Half rhombic deployment: good results.

A very calm day started early this morning for me at 05:30UT, when I took to the still dark coast to see how well a simple half-rhombic would perform.

Here's how it looked later in the morning:

The eastern (beaming direction) end was grounded via a terminating resistor:

The 'missing side' of the feed was also grounded (see below). A good background to this antenna is found here.  There's also a lot of useful modelling (treat with caution) here, though the comparisons with stacked Yagis for 40m is, well, typically American and utterly impractical, next to a simple wire.  Try putting up stacked 40m Yagis up on your own, on a beach, in the rain...

The feedline is 300 Ohm twin going back to a 4:1 balun, and a very short piece of coax from that to the transceiver.  This is a standard, ultra-low line loss, multiband arrangement I've used over many years for a multitude of different wire antennas:

Did it match up?  Well, I sat there, feeling a bit dejected when it wouldn't match on anything other than 12m.  The key fact is how early I got up - and how being tired led me to miss that the TS480 selector was on 'Ant 2' for every band except 12m, when the antenna was connected to 'Ant 1'!

With brain re-engaged, I found the antenna could be easily matched on all bands from 160m to 6m.  This is quite typical of grounded antennas like this. Remember, as you read the following, I did not at all plan to use this antenna below 17m, so this is all a bonus.

Time is, of course, the enemy in making antenna tests. Starting with just a very few minutes' work at 80m, even though it was well into daylight, I was not getting out very far at all, but the receive was quite surprising for the time of day:

Just a couple of TX/RX cycles at 80m WSPR (1W).  Two US stations, even in daylight.

I then went straight into 17m WSPR work.  This was hopeless, because there are now practically no WSPR stations active on that band.  The best I could do, which can't be relied on, is a path along the beam direction to Russia giving 10dB better than my 17m delta loop at home.  It's just one spot, and the sea gives that kind of gain anyway.  So the rest of the antenna assessment is, for now, largely subjective.

Changing to 17m FT8 (10 Watts), the results were encouraging.  The band was usable very early on indeed, much earlier than if I were at home, and good DX from Asiatic Russia, Japan and VK kept coming in at good signal levels.  QSOs as far as Asiatic Russia were made:

17m results, FT8.

On 15m, the signals were very strong, and had all the feel of operating something like a 3 or 4-ele beam.  I didn't bother with WSPR, but FT8 got as far as VK.  Difficult, due to the bias of the time of day, to say how directional the antenna is at this wavelength, but it does seem to be at least reasonably narrowly-focussed:

15m results, FT8.

On 12m, it was again like using a beam, and the directionality was significantly sharper, with the strongest SNR reports falling in a very narrow 'corridor', which you can easily extract from the plot below.  

When I cross-checked with the 3-ele back home, the 12m band was clearly in quite poor shape, and so the results I got from the beach do seem to represent a very significant improvement on the Yagi, perhaps equivalent to a 5 element or more.  I even made a number of DX QSOs as far as Western Siberia from the beach.  From home, all my 'CQ' calls went unanswered, and the only two signals I could hear were very much weaker than at the beach:

12m results, FT8

In carting a load of stuff to the beach, I forgot the antenna analyser.  Even so, the approximate SWR figures, as given by the transceiver, were as follows (at the end of 300 Ohm twin and a 4:1 balun).  Remember that, with twin wire, line losses at even very high SWR are negligible, at only a small fraction of a dB.  All these bands matched easily and quickly with the TS480's internal tuner:

160m: 3:1

80m: 1.3:1

60m: didn't measure!

40m: 1.3:1

30m: 1:1

20m: 1.7:1

17m: 3:1

15m: 1:1

12m: 1.3:1 

10m: 1.7:1

6m: 1.4:1

So, is this an antenna worth continuing tests with?  After some thought, I concluded that it is - even though most texts give a terminated rhombic an efficiency of somewhat less than 50% (but this isn't really a good way to judge an antenna, especially down at the beach). 

Firstly, it's a true single-wire, all-band antenna.  It probably doesn't give a super-effective signal out on the lower bands, but then, it's always better than not having any access to those bands.  Receive on those bands seems to be exceptionally good, subject to further testing.

Secondly, it is easy to put up.  The most difficult thing is getting a sturdy enough support for your central pole.  I used, for the first time this outing, a 90-degree angle iron hammered into the ground (with wood, to avoid mushrooming the metal), which went into the ground very easily, and gave more than adequate support for stong winds.  I plan to weld small side steps so that I can simply stand on it to drive it into the ground, rather than hammer it.

Very simple, cheap 10m pole support.  90 -degree steel, with a sharp spike cut into the bottom.

 

Thirdly, the antenna will tolerate high winds easily when the wind is perpendicular to the wire beaming direction.  When it is along the wire direction, the central support will bend a lot, and stress the upwind wire.  This is not a problem, so long as you use something like kevlar-cored wire, which can take the load easily.

Finally, the first, admittedly not very complete testing shows that, especially from 17m up, this is likely to be a very good, directional antenna, especially when used near watery situations.

The next step is to make a version with its focus on the 14MHz band.  That will make comparisons with past data, and new data yet to be gathered, much simpler.  Wire is already on order!

Again, it was very nice to be approached by a number of people, interested to know what I was doing.  I even seem to have informed them in a way they liked!  Meanwhile, the UK's newest polar research vessel 'Boaty McBoatface' (actually the Sir David Attenborough), was undergoing its first sea trials just offshore from my antenna!

The RRS Sir David Attenborough, named in a popular vote as 'Boaty McBoatface', leaving Liverpool some days ago for the Irish Sea trials.