Thanks for adding these facts to the discussion Joe.
This is indeed what most people don't know or understand about the
modern digi modes. There is no signal "under the noise", it is there.
Just to clarify a bit further, the tone the software is looking for in 5
Hz BW only needs to show it's presence, it contains no info. The
information is built up by listening to many tones in 5 Hz filters and
with precise timing.
Except for shorthand messages where the software only listen for the
presence of two tones at a given spacing, detecting them in say 5 Hz
filters. No need to build up a message, the spacing determines what
message the software presents to the operator in the GUI.
Imagine the difference compared to copying a CW message like "W7XXX de
SM2CEW RRR ur 449 in KP15" on a single channel to complete a QSO.
That's why CW is KIng in my world, real challenge, operator is fully
involved. And ANY information can be conveyed via the air waves to the
other end of the contact.
As this thread is about filters, sorry for the extra info above.
If someone feel up for a challenge, there's a fairly long CW message at
-17 dB in SSB BW on my website that is certainly readable if you use
your favorite audio filter.
https://www.sm2cew.com/wavefiles.html
73
Peter SM2CEW
Den 2026-02-07 kl. 17:31, skrev Joe Subich, W4TV:
On 2026-02-07 12:19 PM, Tree wrote:
Many people are copying signals way below the noise level with their
DSP radios and FT8.
That depends on the way one defines the noise level. FT8 (and the rest
of Joe Taylor's modes) measure the noise floor in an SSB (2.5 - 2.7 KHz)
bandwidth. However, the actual detection bandwidth for each tone is
in the 5 Hz range. If one adjusts for the detection bandwidth, the
"-24 dB" minimum s/n of FT8 is more like +3dB for tone vs. noise.
How is that possible if that signal just isn't there?
The signal is quite obviously there ... it's a matter of how one defines
the noise.
73,
... Joe, W4TV
On 2026-02-07 12:19 PM, Tree wrote:
So is the takeaway that the older superhet top line rigs are then the
optimum for 160-meter DX?
I guess this begs a question about FT8. Many people are copying signals
way below the noise level with their DSP radios and FT8. How is that
possible if that signal just isn't there?
Tree N6TR
On Sat, Feb 7, 2026 at 8:08 AM Rick Kunath via Topband <
topband@contesting.com> wrote:
So is the takeaway that the older superhet top line rigs are then the
optimum for 160-meter DX?
Or is there something else about the SDR that wins out?
Ir seems like hearing is what it is all about down here.
And an excellent review, thank you.
Rick Kunath, K9AO
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