Half Sloper Success!

A few years ago, I was pretty active on 40m, using a simple end-fed multiband wire (Hawaii Emergency Radio Club) up a 10m fishing pole.  It certainly worked, and brought in plenty of DX.

The problem for an extremely windy site like mine is that keeping a wire up at 10m is pretty difficult - and impossible during the severe winter gales that reach in excess of 70mph, sometimes a lot more.

One thing that does take the battering is my modest, ex-lighting tower that props up my 12m LFA Yagi.  So it seems to make sense to use it as much as possible.

Having become a little irritated that I have done practically no 40m work recently, I mused over a half sloper.

So, out came the 40m dipole, and up a ladder I went to fix it as a half sloper - one end sloping down to the bottom of one corner of our garden, and the other just dangling down to the ground as a counterpoise.

Analysis with the SARK-110 showed that this wasn't a disastrous set-up - the SWR was about 1:2.8 which, at 40m isn't a big deal in terms of coax losses - 10W out still yields about 9W out, even at that SWR.  Here's the screen grab of the 'dangling-down' sloper:

A pretty good impedance, and the SWR isn't too bad at 40m.

The ARRL texts say that the SWR does tend to be quite high with a half-sloper, so the SARK confirms this for my set-up.

But wait!  I tried to extend the counterpoise, of which there were a couple of metres spooled on the ground, to see if the SWR would change.  It did - but in the wrong direction; it now sat at 1:3!  This was also the case, rather oddly, when I connected to ground via a copper rod.

Here was a clue: the SWR dropped again as I brought the counterpoise closer to the tower, which suggested some inductive effect was at play.

Simple!  Just a 1/4 wire at the operating frequency, and a short direct connection to the tower.  Drawing by K4EFW. 

So, up the ladder again with a short piece of wire in hand, and off came the dangling-down half of the 'dipole', to be replaced with a direct connection to the tower metal itself.

One wire off to the left, down to a 1.5m fence post, and the coax braid connected to the tower itself.

Now, the electrical continuity of a sectional, extendable tower can be dubious, so I connected to the topmost section, which is bonded to my Yagi, giving a pretty large lump of metal to act as a top counterpoise.  I used a stainless Jubilee (hose) clamp and some conductive grease (Innovantennas) to ensure a good connection and protection from our corrosive coastal atmosphere.

The result was really surprising, and way beyond my expectations, as the SARK reveals:

Direct bonding to the tower = good job!

I still can't quite believe that just bonding to the tower brings such a great match!  It could be improved upon, but for the moment, there is no real need to do so - it is performing far better than the ARRL texts say should be expected for this arrangement already!

So, with darkness falling, I set the antenna to WSPR.  The earlier, two-wire arrangement was pretty good, in line with most other 40m WSPRers.

But, with the tower-bonding, I was up there as the best, or with the best 40m WSPRers anywhere in the UK or beyond.  If this sounds like wishful thinking, here's this morning's plot of VK5MR's reception over the three hours prior to 08:00UT, taking in the all-important grey-line and long-path period:

You can't corrupt WSPR - the results speak for themselves!

Now, there are an awful lot of WSPR transmitters on 40m, and to be the only one over this important period to be heard in VK is nothing short of remarkable.  Further WSPR tests later on have confirmed the outstanding performance, and I'm very happy with it. 

A quick test with my simple RF meter showed that the field was very strong in the vertical plane, much better than the modest field measured in a diagonal plane with the earlier, two-wire arrangement.

So, accepting that the elevated position and outstanding ground conditions are vital factors, it does show that the half-sloper can be a world-class antenna!

One might wonder how this can be.  Curious, I modelled my terrain out towards North America, using a horizontal dipole as the reference, because HFTA doesn't handle verticals or slopers.

Looking at my results compared to an operator with a horizontal dipole just half a mile - but down hill from me - shows some interesting features.  First, let's look at a dipole at 6m, at 7MHz at my QTH:

Horizontal dipole at 6m (blue), terrain out to USA/NA, compared with a 10m dipole down the hill from me (red)

That already looks good, especially at low angles, and is streets ahead of the dipole at the bottom of the hill.

Now look what happens when the dipole is lowered to just 4m at my QTH:

Modelled dipole at 4m (blue), again compared to the dipole down the hill (red).

Lowering the dipole to 4m, which we can loosely accept for the sake of argument as an analogue to the average height of my sloper (not taking the vertical radiation into account), you can see the gain increases by well over 2dBi, yielding a total gain of nearly 7dBi - which occurs at a spectacularly low 1.5 degrees above the horizon.

This, together with the strong vertical component, explains why this antenna, simple and low though it is, is in fact ideally mounted for my terrain. 

Oh, and measurements on soil up here has recently showed a dielectric constant at low frequency to be - wait for it - 3500 within the copper mine proper, dropping to 885 at the QTH.  That is, also, pretty amazing.  A future blog post will focus on this soil work.

