PA8W Amateur Radio

Wil, PA8W,  E-mail: PA8W@upcmail.nl           
Back

The DL/PA8W portable antenna

Desired: A good dualband holiday antenna.          Answer: a simple end fed wire.

I love to take a transceiver down to our weekend home in the German Eifel mountains.
As it is located in a small, deep valley of the Rur river, the nearby hills run up an extra 200 meters in most directions. 
Therefore, only the 80m and 40m band are the most useful as they work with high angle signals most of the time.
 
So what I wanted was a simple wire antenne that could easily be put up -and taken down- to make me QRV on 40 and 80.
This is what my experiments led to:



The above picture shows our weekend appartment, with the 17m end fed wire (marked red for visibility) 
running up and away into a tree.
I was standing virtually at the bottom of the small steep valley in front of our appartment building, when I took this picture.
Therefore, it looks like the wire is running up immediately from its fixing point, but this is not the case; the first half of the wire length is almost horizontal, and the second half starts to gently slope up into the tree of which you just see a few branches at the top of the picture.
The wire is kept in place there by a small weight which is also necessary to swing the wire up into the tree.
At the appartments raingutter, a metal hook with a M8 bolt as one side is hooked onto it.
The hook has an end insulater that holds the antenna wire, and of course the feeder.
The M8 threaded bolt ensures good electrical contact with the metal of the gutter, as it scrapes into the surface of the metal.
That is desired, since the cold side of the feeder is connected to it, so the raingutter acts as a counterpoise.
From there 6 meters of a sturdy type of 300ohm ribbon feeder runs down and enters the building through the PVC window frame.

Just before reaching the rig, the 300ohm feeder is connected to 1m RG58 coax running through a few ferrite cores acting as a mantle current choke.
From there the coax runs into the IC746pro and the internal ATU turns it into a decent 50ohm match.

With this simple antenne I can put up a good signal within western europe on 40m, with 100watt only.
Regularly, I am often comparable with other hams with fullsize antennas, or even with 3x more power.
On 80m, I am generally comparable with most Dutch stations, lots of them running more power or bigger antennas as well.

So how can this make-shift antenna be so effective?
Here's two possible answers:

1, I kept losses to a minimum.
2, I optimized my SSB audio.

The second point is discussed on several pages on this website.

The first point will be explained next:

 

Minimizing losses:

I did not try to make the antenna resonant on 40m; an end fed 20m wire would need a high impedance feeding arrangement, which is not practical on the 80m band, where the wire would have a low impedance.
So I sticked to the 17m that proved to be a good length to swing over a nearby tree.
This 17 meter is a bit shorter than half wave on the 40m band, so the antenna will not pose an extremely high impedance.

The feeding system uses very low loss 300 ohm feeder, and no lossy balun/unun/transformer.
Instead, I use a mantle current choke on the last part of the feedline, which is made of RG58 coax.
This small choke heats up slightly after one minute of 100w carrier, so maybe just 5 to 10 watts is converted into heat. 
That's less than 1dB loss.
Losses in the 0,75mm2 antenna wire may be a little larger, but still I am confident that overall loss is less than 3dB, so quite acceptable for a holiday antenna!

The following modelling output will give a good impression of current distribution and radiation pattern on a few bands.
The graphs on the right show the antenna wire, running from its feedpoint (at the junction with the other "wires") towards the left upper corner of the picture, and bending down vertically at the end.
The other "wires" are the counterpoise; the metal raingutter and its connections:

 



A real cloud burner on 80m, very suitable for short skip traffic up to 500km.
Please note the serious current running in the left part of the raingutter...



Also a cloud burner on 40m, very suitable for short skip traffic up to 1000km.
Please note the serious current running in the right part of the raingutter...

It would not help a lot if I would give the antenna extra height; if I would put it too high on 40m then it would still be a no DX antenna because of the surrounding steep hills...

So what is does is: it uses the possibilities of that particular spot very well with a minimum of effort and visibility.
And that's what it's all about during a relaxing, lazy weekend at one of Germany's most beautifull spots.

73, Wil.


Back