Starfish Suborbital Nuclear Tests, 1962.

I recently came across the very interesting, if not highly disturbing, history of suborbital nuclear bomb tests, mostly conducted in the 1960s.  I had never really heard of them before.

I started my learning with a long but highly interesting scientific paper, which is available free of charge, covering the EMP aspects of nuclear bombs, and also the modification of the Van Allen belts by VLF transmissions.

Here's a 2-minute video of some of the tests:

And here's an hour-long video of declassified material:

Early signs of a grand minimum?

Interesting article:

https://watchers.news/2017/12/20/solar-activity-cycle-falls-to-the-bottom-1-5-years-earlier-than-expected/

WSPR: More Environmental Evidence Emerges

A long time ago, I wrote about (forgive the dead image links!) my experience, during only one QSO, of a comparison between my vertical delta loop and another operator's 3-element SteppIR in south Wales.

I didn't expect many to take much notice of that little exercise and indeed, as expected, one person was sufficiently aggrieved to comment on it being of no consequence.

Since then, things have moved on significantly.  WSPR provides a wholly human-free means of testing antennas (unless you're one of the very few who transmit more power than advertised!).  WSPRlite then came along and gave us accurate (within about +/- 11%) QRP outputs, with most choosing to transmit 200mW.

Last night, I received an email from an operator about 37 miles from me, living within 1 mile of the Irish Sea.  Like me, he has a fairly quick drop-off to the coast, although that land is, unlike mine, densely developed, albeit mostly with fairly low domestic buildings.  He wanted to know a bit more about WSPR SNR reports.  I gladly assisted.

Unlike me, though, the operator in question has a very fine multiband 2-element quad at 12m up.  Interestingly, he was comparing his antenna with another station fairly close by, running a three-element Yagi.  Both directional antennas were beaming the US at about 315 degrees.

Now, my antenna for 14MHz is and always has been a vertical delta loop, with a perfect match through a 6:1 balun. A lot of people, especially Americans, claim the antenna is 'only' a simple wire and is 'too low' to be very effective, and 'certainly' can't match a multi-element beam.

This certainty probably makes them feel good.  But they are very wrong.  They are ignoring, above all, the environment from which the antenna works.  Ground conditions given by an old copper mine, a clear, elevated and undeveloped horizon in all directions, and the sea being about 1.5 miles way at closest, all add together to give great performance.

Now I had the details of the quad in use at GW0ADC, I could see how well my delta could do.  The time of day and propagation conditions meant that almost all signals being received were from the US (largely eliminating any performance 'boosts' that may otherwise come from the omnidirectional nature of my antenna).

Firstly, here's the HFTA terrain plot for both GW0ADC (blue) and myself (red).  The terrain is measured on a digitised Ordnance Survey map, and then manually entered into HFTA:

Here's the plot of overall distances achieved by both over a part of the day:

Not bad, eh?

How about simultaneous spots and reported SNR?  Surely, my delta must do really badly?

Can you see that difference at the bottom left?  A 0.28dB difference - i.e. essentially no difference at all - between my single element (plus its ground image) vertical delta loop and a full-blown 2-element quad at 12m height.  No human bias involved!

To be fair, these spots include the very few that were coming in from the EU, away from the beaming direction for the quad.  If we eliminate these by limiting the spots to those from beyond 3400km, the quad does better, beating my omnidirectional delta by 2dB.  That's a small improvement in SNR given the complexity and expense of a 2-ele quad on a tower over a simple fishing pole vertical delta wire!  At about 4000km, the difference was only about 1.5dB, but it increased to the same 2dB beyond about 5000km.

 

The comparison with the 3-element Yagi was even better.  First, the terrain plot, blue being GW3TMP, red being me:

Next, the system gain figures (again, blue is GW3TMP, red is mine):

And finally, the resultant simultaneous spot strengths for spots beyond 3400km (again, to eliminate all 'off-beam' spots, limiting them to only those from the US): 

Simultaneous spots for GW3TMP (3-ele Yagi) and MW1CFN (vertical delta loop), limited to US-only spots.

The poorer terrain for GW3TMP's Yagi yields a nearly 4dB advantage for my delta loop, even though it's omnidirectional.  This example clearly shows the importance of very low angle take-offs.  So much for the old addage that a vertical antenna simply 'radiates equally poorly in all directions'!

