Vacuum Capacitor - From Russia (Via Ukraine) With Love

For a long time, I've been looking out for a decent vacuum capacitor to reliably tune my 20m magnetic loop antenna.

At long last, and just before Christmas, I 'won' an ebay auction for an 'new old stock' vacuum capacitor, sold by stas3105, based in Kiev, Ukraine.

Now, you may feel a bit nervous dealing with Ukraine.  Happily, I can reassure you in that I've only ever had very good service from several Ukrainian sellers.  There seem to more ham operators in Ukraine than any other country on Earth!

Wow!  These Russian capacitors are huge!  They have a very good reputation for quality, according to fellow hams across the EU.

The capacitor, far from being some dodgy second-hand unit, really is in brand-new condition, liberally covered in protective grease and oil.  According to the accompanying leaflet,  it was made in 1990. It set me back a very modest £69, including the necessarily hefty carriage bill, the item being rather delicate.  I obviously managed to get a good price by buying just days before Christmas, when there was less interest than usual in this stuff.  It only took about a week to get here.

I happened to have a lot of tinned copper braid in the junk box, so this was ideal to make the connections, using jubilee clips to secure the braid to the capacitor tips.  It took a few minutes to find the correct tuning for the loop. 

WSPRing across the globe - 5W, 75cm off the ground in the kitchen!

Once tuned-up, the loop ran on WSPR for a few hours at 5W.  Unfortunately, the internet was on the blink most of the time, so only those stations hearing me are recorded for the most part.  Spectacularly, and again it was missed by broadband outage, I heard a signal from ZK1DRP in the Pacific Cook Islands.  That's pretty good going for a tiny magloop working indoors!

Magnetic Loop Antennas - Why You Should Have One.

Magnetic loops are quite well known in the ham world.  It's just that they aren't all that well-used.

This is very odd, because over the past couple of winters, I've been playing with my own homebrew version, and the results are spectacular.  I would also refer you to the WSPR results of my colleague, Ken Franklin G3JKF, who has some of the most carefully-made loops producing amongst the best signals in the EU on several bands.

Thanks to this nice image by M0UKD, you can see how simple, beautiful and practical a magloop really is. Once you start trying to make one, you will realise they are not as demanding or difficult to tune as many make out.

By 'spectacular', I don't mean 'it will beat the pants off a yagi at 120 feet'.  That's just a silly comparison.

But, if you have ever put up a dipole and been a bit disappointed with the performance and noise levels, then the magnetic loop should be next on your 'to do' list.  Note: not on your 'to buy' list!

The reasons I say a magloop is worthwhile are as follows:

• Physically small - about 1.25m per side for a 20m version, which you can also tune to the higher bands with a suitably rated capacitor.  

• Does not need height for proper operation.  A metre or so is enough.

•  Because of the size, is a (perhaps the only) solution in very high wind areas (like mine!)

• Won't be recognised as an antenna by most, giving you far less likelihood of neighbour and planning problems (loops for 20m are generally within planning rules, if you live in such an intolerant area.)

• Magloops can be used very successfully indoors.   Mine gets across the world on 5W WSPR beacon mode, at 0.5m off the kitchen floor.  The difference in signal between a quarter wave vertical with elevated radials out in the wild weather and the loop indoors can be undetectable (WSPR tests.)

• Magloops are essentially immune from household mains and local noise, allowing effective use in proximity to such sources. 

• Built from 22mm copper tube, are very cheap to build for the 20m and higher bands.  Even at 80m, with a perimeter of 15m and made of wide 42mm copper tube, the price is hundreds of dollars lower than a commercial loop.

• Capacitors can be found second hand, homebrewed, or bought.  If you are good with heavy duty soldering and electronics, a comb-type capacitor can be made and the loop tuned by opening and closing the two halves of the loop (which does, admittedly, demand high insulation and construction standards.)  Vacuum capacitors are to be preferred, as they are very reliable and predictable in tuning.

• Performance is often said to be similar to a dipole, but without the height.  I think this is a fair comparison, though allow for much lower noise and QRM levels from the loop.  I find a horizontal dipole is rubbish next to a magloop (or, in fact, much of any other antenna type.)

There's a lot of stuff written about loops that tends to put people off.  Chief amongst these is talk of very high voltages across the tuning capacitor.  This is really silly, because, whilst it is true there is a high voltage present, this is not something that should scare off those comfortable with basic radio and electronics.

