ignored when no valid OFDM signal is being received.
Receive Waterfalls
There are two waterfalls, the ‘classic” waterfall with its sweep from the bottom of the display to the top. The OFDM spectrum will be shown with an even intensity level across its 2.3 or 2.5 KHz band width. Typically, some change in intensity at the bottom and top of the spectrum (darker area) may be seen but should not affect performance. Within the waterfall, three frequency pilots (carriers) of slightly higher intensity can be seen. They stand out in the waterfall because they have higher gain (transmitted at twice the power). These pilots are modulated with known fixed phases and amplitude which optimize DRM’s performance for initial synchronization duration and reliability. The high-lighted red markers of the waterfall’s sweep indicate where these pilots are located when the transmitter and receiver DC offsets match. The “moving” waterfall moves from top to bottom with the red marker’s indicating the position of the pilot signals remaining fixed at the top of the display. The moving waterfall adds a visual method to monitor the health of the decoded signal in the form of a vertical line on each side of the waterfall spectrum. During the decoding process, green vertical lines indicate data is being received without errors and red lines indicate errors were received (segments lost). These green/red indicators move with the spectrum instantly showing when and where data errors occurred. The horizontal line across the top of this display indicates the bandwidth of the OFDM signal. The signal in the waterfall should fully extend the width of this indicator. Note: This display shows the affects of multi-path cancellation as shown by the darkened areas. The carriers in this area are being attenuated due to these phenomena. The two bright lines (on the bottom left, just before the start of data) is unwanted noise (probably caused by a ground loop between the transceiver and the PC soundcard) on the Speaker Out audio line to the transciever’s Mic input. Every effort should be made to eliminate this type of interference when connecting audio cables between the PC and the transceiver. To fix ground loop and/or RFI problems associated with sound cards and the transceiver, refer to very informative papers found at: http://audiosystemsgroup.com/SAC0305Ferrites.pdf
and http://audiosystemsgroup.com/Ferrites-Ham.pdf
Input Level (receive)
This display graphically shows the received audio. Sound card (recording) Line Input may be set to approximate the level as shown in the display above.
Shifted PSD (receive)
This display plots the “estimated Power Spectrum Density (PSD) of the input signal”. Here the incoming DC frequency (350 Hz) is mixed with 5650 Hz to give a 6 Khz (the blue vertical line is correctly shown in DRM mode B only). The peak on the left is the mirror image (5650 – 350 = 5300 Hz) and is partially suppressed by the WinDRM’s internal IF filter. If a peak is displayed between the signal and the mirror signal, a 50/60Hz noise getting into the transmitted audio (probably a ground loop problem). The main signal rectangle wave form will resemble a square wave. The three peaks seen at the top of the waveform are the pilot carriers (twice power of other carriers). Any roll off or dips in the waveform indicate the carriers in these areas have a loss of power caused by QSB and/or attenuation in the band pass of the transmitter or receiver. If the transmitter or receiver is not allowing the 2.3/2.5khz wide DRM signal to pass without attenuation, this waveform will be rolled off on the either end (or both!). For further info refer to: www.qslnet.de/member/hb9tlk/drmif/index.html
Transfer Function (receive)
This plot shows the “squared magnitude of the channel estimation at each sub carrier”. The green line is the correct signal while the blue line shows the phase distortion of the channel.
Impulse Response (receive)
This plot shows the “estimated Impulse Response of the channel based on the channel estimation.”
Fast Access Channel (FAC) (receive)
This plot shows the 4 QAM rectangular constellation. (See FAC under “State” for more info) The higher the SNR, the “tighter” the constellation will be displayed in the 4 quadrants. For more on how QAM works, see: http://en.wikipedia.org/wiki/Quadrature_amplitude_modulation
.
Main Service Channel (MSC)/Amplitude (receive)
This plot shows the various constellations for 4 through 64 QAM logical channel that provides the voice and file data. The higher the SNR is the “tighter” the constellation but some scattering is normal on HF. These are displayed in the 4 to 64 quadrants. Quadrature Amplitude Modulation is used to modulate the OFDM MSC carriers. QAM varies the amplitude and phase of each one of the carriers (for 16 QAM and up). Then, through frequency multiplexing (adding all these carrier together across the 2.3/2.5 kHz BW) the OFDM is created. 16QAM is shown here. Note the relative high SNR to achieve this display.