So, what's that I'm saying?  That a single element vertical delta loop can be almost as good as a 2-element quad at 12m high, and better than a 3-element Yagi also at 12m up?  Yes!

Am I crazy?  No!  The results speak for themselves.  The reason why my delta is nearly matching or beating the performance of much 'manlier' antennas is that the environment is better, at least in that beam direction. 

If you are still shaking your head and tutting, let's return to the computed system gains (i.e. antenna plus ground), for the 2-ele quad at 12m and a dipole (HFTA can't compute vertical antennas) at 6m (the equivalent mean height for my vertical delta loop, which may be a valid comparator antenna):

System gains at two different locations.  2-ele quad (blue), vs vertical delta loop (red)

Now my claims are supported by HFTA evidence.  The crucial area is the very low angle region.  Here, the total system gain (i.e. antenna plus ground gain), despite the very different antenna types, is only 1dB different.  Obviously, there is a very much bigger difference for higher angles, but those are normally less important for longer DX.  The story is the same with the Yagi comparison.

Unfortunately, because of HFTA's limitations in relation to not computing vertical antennas, we can't be sure this is the whole story.  But the logic - and results - seem to hold up pretty well using a horizontal dipole at equivalent effective height. 

The quad's pattern looks like this model from MMANA-GAL modelling software.  Notice how, at 1 degree elevation, the gain is minus 8.5dBi, though the sloping ground at GW0ADC may tip this pattern over clockwise, to the right slightly. 

Yagi elevation pattern.

My delta looks a bit more like the plot below, partly due to sloping ground, and partly due to high conductivity ground.  The pattern has been confirmed with an RF meter here, where peak gain is at, or even very slightly below the horizontal.  Notice that the peak gain at the horizon is plus 7.4dBi:

Vertical delta loop pattern is more like that for perfect ground at this QTH.

And as a last piece of evidence that the environment is indeed better at my location (red) than at GW0ADC (blue), here are two modelled dipoles, both at 12m at each location, with a focus on the 300-315 degree beam heading. In fact, this shows a very slightly better low angle gain at GW0ADC, which may again suggest the US stations receiving us at the time were coming in at angles of about 3 degrees, or above:

Theoretical dipoles at 12m at each location.  Red is my QTH, blue is GW0ADC.

The story is, again, the same (and more marked) for theoretical dipoles at GW3TMP - the Yagi QTH (blue) - versus my QTH (red).  For The Yagi, though, the bit of high ground at about 10,000 feet distance has a significant impact on system gain; except for a small blip, it stays below mine until the mid-twenties degrees, where it is of little DX use.

So the WSPR results first showed something amazing was happening with a simple antenna.  Then the outcome is supported by terrain modelling.  Anybody continuing to argue that there is 'no way' this can be true is simply falling victim to the thing I have strenuously removed from all my work: human bias and prejudice.  I do keep repeating it, but Les Moxon certainly didn't fail to recognise the importance of antenna environment, and he was no idiot.  His colleague, G2JKF, once told me that Moxon always sought a hillside location when moving home.

Presumably, if the quad and Yagi could be moved here, they would beat my delta at that point.  In fact, running the HFTA model again shows the quad would have about 2.5dB more total gain if located here.  Not that a huge multiband 2-ele quad would survive our terrible winds, anyway.

So there we go.  Yet more objective evidence that the environment is really very important to antenna performance.  It doesn't feature very much, if ever, in antenna articles I read.  But it very much should.  Indeed, the failure to discuss antenna environment might be the last remaining human bias in antenna testing, because very few authors have such a good environment, and may never have had the chance to evaluate a better one - or even realise they exist.  Worse, they may be wilfully ignoring the environment because they can't change their lot!

Vector Processor

My friend Ken Franklin, G3JKF, has been in contact with me over the past few days, concerning:

"...a Brochure and User Manual on a system I developed in the late 1970's. I attach a brochure copy. The system was designed to allow control over the front-to-back ratio of Yagi antennas. It would be very useful for reduction of on-frequency RFI for Yagi or any other antenna, and is relevant to our Solar Power discussion. I remember vividly some tests I conducted with G6RC when he lived only 2 miles from my QTH in Crawley. We both had Vector Processors. On 10m with strong echoing type propagation we rotated beams back to back. We were able to virtually eliminate the direct ground wave signal and communicate over the very long path around the world. I wish I had audio recorded the results. Fascinating stuff!

