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Author Topic: 30W max on PSK31??  (Read 12804 times)
AA4PB
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« on: February 05, 2010, 07:46:56 AM »

I'm not advocating excessive power, but who decided that 30W on PSK31 is okay but 50W will overload everybody else's receiver? The difference between 30W and 60W is 3dB (about half an S-unit). Propogation can cause differences on the order of 20dB or more. At any particular station I could be +10/S9 with 5W while some other location could be S2 with 60W. In addition, a guy with a 20M Yagi at 60 feet can be a lot stronger than the same power applied to an attic dipole.

I think the bottom line is to follow the FCC rules and use the minimum power necessary to maintain communications. Of course you also need to keep it down to the point where it doesn't overheat the transmitter or cause the IMD to deteriorate.

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N3OX
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« Reply #1 on: February 05, 2010, 08:37:53 AM »

I'm not advocating excessive power, but who decided that 30W on PSK31 is okay but 50W will overload everybody else's receiver?

Someone who doesn't understand propagation or decibels.

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
W6OP
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« Reply #2 on: February 05, 2010, 11:40:10 AM »

I would like to have a little more info, too. Nobody ever explains what actually is the problem. I end up with about 40 watts out with no ALC when I run PSK31. Now if I were to turn on my amp and get 300 or so watts out, what does it actually do to the signal.

Pete W6OP
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AA4PB
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« Reply #3 on: February 05, 2010, 11:58:37 AM »

The basic problem with strong signals on PSK31 is with those who use SSB filters and allow the whole waterfall full of signals to enter the receiver. Say you are copying a weak signal and suddenly a 20/9 signal appears 1KHz away. The receiver AGC rises to reduct the receiver gain and your weak signal disappears. The problem can be avoided by switching in a narrow filter once you are copying your weak signal. Then the strong signal remains outside the IF passband and creates no increase in the AGC or reduction in receiver gain.

The fallacy of limiting power to 30W, in my opinion, is that propagation and antenna differences impact signal strength far more than the difference between 30W and 60W.

Using a receiver bandwidth of 3KHz to receive a signal about 30Hz wide is akin to using a receiver that pulls in the entire 20M band to copy a SSB signal and then complaining about all the QRM you are receiving.
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G0GQK
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« Reply #4 on: February 05, 2010, 03:01:10 PM »

I don't believe that anyone, anywhere has advocated using 30 watts of power when using PSK, its just a nominal figure which many seem to use.

Back in 1999 when PSK was first introduced, it was suggested by a number of software providers, and the inventor of PSK, that all that was required was 10 watts of RF to talk around the world. Radio conditions from 1999 onwards were better than they are today, so that operators increased power as the  conditions deteriorated.

I can recall when most PSK users only used 20 watts, and their transmissions produced a nice, neat, steady trace with a chain link effect, something rarely seen these days ! I've observed since we have suffered poor propagation that many operators "turn up the wick" as they would  when using SSB, with the corresponding raspy audio mostly associated with contest operating. Have you noticed the S meter when one of these stations with a wide trace and a red line down the middle starts up ?
Have you noticed how their excessive power "blacks out" the screen and causes loss of signal strength with your QSO ? You may even find that your contact disappears completely, and if its a DX contact, they certainly WILL disappear !

I've seen some stations mention they use 100 watts, one even that he was pushing 300 watts. Why ? When conditions are bad high power is of no use, its only making it difficult for others. Today I was being affected by a Russian station about 1,300 miles away, so I changed bands. There's just no need for excessive power using PSK

Mel G0GQK
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N5YPJ
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« Reply #5 on: February 05, 2010, 04:58:30 PM »

I'm with G0GQK. I don't think that anything was ever established and 30 watts just came up somewhere then got caught up in the snow ball effect. I run at 20 watts after checking my signal on a nearby friend's waterfall. It does fine for me.

Gee I can't stand some OMs on 40 I've heard "cranking up the power" to overcome the QRM. Danged lids kill my RX.

In regards to this it would be nice to get some realignment of the sub digi band (7.070 Mhz) since our PSK-31 is right in the middle of the XE phone band and for us  nearby southern residents a constant source of QRM and irritation to them and us.
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AA4PB
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« Reply #6 on: February 05, 2010, 06:35:02 PM »

Watch the strays here on e-ham. Every so often it comes up - 30W maximum on PSK31. More will disturb the other users. I was told by one fellow on PSK31 that PSK31 is designed for low dipoles and attic antennas and that I shouldn't be using my antennas up on the 60 foot tower :-)

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N5XTR
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« Reply #7 on: February 05, 2010, 07:10:15 PM »

To AA4PB:
Here is The Stray -
20 or 30 watts output on PSK31 is plenty of power. Do not be tempted to run 40w, 50w or more. It will overpower other receivers and end up ruining a QSO's for other operators.

