Viaducts On The Air?

I had some some good results with the MTR3B and end fed half wave antenna at Bilton Viaduct, but was asked if I’d checked SWR. So I went back tonight, this time with the 30m end fed antenna, the Elecraft KX3 and a Mini-VNA to measure the antenna. The antenna is 15 meters long, plus a little more for the counterpoise and feeder at one end and guyline at the other.

Equipment – Mini-VNA, Bamakey TP-II, KX3 and antenna for 30m (10MHz) band.

I located myself along the bridge having seen where the river passed between the supports. Drains spaced along the bridge offered some confidence I’d found a span, as the drains would tend to drain into the open space. The end of the guy line was tied to a stick and thrown over. It was allowed to swing, and I observed that it spent some time against the bridge and some time swinging out my side, implying it was swinging into space beneath me. I found out later that with the guyline the whole thing was quite long, the stick only just above the gravel bank below. It’s a good job nobody was down there!

SWR was measure with the Mini-VNA. The resonance is quite sharp with the tuned matching circuit. SWR slightly high but not too problematic.

The KX3’s ATU was able to achieve reasonable match given the antenna, though bandwidth was reduced when the ATU was used. Quite a few signals came in with slight fading and I listened to a station running and eventually dealing with a pile-up.

I tried answering a station calling on a higher frequency, and after a couple of attempts to respond to the original call had OH3GZ, Jack, call me with a really strong signal. We had a nice conversation. At first at my end someone came over and was asking me to explain what I was doing. This made concentrating on the Morse slightly harder! Once he’d gone I was able to explain to Jack what had happened and we had a couple more overs before saying goodbye.

Contact with Jack in Finland. He sent his location which I tried to note down.

Another contact later, the weather starting to get cold, and the local teenagers starting to congregate, it was time to go home. I left the antenna in place to photograph it, though it is very thin wire and hardly shows in the photos. It was hard enough at first to find it by eye. Very much a stealth antenna!

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.