The Vector Processor information should be in the public domain. It has probably been overtaken by more modern designs but the content of the Manual is still interesting and relevant. If you consider it worthwhile perhaps you could place it somewhere accessible to others."

Accordingly, here's the information received thus far.  Whilst they are reproduced here, they remain fully the sole copyright of Ken Franklin, G3JKF:

Should self spotting be banned?

This week, after some difficulties with DXMaps, I switched to DX Heat for my occasional cluster service.

DX Heat is very good, not least because spots appear immediately and reliably, unlike some others.

The only trouble is, DX Heat won't allow the occasional self-spot.

No announcing yourself!  Image: Wikicommons/Sn1Per.

But why would I want to self spot?  Isn't it cheating? 

Other than breaching the relatively few strict and legally-enforceable licence conditions, there is little one can do as an operator that amounts to something that is, in law, wrong.

So these traditions, such as not self spotting, are merely that - ways of doing things that have come to be accepted by the majority as 'not the done thing'. 

The only thing that is meant to be 'wrong', as of tradition, is that you should not announce to others, by means other than radio, that you are present on air.

Having established that self spotting is not a legal wrong, and that it relates only to not announcing your own presence by non-radio means, let's look at a few other situations relevant to amateur radio where we could use the same logic as is used to frown at self spotting, but that leads to no sense at all.

(1) A scheduled contact - a 'sked'.  This has been a feature of amateur radio since its very inception.  Marconi used a sked to test whether radio could travel across the Atlantic in 1901. By its very nature, a sked is usually arranged by a method other than radio alone.  E-mail, letters, word-of-mouth, prior knowledge and telephones have all featured as means of facilitating a QSO, by making known to others when you will be active on air by means other than radio, so avoiding wasting time, waiting for a chance contact.

This would be 'wrong', according to the logic of prohibiting self spotting.

(2) Announcing in the amateur radio press or web sites that there will be a DXpedition to some far-flung place.  This alerts others to their presence by a means other than radio.

This would be 'wrong', according to the logic of prohibiting self spotting.

(3) You send a spot of hearing or having a QSO with someone else to the online cluster.  This announces to others of the station's presence (including your own, which is often used as a back-door method of self spotting) to others, and via a means other than radio.

This would be 'wrong', according to the logic of prohibiting self spotting.

(4)  You publish your grid square/WAB square/IOTA/ITU region etc. on your QRZ.com page, which is making these details known by a means other than radio.  Correctly receiving these details by radio is usually a fairly strict requirement for award and contest claims (and most digital modes send them out at CQ by default).  Yet, they are published as standard by just about every operator that uses the internet.  Who hasn't been in the situation where you heard the station's callsign clearly, and even had a good QSO, but forgot to request the grid and then looked it up online?  Is that cheating?  According to the rules, yes.  According to common sense and people reasonably using information available to them, no.

On the less active or just-about-opening bands, there is, by definition, little activity.  People will gladly flock there if someone sends a report that the band is open, or a spot of a station heard calling, or even having made a QSO.

So, rather than calling into the void, waiting for the herd mentality to kick-in, it's often a good idea to send a self spot.  That way, it's more like a sked, where people know you are calling (announcing by some method other than radio), and listen in to make a proper, legitimate QSO using only radio and without having to sit around all day, just in case.

I humbly suggest that those who seek to prohibit self spotting ask themselves: how does it really differ from any of the four points identified above? Is it not actually simply a case of old traditions having failed to keep up with developments over the post-internet years, now some 30 years in age?

Analysing my baluns - and an opening to VK on 12m!

Last week, I was reminded by a radio friend about the existence of SARKPlots - the PC-based software that takes input from the fantastic SARK-110 anatenna analyser.

Somehow, I had completely forgotten that SARKPlots was available, so immediately set about looking at my 4:1 baluns - one commercial, the other home brewed - with the analyser.

