15m Magnetic Loop Tests

Love them or hate them, magnetic loops remain a fascinating antenna concept.

Over the years, I've built quite a few magloops, more recently being inspired by the work of G3JKF and other, careful experimenters.  I did go through a period of disillusionment with loops, but came back to them after I realised that some of the less impressive results were simply the result of too much operating them indoors.

Since the advent of the digital weak signal modes, the need to 'QSY' - or change frequency to make different contacts - has, in effect, been eliminated.  You just dial up the mode's standard frequency and shift the audio tone up or down.  So the traditional 'problem' of loops being very high Q, narrow bandwidth antennas has also, as a result, become less of an issue.

To reduce costs and space requirements, I built a small loop for the 15m band yesterday.  Instead of the usual copper pipe, I used a spare, 1.5m-long piece of thin brass sheet about 100mm wide..

The advantage of sheet is that it is flexible, and can conceivably be 'unlooped' and removed from the support structure in larger antenna builds where car transport to site might be a consideration. Other than potentially being a bit too much like a wing in windy weather, I wasn't sure if the sheet would display any disadvantages. 

I ran the loop on WSPR using 1 Watt, though because of cold, windy and very wet weather, I kept the antenna and its unhoused air spaced capacitor inside my kitchen-cum-shed-cum-shack.  You have to take this into account when evaluating the outcome.

First, here's the distance plot of my loop, indoors, against an M6 station with a Cobwebb antenna at 200mW on top of a high rise building, with a nice, semi-rural aspect all around, in Kent.

Looking across without much analysis, and taking into account the different power outputs, the signals appear, on average, broadly the same.  Let's look at how the simultaneous spots results come out:

Unfortunately, there are not very many simultaneous spots.  But there are just about enough to make the outcome somewhat reliable.  The difference in favour of my antenna is 5.5dB, which supports the subjective assessment of the distance plot as being similar, because the M6 station is putting in about 6dB more signal into his antenna (which, remember, is outdoors on a high-rise building).  Also, the magloop is directional (I was running the main, vertical lobes in a NW-SE direction).

When looking at the geographical plot of spots, it does seem that my loop is able to take advantage of the good ground gain afforded by the local environment.  One spot (highlighted) shows an enormous, 16dB stronger signal for my loop over the Cobwebb.  And the only other US spot, from Florida, was of my loop - the Cobwebb didn't make it.  Whilst these are very few spots on which to make firm conclusions it does, at least initially, look quite good.

The following day, I was pleased to see G3JKF had joine me on a rather dead 15m band.  An EA8 station provided the only spots for most of the day, which at least made comparisons simple!  Later, I heard a 9L station but, unlike G3JKF, did not receive a spot from him.

Overall, the results are again quite encouraging - only a 1.5dB advantage for G3JKF, with a triple array in a good outdoor environment.

If you're new to loops, you'll notice that G3JKF and my loops never use the primary, 'Faraday' loop feed mechanism.  Those can lead to trickier matching.  We both use what could be described as a pseudo-gamma match - a mixture of direct and induced coupling, and usually running through a 4:1 balun.

You can find plenty of good images if you search 'magnetic loop gamma match' online.  But I would caution that all my loops show best matching when the gamma match is connected a good 1/2 to 3/4 way up one side of a loop, rather than the much shorter feed shown in most images.  An antenna anlayser makes progress infinitely quicker than being without one.  Use a crocodile clip on your centre pin matching wire for initial investigations of the best point for your feed to attach, then you can mark and solder the wire permanently, without the clip.

Over the weekend, I made this four parallel loop array, nominally for the 15m band.

Today, I'm running the new, four loop array for 15m made from 10mm microbore copper tube, but now outside, despite currently experiencing some windy, very cold weather from the Arctic!

Dry. if cold weather permits some WSPR testing at 21MHz

The results, running against G3JKF's triple-loop array now follow.

