RSGB Books - Tired Old Reprints?

The RSGB has been latching-on more and more of late to the fact that its book sales are doing a lot towards its financial health.

This is a good thing, and most of us enjoy soaking-up as many ham radio texts as we can.

This year, there's been a big push, together with a £5 blanket book token for all members, to sell - yes - more RSGB books.

A good book, though the material is often very old.  Image: RSGB

I duly bought the 2015 Radio Communications book - a big, fat 'bible' of radio facts and tips.  It's not, by any means, a worthless book.  But, if you've been a ham for a while, the vast majority of the text will be sadly very familiar to you.  Simply other books and RadCom articles rolled into one compendium, albeit with a handy CDROM of the contents.

OK, in this, the RSGB book is a plain analogue, right down to the CDROM, of the ARRL Antenna Book, which never fails to sell in large numbers.  Perhaps it's easier simply to buy these large compendiums than fork-out for a large number of smaller books.

Personally, I think the RSGB books need a huge revamp and update in general.  The section on planning and the ham operator is very old - I've not seen any updates to it over the past four years, at best.  In places, it is misleading. 

For example, it states that 'legal action can quickly follow' in the event of a planning breach.  That's sometimes true, but it fails to point to the government's own guidance that planning breaches are firstly not a breach of the law in themselves and, secondly, that any breach is more often than not brought to a resolution through cheap and easily-achieved negotiation, not wildly expensive and time-consuming litigation.  In many cases, antennas are not major breaches, and often of minimal objective impact of any sort.

Another book I bought this Christmas was the RSGB 2015 Yearbook.  This is a total joke!  Basically, it's a few pages of ham radio stuff and then a printed directory of members.  Why on earth does the RSGB produce this tat when that data - and much more - is freely available on QRZ.com and other sites, and could also be available - maybe it is already - off the RSGB web site?

Earlier in the year, I bought a book about Radio Propagation, also by the RSGB.  It's OK, but very thin on detail, hardly any references to scientific research, and clearly out of step with latest findings and modes - there's nothing at all about the WSPR beacon revolution, for example. 

Come on, RSGB!  There is hardly a lack of new stuff to write - and write lively and well - about.  Let's hope 2015 sees the tired, repeat-published stuff start to fade away, and fresh stuff make an appearance. 

Building a G3JKF Magnetic Loop Array

Despite having a plethora of conventional and well-functioning antennas outside, I keep a constant interest in magnetic loops and their various designs.

The attraction of a loop is clear: small, not very prone to electrical noise, wide band coverage, and eminently suited to indoor use.

For a couple of years, I've been in touch with Ken Franklin, G3JKF, who has very carefully developed and tested, over a long period of time, a three loop array.  If you ever catch him on WSPR mode, you'll be amazed at how well his loops do.  A characteristic of Ken's signals is that he reaches just about everyone that any other, full-sized antenna operator reaches, often with comparable (or even better!) signals.  Rarely are signals from Ken significantly down on full antennas.

So, having messed about for ages, I decided I'd make use of a day off, and put together a G3JKF loop for 40m-10m. A 7.5-350pF Russian vacuum cap has just enough low-side range to tune 10m to a perfect match at the digital end of the band.

Before I start detailing the construction, remember that soldering with a blowtorch can be pretty darned dangerous! This is especially true of this build because you may find yourself soldering 'upside down' fittings, which may drip hot flux and/or solder onto your skin.  Eye protection and some decent heat-resistant gloves are advised.  Flux is also very corrosive, and generates noxious fumes that can give you a belter of a headache.  So plenty of open windows if you are working indoors.

You need pre-soldered, 15mm fittings as follows:
14x 90 degree elbows, 4x 45 degree elbows and 6 tees.  

You need a total of about 13 metres of copper pipe, but there is scope to recycle some you may already have. 

You need a pipe cutter, soldering flux (this is essential), and a gas blowtorch.  You can also use an electrical pipe heater, but these are too slow for me!  Also, some coarse wire (steel) wool.

Remember to clean each joint immaculately with wire wool before soldering, and add a liberal amount of flux to the pipe to be fixed. 

Start by making the complex-looking top joint for one half, as per the image.  This first one has to be assembled in a vice, all the fittings made square, and all of them soldered together in one go.

The first soldering is the most complex.  The arms are cut to 130mm each.

