DXpedition Antennas- Vertical vs. Yagi

Posted: February 21, 2014 in Uncategorized
Image
Vertical antennas for the low bands are pretty much the norm for DXpedition antennas, particularly for a small island surrounded by salt water.
 
I’m more concerned with the verticals only antenna choice for the higher bands by the Tromelin team. While vertical antennas in and adjacent to salt water can work amazingly well, they can also be subject to factors out of the DXpeditions control.
 
When we were motoring to Rotuma Island for the 3D2R DXpedition in 2011, I experienced just how wonderful a vertical at/in salt water could be. Our team member Krassy-K1LZ set up a multi band vertical antenna on the transom of our boat just a foot or two above the sea. He ran extra wires the length of the boat and even behind the boat in the water. It was amazing to work the entire world with huge signals as we were motoring to Rotuma.
 
It was a different story once at Rotuma. We were positioned on a breakwater surrounded by sea water. Our four squares for 40 and 80 meters were quite effective, however this same vertical antenna that had been on the transom of the boat was now about 40 feet from the sea and even further at low tide.
 
The salt water reflection effect was largely gone and the three element Yagis that we brought were much more effective. These same Yagis allowed us to direct our signals to the furthest area which was Europe. In 2012 at Conway Reef, I was able to experience even more first hand experience with Verticals and Yagis.
 
I asked our DXpedition Leader, Hrane-YT1AD why he preferred Yagis over verticals at salt water. He explained that a vertical must be at or within about thirty feet of salt water to get the reflective effect. Anything more than 30 feet and the Yagi was better as he explained. He also said that verticals at or in the water are prone to being knocked down or falling over by the tidal action and that they must be stood back up frequently. The tidal action at Conway Reef was such that the tide went out several hundred feet at low tide. We tried a vertical on the beach and it seemed effective when the sea water was very near but most of the time the Yagis were much more effective antennas.
 
We’ve seen recently how verticals in or at salt water were used very effectively as was the case at VU7AG and K9W. We have also seen how verticals on a soccer field away from the sea water were not very effective.
 
I know that the Tromelin team has severe weight restrictions, but they could easily bring a five band Spiderbeam Yagi. My Spiderbeam was very effective at ST0R, 7O6T and XZ1J. The Spiderbeam needs to be elevated. Twenty feet is okay but thirty feet is better. The Spiderbeam Yagi will work just about anywhere whereas the vertical really must be in or at salt water to be effective. Tromelin is rare enough and well funded enough that they ought to bring both kinds of antennas.
 
What do you think?
 
Advertisements
Comments
  1. ky6r says:

    Check with Stu – K6TU, who is working with the team – and contact them directly. I agree for the low bands – verticals are it – and if you don;t have the verticals right near salt water – the biggest problem is that just sand or sandy soil is even a worse reflector than the soil in my backyard- which is “average”.

  2. Jim says:

    It has nothing to do with “salt water reflection”. It is all about losses in the antenna system. If the losses are high (poor counterpoise) with the vertical, there is far less energy that can “benefit” from salt water reflection. The Christmas Island operation also proved this. The vertical had one radial and was located in a parking lot. Yes, it was near the ocean, but the losses in the counterpoise was so high, there was little energy left to take advantage of the salt water reflection.

    Jim
    WA9ZBV

  3. Chas - N1RR says:

    The issue is the distance from the feedpoint of the antenna to the “good sea water ground'”. N6BT says to be within 1/4 wave… on 10M that’s 8 feet. Since your multiband GP was 40 feet away, it would have only been enhanced by the seawater on frequencies below about 6 Mhz. /Next time, move the multi-band vertical closer to the water.

    • n6pse says:

      Chas, I agree with you fully, however it is very difficult to make a three point guy in the sand that close to the ocean. The ocean tents to tear down your antenna as fast as you put it up. That is why antennas at the ocean’s edge are not always practical or possible. We find that a tri-band Yagi works well for those reasons.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s