First, the plot of distances achieved, remembering that 15m is quite quiet at the moment, and that for much of the day, only one station was hearing us (EA8):

This result was fairly poor relative to G5TA's multiband vertical, though one has to remember the loop is only the size of a supermarket shopping bag:

Compared to G3JKF's loop, the outcome in terms of signal strength was, allowing for the low number of spots, the dramatic, rapid swings in propagation on 15m, and a difference in latitude that generally favours southern England over north west Wales, my loop is doing reasonably well and perhaps much the same.  For about an hour in the morning, my unweatherproofed loop and vacuum capacitor was also soaked by a big shower, which impacted its matching to the extent of raising the SWR from 1:1 to 1.5:1 until the cold Arctic air dried it out.

Overall, I can certainly say my loop is working almost or as well as G3JKF's loop, which is reassuring in terms of build quality.  My loop could be a bit higher, but that can't be addressed for the moment.

Unfortunately, 15m is too variable a band at the moment, and too quiet overall to permit a good set of data to be collected that yields a robust comparison with either G3JKF or much of anyone else.

That said, I did run a one-after-the other series of tests over a couple of hours, comparing the loop with my vertical delta loop for 15m (via a 2:1, corner fed, SWR = 1:1).  The result?  Lots of QSB that made comparisons tough even on a 4 minute timescale.  But a figure of about 7dB in favour of the delta loop eventually emerged from the noise.

7dB against the magnetic loop will be a killer for many - hence the 'dummy load' claims that are made.  But nobody, graced with lots of space and no neighbours to complain would use a magnetic loop as a first choice.  Magloops are for those with much less space, perhaps wanting some noise reduction, and the ability to use an antenna across multiple bands, perhaps from indoors.  With an indoors 1.2m-square loop, I've had good SSB QSOs as low as 60m using just 35W.  With digital modes, the possibilities are quite good.

Still, now you know that a reasonably effective 15m loop can be built from 10mm microbore copper tube, merely by cutting four loops out of the coil of tube that comes wrapped in plastic in a shop and soldering them to two pieces of 15mm copper tube or stiff copper strip - no bending required!

Triple Magnetic Loop Array vs. Low Half Sloper - WSPR Test

Ken Franklin, G3JKF, is a good man.  Good, because he is an experienced, skilled and and diligent person who has developed his triple magnetic loop array carefully, over many years. 

It is almost a fashion amongst many operators to dismiss magnetic loops as 'useless dummy loads'.  Whilst it may be a fashion, it is absolutely and certainly wrong. 

Firstly, regular readers may recall my tests in early 2017, of a single loop against many full-sized wire antennas across the UK.  The outcome blew any notion that a magnetic loop is necessarily worse than a full wire antenna out of the water.

Over the past few days, I was again in contact with Ken by e-mail.  We decided to run a 1W WSPR test of his triple loop array, which would fit in just about any UK garden, against my very low 80m sloper, which is fed against a 6m-high tower with a 3-element LFA Yagi on top.  The tower is relatively low by most operator's standards, because it is already on top of a 15m-high ridge, 100m above sea level.  This low additional tower height, for my Yagi, permits high levels of extremely low-angle gain afforded by the terrain to be exploited.  But that is another story!

Remember that I have already said my sloper is very low.  It was only put up to get some signal on 80m because it was convenient, and the band is not really of much interest to me.  If you have a 30m-high tower, then a half sloper against that is likely to be a very much better performer.  So this is not a 'slopers are useless' sort of article.

Well, the results speak for themselves!  A small loop array (details available freely here, and images here (all protected by copyright)), beats the absolute socks off my wire sloper. 

Whilst my wire gets reasonably good comparative distances, its signal strength is poor - down by a whopping 14.6dB overall - as this distribution plot of simultaneously-received spots across all distances shows:

The only saving grace for my poor sloper comes from considering relative received signal strengths beyond about 1200km, where the difference falls to a somewhat less embarrassing 7.4dB in favour of the loop:

Here's how the map of spots works out: 

Clearly, my antenna was failing entirely to reach the US, whilst the loop was managing to make it across the pond.  A couple of spots, such as from EA8 and UA3, showed a 2 and 4dB difference, respectively, but again in favour of the loop.  The consolation offered by them is slight, to say the least!