When soldering, heat the pipe ahead of the joint first, then move on to the joint itself.  If you heat just the joint, solder may run, but the underlying pipe may not be quite hot enough.  When you see a complete ring of solder appear at the joint, stop heating.  

When soldering pieces of tube, you may need to support them to make sure they're reasonably square and not sagging - there is some play in the soldered fittings.

With care, you should be able to control the heating well enough to melt one side of the connectors whilst the other just about remains solid.  When one joint is done, move straight to the nearest next connection to be made, until completed.  Give a good 15 minutes or more to cool down, as copper retains heat for a remarkably long time.

If, for some reason, a joint looks a bit suspect, you should first heat it to get rid of any blobs of solder, then clean it thoroughly with wire wool.  Add some flux at the joint, and heat the joint until solder melts into the join.  This should fix most failed joints, which will happen sometimes.

You then need to add the 45 degree elbows, and two pieces of copper 525mm long.  Solder these to the arms coming off the central connecting section.

The completed top joint for one half of the loop, plus the 45 degree bends.  The longest, topmost tube is just a connection to the capacitor, however you configure it.

At the end of these pipes, you add a further 90 degree elbow, and a 1m long piece of copper pipe.  Continue adding elbows and 1m copper pipe until you get to the point where it needs to join the second top joint section.  Repeat for the other side, at which point you will have nearly finished two complete loops of the array.

To join the bottom elbows, which you can't really access at times, use a large wood saw's blade near the handle, to act as a reflector of heat, a hint sink with an air gap to stop the floor being burned(!) and  a catcher for hot solder or flux.

You then need to make a second top joint, exactly like the first, and eventually join its arms to the outer loops.


The central loop vertical tubes have to be a bit bigger - 1100mm - to allow for the 'up and over' as a result of using a tee at the top joint.  The arm from the elbow at the tee to the second, down-going 90 degree elbow is 395mm long, of which you need two, of course.  Complete the loop all the way round.


My support is a simple lattice of light timber, held aloft at about 7 feet with a timber stand.  PVC clamps hold the loop firm. Details as per the photo.

You now simply need an air spaced or vacuum variable capacitor.  Anything in the range 10 - 1000pF should do, but my vacuum cap is 7.5-350pF, and tunes 40m-10m. The feed point is a simple SO239 connector to a gamma match.  A very short wire runs from the outer to the centre of one of the outer loops. The centre pin is connected to a piece of drawn copper or similar, which is soldered about 80% of the way up one of the sides. There are many matching variants, and you may prefer another.

 
Et, voila!  You have what must rank as the pinnacle of magnetic loop design.  Being 1m cubed, more or less, I can't actually get mine out of the kitchen where I built it without chopping the loops in half!  Eventually, I plan to house the loop in a timber frame with fibreglass panels and 'Coraline' corrugated roof; that' much easier than weatherproofing the capacitor, and avoids the effects of our heavy winds.

The completed loop, now with vacuum cap 7.5-350pF.  Braid straps to the cap ends are kept to the bare minimum - about 1 inch.

Very short, wide copper braid to the loop, kept in place with steel clamps. You should not use this method other than for testing, because soldering is better to reduce losses.  Cap is held in place with a ring of cable ties, and another to the copper tube each side.

There are very few of these loops that I know about, so if you have the time, the inclination to do some soldering, and a small amount of space to spare, why not have a go and put one to work on WSPR?  Total cost, even if you bought all the materials and tools, is only about £120, and much less if you already have tools and some spare lengths of copper around.



UPDATE (i):  Today (22/12/2014), 19 pairs of 21MHz WSPR reports heard by a combination of the respected stations, K9AN and N2NOM yielded, for both stations, a median difference of 0dB between my indoor three loop array and, in most cases, the sloping dipole operated by the well-run station at G8VDQ.  M1AVV and M0XDC added a couple of data points to the total.  Spots excluded the time during and leading up to the grey line, as there are significant differences in signal enhancement due to even quite small longitude separation between stations.

UPDATE (ii): Following discussions with G3JKF, the feed system has been modified to a 'parallel gamma' match.  Firstly, the coax goes into a homebrew or commercial 2:1 or 4:1 balun, rather than directly to the loop. In my case, a 4:1 balun yielded a perfect match at the upper end of the array's range, but a 2:1 didn't.

