Friday, April 26, 2019

Antenna ideas for the 60m (5 MHz) band

Amateurs in many countries now have access to the 60 m or 5 MHz band. Often it's just a few spot frequencies. And there might be output power limits. Unlike on other bands these may be expressed as EIRP (effective isotropic radiated power) so you can't get around that limit by using a high gain antenna.

Before thinking about what antenna to use on 60m it's worth thinking about the band's characteristics. Right now, in the low part of the solar cycle, 7 MHz is somewhat unpredictable during the day for intermediate distances up to a few hundred kilometres. But 5 MHz may still be okay. And it may have less absorption than 3.5 MHz. An antenna with a fairly high angle of radiation, like a dipole around 10 metres above ground, would be excellent for this application.

Then there are DX possibilities. Given the low power limits that often apply this may be a challenge. A full sized quarter wavelength is 15 metres which you may just be able to hang from a tower if you have one. Or if your support is smaller then an inverted L (with as much vertical as possible for DX) would be a good pick.

Another possibility, to save the clutter of wires, is to see if an existing antenna can be made to work on 60m. Your chances are best with a tuned feeder dipole. The old 102 foot (31 metre) long G5RV is pretty much exactly a half wavelength dipole on 60 metres. So you can expect excellent performance from one on the band. If you lack the room them a tuned feeder dipole that's 20 metres end-to-end (ie a half wavelength on 40 metres or 7 MHz) will also still be efficient down on 5 MHz.

Since 5 MHz is so narrow, bandwidth shouldn't be much of an issue. So if you're really pressed for space you could use a short dipole with loading coils. You may be able to get it so the antenna is full sized on (say) 7 or 10 MHz with the loading coils allowing 5 MHz as well. A trapped dipole is another possibility.

Want something quick for portable use? An L-match and 30 metres of wire should be fine as an end-fed half wavelength. That length of wire is getting a bit long for a single 8 or 9 metre pole (it will sag) so find somewhere where there's a tree to hold it up at the other end. Or take a second pole.

What about magnetic loops? Many homebrew designs go down to 7 MHz. You could add extra capacitance to get 5 MHz. There will be a substantial drop in efficiency but you should still get contacts. And, bear in mind that where the 5 MHz power limit is expressed in EIRP terms you can increase power going into the loop to compensate for its losses. Just be mindful of not sparking across the loop's capacitor if you designed the loop for QRP operating.

So there are many possibilities for 60 metre antennas. M0MCX has some more ideas here.

PS: Want to learn about portable antennas? You'll find many ideas and projects in the top-selling Hand-carried QRP antennas.

1 comment:

  1. Some more tips for antennas and working on 60m can be found here:

    I can tell you from experience that a 15m wire from a steel tower and radials below it does not work well, not even on DX. Using the tower in unipole configuration (with a kind of big gammamatch) does work well. So far I have good experiences with just my multiband inverted-V. And in the past my horizontal loop.

    A big magnetic loop might also be interesting especially if living on a small lot in a city.

    73, Bas PE4BAS


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