The first test was of my G-Whip 4:1 voltage balun into a 200 Ohm load.  It's spent several years outside, but is made of high-quality materials and fully potted.  Here's the output:

Commercial 4:1 balun by G-Whip (made ca. 2012)

Certainly, there's nothing much to worry about there, although the impedance transformation to 50 Ohms is, surprisingly, more imperfect than one might expect, more especially towards the higher end of HF.  It ranges from about 56 + 4j Ohms to over 60 Ohms.

Now I tested my 4:1 current balun, which has also spent much the same amount of time outdoors, and also uses high quality components, including marine-grade stainless steel for the contacts (it is very wet and salty here, by the sea!):

Home brew 4:1 current balun, made ca. 2013.

I have to say I'm rather pleased with my own creation!  It has a very good impedance transformation (about 53  and less than -1 j Ohms, and resultant low SWR.  The small dip near 18MHz is beyond my ability to explain, but it is very small, and is a change in the better direction to 48 - 0.6 j Ohms.

So that was baluns tested.

Next, a bit of real operating!

This morning, the propagation forecasts, which I never take seriously, didn't look too good to Europe, let alone anywhere else.

So, I left the radio running in the background.  Sure enough, at 09:31UT, I heard a pretty stable -12dB S/N FT8 mode signal from VK2EW.  After a couple of weaker CQs from him, I ventured to respond.

I was heard the first time, but at a pretty weak -22dB S/N (remember these S/N numbers are relative to an unrealistic, 2500Hz bandwidth, where FT8 only occupies 47Hz).

Unfortunately, the only direction I am rather blind to very low angle signals is in the short path to VK, where I run at a tangent and slightly into the copper mine hill to the NE, and then into another hill about 2km away.  HFTA modelling (blue line (red is to the central US, and much, much better)) clearly shows the low ground gain available at 066 beam heading.

Terrain profile to VK short path (066 degrees)

Ground gain VK short path (blue).  Red is to central USA.

Overall, taking antenna gain (+8.5dBi) and ground gain at the expected low arrival angles into account, I was putting out just over 400W ERP from an approximate input of 60W to generate that weak received signal at a well-equipped station in VK.

Oddly, I've never tried to work VK on long path, and I don't even know if long path is applicable at 24MHz, though it certainly is at 21MHz.

It must be worth pointing the antenna to the south west one morning, to see if anything can be done on the long path.  The ground-plus-antenna gain figures rise, depending on propagation angle, to anything between 500W and 4.1kW ERP!  Sadly, HFTA doesn't compute for the important angles down to and very slightly below the horizontal (elevated QTH).

Terrain profile, VK long path (220 degrees)

Ground gain, VK long path.

Whilst I was busy doing other things, a couple more VK stations called at about -15dB S/N.  They will have to wait for another day.  Not bad for 12m at this point of the solar cycle!

Geminids revealed by RADAR

I missed most of the 6m Geminids meteor scatter period yesterday.

However, I was interested to see quite extensive, moderately strong returns from the middle atmosphere this morning, as shown by the MST radar at Aberystwyth, Wales:

On HF, Es-type QSB and occasionally very strong, short-skip signals were evident at 12m.

EURAO FT8 QSO party - a mess!

This week saw an e-mail come through from EURAO, which is pitching itself as a new pan-European representative body for amateur radio.

The message announced an FT8 QSO party this weekend (16-17/12/17) to promote EURAO, which seems like a perfectly good idea.

Unfortunately, things quickly started to unravel when EURAO realised a lot of its announcement made absolutely no sense at all.

Oh dear!

In what appeared to be a 'copy and paste' failure, EURAO advised operators that this wasn't a competition, and that we could talk about anything we liked on air.

For those who are not familiar with FT8 - which seems to include EURAO - FT8 is not a ragchew mode and, due to its sheer speed, is only suited to standardised CQ, report and 73 messages.  It's also impossible to even call CQ in the way prescribed, because, whilst you can type the message in full on-screen, on transmitting there is no room left in the protocol to send it in full, let alone that plus the callsign.  It actually comes out as 'CQ EURAO PART'!

This is how the wording went (accessed 13:42 12/12/2017):

'Call: "CQ EURAO Party".
Exchange: because this is a QSO event, not a contest, you can talk about whatever you want, in any language, and for as long as you like. Here are some topic suggestions to get the conversation going: name, city, locator, weather, antennas, rigs, etc. callsign, locator and signal report, the only data that FT8 allows to exchange.
Also talk about QSL interchange. Tell the truth. Say "no, thanks" if you are not interested in QSL cards. But if you would like to have a memory of your contact, feel free to use our EuroBureauQSL.'