Setup
Codec
Either Linear Predictive Coding (LPC) or SPEEX codec may be selected for digital voice. LPC is the default. Either codec requires 2.5 kHz bandwidth (see DRM transmit settings). For further understanding of these Codecs, see: http://www.otolith.com/otolith/olt/lpc.html and http://www.speex.org/ New codecs with higher MOS (Mean Opinion Score, a voice quality measurement) may be come available on future releases. Quality DV is not “easy” to do on HF and it may not be for everyone. Unlike, SSB where two or more stations can be heard and understood in some conditions, only one DV data stream at a time can be decoded and who ever has the best signal will be decoded. Time is required (couple seconds) to obtain sync and then decode data. Fast break-ins are not currently possible, however this too may be shortened in future updates. Note: A third codec, MELP (Mixed-Excitation Linear Predictive) is being tested as this doc is being written. MELP is capable of producing a more natural sounding speech than LPC or SPEEX. MELP will require an additional file (melp_dll.dll) which may be found at: http://www.rarewares.org/files/others/melp_dll.zip
Setup
Text Message
Edit TX Text Message
Selecting “Edit TX Text Message” will open up a window to enter text.
Up to 60 ASCII characters (including spacing) may be transmitted. Greater than 60 will be truncated at the receive window. Text messages can not be sent with data (file/picture transmissions). Text messages may be sent, changed or deleted during a voice transmission. The data rate is only 80bps, but the message is continuously transmitted during the voice transmission. Here you may use this give the wx and /or your station info.
Allow RX Text Message (default)
Default provides a window for receiving the transmitted messages. This text message window remains open for further review after the transmission has ended. (for more info, see previous “Edit TX Text Message” description)
Setup
Save Received Files
Checked (default) indicates files received without errors will be saved in the sub-folder named “Pictures”. If a file is missing segments, it will be saved in the “Corrupted” subfolder. Both of these folders are initially created by WinDRM.exe.
Show Received Files
Checked (default) indicates error-free files will be displayed (when associated with other programs i.e. Irfanview) after received. Irfanview is a free “viewer of choice” and may be downloaded at www.irfanview.com Irfanview’s plug-ins are also required and must be associated with the file extensions (.jpg, jpg2000 etc) to show the pic. Note: Received files and pics will be saved in the Pictures and Corrupt folders even if no viewer has been configured.
Show Only First Instance
Checked (default) indicates only a single instance of an error-free file will be displayed when received multiple times (when associated with other programs i.e. Irfanview).
Soundcard
Open mixer displays the sound cards “Recording” and “Playback” sliders for Audio in and out. These are associated as follows:
RX Input = Mixer Recording Line-IN (from xcvr’s speaker out)
TX Output = Mixer Playback Line-OUT (or speaker out) (to xcvr’s microphone input)
Voice input = Mixer Recording Mic-IN (PC microphone into jack on soundcard)
Voice output = Mixer Playback Line-OUT (or speaker out) (to xcvr’s microphone input)
For Digital Voice, inputs are switched under program control (line-in switched to mic-in for transmit). Adjust mixer sliders for proper input and output levels. Start with the “sliders” approximately one-third up. Only RECORDING microphone should be enabled. For transmit, both Speaker (or Line) Out and Wave must be enabled (selected). Disable (un-check/un-select) all other inputs/outputs. For decoded Digital Voice, Mixer Playback line-out (speaker out) must be manually switched to amplified Speakers to hear the audio. Where two sound cards are available, set up one card for Receive and one for Transmit. No manual switching will then be required.
DRM TX Settings
Mode A/B
MSC Protection
BandWidth
Interleave
MSC Coding
DC Offset
Clicking the Default button will result in the following DRM TX settings:
Mode MSC Protection Bandwidth Interleave MSC Coding DC offset
B Normal 2.3 Short 4QAM 350
Robust lowers the transmission BPS by changing 16QAM to 4QAM. Speed raises the transmission BPS by changing Mode to A, MSC protection to Low and Interleave to Long 2 seconds. (Digital Voice transmission requires 2.5kHz bandwidth). 16QAM on a HF channel requires a high SNR and minimum multi-path to perform well.
Note: A BSR request may be made using different DRM TX settings. This is sometimes done under poor band conditions in attempt to get the request through lower SNRs. However, the originating station responding to this request should always send the response to this request (“Send bad segment report”) in the same DRM TX settings it was originally sent.
DRM RX Settings
Default settings are:
Freq. Acq. Sens. Search Window Size Audio Filter
60 350 not enabled
Higher settings increase sensitivity for weak signals but with higher probability of false sync. Audio filter is user preference. Filter may improve speech intelligence for either codec by removing some low frequency in the audio spectrum.