Nowhere does it say "maximum"
Strays are for helpful advice.  Take it or leave it.  If you want to run 100w from your rig and your big beam and whatever else then do it.  My signals at 20w are clean.
But at least paste the stray before bashing it OM.

Joel - N5XTR
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AA4PB
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« Reply #8 on: February 05, 2010, 07:16:10 PM »

"Do not be tempted to run 40w, 50w or more. It will overpower other receivers and end up ruining a QSO's for other operators."

That sounds like a "maximum" to me.
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N3OX
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« Reply #9 on: February 05, 2010, 10:51:24 PM »

I've seen some stations mention they use 100 watts, one even that he was pushing 300 watts. Why ? When conditions are bad high power is of no use, its only making it difficult for others.

When conditions are bad high power is of no use?

This is such a weird attitude. 

High power is *not* the problem.

The problem you're having (aside from dirty signals) is with *loud signals*, and it's caused by lack of selectivity in the most popular receiving technique and a failure to adjust the receiving system for maximum dynamic range.

Not every loud station is running high power and not every high power station is loud.  I've heard plenty of kilowatt CW stations that were right at the noise level, and I was very, very glad that they were running that kilowatt.  Without it, I would not have completed a contact with a rare location.  Insisting that all PSK stations run low power means that some of them will be too weak to be heard in very distant parts of the world.

Furthermore, even (incorrectly) presuming that every loud station is running high power, there's a serious deficiency in our receiving technique if our system can't handle 13-15dB more signal of a kilowatt vs. 30W or 50W.  That's *just not that much difference.*    If 300W causes a problem, that's even worse.  You need to ask yourself why your system has 10db dynamic range... :-)

Now, I think it's probably the case that the 100W stations are not leaving enough headroom in their final amp because they're cranking their barefoot rig too high.  If they're putting out dirty signals by doing that, that's a problem.

But a clean 100W or 300W or 500W signal shouldn't be a problem.  I personally would just click in my 300Hz filter and center the passband on the station I want to work.

73
Dan












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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KF6QEX
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« Reply #10 on: February 06, 2010, 02:51:33 AM »

The reason behind running PSK with no more than 30 Watts (assuming you are using a 100W SSB rig) is the same reason why the same rig will only put out 25-30 watts when running AM.

Nobody "designed" PSK for "attic dipoles" Smiley C'mon now Smiley



Dimitri

might want to read the Duty Cycle section here: http://www.mkars.org.uk/modes.html#howdo
« Last Edit: February 06, 2010, 02:56:19 AM by Dimitri Patakidis » Logged
AA4PB
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« Reply #11 on: February 06, 2010, 06:33:27 AM »

I'm not talking about the guy who is overdriving his transmitter and putting out a dirty signal. I'm talking about the guy running some power, who knows what he is doing, knows he is not overheating the Tx because of duty cycle limitations, and has checked his output to make sure it is clean. I have checked the output of my 756PRO using a second receiver and with IMD meter and the IMD doesn't begin to deteriorate at all until about 80W output. The Tx is rated 100% duty cycle on RTTY so that is not an issue. I normally run much lower but it is there if needed.

My comments arereally related to what appears to be a general attitude among PSK31 ops that running more than  20-30W is poor operating practice. My opinion is that the receiving stations on the band need to accept some reponsibility for QRM when the "standard practice" is to run with SSB width filters and the receiver IF wide open. The convience of the waterfall display has sent many down the wrong road, in my opinion. We need to learn to use filters to isolate the station we want to work on PSK31 just like we do on any other mode.

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KF6QEX
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« Reply #12 on: February 06, 2010, 07:16:54 AM »

AA4PB:
>My comments arereally related to what appears to be a general attitude among PSK31 ops that >running more than  20-30W is poor operating practice.

Do you mean other ops are considering running more than 30Watts poor practice and they complain "Hey , your power is screwing up my waterfall" ?



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AA4PB
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« Reply #13 on: February 06, 2010, 07:38:22 AM »

KF6QEX: Exactly. Every time you key up, my waterfall dims down. Sort of equates to the neighbor who says every time you get on the ham radio my TV messes up so you need to stay off the radio.

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W6OP
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« Reply #14 on: February 06, 2010, 08:37:49 AM »

Ok, to kind of summarize what everyone is saying. For a normal QSO run low power as a courtesy to everyone else. We should be doing that on every mode anyway.

If I am trying to get a DX station or Dxpedition it is ok to use the amp. Since my amp would probably go up in smoke if I tried to pump PSK31 through it at full drive, I would be using even less power from the exciter. Maybe only 10 to 20 watts and therefore should still have a clean signal.

Is that correct?

Pete W6OP
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