So, a big set of mistakes that leaves EURAO looking like a big, fat lemon.

Update, after the EURAO QSO Party weekend: 

I didn't see a single station calling the prescribed CQ call.

The Year in Amateur Radio, 2017.

Here we are again, folks.  Silent Keys excepted, we have managed to make another orbit around the Sun.

2017 has proved to be a surprising year on radio.  Whilst the higher bands proved to be rather dead earlier in the year, from about July onwards, things picked up remarkably, at least up to 12m.

12m - as we might not expect to find it at this point in the solar cycle!

Indeed, the autumn of 2017 has seen the kind of activity levels on 12m that one used to see a couple of years ago, closer to sunspot maximum.  Even SSB across to the US featured on the band from time to time, and 10m showed occasional flurries of digital activity, too.

2017 saw the storming debut of FT8, a digital mode I described as 'like being on drugs' (I should imagine!)  Fast, efficient, and fairly sensitive, it has seen JT65 and JT9 swept aside as irrelevant for large parts of the radio community.  But some are fighting back!  I'm one of them, finding FT8 great for some situations, but just too fast, tiring and mindless for longer-term operating.

Another thing that stormed was the atmosphere!  Spectacularly deep depressions blasted my poor antennas, perhaps indicative of a warming ocean.  In February, just when we thought the worst was over, storm Doris threw 85-90mph winds at us for several hours.  Somehow, everything survived, although I lost a slate to the roof and some lead flashing was bent over.

 

Ophelia slipped, but didn't damage, my 12m Yagi, here luffed over during the 85+mph winds.

During the autumn, ex-hurricane Ophelia brought similar, perhaps worse conditions for very many, long hours.  My Yagi slipped and spun 90 degrees on its stub mast, forcing the tower to be luffed over (during 75mph gusts!) for the first time ever.  No damage was sustained.  Few will forget the smell of Portuguese wildfire smoke in the warm air, and the spectacularly red, midday sun.


2017 also saw the very rapid uptake of WSPRlite, the tiny transmitter that has taken all human bias and wishful thinking out of antenna and propagation testing.  Perhaps the best £60 I have spent in a while.  It remains to be seen whether the rapid deployment of transmit-only devices poses a problem for the wider WSPR community.  After all, if we are all just transmitting, and not listening, WSPR becomes useless.  Towards the end of the year, WSPRlite Flexi appeared, opening up bands up to 6m for this pseudo-beacon mode.

Game changer - and possible disrupter?

April saw my daughter pass her Foundation Licence.  Great thanks are, in all fairness, due to the Dragon Amateur Radio Club in north Wales and John Pritchard, MW0JWP especially, for his ability to encourage a youngster.  I can't say my daughter is yet an enthusiastic operator, but she is mightily proud of her qualification, and does clearly have the seeds of an interest for the future.

MW6PYS - licenced to operate, including on this local, 70cm repeater.

2017 was also the year my antenna tower and Yagi (and a few attached wires), for which I made no application for planning consent, became immune from planning enforcement and, therefore, lawful.  This was quite an achievement, because one of our neighbours is a malicious, sociopathic sort who never stops trying (but never succeeds) to cause damage to my family through puerile and sometimes very unpleasant acts.  As well as failing, at the age of 70, to realise he should do something useful and kind with the remaining few years of his hopeless life,  he's utterly failed to get planning to 'do something' about my tower and antennas, placed right under his nose.  What an idiot!

Summer, 2013. Four years later, my tower and Yagi are lawful structures.

And what of 2018 to come?  Well, magnetic loop antennas continue to fascinate and provide endless ways to experiment.  One idea that I hope I can realise is to create a very wide diameter, aluminium loop array (at least three loops) covering down to 60m and, possibly, 80m.  Aluminium is much cheaper and lighter than copper, and is available off the shelf in diameters up to several inches.  I am also wondering about metal sheet loops.


If you were hoping for a review of the year's DX and DXpeditions, sorry - I don't do that sort of thing!

Happy Christmas!

