eHam

eHam Forums => Digital => Topic started by: K1YTG on January 17, 2017, 05:16:40 PM



Title: Several psk31 stations are 10 times stronger than the rest- High Power?
Post by: K1YTG on January 17, 2017, 05:16:40 PM
on 20 meters I consistently note that a few stations are dominant as far as strength each day.
I find it hard to believe that they are achieving that superior strength with a better antenna system.
But some state that they are running 50 watts and  wire antennas.
So I ask those who have been at this longer if it is common for some stations to run linear amps in psk31.
And if so why do they claim otherwise?

Perhaps I am wrong to suspect some ops of giving false info on their power level.
But it sure looks like high power to me.

Norm


Title: RE: Several psk31 stations are 10 times stronger than the rest- High Power?
Post by: K6BRN on January 17, 2017, 07:57:41 PM
Hi Norm:

I'm sure some operators run significant power on low power digital modes, which can be rude.  But distinguishing between high transmit power, high effective radiated power (really good antenna) and propagation conditions can be very difficult.

Recently, I've been running JT-65 on a wire dipole and have had reciprocal signal reports of -1 (very, very strong), when running 25 watts, at distances of 1-2,000+ miles, limited to very distinct geographic areas - not always the same.  A friend of mine is having similar experiences with similar power levels and antenna.  We've come to call this "spotlight propagation", and when it happens, it can be simply receiving a very good signal or ones that "blow your doors in".  It generally does not last long - from a few minutes to 1/2 hour.  In one such exchange, the operator on the other end (mid-West) and I (Southern California) began exchanging nearly real-time messages via email because the conditions were so pronounced.  Signals from his area were overloading my station, and vice versa - we had to drop in some attenuation to communicate.  It was like we were a block apart and were running 500+ watts to yagis.  But we were not.

It's always OK to politely let someone know they are generating interference, but knowing whether that overly strong signal is due to a "Killerwatt" amp or other factors is hard.

Just my 2 cents.

Brian - K6BRN


Title: RE: Several psk31 stations are 10 times stronger than the rest- High Power?
Post by: N0IU on January 18, 2017, 02:21:39 AM
I'm sure some operators run significant power on low power digital modes, which can be rude.

It is a common misconception that power alone causes a "dirty" signal and this simply is not the case. What causes a signal that splatters all over the waterfall is generally caused by over driving the audio. You can run a very small amount of power and still splatter and by the same token it is possible to run considerably more than 30-40 watts and have a perfectly clean signal.

Two things some people forget are:
1) There should essentially be no ALC movement.(This can vary from rig to rig and manufacturer to manufacturer)
2) Compression needs to be turned OFF.

There is absolutely nothing wrong with running a bit of power (except for possibly violating 47 CFR ยง97.313(a)) as long as your signal is clean.


Title: RE: Several psk31 stations are 10 times stronger than the rest- High Power?
Post by: ND6M on January 18, 2017, 05:43:49 AM
FWIW, just because certain modes are "weak signal" modes, does not necessarily mean they are low power modes.

Try doing some "weak signal" EME with 50 watts.


Title: RE: Several psk31 stations are 10 times stronger than the rest- High Power?
Post by: K6BRN on January 18, 2017, 11:47:19 AM
Scott (N0IU):

Overdriving audio on transmit for JT-65/JT-9, etc can indeed cause TX splatter.  However, on the Yaesu FTDX-3000 and FT-991 (and I'm sure others) with built-in sound cards, significant ALC indication is not just fine but necessary for best performance.  With these radios, TX levels can be set to run in the middle of the ALC "blue" (safe) zone and power is adjusted using the built-in rig power control.  No splatter, per my spectrum analyzer measurements.  So, you're right - the correct setting does vary by radio type - dramatically. 

The other cause of apparent "splatter" is RX levels set too high, causing saturation in the sound card ADC or overflow in arithmetic processing.  These effects often result in aliasing, so that a strong signal appears twice in the RX window of WSJT-X - first as a strong signal and then as a much weaker image signal elsewhere in the band.


James (ND6M):

I don't think Norm is talking about moonbounce.  And you're right about weak signal modes - the convention is to use just the power needed to close the link, be it 5W or 100W, contrary to dedicated QRP'er wishes.  Or more, for moonbounce.  But during periods of heavy activity on the very narrow and crowded digital segments, it's not very good practice to crank power up just to stomp other signals.  But some do.  And its usually hard to tell whether this is being done deliberately, or is due to propagation conditions.

Brian- K6BRN


Title: RE: Several psk31 stations are 10 times stronger than the rest- High Power?
Post by: K0UA on January 19, 2017, 09:24:54 PM
Well, everyone has an opinion, and some very good points have been brought up about power and clean signals.  Now for mine.  IF I did not see some very strong signals I would think it unusual, as propagation is often very very good to somewhere.

Sure, maybe some guys are running more than the usual 25 to 50 watts, but it is also very likely in my opinion you are just seeing the effects of the variances in propagation.  You often see signals peak to very strong levels just before the band "falls out" to that location.  How many times have you talked to some guy with 100 watts and a dipole that is 30db over S9 one minute and barely copyable the next?   Plenty of times for me.  With any given signal, I don't think you can really know. Many times when I have a QSO with someone with loud signals, I decrease my power from my usual 100 down to 1 watt and the guy on the other end doesn't even notice the 20db drop.  So I go from 20 over to S9... so what?  the guy will think that is normal QSB.

My point is, propagation has a lot more to do with signal strength than output power.

73 de K0UA