Again, this is not intended to be a polemical discussion. If you have suggestions about how I might improve my testing methods, I would appreciate your comments.
RTTY capability is important to me
During my ham career I have tried to improve my RTTY reception. I started with an AEA PK-232 which did a pretty good job, especially after modifying the board to 170 hz shift. Later I purchased a Hal ST-6000 and later a ST-8000. Then MMTTY came along and I had to explain to my wife why those expensive boxes were in a cabinet in the basement. But during a recent QSO a ham commented that the software I was using was not very sensitive. I decided I needed to find out if he was correct and whether there were significant differences in the packages. Here is what I found.
How were the tests done?
- A 2300 character text file of ham calls was created.
- The text file was fed into MMTTY to generate a wave file of about 10.5 minutes with several seconds of "diddles" before the text began. Standard RTTY audio frequencies were used (2125/170).
- Virtual Audio Cable was used for all audio connections so the testing is independent of the quality of any physical sound card.
- The recording and playback was done in Audacity.
- PathSim, from AE4JY, requires a 16 bit, 8 khz mono wave file as its input and exports a similar file after adding noise to the signal.
- The 8 khz wave files from were loaded into Audacity and resampled to convert them to 11.025 khz sampling rate with its high-quality sinc interpolation with triangle high-quality dither.
- Parameters on each software package were set as a ham might change them during a QSO when he was experiencing difficulty copying the other stations. As each program was used, I set that process to "High Priority" in Windows XP. I saw no evidence that the performance was limited by CPU availability for either the RTTY program or Audacity.
- Unshift On Space was turned on.
- AFC was used in a trial run to check the tuning and then turned off when data was collected.
- The text resulting from the tests was pasted into RttyCompare from VE3NEA which compares the received text to the expected text and calculates the number of errors. Alex's work with RttyCompare essentially drew a map showing how to do this experiment. His data also called my attention to TrueTTY.
TrueTTY 2.76.2 -- Used the "Optimal" filter setting.
MixW2 2.16 -- Used the "2 Filter" setting
MMTTY 1.66G -- Used the default conditions -- no band pass filter or notch
MMTTY with WinWarbler 6.6.2 front end using the WinWarbler Hyper Sensitive profile with notch and band pass filter
I am more familiar with certain of these programs than others so I may have erred in finding the optimal settings. But I would be interested in how I might modify my procedure to gain more meaningful results. Also, these results include no attempt to simulate the many insults a signal suffers during its trip through the ionosphere.
So which RTTY software should I use?
There are many reasons to choose a RTTY package other than sensitivity. One of the most important is how it interfaces with the logging software. But this data may be starting point for finding a software tool that meets your particular needs.