Even with lots of additional radials and careful attention to my sloper, I doubt I could get much more than a couple of extra dB out of it.  The height is simply too low.

The real message is this: loops work.  Loop arrays work even better.  Loops are very small in relation to operating wavelength.  They are far less prone to high winds, notwithstanding Ken's occasional experiences with broken timbers, as we all have from time to time!  Loops will fit in most UK gardens, which are typically very small.  Even better, small loops are unlikely to feature prominently in the list of priorities or concerns for planning officers and, in most cases, likely to avoid any planning problems at all.

Kids and Ham Radio

Yesterday was a bit of a boring sort of Sunday.  The kind where it's cold outside, the kids have nothing to do, and TV is just not worth watching.

My daughter - who passed her foundation licence at the age of 11 - had a friend around to make the day pass a bit quicker.

After some cake and playing, I thought I would play the eccentric dad and get both girls to say a quick 'hello' on the radio.  Even with a licence, talking to retired men on the radio is not high on the list of girls' things to do at that age (or at any age, given the lack of women in radio).

I tried a very popular and energetic station in New York first.  Asking whether he'd mind just saying a quick few words to the kids, the operator just said 'er, yeah, thanks for the 59 (which I hadn't given him), 73'.  Eh?  I mean, New Yorkers aren't exactly known for their reluctance to talk!

Then I tried a rather less earnest Italian station.  He did say "hello!", but when the kids said "hello!" back, he just didn't bother any further and called "QRZ?"  It wasn't as though, with a 59+10 signal and perfect English, he couldn't hear or understand us.

 

This is all terribly sad.  I mean, what is it with people (men) when they can't be bothered to make a little moment for two kids - a moment they might enjoy or be encouraged by?  The kids were genuinely interested and excited, even if they didn't want to talk for 30 minutes about the latest amplifier. With such a reluctant and, frankly, dismissive response from the community, it's easy to see why kids don't feel radio is for them.

I'm not the first one to note this kind of behaviour towards youngsters on air.  It's featured a few times within the covers of RadCom, which generated a flood of condemnation, empathy and, I was glad to see, an acceptance by many that operators needed to be much more embracing of such contacts. 

I have met some fascinating, accomplished and very friendly people on air who have gone out of their way to embrace and encourage kids.

A shining example, I must say, is VK5PAS -  a very well-known and active operator who, nevertheless, and more than once, sent some cuddly toys and photos from Australia.  I think the grumpy old men have long forgotten the joy and wonder of receiving a surprise package from far away.

Many years ago (during the wonderful era of the TS50S), VK5PAS made my kids very happy.  What a shame others can't even try.

Another one I remember well is E51JD, who sent the kids a rare, mis-struck and withdrawn from circulation South Cook Islands coin.

But people like Paul and Jim often seem to be in the minority, and far too many are hiding behind their microphones, being grumpy and too ignorant to even try and encourage kids.

RadCom - December 2017 Edition

Ah!  It's near that time of month again when most people run out of money and RadCom drops through their letterbox.

This month's is the advertising-spectacular, Christmas 2017 edition.  The cover is a strange sort of blurred-out snowflakes falling image.  You could say it's like trying to listen to HF radio - the signal is there, but masked by the RFI.

Regular readers will know that I have a love-hate relationship with the RSGB.  I'd love to get behind it, but I hate the way it goes about things.

Happy Christmas 2017!  Bah!  Humbug!

I was glad to see EMC/RFI issues - and there are now a lot of those - get some prominence and depth in this month's edition.  The EMC committee chairman is clearly doing a lot of work, but perhaps is inundated by the sheer number of EMC problems and those complaining about them.