Echolink on GB3AR Repeater

The Arfon Repeater Group's GB3AR repeater is located in an enviable position on the foothills of Snowdonia that dominates the Irish Sea coast.

Some Irish Sea region repeaters, including GB3AR.

 
Despite this, the repeater has seen almost no activity, which has taken a further dive over the past two years, as some of the ex-CB brigade drop dead.

GB3AR-R.  Image: Arfon Repeater Group

So it was a pleasant surprise, a few weeks ago, to find Echolink had been connected to GB3AR.  Whilst this has not seen a dramatic increase in traffic, one does come across the occasional curious Echolink operator connecting up and calling 'CQ'.  This seems to have prompted a few more local operators to work the repeater, too.

UPDATE: The Echolink facility has recently vanished!

I don't think the precise way in which we make a QSO is very important.  It's having the QSO that's important.  A significant benefit of Echolink is that it permits a QSB and RFI-free ragchew to take place between, for example, as last evening, North Wales and the eastern seaboard US.

So I am rather glad that traffic has been improved, if only slightly, by the adoption of relatively new techniques.  The Echolink app or PC software is free, and there is no need to 'choose this system or that system', as afflict those of us wondering about digital 2m modes.

Oh well!  DOD photo by U.S. Navy Petty Officer 2nd Class Dominique A. Pineiro

At the end of the QSO with the US last evening, I had a good chuckle as the operator signed off with a dry 'apologies for our President, and 73!'

Quite.

Breaking news: DXplorer to be free!

A report of correspondence this week between SOTABeams and a UK radio operator alleges that Premium features of DXplorer, the WSPR analysis webware, is to be made available without an annual fee for those who own a WSPRlite.

The report suggests that the £20 annual subscription after the first, free year's access following purchase of a WSPRlite transmitter, has now vanished.

This seems to be confirmed by looking at SOTABeams' website this morning (11/12/2017), where the following text appears:

" Use of DXplorer.net is free for any WSPR user but WSPRlite users access Premium facilities including detailed antenna comparisons. "

EURAO Meets IARU: Latest

After a year of rather difficult relations between IARU Region 1 and EURAO, it seems things are beginning to thaw, albeit very slowly.

EURAO and IARU have just made a joint announcement about future cooperation, which can be read here.

Unfortunately, the joint statement is very much worthy of a Brexit-style negotiation.  Very little is given away, and the words about working together are as vague and general as could be imagined.

I think EURAO, which claims to be trying to modernise and energise ham radio representation, must be careful how it proceeds.  I accept it's not easy, and established committees are notoriously difficult to change.

But change must happen.  Tens of thousands of operators are, to put it bluntly, about to go to their graves, with nobody to replace them.  The age profile increases every year, in lock-step with the increasing age of members.  RFI is making shortwave radio, if not impossible, then highly unattractive to most people in the developed world now.  Who is representing us in challenging and improving matters?  For me, it feels like staring into an empty space.

At the moment, whilst nobody wants to see a fight develop, EURAO might appear in danger of being dragged into the kind of obscure, British way of doing things that, frankly, leaves most hams utterly ignorant of what it is IARU R1 actually does for them.

As previously reported on this blog, a request for general information to IARU (global) HQ in the US yielded absolutely no response whatsoever.  That is not the kind of accountability and representation that will work in today's world.

Social media is a case in point.  EURAO has a reasonably regularly updated page, although it does often seem to lack direction, leaving the outsider wondering what it is the organisation is trying to do.  And I say that as a strong supporter.

But EURAO are doing much better than IARU R1, which has not, at the time of writing this, posted a single thing since January 24, 2017, and not very much activity took place before then.

Both EURAO and IARU R1 might wish to reflect on a phenomenon that entirely changed the face of democratic representation during the last, June 2017 UK general election. 

Labour undertook a hugely energetic social media campaign that reached - and persuaded - millions of voters, especially younger voters.  The Conservatives, meanwhile, operated a very much weaker campaign.  As a result, the Conservatives saw their already weak majority fall to no overall majority, forcing a link-up with the DUP - a link up which many find distasteful.

