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Author Topic: Modify top-band inverted L antenna for 2200 metres?  (Read 362 times)

XW0LP

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Modify top-band inverted L antenna for 2200 metres?
« on: July 07, 2021, 04:46:05 AM »

Easy to do?  From what I see, one needs to add a large coil at the base of the inverted L to achieve resonance (with very low radiation efficiency) on the desired frequency.

I'm just thinking about this, since there is activity on this band from Japan, and I'm within spitting distance (well, 3-5,000 km) of Japan :)

Simon - XW0LP
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W9IQ

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Re: Modify top-band inverted L antenna for 2200 metres?
« Reply #1 on: July 07, 2021, 05:45:31 AM »

That is a common approach. The builds often use a 5 gallon/19 liter bucket as the coil form. Then there is the trip to the DIY store for the large spool of wire to wind the inductor.

If you entertain the idea of running some real power, you will also enjoy the pictures of such things going up in flames. No Q problem there!

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

VK6HP

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Re: Modify top-band inverted L antenna for 2200 metres?
« Reply #2 on: July 07, 2021, 08:21:06 AM »

Empty 20 l containers used by restaurants for cooking oil etc. make good coil formers.  There's a lot on the web but one practical compendium is by ON7YD:

https://www.qsl.net/on7yd/136brew.htm

If you're putting together a system for 2200 m, you might as well put some intermediate taps on the loading coil to allow 630 m operation as well.  Tuning the antenna is typically done with a variometer but there are other ways: I just use a moveable clip on a fine-tuning coil, for example.  But variometers are fun to make!

The new WSJT-X FST4 modes are being widely trialed and no doubt some of the JA hams are already using them.  You would be quite strategically placed for LF/MF operations.

73, Peter.
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RFRY

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Re: Modify top-band inverted L antenna for 2200 metres?
« Reply #3 on: August 29, 2021, 01:24:43 AM »

As maybe a data point on this topic, below is a rough analysis of an electrically short vertical monopole on 136 kHz when driven against a set of 24 x 10m-long radial wires buried in 5 mS/m, dc 13 Earth (average soil) — from a spreadsheet using equations found in antenna engineering textbooks.

I added a blue rectangle around some rather eye-opening operating values that might be present in such antenna systems.  The very narrow r-f bandwidth for an acceptable load match would be difficult to find and center on the operating frequency; also to maintain there once it was.

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