BSR (Bad Segment Report – automated)
BSR provides a procedure to repair (sometimes called a “fix”) a defective file (i.e. picture). Normally, a defective file is caused when the received station does not receive all the memory segments error free (segment failed CRC check). When this happens, clicking on the “BSR” button will open a window and show the number of segments “missing”. The received station may then send a BSR “Request” to the sending station and request these missing segments be resent so the file (picture) may be repaired and displayed. This is the manual method, requiring user intervention. The “automated” BSR completely automates this procedure for P2P (peer to peer) transfer of files (pics). Auto open BSR request, TX ARQ and RX ARQ must be checked to initiate this procedure. Note: WinDRM does not look for activity on the frequency. The procedure simply relies on “timing” between the tx to rx and rx to tx change-overs. Therefore, users should maintain control of the station while this automated BSR is being executed, i.e. “attended” operation.
Load last RX file
With this checked, the last error free file (pix) received will be loaded in the “Select Files” window (from TX Pic). This is normally used when the entire file is to be re-sent.
Auto open BSR request
Automatically opens up the BSR window when a defective file is received. This must be checked to initiate the automated BSR procedure.
TX ARQ
Automates the “send” request for the BSR
RX ARQ
Automates the “receive” request for BSR
BSR (button)
Bad Segment Report
When a picture is received with segments missing, a left click on this button will display the number of segments. Press “OK” to request these segments be re-sent.
SPA (button)
Show Picture Anyway
Left click on this button will attempt to associate and link the last received Picture. If header and some other “minimum display data” are received, the picture will be displayed “with errors”. Dependent up on the errors and preference of the received station, the user may then click on the BSR button to show the number of segments missing and then initiate the request to “fix” the picture. Picture show is an example of a one missing segments displayed using SPA.
Picture shown “repaired” after receiving the missing 35 segments using the BSR request procedure. Note: This entire procedure may be automated with The “Auto Open BSR,” “TX ARQ” and “RX ARQ” checked.
Example of the transmitting station’s responding to a BSR request. Note: This is not the data used in the previous repaired picture.
G (button – works under Windows XP only)
Good (good picture received)
Left click on G will transmit a pre-recorded wave file displaying “GOOD” in
the received station’s waterfall. Filename: g.wav
B (button – works under Windows XP only)
BAD (bad picture received)
Left click on B will transmit a pre-recorded wave file displaying “BAD” in
the received station’s waterfall. Filename: b.wav
ID (button – works under Windows XP only) Left click on ID will transmit a pre-recorded wave file displaying the transmitting station’s call sign in the received station’s waterfall. Filename: id.wav For help in creating these wave files, go to KB4YZ’s web site: http://www.kiva.net/~djones/index.htm
TUNE (button)
Left click on TUNE will transmit a pre-recorded wave file for setting the proper output level of the transmitter. Three (3) sync (pilot) carriers will be displayed in the received station’s waterfall.
TX Pic (button)
Left click opens a window to add or remove files for transmission. Radio buttons enable from 1 to 3 instances of the file be transmitted. Additional instances of the same file may be sent by adding the file multiple times in the Select Files window. Long leadin increases the time sync data at the beginning of the transmission and is sent for weak signal or when in presence of QRM. Return button closes button and returns to opening WinDRM screen. TX button starts transmission of sync data followed by the file data.
TX Voice (button)
Left click starts voice transmission. Microphone must be connected to the “MIC” input. This display graphically shows the transmit microphone level (sound card’s microphone input). Adjust the mixer’s Record slider to set the level while speaking across the PC microphone. Best results will be found when the microphone input level is kept rather low while speaking with a louder tone of voice. Keep the average level just below the mid-way point to avoiding peaks that will cause severe distortion at the receiver’s end. Some PC electret microphones have poor response and tend to accentuate the highs which cause high peaks and thereby distortion. Experiment in this area to find the best microphone and level for the best speech quality. Linear Predictive Coding appears to have the better speech quality. The RX filter does not affect transmitted audio. The filter may help the intelligence of the speech in some conditions but at a loss of lows. Speex “sounds” like it adds more fidelity to the speech but at the same time, it has a muffled sound and tends to “flat top” the input easier. This is an area that, perhaps a well chosen microphone (such as a one from Heil Sound) will improve the voice quality. The input impedance of a sound card microphone is approximately 2500 ohms. This may vary within sound cards but should be a consideration when choosing a microphone. Best speech occurs when the mic’s sound card level down and speaking loud into the microphone while closely watching the peaks. Bandwidth under DRM TX Settings must be set for 2.5 kHz. The TX button name changes to “RX” while transmitting. “Echo” of the decoded voice may be heard using some combinations of PCs and soundcards. This is thought to be caused by what some refer to as “soundcard latency” which is related to the timing and transfer of data. Changing sound cards may correct this problem. Known “good” sound cards include Turtle Beach and Sound Blaster Audigy series.
RESET (button)
Reset re-starts the sync process in receive.
About
Info
About
Help
--------------------------------------------------------------------------------------------------
updated 08-Sept-2005
copyright 2005 by Mel Whitten, KØPFX – mel@melwhitten.com
