Gain vs Wave Angle

Something I've noticed is that most don't consider is the whole picture when it comes to antenna gain. Often only peak gain at the wave angle it occurs at is quoted. Sometimes a pattern is shown with no gain figures which is useless, this is often the case with verticals.

To build a picture of what one might expect when considering low band DX antennas, I feel it's better to consider the gain at different wave angles.

To illustrate this, I created a table in a spreadsheet with several different antennas and the gain they have at different angles. LiberOffice Calc has the option to fill cell background color based on the value. The table is sorted based on the gain at 5 degrees.



I used MMANA-GAL for the modeling of these antennas. Most are 40m antennas, those that can be matched on 80m are also shown.

Wire antenna heights are 40ft/12m, the inverted Vs are 15m/50ft, the delta loops have a minimum height of 1m/3ft.

Nov 15 2019:
Looking at the models of OCFDs again - I realized due to the lobe formation being either side of the X or Y axis on 40m and above, the far field plot does not show the peak gain as its simply sliced down the X axis. The geometry would need to be offset such that one of the main lobes aligns with the X axis. Comparing the elevation and gain results on the calculation tab with a plain 40m dipole vs an 80m OCFD on 40m band, the OCFD has around 1 dBi more gain at the same elevation angle (52 degrees when 12m above ground), which comes from the two broadside nulls that form. Under far field plots, the far field elevation angle can be changed, comparing gain at 40, 30, 20 and 10 degrees shows the OCFD having about 1 dBi more than a dipole at the same height.

I'll need to update my table..

ZS6BKW Antenna

What else is there that's under 100 ft, at a minimum covers 40 and 20m with out the need for an ATU, and will work on 75m?

After considering a few ideas, I took a closer look at the ZS6BKW antenna which is an optimized variant of the well known G5RV. This antenna checks the boxes on these points:

• Light weight - no traps, coax etc hanging.
• Low SWR on 40 and 20m, can run ~1kW with the AL-80B.
• Respectable gain on 20m if you have the luck or luxury of orientating the broadside to favor somewhere of interest.
• Will work on 75m with the remote ATU I already have. It's essentially a 1/3 wave dipole, as such has reduced efficiency since the resistive component falls rapidly when a dipole is under 3/8 wave length.
• Also covers 17, 12, part 10 and 6m with low SWR.

Spent a couple weeks reading everything I could find, and playing with models - one is included with MMANA-GAL, others can be found online.

Decided it was worth trying out. Initially I was going to order the parts from The Wireman and build it my self, but found a source of these pre-made cheaper and better built for $60 (normally $90) plus shipping from Amateur Radio Supplies => ZS6BKW G5RV 80, so went that route. 

Current setup:

• Antenna apex at 50ft, ends in inverted V configuration.
• K9YC inspired choke balun - 7 turns of RG-8X through two mix 31 clamp on ferrites.
• Remote ATU between the choke and coax to the shack. 

How does it work?

• Except for 15m, low SWR on six bands from 40 to 12m, parts of 10 and 6m.
• Remote ATU dials it in on 75, 60, and 15m, brings the total to nine bands.
• 30m is the odd one out, ATU fails to find a match in my case.
• Performance on 75m wasn't great on transmit, but it's better than nothing. My OCFD is notably better on 75m being a full 1/2 wave on this band. This may be why the G5RV is popular, at 10ft longer than the ZS6BKW that might make enough difference on 75m for it to be "good enough".

Nine bands where only three need an ATU, with 93 feet of wire in the air is OK by me. 30m might be an issue for some, but you can't always win 'em all :-) 

Links to further information:

• G5RV Facts - W8JI.
• The G5RV Antenna System Re-Visited Part 3: The Almost-No-ATU ZS6BKW - Cebik.
• Analysis of the G5RV by G3TXQ.
• ZS6BKW Modifications (web.archive.org), more bands with out an ATU - W5DXP.
• ZS6BKW vs G5RV - AARA Presentation, includes charts, plots, and MMANA-GAL files.
• ZS6BKW construction details - VK2ACD.
• How to build a ZS6BKW Antenna - VK2KMI. 
• eHam Reviews of the W8AMZ commercial ZS6BKW antenna - looks to be identical in construction to the one I got from Amateur Radio Supplies linked above.
• The ZS6BKW antenna from the horse's mouth - Brian Austin G0GSF (ex ZS6BKW).

Bay of Islands ARC Repeater Site

Note: As of 2024 this site has been dismantled. The land owner decided the subdivision would fetch a better price with it gone.

Following on from the Auckland VHF Group Repeater Site post, some more pics from the archives. This time of the Bay of Islands ARC Repeater Site, photos I took from around 2007 when I had the task of reinstalling the equipment after it had been removed for re-alignment.

This site was established with the help of the Auckland VHF Group in the mid 90s to get the national link extended north via a sister site between here and Auckland called Brynderwyn. NZART map here - its approximate at best. Google Map that I created here, the locations are with-in tens of feet in most cases.

Since these photos were taken when I was last there, the 2m repeater has had some changes with the addition of CTCSS for IRLP node 6398 link, there are more recent pics on their homepage and some from when the tower was erected.



Pic of the tower and antennas. Like Klondyke, the 2m repeater antenna is constructed from angle iron, welded, and hot dip galvanized, but is a simple pair of 2 half waves in phase for around 10 dBi of gain, hard to see as they are end on in this pic. At the top is a 4 dipole stack for the the 70cm repeater. This configuration resulted in the 2m and 70cm repeater performance and coverage being closely matched in most cases. The link to Brynderwyn is a set of four 7 element Yagis with around 17 dBi? of gain, the Brynderwyn end has the same antenna configuration, this is needed because the 70 mile path is not ideal.



Inside the building.
Tait T300 gear.
146.750- also had a 50W PA in the back.
439.975- had the matching Tait 50W PA.

New Desk

After using a folding table for the last few months, 'twas time for a something better.

I had considered The Great Ham Radio Desk Project, but after looking around IKEA I found something I liked better, more so since IKEA was having a sale at the time.

The spare room/office/shack is 120" wide across the back wall. What I ended up getting were three sets of draws and two table tops, the table tops are 59" x 29", the 29" width is nice, as it allows plenty of depth for radios, computers etc with space in-font.

• LINNMON Tabletop
• ALEX Drawer unit

The total was about $270 less tax and delivery fee, took an afternoon to put together.



Left to right, Ameritron AL-80B, Kenwood TH-D72A HT on top, Motorola MCS 2000 33cm/900MHz radio, Kenwood TM-731A, Icom IC-7300, 27" iMac (2014, 5K), under the iMac is a Windows 7 laptop which runs all the ham radio applications.

Plenty of room for more stuff! Plan to add some shelves to mount the Kenwood and Motorola mobile rigs, control boxes, and antenna switches etc.

22 Nov 2019:

This arrangement has been superseded with New Desk version 2.

WSPR - 40m, ZL5A Scott Base Antarctica

WSPR pulls out another surprise.

Adam Campbell / ZL5A from Scott Base Antartica: