Reasonable power output for PSK-31

Discussion in 'Working Different Modes' started by KB1JCY, Jul 23, 2010.

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  1. KB1JCY

    KB1JCY Ham Member QRZ Page

    A station I was working 40m PSK-31 commented that I was splattering. At the time, I had my radio set to 90 W out. What's a reasonable power setting for PSK-31 communications?
  2. KR2D

    KR2D Ham Member QRZ Page

    25 or 30 watts is normally sufficient. PSK is a good weak signal mode, and there is generally no reason to run more than that.

    "Splattering", which is another name for Intermodulation Distortion (IMD) is not caused by power level alone. It is caused by running your radio system in a range where it is non-linear. With PSK, it is very important that your system is linear, or your signal will be distorted (splatter). Pushing 90 watts out of a 100 watt rig is usually getting into the non-linear range - OK for SSB voice (or CW or FM), not so good for PSK.

    Here's a good way to adjust your setup:
    - Set the RF power out on radio to maximum.
    - Set your sound card output level to minimum.
    - Set your PSK software to transmit.
    - Increase your soundcard output until your watt meter reaches the desired level.
    - There must be absolutely no indication of ALC! If your ALC meter (or light) starts to indicate any level of ALC at all, back off on the soundcard output level.

    I have seen perfectly clean PSK signals from folks running 100 and even 400 watts out. Those folks know how to adjust their systems for a clean signal. 400 watts is extreme, but the two ops (one in MidWest USA and one in England) were the only QSO on 20m at the time - the band was completely dead!
  3. KF5FEI

    KF5FEI Ham Member QRZ Page


    I was goofing around on 20m this evening and made a contact in NV, VA and TN on about 2 1/2 watts into a 40m OFCD. Previously worked Canada and Cuba with same setup.

    FYI -- I used the same suggestions mentioned previously to set things up, with a few slight alterations per the FT-817 gurus
  4. G0JKZ

    G0JKZ Ham Member QRZ Page

    I find that somewhere round the 1-200w region is perfect in very flat conditions but normally 50w is enough.

    Ron KR2D has it spot on. When I run 100w I actually have the radio only running 20w and let the linear amp take the strain. If you keep the ouput of your radio linear than you will not splatter everywhere. Also, with keeping the radio and linear powers low, nothing is being stressed and your equipment will last a whole lot longer.

    Most radios are only rated at 50w for continuous modes anyway but a lot of people don't read that in the manuals....
  5. G0GQK

    G0GQK Ham Member QRZ Page

    There is no need for using high power with PSK. When the mode first appeared 10 years ago it was recommended that 10-15 watts was quite sufficient, and in many instances, it is. Consider these facts

    The PSK idle signal is TWICE the average power, so that if your power meter is indicating 30 watts you will be transmitting 60 watts PEP

    It is recommended that the transmitted power is about 25-30% of the tranceivers rated PEP power. With a 100 watt tranceiver adjust for 25/30 watts of average power on your power meter which will produce an output of 50/60 watts

    Anyone using 200 watts will be transmitting a non linear signal, it won't get them any further and will most certainly upset the stations transmitting nearby and will totally wipe out their contacts when the waterfall turns "black" each time they transmit.

  6. G0JKZ

    G0JKZ Ham Member QRZ Page

    this is the only bit that I don't agree with.

    why would it be non linear?

    if the radio is only running 25% of its rated power and the linear amplifier is only operating at 25% of its rated output, well within the biased range then how can it be non linear? if the transmission is linear and not in any way splattering or clipping then how will the signal be any wider than one running 2w or 30w? How would it then be wiping out the whole waterfall on another receiver?

    granted, if it was within a couple of streets of another station it could, but then it would do the same on any mode.... I know this because another station is only 2 streets from myself and if we are on the same band then we both know it!
  7. KR2D

    KR2D Ham Member QRZ Page

    It is perfectly possible to transmit a linear signal at 200 watts. The equipment must be capable, and it must be adjusted correctly.

    Making the "waterfall black" and "wiping out contacts" is a problem that lies entirely within the receiver of the affected station. Using proper filters for the mode and conditions will solve the problem entirely.
  8. WS9K

    WS9K Ham Member QRZ Page

    I usually run 20 watts.
  9. AE5JU

    AE5JU Ham Member QRZ Page

    From my QTH on the Louisiana gulf coast I've worked all over Central and South America, the Carribean, Canada, and into Europe on just 20-25 watts. I've gotten a QSL from a Polish SWL'er.

    A few days ago I was just getting my Ten-Tec Jupiter on the air with PSK31 for the first time, using a Donner Digital Interface. Previously I had done PSK31 with an Icom 718. As I adjusted my power level for 20 watts while transmitting a CQ, a guy in Canada immediately came back to me.

    You just don't need any more power than that, and if you do use much more you just screw up the band for everyone else.
  10. M0WAN

    M0WAN Ham Member QRZ Page

    A reasonable power level for BPSK31? 10 watts. You will be seen if at all possible, and if not, 100 watts is unlikely to change that. Please don't encourage the numbers race!
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