The rest of RadCom is the usual mix of stuff that we all like to read about.

Sure, none of us want a magazine that is just full of doom and gloom.  But, equally, we don't really want a magazine that perpetually paints amateur radio as something that we can all enjoy without much difficulty.

Tell that to one operator who I looked up last night after hearing him on WSPR:

'What a shock to find the HF spectrum so full of garbage from SMPS, PLT network adapters, Low energy (high qrm) light bulbs, VDSL QRM from the telephone wires, plasma tv sets etc etc etc. What an appalling mess !!! I am even picking up one of the neighbours music collection all over the HF bands with a very distorted unstable wideband FM type signal, what's that all about ?'

I read these kind of accounts without ever looking for them - they are commonplace and they fill me with sadness.

Sadness, because it tells of a time when HF communications is either seriously impaired or made essentially impossible for the current, let alone future generations.

RFI?  What RFI?  It's lovely down here!  Image:Fwaaldijk/Wikicommons.

Sadness, because the RSGB is not putting EMC at the very top of its agenda.  It tries to influence OFCOM, which is a bit like trying to kick a dead donkey.  It doesn't seem to try to lobby parliamentarians, which is where the hard work needs to go in.

Does it matter that RadCom and the RSGB seem like ostriches, ploughing their heads into the sand?

Well, about 30-odd years ago, I was a fairly keen fly fisherman.  The local club was active and lively.  On an warm summer's evening, you might find it difficult to find a spot to fish from, even across a fairly large lake.

Today, that lake is empty of fishermen.  The club, you see, was run by old men, many with plenty of money and only winning a fishing contest on their minds.  The company that owned the lake was more interested in reducing legal liabilities by getting rid of fishermen and visitors.  Accordingly, and failing to see the changes to the world around them, the old men did nothing to encourage youngsters and newcomers, and the hobby died on its feet - at least at that lake.  Sound familiar and transposable to ham radio?  I should say so.

I might sound very negative during these more political posts.  In fact, I am very positive by nature.  The negativity comes from the sheer frustration of seeing 20,000-odd people simply pay their subscription, so they can have magazine every month, with very few demanding the RSGB change its approach to leading the hobby.

Low Dipole Test

It's long been evident from my QTH that the nature of the terrain and electrical characteristics of the ground provide outstanding radio performance with the most basic of antennas.

Terrain modelling with ARRL's HFTA supports this practical experience.  Interestingly, HFTA predicts that, for very low angles, the gain available to a low horizontal dipole (HFTA cannot compute vertical radiation) is really quite remarkable.  Here's the output for the low dipole (red) at 3m, and then the same antenna at 10m (blue):

Earlier in the week, I was re-reading the late Les Moxon's excellent 'HF Antennas for All Locations'.  Unlike today's internet-based bluster, Moxon was an intelligent and experienced professional radio engineer who carefully considered objective evidence.  More importantly, Moxon strongly tended to ask humble questions and put forward suggestions, rather than assert any radio matter was ever fully worked-out for good.

In the book, Moxon discusses his 25mW (presumably CW) QSOs with VK during long path time from a hillside, and his expectation that spectacular possibilities exist from such locations.  Most people would already consider a 25mW QSO with VK to be spectacular!

Since Moxon's time, things have moved on.  Notably, WSPR now permits entirely objective, human bias-free assessments of antennas and their environments. No more 'S' point signal guessing!

I decided to build a simple 14MHz dipole and test it out, hanging at just 3m, using WSPRlite at 200mW. Its orientation (long dimension), was N-S, so the figure-eight gain pattern was E-W.

The results from the low dipole are really quite encouraging, and confirm that the QTH is superb for radio.  KK1D was reporting -26dB for my signal.  Under very tough geomagnetic conditions, only a couple of other UK stations were making the same trip, and even those that were received reports of -23dB from an input of 5W.  If my mental maths is right, that's roughly a 9dBdifference in real-terms signal performance.

