Topband: FT-8 question
W0MU Mike Fatchett
w0mu at w0mu.com
Sat Dec 2 16:47:16 EST 2017
Give FT8 a try. I worked my first EU the other night and then a few
last night in the contest, G, F, EA and CT9. Not much Caribbean or
Africa on. I did copy a couple of JA's the other night while the
antenna was at EU while I slept.
Remote is where many of us will be as we continue to fill up the world
and cities with noisy electronics.
On 12/2/2017 10:07 AM, Jim Thomson wrote:
> Folks on FT-8 use a 2.5 khz ssb wide RX filter. FT-8 is supposed to be good for 20 db below the noise floor.
> I assume that means 20 db below the noise floor of the 2.5 khz RX filter ?
> But a 250 hz cw filter would drop the noise floor by 10 db... vs the 2.5 khz wider filter... if CW mode used.
> So if Im reading this correctly, FT-8 mode, using a 2.5 khz filter....is really only 10 db better than a 250 hz cw filter, using cw mode ?
> If that is the case, being able to copy signals 10 db weaker than the noise floor of a 250 hz filter is still nothing to sneeze at.
> The issue I see with FT-8.. on any band is the requirement for a 2.5 khz filter.... and possibly being prone to qrm.
> Right now, my issue is extreme high noise levels on 160m... on a 100 by 130 city lot. Point a semi directional RX ant in the desired direction.... and its
> also pointed at a noise source. Seems like I am surrounded by noise on 160m. Im going to drag out by noise canceller and try some more rx experiments,
> b4 I throw in the towel. FT-8 might just be an option for folks like myself that are plagued with high levels of noise. Another possible option might be
> the use of real time remote RX. Another possible option might be using my 80m rotary dipole for 160m RX. As is, its infuriating listening to high noise
> levels on 160m. If I cant hear on 160m...except for the usual louder stations, Im not going to even try TX.
> I have tried using a pair of 500 hz filters, and also a pair of 250 hz filters, and also a 125 + 250 combo, in both my MK-V..and also 1000-D.
> The MK-V also has a 240-120-60hz dsp filter. The 1000-D has a tunable audio cw filter. The problem with the narrow xtal filters is...
> with noise levels so high, the noise... rings out the filters. The signals coming out of each filter... get stretched a bit in time duration.
> What Im left with is this mess whereby the desired signals + noise end up all mashed together. Typ noise on 160m, using a 2.4 filter
> is S9 to S9 + 10 db. Right now, Im trying to evaluate if 160m is even worth the effort required. Are the rest of you on 5 acres out in the woods ?
> Jim VE7RF
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