Guess I got a few replies to my comments. I will try to respond to
all in this one:
James-w6jhb: Bob did reply back and was referring to using digital
on 160m, which is harder to work than upper bands like 20m. More
power helps. I have done some operating on 600m (before it became a
ham band) and FCC limits 630m operations to 5w EIRP which is a real
test of ability and equipment. Yet CW and digital modes are making
some surprising DX contacts on a band that is not known for
ionospheric prop (D-layer only).
Wes-N7WS: Uh, I never mentioned running 10mw. I did suggest 10% (of
full power) might be quite adequate on digital. So that would be
150w for a KPA1500 or 50w for a KPA500. Yes, I have heard that some
are making HF digital contacts at 10mw (or such) but that is a
personal challenge (as I see it). Again 160m is a special case with
limited prop as compared to 20-10m. I would probably use full power
if I were on 160m (currently that is 100w from my KXPA100).
Many still use CW on eme but that is on 432 and up these
days. 6m-eme is 100% digital and 2m-eme is 99%. I made some of my
early 2m contacts using CW.
Fred-K6DWG: Sorry but you are not correct on how JT65, FT8, and
other WSJT modes work. Yes, you run the receiver RF bandwidth at
nominal 2.5-KHz (SSB) width but that is just to make operating with
various Doppler offsets easier (as you can see all the signals within
the wider bw. But the detection bw of JT65 is 4.7 Hz and that is a
large part of why it is approx 10-dB more sensitive than CW. S+N/N
of 4.7 Hz over 50-Hz (apparent detection bw of the human ear/brain)
does reduce the noise power vs signal. JT-65 and other of these
digital modes are FSK with the sw detecting single tones. The shift
freq of JT-65 is over a wider range but that does not affect
detection. I believe psk-31 is much wider detection bw (often
referred to as RBW) so it is not near as good for weak signal
operation. I understand that more power may be needed to overcome HF
noise floors that are much higher than VHF+ where eme is done. Still
not convinced that one needs QRO for terrestrial path loss. QRM
maybe requires it. I have no local eme QRM. Pile ups are on the
receiving end of multiple stations calling me (KL7 is rare on eme).
Bob-K4TAX: Yeah I get it. It depends on frequency band as far as
how well signals reach. As I already stated, I never mentioned
10mw (Wes thru that into the discussion) but I do think one does not
need to run the same power as a CW or SSB contact if using a NB
digital mode. Of course that varies with band conditions and
distance worked. FT8 (in particular) is getting thru when poor band
conditions prevent CW/SSB from happening. Using the power necessary
is a given - just don't see that running (near) max power is
necessary (all the time which seems to be the HF mentality -
regardless of mode or conditions).
BTW my 495 KHz 5w EIRP CW signal has been detected about 4,000 miles,
so its quite possible. FCC limits 630m ham operation to 5w EIRP
(which is about what I get running 100w output from my PA and due to
4% antenna efficiency).
Thanks for bearing with this multi-part reply; figured it would use
less list bandwidth with this approach. Probably not worth further
on-list commentary; reply direct to me if any of you want to continue,
73, Ed - KL7UW
http://www.kl7uw.com
Dubus-NA Business mail:
[email protected]
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected]
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected]
