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Technical Topics => Equipment => Topic started by: ThaDood on January 26, 2023, 1826 UTC

Title: Fiberglass whip – short vertical antennas for MW broadcasting by Valcom?
Post by: ThaDood on January 26, 2023, 1826 UTC

https://labsdl.wordpress.com/2018/09/06/interesting-am-broadcast-antennas-part-1-wiry-and-wzbr/

I think that these were covered before, but they are intriguing. Hmmmmmmmmm... I wonder how were they'd work for the 160M band?

Title: Re: Fiberglass whip – short vertical antennas for MW broadcasting by Valcom?
Post by: ~SIGINT~ on January 27, 2023, 0032 UTC

Thanks for sharing the article. Very interesting. I have in the past and continue to deal on occasions with VALCOM and have been at their manufacturing and R&O facilities on many occasions.

The original design of these antennae were for Naval ship to shore operations. There are similar ship board versions of these (minus the top hat). I believe this particular one's original intended design may have been for use with NDB stations.

VALCOM is a prime defence contractor and R&O facility which has over the years expanded / adapted their product line to cover some of the commercial market applications.

Title: Re: Fiberglass whip – short vertical antennas for MW broadcasting by Valcom?
Post by: RobRich on January 28, 2023, 0656 UTC

I suspect the loading coil has an extemely high Q tuned for only a few KHz of workable bandwidth at a station's set operarating frequency. Probably just enough bandwidth to keep the SWR curve within the transmitter's tolerance.

The top loading is interesting from a space saving standpoint, but assuming apreciable horizontal space is available, dramtically increasing capactive top loading should substantially improve performance. Once upon a time, there were AM BCB stations using such T antennas. Building a couple of shorter support towers could be more affordable or practical than the skyscraping towers we normally associate with mediumwave broadcasters.

Title: Re: Fiberglass whip – short vertical antennas for MW broadcasting by Valcom?
Post by: Ray Lalleu on February 06, 2023, 1126 UTC

Capacitive top loading can even be used on antenna arrays for directional patterns.
I remember the LW antennas of Europe 1 in Saarland. The hats were made with 3 slanting wires for each mast, those wires barely visible in the sectors between the strong halyards. The towers were all in the 300 meters high range, still short for the 183 kHz frequency.