The centre pin from the balun is connected to a triangular section of microbore tube or thicker copper wire, which attaches to the loop at the same, 80% point up the side of one of the outer loops.  This returns to the centre pin parallel to the side of the loop, spaced by about 2cm, and then parallel to the bottom of the loop.  Adjusting the spacing can lower the SWR somewhat, and I found it was better to be at 2cm than 1cm, for example.

The 'parallel gamma' feed arrangement.  4:1 balun centre pin to triangle, attached to loop at 80% up left side; outer to short wire connecting to the centre of the lower leg of the loop. 

The outer conductor goes from the balun to the centre of the lower part of the loop, as it did under direct coax connection.

These changes bring the loop to a perfect match at 10m, whereas previously, it was nearer 1.5:1 or greater.  WSPR tests show the loop works very well at 10m.

~5:30-9UT 40m results, 2015 Jan 18. 

17m + 15m Magnetic Loop

Loops are always under test in one form or another up in the old shack.  Winter is a great time to build small antennas, because it can be done comfortably, indoors!

In cutting up an old design that resonated too low for what I needed, I recycled some copper tube, including recycling the expensive bend fittings, into a 17m loop.

A very hastily cobbled together test loop for 17m and above.  Just 0.55m a side!

The initial experiment was two loops in a figure of eight fashion, each loop being just 0.55m  on a side.  The antenna worked fine, but I found that it behaved much like a single loop of the same total perimeter.  So, that being the case, it was more of a 20m and below loop.  Handy, because it's more portable than a single 4 or 5m perimeter loop, but not what I was after that day.

So, chop off one loop, use just the other.  At 0.55m a side, the loop is at the lower limit of an ideal size for a 17m loop; this was a product of making the loop such that it would work well on higher bands, too.

The capacitor is a wide-spaced, roughly 10-250pF air spaced type, manually tuned.  The loop being borderline size, it's a little fiddly at 17m to tune, but much easier on 15m.  However, the old 'by ear' tuning system works easily enough!

The very simple Flexweave primary loop, just 0.44m long.  Matching is easier with a primary that overlaps the secondary.

Result?

It's working indoors, so a clear-site, outdoor test will have to wait.  But, it was picking up a JH station nicely on the grey line at 17m this morning, and is putting out a very strong signal across the EU.  It's certainly working properly.  As I write this, R0AU had picked up my 5 Watts at 3534 miles, at -27dB.  Weak, but it's early yet...

Remember that we're not trying to out-do SteppIR beam twiddlers here.  But we are offering a cheap, very simple to build loop for 17m that gives those living in apartments, HOA and other antenna-hostile locations a chance to go live and work the world, albeit more likely on low power digital and CW modes, on a band that otherwise needs a fairly extensive piece of wire.

Oh, and ignore those folks - and models - that say loops are not efficient.  They are.

The next step will be to revisit the multi-loop development, closely following the fine work of G3JKF, who has the most efficient magnetic loops I have ever seen.

RSGB Volunteer

A strange, knobbly letter arrived in the post, franked 'RSGB' this morning.

What on Earth?

Turns out it was a standard letter, with text identical to that of an article in the current (Dec. 2014) edition of RadCom, and a smart little pin badge with 'RSGB Volunteer 2015' inscribed upon it.

I'm an RSGB Volunteer!

This morning's post...

I presume this is as a result of enquiries with Graham Coomber as to whether the society might like me to continue keeping abreast of planning issues across Wales, something I've been doing anyway for a number of years.

Nothing in the letter tells me what the RSGB thinks I'm doing as a volunteer, of course!  Neither have I had any response from the planning committee, who were meant to be consulted on volunteer involvement.

I suppose I can read it as a 'gauntlet down' situation, in that, if I'm so convinced I can make a contribution well, get on with it!

Fair enough, I'd say.

So there.  I will have to network like mad and do some proper work now!

Hellschreiber

Hellschreiber, more commonly known simply as 'Hell', is a great mode, with a speed that allows you to have a nice chat, and plenty of time to edit a macro or just live-type.


Sadly, there aren't very many users.  Or so it seems if you scan across the bands.

Old school Hell.

This morning, RA6BG was sending Hell on 12m; it's the first time I've heard the mode on 12, so I gave him a call.  I sent a spot to the cluster, to find a remarkable number of people joining in the Hell fun!

So, it seems there is plenty of interest out there in Hell, it's just that someone has to jump in first!