CQ DE VK7BEN

Just another Amateur Radio Operator

Stuffing the Smoke Back In!

Loads

This post will end the saga where I let the magic smoke out of a somewhat expensive commercial antenna.

Today a package arrived in the mail from china which greatly excited me. In it was 100x 10k ohm 3 Watt carbon film resistors from eBay, costing around $8 including delivery. with these, some Veroboard and a little bit of patience I was rebuilding the resistive loads in the antenna. one of the old loads is on the left and the new home brew one is on the right. The damaged resistors are marked as 10k ohm, but measuring them with a multimeter gave a reading of 1.1k ohm.

One of the things that concerned me a little bit about was that the replacement resistors were substantially bigger than the components I was replacing. I’d done a bit of a guesstimate when ordering that I would need 3 watt resistors and the 2 watt ones looks a different shape. The larger size meant a snugger fit in the housing and I added some copper winding wire to make it easier to connect to the antenna.

Load in Housing

As you can see in the above image, the look just fist in nicely. with connection to the inductor underneath intact I just soldered my copper wire onto a heavily soldered swage. The swages butt against the housing wall. strain relief is done by two swaged loops in the wire (seen going through the top of the housing, so the stainless will not get ripped out of the load.

Good old electrical tape was used to hold it together temporarily while the antenna got tested. I was quite nervous hooking up the antenna analyser and switching it on, waiting to see the SWR after starting up, knowing I had failed if it was above 2:1 on the 40m band….

1.14! 1.14:1 SWR on 40m. 1.4:1 on 20m. Success! I had put the smoke back in for $8 and some Veroboard I had lying around! I will say that this cost was a lot less than what buying replacement loads commercially cost.

Took it back to the workshop and hot-glued the housing together and it’s ready for use again!

However I still have my Carolina Windom and it works a treat, so the loaded dipole now will be my primary antenna for mobile HF operations, which means I won’t need to use the ATU as I had been.

It also means I will never make the mistake of transmitting 100 watts PSK31 into an antenna only rated for 50 watts continuous duty again, but if I do, I still have 82 spare resistors to fix it 🙂

Here ends my dipole saga.

 

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2 Comments

  1. Eric

    You mentioned measuring the old resistors as 1.1k but was that in circuit or with them removed?

    If they were in circuit, you have 9 x 10k resistors in parallel and 1.1k would be the correct resistance of that combination.

    • ben

      Thanks for the question Eric! Yea, it was pure coincidence that was the value on the tested resistor, which I clipped off the board. Other resistors did not fair so well and their readings were all over the place.

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