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Digital Modes: Antenna Gain vs RF Output

Discussion in 'Working Different Modes' started by KZ4TN, Apr 29, 2020.

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  1. KZ4TN

    KZ4TN XML Subscriber QRZ Page

    I would like to know the following as it pertains to digital modes such as FT8. It is recommended that you keep your power output low, for example 5 watts. If all of the other variables relating to the setup of your digital station are optimum, such as sound card input and output volume, is there an advantage to using a gain antenna to increase your signal strength? In other words, are you better off increasing your signal strength by increased antenna gain or can you accomplish the same increase in signal strength by increasing your power output? Is there a greater danger of creating QRM by increasing your power output? The reason I am asking is that I want to operate portable and choice of antenna is important. Thanks so much for your comments.
     
  2. K7TRF

    K7TRF Premium Subscriber QRZ Page

    In any communication mode it's better to improve antenna system efficiency including moving antennas up higher or using gain antennas rather than just increasing transmit power. Improving your antenna system improves not only how other stations receive your signal but also improves how well you receive those other stations. Increasing transmit power can help your signal but won't do a thing for the signals you can't quite decode.

    There's nothing inherently wrong with running a bit more power on FT8, it's a weak signal mode but that doesn't mean it has to be a QRP mode. There's just no sense in running more transmit power if you reach the point where other stations can receive and decode your signal but you can't receive and decode theirs. That's the digital modes version of being an alligator.... all mouth and no ears :)

    There's never harm in improving your antenna system, but if you consistently get worse S/N reports relative to what you're sending to other stations then bumping up your transmit power might be a good idea. If you're relatively balanced with the S/N reports you send out vs what you receive or if you're getting back much better S/N reports than you send out then there's no sense in increasing your transmit power.
     
    WD4ELG, KP4SX and AA4PB like this.
  3. KC2RGW

    KC2RGW Premium Subscriber QRZ Page

    Duty cycle and heat is the main reason to run lower power. Depends on the rig’s cooling system.
     
  4. WA9UAA

    WA9UAA Ham Member QRZ Page

    Antenna gain can only be had by sacrificing signal in one direction for another, so the operator really needs to know what direction the antenna should cover.
    73,
    Rob
     
    AG6QR likes this.
  5. AG6QR

    AG6QR Premium Subscriber QRZ Page

    That, and keeping the signal clean. Many rigs will produce distortion when driven to their maximum power, and this can cause intermod distortion, splatter, and other artifacts that cause problems beyond the frequency you intended to transmit on.

    These issues will vary from rig to rig, and it's not just the radio that enters into it. Clipping or nonlinearity anywhere in the chain from the soundcard through the final RF power amplifier can cause problems.

    But a high-gain antenna won't add such issues. Nor will low-loss coax.
     
    KC2RGW and WA9UAA like this.
  6. W4HWD

    W4HWD Platinum Subscriber Platinum Subscriber QRZ Page

    There’s always a benefit to increasing your antenna gain - for both receive and transmit - and who told you FT8 had a power limit of 5w? That’s incorrect.
     
  7. W4HWD

    W4HWD Platinum Subscriber Platinum Subscriber QRZ Page

    That’s what rotators are for;)
     
  8. KZ4TN

    KZ4TN XML Subscriber QRZ Page

    KZ4Tn here. I chose 5 watts as a "what if". I am currently running 35-50 watts on FT8. I am in the queue for one of the Dave Benson designed Phaser digital XCVR kits that outputs ~4 watts. As I like to operate portable my intent is to use low power due to the savings in current drain on my power source. As we eventually start to climb out of the current sun spot minimum I am looking forward to good QRP DX on the digital modes.

    Thanks to all who have contributed comments to my original posting.

    73 de KZ4TN
     

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