Burned Hexbeam SP7IDX (sk)

16/09/2021

 

A HAM operator nearby called me to say that his hexbeam had a high SWR on all bands.
A few days later I went to measure and saw the 20m and 6m cables burned into the middle tube of hexbeam.

We first cleaned those connections and measured again and the problem remained the same.

We then removed the middle tube where all the wires come to and I took it to my house.

After I took everything apart I saw what was going on inside.

Now I didn't have to wait to take it apart the smell in the alum tube was very hard.

The photo above shows the result of 1500w on a hexbeam, according to the site of SP7IDX it should be able to handle this.

The rubber was gone, burned I had to saw off the bolt myself to get it loose.

As you can see this doesn't seem right to me.

Whether you really have to use 1.5Kw on a hexbeam is not for me to judge.

 

 

 

 

 

 

The 6m connection you can see that the rubbers are just melting.

SP7IDX uses a rubber to slide over the bolts and then slides in another when everything is back together to keep the core isolated from ground.

It seems to me very difficult at the moment to get replacement parts from SP7IDX because he unfortunately passed away unexpectedly. 

More info can be found on his site.

 

 

 

After some thought and after consultation with the owner of the hexbeam, we came up with the idea of using what is shown in the photo as a replacement for the taps.
Correct name is connecting screw I used those things to fasten cabinets together and it's in nylon.

 

 

 

 

 

I then replaced the rubbers with a piece of a hose and cut them to the appropriate length.

That rubber is also just the diameter I need where the nylon part can slide in.

 

 

As you can see everything has been cleaned up again.
Don't have a picture of it but even the aluminum plate has undergone some kind of a welding look.

That aluminum plate is 2 cm wide and I noticed that the distance on the inside of the tube (ground) and the core is very minimal.
That plate is also not extra insulated, so that transshipment (from core to ground) by (High) power is certainly possible.

 

 

 

To put a little more insulation on the plate, it was wrapped a few times with tape

 

 

 

 

 

 

 

Because my white nylon tapers are  less thick, I have added an extra rubber.

 

After everything was put back together I returned it to the owner.
I said that such a hex is not really made to use with so much power and certainly not for a long period of time.
It is of course also possible that those rubber have started to endure, which may have accelerated the problem.
I don't know the age of that hex beam.

In the meantime, the hex is already back in the tower and the problem was solved.
total repair cost was 0.65 euros.