SOTA – First use of a ZS6BKW Antenna

Friday 1 February 2019 – Today is the 6th anniversary of SOTA in VK1 and to celebrate the occasion four VK1 SOTA activators are heading for the hills; Bill VK1MCW, Tony VK1VIC, Dermy VK1FDHA and myself. My plan is to activate Mount McDonald 17 km west of Canberra GPO. Elsewhere in VK3 a contingent of VK1, VK2 and VK3 SOTA activators are heading to the Victorian high plains for the annual ‘Hotham’ SOTA S2S fest held at Mt Hotham and surrounding 10 point summits. The VK1 contingent is made up of two experienced SOTA activators Andrew VK1DA and Wade VK1MIC.

Back to the ZS6BKW… two years ago I constructed a ZS6BKW antenna using Dx-Wire and lightweight 300 ohm twin-lead feedline and promptly placed it in my storage box of portable HF antennas. My excuse for not using the ZS6BKW in 2 years, well I was waiting for an opportunity to visit Mount McDonald. The summit of Mount McDonald is flat like a table and has a large open area free of trees where one could erect a 160m (1.8 MHz) half-wave dipole.

Ok, if you are in Australia you are now wondering where did I find 300 ohm twin-lead TV feedline? These days 300 ohm feedline is as rare as gold-plated hen’s teeth, commonly found in home TV antenna installations in the 60s and 70s, but no longer. Two years ago I was fortunate to visit a local hardware store and to my surprise what did I see on the shelf, crikey! a 100 metre roll of 300 ohm TV feedline. I purchased 15 metres, I should have purchased the 100 metre roll!

Now we all know the internet is a minefield for HAM antenna designs and construction methods. Eyes wide open and take what people write with a healthy amount of scepticism. After consulting a number of well-known published antenna design books and a lesser number of reliable websites, I chose the following ZS6BKW dimensions, Oh and before moving to antenna dimensions, this post is not intended to be a comprehensive analysis of the ZS6BKW antenna radiation patterns in a computer model or its theoretical gain. All I am offering is my experience with this antenna operating from a SOTA peak with real-world conditions, be they during good or poor propagation or having a good or poor earth dialectic. What you see is what you get. 🙂

ZS6BKW Antenna Dimensions start point: Radiator 1.35 x wavelength at 14.250 MHZ is 28.4 metres (93.2 ft) comprised of two equal sections 14.2 metres each and 11.1 metres (36.4 ft) of 300 ohm feedline 0.82 vf. I chose this version of 300 ohm twin-lead for its lightweight and flexible properties.

ZS6BKW Antenna

Homebrew ZS6BKW antenna and a 1:1 common mode current choke. Two halves of the dipole and 300 ohm feedline.

1:1 Current BALUN – design by VK2OMD

Post Update – VSWR Plot: RigExpert AA-600 on 6 April 2019

VK1AD ZS6BKW Antenna VSWR Plot at 8 metres above ground level

For today’s activation I am using an Icom IC-703 10 watt QRP transceiver with an inbuilt ATU.

With an ATU (manual or auto impedance matching device) the ZS6BKW antenna is usable on 80, 40, 20, 17, 12, 10 and 6 metre bands, however the ZS6BKW is definitely unusable on 15m (21 MHz) and 30m (10 MHz) due to a very high VSWR on both bands. The IC-703 inbuilt ATU refused to play ball on 15 and 30m. That’s ok, I’m not particularly interested in 15m (21 MHz) as a viable option for VK SOTA.

One drawback with having a 11.1 metre feedline, you need a 9 to 10 metre telescopic pole. In the pictures below you can see I had to improvise to keep the feedline elevated above ground level. On a summit with trees or shrubs you could drape the feedline over a tree branch or lay it across a shrub. Adapting to the summit environment is one aspect of SOTA I find very rewarding. 🙂

300 twin-lead is terminated at the 1:1 BALUN.

short length of RG316 feedline between the ICOM IC-703 and the 1:1 BALUN

Operating on 80m 3.625 MHz SSB

Operating on 17m, 18.140 MHz SSB working John ZL1BYZ

VK1AD SOTA Shack at Mt MacDonald

Antenna view – difficult to see against the grey sky

Plot of SOTA Chasers in Australia and New Zealand – 31 January / 1 February 2019 UTC (Friday working day). Maps and QSO data courtesy of SOTA data and SOTA mapping project.

