Old Heatsink Lets Ham Push Duty Cycle for Digital Modes

Listen to the amateur radio bands long enough, and you’ll likely come to the conclusion that hams never stop talking. Of course it only seems that way, and the duty cycle for a transmitter operating in one of the voice modes is likely to be pretty low. But digital modes can up the duty cycle and really stress the finals on a rig, so this field-expedient heat sink for a ham transceiver is a handy trick to keep in mind.

This hacklet comes by way of [Kevin Loughin (KB9RLW)], who is trying to use his “shack-in-a-box” Yaesu FT-817 for digital modes like PSK31. Digital modes essentially turn the transceiver into a low-baud modem and thus messages can take a long time to send. This poses a problem for the 5-watt FT-817, which was designed for portable operations and doesn’t have the cooling fans and heavy heatsinks that a big base station rig does. [Kevin] found that an old 486 CPU heatsink clamped to a lug on the rear panel added enough thermal mass to keep the finals much cooler, even with a four-minute dead key into a dummy load at the radio’s full 5-watt output.

You may scoff at the simplicity of this solution, and we’ll concede that it’s far from an epic hack. But sometimes it’s the simple fixes that it pays to keep in mind. However, if your project needs a little less seat-of-the-pants and a little more engineering, be sure to check out [Bil Herd]’s primer on thermal management.

[via r/amateurradio]

18 thoughts on “Old Heatsink Lets Ham Push Duty Cycle for Digital Modes

  1. I wonder how well this would work if you do the software 10w FT-817 hack?(needs ext pwr, the batt-pack can’t hack the higher draw)
    As a kid in the 80s and 90s I had always thought that it was the reflected wave doing electrical damage to the finals, turns out though it was just heat, so heatsinking is the magic to keep the smoke in.

    1. It’s kinda both. If the reflected wave is perfectly 1:1 SWR, there’s very little extra power needed through the finals, so generally less heat produced. If the SWR is too high, your finals are going to be working overtime to kinda keep that standing wave “pumped”, so your useful output is less, or your finals are getting a lot hotter, or usually both.

    1. Adding a heatsink to a component in a manufactured device as part of a project to operate it outside its spec doing something it was never designed to do is not a hack per your definition? Fuck off.

    2. And yet to the numerous people reading this who were unaware that this particular technique could be helpful to them, this is brand new information.
      Don’t be such a know-it-all. Do you go into a 1st grade classroom and berate the teacher? “Reading. Who would have thought of that! Sigh.”
      Grow up.

      1. Are we also going to add “and he made an electrical connection to make the electric motor work”? Some people have never done it either. There is a fine line between a hack and a simple tutorial. This one is a tutorial. I agree with Chambo. If HAD lists these things as hacks then there is no point in HAD.

    1. I’ve done experiments comparing thermal contact resistance with and w/o thermal paste. If the joined surfaces are clean, smooth and in firm physical contact there is little benefit in adding thermal paste, and too much paste can make things worse

  2. I used to play with RTTY and AMTOR when I was in college. I had a 400W tube amp, but that rating was for CW/SSB and I didn’t know it was supposed to be derated for full duty modes. I had those tubes glowing CHERRY red and finally they failed one day rather spectacularly with blue arcing and a nasty sizzling noise. I had to replace them all, and it was a bit of a chore, since tubes were already passeé and this was before the WWW.

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