The main thing to contend with is very sharp tuning.  So you need good quality, stable and weatherproof means of installing and adjusting your capacitor.

A loop is, purely and simply, a fairly short perimeter of copper tube - make it as wide as resources and the cost-benefit analysis allows- with either a direct feed using various matching legs, or via a Faraday loop, which is an even shorter bit of wire made into a loop and connected to the coax feed.

Somewhere in the loop, usually the top, you must install a capacitor - either a high voltage butterfly air spaced type, or a vacuum type.  Vacuums are available on e-bay from eastern European or Russian sellers regularly, at prices well below $100.  I've never yet had a problem with sellers from those regions.

The only care you need to take is in making very good connections to the loop and capacitor.  A rush job won't do.  Use wide copper braid or heavy duty cable, and don't mix metals by using stainless steel clamps bonded to copper, which can lead to much lowered efficiency.

Having used all sorts of wire antennas, the magloop is the one that stands out as being a very good performer, immune from heavy winds, can be used indoors with little performance reduction, and can be practically scaled with only modest cost impacts to 80m (or lower!) 

Hills, Sloping Ground and Cliffs

This winter's surprise has been the finding, mediated by objective WSPR tests, that my simple equipment wire, 80m inverted L, is putting out the strongest signal of any station from the EU on DX paths.  By this, I mean, typically, the path to the US.

Is this self back-patting?  No.  I have tested many antennas, and many are useless.  Horizontal antennas usually fit into this category for this QTH.

A hill by the sea.  The perfect DX location!

What is going on?  There are people across the EU with very capable antennas - a few full-sized quarter wave GPs, half-Ls like mine, and probably infinitely more experience and care behind them than I will ever have!

The answer is both interesting and useful for others to note.  Firstly, this QTH has reasonably steep sloping ground in all directions bar to the NNE.  The slope is 6 degrees for just about all of that horizon, being a bit steeper to the north.  This is without doubt a very important feature in obtaining the best performance from simple wire antennas.  I have noted the same phenomenon with delta loops for 20 and 17, vertical GPs and end-loaded dipoles for 20m.

Secondly, the surroundings of the antenna are clear of any substantial buildings.  Our home is a small Welsh cottage, nestled into the hillside.  There are some electricity supply lines of domestic ratings nearby, but these seem to have little or no effect, apart from a degree of de-tuning if you place an antenna too close!

Lastly, and perhaps of little comfort to others unless you live in South America or Australia, is the very high degree of mineralisation due to the QTH being on top of an old hydrothermal vent, more latterly a copper mine.  It is almost certainly soluble iron, and not other minerals, that is responsible for the excellent ground conditions.  Digging a deep hole for my tower some years ago revealed a thin layer of soil, a thin layer of red clay - which is known to particularly enhance RF ground conditions - and then very friable ground-weathered shale that has dissolved iron slowly flowing around within it.

So, whilst the latter element is probably very rare in coincidence with a radio station, the message about sloping ground and an environment as clear of obstructions as possible is something anyone willing to pack their kit onto even a modest hill, cliff or mountain should be able to benefit from. 

And of course, don't forget to try sticking a quarter wave GP at the surf line, where you will really see some spectacular benefits!

Radcom - December Update

It's in some sense satisfying to see more readers hitting this blog about the time of Radcom's arrival in the post each month.  Perhaps it's a quirk of searches prompted by the magazine.  Or maybe people have come to expect monthly comments upon it!

Either way, it's been interesting to see response to my musings recently on the future of the hobby within the 'letters' pages.  It's been very positive, and there are clearly a minority out there who 'get' what the concern is all about. 

Change you say?  You button-twiddling, buy-it-off-the-shelf imbeciles! 

 
One writer declares quite openly that RadCom is "editorially still the same as it's always been."  Perhaps that's true of the overall content, but at least the current editors are not censoring constructive criticism.

Disappointing in his response was the 'owner' of the GHz section.  The author spends a surprisingly numerous initial sentences claiming he's "noted" my claimed lack of material that would help an ordinary mortal - and not a lifelong RF engineer - into that aspect of radio.  Having done a bit of sounding democratic, he then concludes by saying, unless he gets any suggestions, he'll go his own way with the articles. 

Well, that's fine and dandy, then!

