I have been using the little FlexRadio FLEX-1500 for many years, mainly for WSPR operation.
I am posting this because I recently ran into an FT8 issue and could find almost no information about it. The FLEX-1500 may be old, but it is still a very capable radio, and I suspect there are many of them still in use today.
I would not recommend it for CW operation. The latency is simply too high. However, I believe this is a limitation of many SDR transceivers from that era. I am used to the CW performance of the Elecraft K3, which sets a very high standard.
The receiver itself is excellent. With dedicated switched band-pass filters on both receive and transmit, the FLEX-1500 is truly a hardware masterpiece.
I owned the radio long before FT8 even existed.
For WSPR, operation was straightforward since only about 200 Hz of bandwidth is required. When FT8 became popular, I widened the USB filter to approximately 3 kHz so I could receive all signals across the normal FT8 passband.
However, I noticed something strange. The bandwidth shown on the PowerSDR panadapter did not match the bandwidth actually being decoded by WSJT-X. Although the panadapter displayed the full 3 kHz, only about 600 to 700 Hz was being decoded. Signals outside that narrow section were visible on the display but never decoded.
I searched for information about this issue and even contacted KE9NS, but no solution was found. I eventually assumed that the FLEX-1500 was simply too old and that this was either a hardware limitation or something related to PowerSDR.
Until today.
While experimenting with the PowerSDR audio settings, I decided to try using the I/Q audio path instead of the conventional audio output.
Suddenly, the problem disappeared.
WSJT-X was now able to decode signals across the entire visible FT8 passband, exactly as shown on the panadapter.
This suggests that the limitation was never in the receiver hardware itself. The bottleneck was somewhere in the audio chain between PowerSDR and WSJT-X.
After years of assuming the FLEX-1500 was simply too old for proper FT8 operation, the solution turned out to be a simple audio configuration change.
Hopefully this observation will help other FLEX-1500 users who encounter the same problem.
Despite its age, the FLEX-1500 remains an impressive radio and is still very capable for weak-signal digital modes.
I used two audio configurations, copying the driver input and output settings to VAC2, and suddenly the bandwidth selected in the pan adapter matched the Wide Graph. The entire 3 kHz was decoded using the same settings, showing that the Flex1500 hardware and software can decode 3 kHz or more. Later, I switched back to VAC1 while running the WSJTx program, which caused a hangup and forced PwrSDR to close and reboot. I realized that before changing audio settings, the connected WSJTx or MSH program should be closed. Now, back on VAC1, everything works as it should with proper bandwidth and decoding. Why it works now? Possibly an internal software flag was reset by using VAC2. In any case, FT8 decoding is working perfectly.
the whole band is decoded like it should do in the first place, jus by accident I got it working..
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