I only have one WSPRlite, so a further comparison of the low dipole with my vertical delta loop had to make use of an old-fashioned, home-brewed attenuator, with a calibrated output (using an oscilloscope) for 200mW.

Now, most texts will tell you that a vertical, apex-up delta loop has low average height that, so they claim, makes it a rather poor performer.  According to most texts I have, this puts the average height of the loop at about the same, 3m height of the low dipole used in the foregoing tests.

So the results, taking into account the different patterns of the antennas, should be the same, right?

Wrong!

Here's the plot of stations hearing MW1CFN - the low dipole, against MW6PYS - the vertical delta loop with apex at about 8m, base at about 1.8m:

It's immediately clear that the low dipole is not doing very well at all in comparison to the delta loop - or at least not where the departure angles at this time of day are in question.  Only one US station heard the low dipole, and at a very much (7db) weaker strength.  The difference is clear in the distribution of signal strengths for both antennas:

The arithmetic mean (dipole 4.77dB worse than the vertical loop) is not really the best measure for this situation; I would suggest the true difference is closer to -3dB for the low dipole, representing half the signal strength (remembering that this is only valid for the stations that actually heard the dipole - for longer haul DX, the dipole simply wasn't heard at all). This is clear from a line plot of distances:

But before we write off the low dipole altogether, let's have a look at how it was doing in comparison to other, known top-performing WSPR stations in the UK.  First, a GI station running a very efficient doublet:

Now the low dipole looks pretty good - almost on a par with the top-performing GI dipole.  The result was even better when compared with a G8 station operating a large horizontal loop, known also to be a top-performing WSPR station in the UK:

So the vertical delta loop is clearly a much better performer than the low dipole at the same location, despite most texts suggesting the two have the same effective height above local ground.  Most texts will also claim the omnidirectional pattern of the vertical loop will give it the same or less gain than the dipole.

There is a possibility - and this will have to be another experiment later on - that the very low angles were not responsible for propagation to the US at the time I ran the dipole test.  As you can see from the HFTA plot, the low dipole only has superb performance at very low angles.   When the weather is less windy and cold, and the Sun quieter, I will run the dipole over a few days, to see if there is a period where HFTA's predictions come true.

Les Moxon tends, in his book, to dismiss verticals on hillsides as 'useless' because, he claimed, the image of the vertical was ineffectively leaning back into the hillside, rather than adding to the real antenna's signal.  But there are hills that you are half way up (as Moxon seems to have been ) and hills where you are on top.  If one is on a ridge, as I am, the local ground is flat, with an immediate steep drop off in all or most directions.  The image then is available to reinforce the real antenna's output.  I think Moxon missed this point entirely.

But the real take-home message is not which antenna is best, but which location.  A clear, undeveloped hilltop location overlooking the sea, and with highly mineralised local ground conditions is the real winner in this experiment.

Missed Es

Quite amazing radar returns from mesospheric height  today.

But for the presence of a very disturbed geomagnetic field, today would probably have been a very productive day on the higher bands.  Ah well!

OFCOM - More Evidence of Not Giving a Damn

The Southgate Amateur Radio Club reports (below) on an intereting aspect of UK communications enforcement, or the lack of it.


All in all, this is just more evidence that OFCOM is merely an issuer of free licences to us, and has no real interest in amateur radio issues.


'Ofcom and Ham Radio repeater abuse

A Freedom of Information (FoI) request was used to ask Ofcom what action they take against Amateur Radio Repeater Abusers

The response revealed Ofcom has never prosecuted any repeater abusers since it was created in December 2003.

When asked how many Field Enforcement Officers they had and how the figure had changed since 2003 Ofcom said "This information is not held".

It would also appear Ofcom don't have a clue how much money they are spending on Amateur Radio.

