Friday, 27 January 2017

A shortened multi-band End-Fed Half Wave (EFHW) antenna for 80-10m

The 80-10m EFHW
This is a shortened multiband antenna, about 23m long, for 80m-10m that offers low SWR (1.3:1) on 80m and 40m, and below 3:1 on 20, 15 and 10m. The antenna has almost 300kHz bandwidth on 80m between 3:1 SWR points. But performance is down about 8-12db on a dipole on 80m.

This design came from attempts to find an 80m antenna that could fit into a small space. This was because Norfolk Amateur Radio Club likes to take part in the 80m Club Championship (we won in 2016), but many members don't have enough space for a full size (132ft) dipole or the 100-102 feet needed for a G5RV or W5GI antenna.

This antenna lets you get on to 80m in a horizontal distance of about 12m (40ft) when used as an inverted sloper with the apex at 8m, although you'll be down a couple of S points on a dipole. But if the other station is 59+20dB, you'll be about 59 +5 or 10db, so all is not lost!

I take little credit for this as it was outlined in PD7MAA's and IK0IXI's blogs after extensive work on the antenna in the Netherlands. However, there was little on their blogs in terms of its performance or SWR characteristics. Hence this write-up.

Download the 80-10m EFHW antenna guide

Update 29/1/17:
I've updated the guide to look at replacing the coil with a 7MHz trap and also putting the antenna up as an inverted V.  The trap and about 14.2m of insulated wire would improve the 80m performance a little, if you have the space, but possibly at the cost of the 14MHz performance. Surprisingly the MMANA-GAL model suggests the inverted V would be worse for 80m NVIS communication.

Update 09/02/17
I thought I would bite the bullet and took the wire and loading coil off and replaced it with about 130ft of insulated wire. This needs some final tuning, but gives a low SWR across 80 and 40m, and SWRs below 3:1 across the higher bands. Performance seems to be similar to a 100-foot W5GI dipole. I'll add the actual SWR figures to the PDF. This is OK if you have the space. The last 10m (33ft) of wire has to go along a wooden fence at my QTH.

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