So, let's see EURAO be a bit clearer about what it intends to do - and how.  As for IARU, well, they have already had years and years to show us why we should support them.  In my opinion, they have failed dismally.  I hope that, in response to a challenger organisation, EURAO doesn't simply get bogged-down in the same, white, middle class, old man mentality that has bedevilled ham radio in the UK for decades.

Images from the Space Station!

This week, the International Space Station is broadcasting (something that we Earthbound operators are prohibited from doing) slow scan amateur radio TV images celebrating various Russian achievements. 

Here she comes!  Image: NASA.

Even mobile phone and tablet-obsessed kids are fascinated by signals from orbit, so I set the little Yaesu FM rig on 145.800MHz early last evening, which uses a simple homebrew SlimJim antenna on the roof.

I used a simple tablet computer running Robot36 freeware (there are many others available), and just picking up the sound without a wired connection.  So long as the software picks up the initial SSTV header signal, it will save the images received automatically.

At the time of the transmissions, the ISS was using PD120 mode (now turn down the volume on your PC!):


The SlimJim has an extremely good low angle performance, which was very evident during a high-elevation pass by the ISS last evening.  The signal faded strongly for a few seconds from the ISS as it passed near the overhead point.  At a later, horizon-hugging pass, the signal was very strong and steady for the whole pass.  A soft Russian female voice was also overlaid on the SSTV signal, though I couldn't make out what the message was.


Even though we know that it's easy to work near earth orbit radio, it's still amazing to me that the signal from the ISS is so incredibly strong with such simple equipment.

Simple, but effective.

The screen captures from my tablet went straight to my daughter's social media account.  It attracted quite a few likes and questions, which just goes to show the power of something new and different in bringing kids on board our great hobby.

Should you pay £850 for a magnetic loop?

Have you seen the MLA-T and similar series magnetic loops?  They offer a good, portable solution to multi-band operation, sitting nicely on a table whilst you work the world.

But the price! The MLA-T is currently (December 2017) selling for about £850!

OK, it comes with a stepper motor but, so far as I can see, the tuning is not automated beyond a couple of warning LEDs.  In other words, you only get a multi-turn loop, a capacitor and a stepper motor for manual tuning for your money.  Some say the manual tuning is difficult, others say it's quite simple.  Being very high-Q antennas, magloops always need a steady hand and tiny steps to tune manually (a vacuum capacitor usually makes it somewhat easier).

Now, the MLA-T gets good build quality reviews, and WIMO doesn't make any wild claim that this antenna is meant to match or beat full-sized antennas.

But let's consider, for a moment, the facts about all magloops, based on my own extensive and careful builds and testing.

First, any magloop is definitely a compromise antenna.  You can pick and choose what, exactly, is being compromised, but the usual criterion is: physical size.  Where more than 50% of the world's population live in cities, any smallish antenna that offers reasonable performance from indoors or a small outdoor space is clearly something of great value.

But it's doubtful anyone would choose a magloop as a first choice if they had a large field and no neighbour or local authority problems to deploy a large wire antenna.

Second, the materials used to make something of the size of a MLA-T antenna (not allowing for the remote tuning), are very cheap.

Let's say you build a sqaure loop version from 10m (4 x 80cm diameter loops, as in the MLA-T) of 22mm copper tubing.  This would cost, including all the 90-degree elbow fittings, about £60 from any number of outlets.  You could use an air-spaced capacitor, which you can pick up, with a bit of perseverance (they are widely sought-after), for about £10 from online auctions or a junk sale.  A plastic box (if you really need one) and some other sundry bits - maybe some wire for the feed and timber to make a stand, might cost you another £30.

Incidentally, according to Underhill  - and my practical experience - there is no difference in performance between shapes, provided the total perimeter is the same.

So, we're looking at no more than about £100 to build your own DIY version of an MLA-T, but without the remote tuning.  For those adept at modestly advanced electronics, the tuning is also easy and cheap to build.

Even if you buy a good vacuum capacitor, you are still only looking at about £200 total.  That's a long way - less than a quarter of the way, in fact, from £850.

Providing the DIY loop is made carefully, the same laws of physics will apply to both it and the MLA-T (or any other antenna).  It is unlikely, therefore, that there will be any real difference in performance between the two.

Leaving aside the debate about just how well you can get out with a magloop, the real question for anyone thinking of using such an antenna is: do I really need to splash out four times more money to get one than if I built one myself?