Read Ofcom's responses to the seven questions they were asked at
https://www.whatdotheyknow.com/request/foi_ham_radio#incoming-1063811

In 2017 Ofcom did send two engineers from the Spectrum Management Centre in Baldock, Hertfordshire, to Londonderry in Northern Ireland to investigate a doorbell which was interfering with other Licence Exempt devices
http://www.southgatearc.org/news/2017/august/ofcom-when-ding-dongs-go-wrong.htm
' 

G2 Geomagnetic Storm!

Last night saw some fairly strong geomagnetic disturbances, with a fairly prolonged period at Kp ~7.  Sadly, strong moonlight masked the visibility of any moderate auroral glows from north Wales.

Storm!  A G2 event on 07 and 08 November 2017.  Image: NOAA/SWPC.

Once again, propagation effects were enhanced due to the geomagnetic disturbance.  14MHz is now, on the approach to the depths of winter,  dying off daily in the mid-late evening. Not so last night!

Nighttime at 14MHz right now usually means no propagation.  A G2 storm changes all that!

Propagation continued to pretty good DX distances, including Argentina, Brazil and South Africa.  Interestingly, the comparison station (red) also running 1W into what I think is a doublet, failed to experience any of the enhancements overnight.  This probably indicates very low angle DX arrival/departure angles that are inaccessible due to antenna and/or environmental characteristics, and perhaps also some (negative) directionality for the dipole that is absent for my vertical delta loop.

Great DX during the period 21:30-09:30UT, thanks to the Sun's tantrum!

Now it's time to see what effect last night's activity had on the upper bands!

Is Ham Radio Just Trainspotting?

I've just come off the HF radio, after a brief spell of FT8 and, I'm happy to report, some much more gentlemanly, slow JT9 work.

Despite FT8's benefit of a rapid-turnaround QSO, I just can't help but feel that the mode - and amateur radio in general - is far too much like trainspotting, where the object is merely to 'get' as many numbers as possible. There is no reward at all between CQ and 73.  No human voice, no subtle hints of CW skill.  Just a machine communicating with a machine.  That is no hobby at all.

Ooh!  How exciting!  Well, for some, maybe...  Image: Wikimedia Commons/Swisstack

That only fellow trainspotters ever get excited about numbers in logbooks is testament as to why it is so very difficult to attract newcomers to hobbies that put gathering numbers as the very purpose of their existence.

Contests are a regular matter of complaint and protest, even from operators themselves.  Personally, I'd rather throw myself into a freezing cold lake than sit there for two solid days, calling out 'CQ Contest'.

I also get rather irritated by the many who take amateur radio far too seriously.  It finds its extreme expression in those operators, who often seem to be split into the most macho fraction of US and former Soviet-bloc countries, that love to pose for magazines, wearing boom mic headsets and 38 rigs and 12 amplifiers in the background.

Well, given boom mic headsets sold to radio operators cost about twice as much as the exact-same model sold to pilots, I fail to see what there is to show off about - other than stupidity.

So, good luck to those with 500,000 QSOs in the latest DX contest.  Congratulations on your ranking in the world QSO-gathering tables.  Just remember that, in the end, it's all utterly futile.  

WSJT-X Update Failure

WSJT-X is a great piece of software that I've been using for FT8 for some months now.

Whilst it's good, the RC03 candidate release, which was effectively a beta-testing version, has it's bugs.  Sometimes it won't stop transmitting when the TX cycle is terminated close to the time markers, which permits the TX signal to appear on one's own waterfall.

So I decided to update to the latest, apparently full release that seems to have undergone minor bug corrections.

Under Windows 10, this update proved a dismal failure.  I was confronted with a screen that had no bands from which to select.  The QRG window worked and was reading the rig, but it stayed adamantly red, trying to say the QRG was out of range for the mode in use (which it wasn't).

All very annoying!

Thankfully, and much to its credit, Windows 10 valiantly went through a commanded restore process, and my old version of WSJT-X reappeared without further incident.

So, if you have a piece of software that is working 99% properly, my advice is to stick with it!