That's rather regrettable - and an inaccurate reflection of reality - because I sent a very polite suggestion as to content last year.  There was no reply.  Apparently, there have been some projects published for beginners.  But those haven't, frankly, been the type of projects this beginner would be able to tackle nor, I suspect, would most others.  I've yet to see hoards of people operating parabolic dishes up the local hill.

And there we go again.  The hobby is a reflection, made worse by its socio-economic make-up, of how society has developed over the past couple of decades.  Dominated by the retired, white middle class, many of whom were not only amateur radio folk, but professional electronics workers, to boot, pontificating on what real men's radio is all about.

It really won't do for the old guard to dig ever-deeper trenches whilst the number of participants in amateur radio falls off a cliff edge.  That is the mentality that dominated the argument for not allowing non-Morse literate users onto the HF bands for what seemed like eternity.  It was always a stupid position, borne of prejudice and selfish interest.  It undoubtedly held the hobby back and lost valuable interest.

And before you get on your soapbox, identifying a group of people - who just happen to be older - as being generally responsible for inertia in the hobby is not equivalent to being ageist. 

But, on the positive side, as the more stubborn and stuck-in-their-ways elders move on to a higher plane, perhaps the message to RSGB HQ that it continues to fail in its recruitment obligations and representation of those who haven't just retired from commercial electronics with a golden goodbye, will become a crescendo. 


Until then, I regret that Graham Coomber's bleating about 'change' and 'corporate identity' and so on will continue to ring hollow - and see our hobby fade into oblivion.

80m and the USA: What's up with that?

Over the past couple of weeks, I've started being active on 80m for the winter time.  Using just a simple inverted L with two elevated radials, I've found myself up there with the best of the crowd. 

It's fascinating to run WSPR, a kind of personal beacon mode where unbiased, semi-objective signal reports are sent back to the user via the internet.  WSPR really does let you see how well your antenna is working, and whether that latest tweak made things better - or worse!

That's your American lot!  Not a lot of 80m WSPR interest, stateside.

It's really odd, therefore, that on 80m, there are only a handful - and by that I mean fewer than ten on most nights, active on WSPR from the US.

Why on earth might this be?  There's plenty of antenna design and construction activity, and tens of thousands of hams out there.

In many places, there are oodles of land and low winds to allow the erection of really very good, full-sized 80m antennas.

Sadly, they just don't seem to be there - at least on WSPR.  It's a big gap in our coverage, and it's to be hoped many more users across the US contribute to understanding their own antennas, those of others, and how the signal propagates between them.

Amateur Radio Foundation Licence: Some Thoughts.

Being a girl, my daughter likes talking.  She was lucky enough to have a brief chat with a girlie expedition to Greenland a few weeks ago, and as a result, it spiked her interest in radio. She's only seven years old.

I decided to sign my daughter up to the Foundation Licence course, which in our case, was a very comfortable affair, held each week at kindly MW0SEC's QTH.

It's a long time since I studied for my full licence, so it was interesting to see how the 'new' system of split licence levels works.

In general, the syllabus is pretty easy, and my daughter, with a bit of help from dad, managed to grasp, at least in some sense, what are often very esoteric facts about electronics and radio. True understanding of many things in the syllabus escapes even very old timers, as any read of forum posts on the internet often reveals!

But there are a few major let-downs if, as we might desperately hope is the case, the licensing body and the RSGB want to attract younger members.

One of these is the very heavy-going part on licensing conditions.   Whilst it's allowed to look at the licence conditions for the exam, the wording is so legalesque that it really does make it quite difficult for adults who are not used to looking at formal documents, let alone children.

Whilst it's difficult to say the syllabus is in any particular sense wrong, it could be very much more user-friendly.  The whole thing does still, I regret to say, have a certain aftertaste of years gone by, when non-Morse licensees (called, in that very British way 'Class B' holders) were sneered at as second-class undesirables.

The place where useful change could take place is in the exam.  Here, I think it would be very useful for children sitting the exam to be helped with interpretation of some of the questions (and not answering them) and the whole mechanism of sitting a formal test, which is quite novel - and very daunting - to someone of that age. If those responsible for setting up the system think back long and hard enough, they might recall just how terrifying an exam can be to youngsters.

A review and change is needed, with an emphasis on making the whole thing a further level less stuffy.  I hope that it comes a little bit faster than the glacial pace, far outstripped by the rate of fall in members, at which the RSGB and Ofcom seem to think is appropriate.  As my flying instructor used to say: "if something's not going right, do something about it straight away!"  Quite so...