That digital modes are all "low power modes" is an unfortunate urban
legend, Ed. PSK31 is very narrow and will work well in very narrow RX
bandwidths. Noise power, being proportional to bandwidth, will thus be
less on each end, and lower powers work well. It's also angle
modulation and moderately immune to at least Gaussian noise. JT65, FT8,
and the other Dr. Joe Taylor modes are "weak signal" not "low power"
modes. They operate in roughly a SSB voice channel bandwidth [~3 KHz]
even though each signal is very narrow. They will decode at negative
(S+N)/N ratios in a ~3 KHz channel where there will be many such
signals. With today's abysmal conditions, even 1,500 W may result in a
negative (S+N)/N ratio on the other end. It's the terrestrial
equivalent of your lunar path, and no remonstration is required or deserved.
73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County
On 10/17/2018 1:34 PM, Edward R Cole wrote:
Bob,
A question about your statement that you run 400w in digital modes
(assuming you mean FT8, etc. and not RTTY). That seems pretty extreme.
I pretty much ignore HF usage as I am not on HF very much (primarily
an eme'er on 6m+). But back at the beginnings of psk-31 I built a HB
interface* for my FT-847 and did a bit of 14.070 operating (with a
dipole). I was recommended to not exceeding 25w (or 25% full power).
Everyone seemed to do quite well on psk-31 with low power and some ran
at QRP (<5w).
I do not get why I hear of running high power digital when 10% would
communicate easily. You may remonstrate me for running 2m-eme at
1500w on JT-65 but the path loss on 2m-eme is 254 dB+ and contacts are
made over a half-million mile path. Certainly not encountered by
terrestrial HF users.
Not picking on you personally, but you made the statement so figure
maybe would reply. Just curious.
73, Ed - KL7UW
* that I/F later was used for JT-65 on eme 15 years ago. Now use my
K3 directly connected.
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