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.
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
-
- Balun Assembly
-
- Inside the Jiffy box. Foam packing to prevent vibration and damage to the ferrite cores
-
- Inside the case. 4 turns of RG316 wound inside two LF1260 ferrite cores separated by double-sided foam tape.
-
- 1:1 balun terminated in a 50 ohm resistor. VSWR to 30 MHz
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:
owenduffy.net VK2OMD Low Power Guanella 1:1 BALUN
Last Update – 6 April 2019 VSWR Plot
Get out of the Radio Shack and Live Life 