From 22:30 UTC 31 January 2019 – Chaser QSOs with an Icom IC-703 QRP and a ZS6BKW Antenna.   Map courtesy of SOTA Maps

From 00:00 UTC 1 February 2019 – Chaser QSOs with an Icom IC-703 QRP and a ZS6BKW Antenna.  Map courtesy of SOTA Maps

How’s this for a coincidence, VK2IO, VK3PF, VK1DA and myself have all deployed ZS6BKW antennas. Coincidence maybe, what’s actually going on is VK SOTA activators are following the lead of Gerard VK2IO who in 2015 implemented the ZS6BKW as his primary SOTA HF multiband antenna.

Extract of VK1AD SOTA Activator Log: 31 January/1 February 2019 – Mount McDonald

Time Call Band Mode Notes
22:36z VK5IS 7MHz SSB Ian s58 r53
22:37z VK7FRJG 7MHz SSB Rod s58 r58
22:41z VK5WG 7MHz SSB Nev s57 r45
22:46z VK5CZ 7MHz SSB Ian s55 r55
22:51z ZL1BYZ 14MHz SSB John s59 r53
22:53z VK4TJ 14MHz SSB John s53 r51
23:00z ZL1BYZ 18MHz SSB John s57 r41
23:11z VK2IO/3 3.5MHz SSB Gerard s59 r59 S2S VK3/VE-009 ZS6BKW
23:12z VK2HRX/3 3.5MHz SSB Compton s59 r559 S2S VK3/VE-009 ZS6BKW
23:17z VK3AFW/P 3.5MHz SSB Ron s55 r55 S2S VK3/VE-104
23:18z VK3BCM 3.5MHz SSB Brian s59 r59
23:28z VK1MA 144MHz FM Matt s59 r59
23:32z VK1MA 3.5MHz SSB Matt s59 r58
23:37z VK3SQ 3.5MHz SSB Geoff s59 r53
23:43z VK1MA 28MHz SSB Matt s59 r59
23:50z VK3PF/P 3.5MHz SSB Peter s55 r52 S2S VK3/VT-018 ZS6BKW
23:55z VK1VIC/P 144MHz FM Tony s59 r58 S2S VK1/AC-040
23:56z VK1FDHA 144MHz FM Dermy s59 r59 S2S VK1/AC-043
23:59z VK1MCW/2 144MHz FM Bill s59 r59 S2S VK2/SM-093
00:02z VK2IO/3 3.5MHz SSB Gerard s58 r58 S2S VK3/VE-009 ZS6BKW
00:03z VK3SQ 3.5MHz SSB Geoff s58 r55
00:04z VK1MA 3.5MHz SSB Matt s59 r59
00:05z VK1FDHA/P 144MHz FM Dermy s59 r59 S2S VK1/AC-043
00:07z VK1VIC/P 144MHz FM Tony s59 r59 S2S VK1/AC-040
00:11z VK1MCW/2 144MHz FM Bill s59 r59 S2S VK2/SM-093
00:12z VK3PF/P 3.5MHz SSB Peter s58 r51 S2S VK3/VT-018 ZS6BKW
00:15z ZL1BYZ 14MHz SSB John s59 r53
00:23z VK2YK 7MHz SSB Adam s58 r56
00:26z VK4TJ 7MHz SSB John s51 r51
00:41z VK1MCW/2 50MHz SSB Bill s58 r58 S2S VK2/SM-093
00:47z VK1MA 50MHz SSB Matt s59 r59
01:03z VK5VGC 7MHz SSB Grant s55 r53
01:50z VK3UFO 7MHz SSB Jim s59 r52
01:59z VK3PF/P 7MHz SSB Peter s55 r55 S2S VK3/VE-060
02:00z VK3SQ 7MHz SSB Geoff s59 r55
02:01z VK2IO/3 7MHz SSB Gerard s55 r555 S2S VK3/VG-004 ZS6BKW
02:02z VK2HRX/3 7MHz SSB Compton s55 r55 S2S VK3/VG-004 ZS6BKW
02:04z VK3PF/P 3.5MHz SSB Peter s55 r52 S2S VK3/VE-060 ZS6BKW

If you are looking for a weekend antenna project the ZS6BKW antenna is a worthy candidate 🙂

Will I use the ZS6BKW antenna in the future? Yes I most certainly will!

Reference: VK2OMD Low Power Guanella 1:1 BALUN

Last Update – 6 April 2019 VSWR Plot