Delta Loop Balun

These past days, I've been trying to get to the bottom of just what value balun my 20m delta loop needs for the best match possible.

My bread-and-butter antenna: a vertical 20m loop, used almost exclusively as a monobander.

This has been a long-running investigation, lasting years with on and off experiments.  But now, with the SARK-110 analyser, life is a lot more enlightened, and progress much quicker.

Like most people, I've been using a 4:1 balun with both my 20m and 17m vertical delta loops (fed with 300 Ohm twin) for many years.  Both can be used at relatively low SWR without antenna matching unit (AMU), but in general, a small amount of tweaking by the AMU makes things tidier.

In other words, these antennas were not in any way 'way off' or being forced to work outside of their natural limits.  WSPR tests showed the efficiency of the antennas was very good, often outlasting other EU stations across the Atlantic on 20m by up to an hour.

The SARK-110 analyser is a real revelation when applied to your antenna systems.

I decided to try a 2:1 (Balun Designs model), which I happened to have lying around from the days when I was too scared to build my own, on the 17m delta.  This brought it to a reasonably sharp and very good match at or near the band.  As a result, I've now kept the 2:1 in place, using a minor amount of adjustment from the AMU, which is principally necessary due to the proximity of telephone and domestic voltage electricity lines across a far corner of our garden.

Moving onto the 20m delta, the main focus of this post, things were quite different.  This was also fed with 300 Ohm twin and a 4:1 current balun for many years, bringing very good performance without issue, and is located much further away from environmental metal.

This is how the SARK-110 saw my 20m delta, about 15m of 300 Ohm twin and a homebrew 4:1 current balun:

My 20m delta at the end of 300 Ohm twin and a 4:1 current balun.

You can clearly see that the SARK proves there was not an awful lot wrong with this arrangement, the impedance and SWR being within acceptable limits.  This is, after all, an antenna that has worked the world many times over for five years or more.

But that impedance interested me.  It was too low for my liking, and surely, the SWR would improve if the impedance could be brought closer to 50 Ohms.

In particular, when you consider that a high imaginary component to the impedance means that a fair amount of energy is being contained in the antenna's near field, rather than radiated into the far field, then this is something worth addressing.

So, the next question to answer was: what does the antenna and 300 Ohm wire look like when connected to the SARK without a balun?  This is the question that you simply can't answer without an analyser, and which makes them essential to a rational approach to understanding antennas:

Here's the result:
 

 20m delta, 300 Ohm twin, no balun.

So, the impedance is up at about 245 Ohms, which results in a SWR of about 5.4.  Now I could see that to get a better match, I needed to divide 245 by some value to get 50 Ohms.  This directs what kind of balun value we need and, obviously, the answer is division by 6 -  a 6:1.

After a lot of online searching, which included searching in Italian, rather than English - yielding different search results - I eventually found a comprehensible schematic for a 6:1 voltage balun.  This transforms 245 down to about 40 Ohms, which is not bad.  Here is how it looks:

Fairly easy to construct 6:1 balun.  The right most lead to the output is a tap on the fifth-but-last turn of one of the trifiliar turns. You scratch the insulation off the top of the wire, and solder carefully, making sure the joint is not dry or weak. Tinning each wire before joining is often the best way.

With wind and rain forecast (again!), I quickly set off outside to disconnect the 4:1 and make some new eyelets to fit the chunky new 6mm outlets of my 6:1.  Somehow, it always ends-up being dark and windy when I work on antennas!

This is the system in place:

Here is how the SARK now sees the new arrangement, fully connected-up, and at the end of a couple of weeks of dry weather, where the ground was beginning to turn from moist to dry:

A 6:1 balun brings near-perfection at an impedance of nearly 50 Ohms real and very little imaginary, meaning pretty much all of the supplied power is radiated.  The SWR is pleasantly low across the 20m band.

And the following day, during a spell of rain, here is how the same antenna system changes:

6:1 attached to the delta, in the rain.

Rain, as one might expect, brings a slight shift in system characteristics.  In this case, the system works rather nicely, in that the best match frequency oscillates within the 20m band, according to the weather.

But the overall result is that the impedance of the system has been brought under very good control, lying around the 50 Ohm mark.

So I now seem to have achieved the best possible match for my 20m delta, where there is little further prospect - or indeed any need - for improvements.  What I do need to do is build a current, rather than a voltage 6:1, now the simpler voltage unit has proven the concept.

UPDATE:

Having now received a fine 6:1 current balun from Geoff Brown, 'G-Whip', the system continues to function as expected, although Geoff's balun yields a slightly higher resonant point than with my voltage 6:1, so I'm sticking with my own unit for now.  After adding about 50cm of wire to the base of the delta, which was known to be slightly short, the antenna is now singing right in the middle of, and shows a very good SWR across, the whole 20m band.  Here's how things now stand:

You can't get better than this with a wire antenna across a pretty wide band!

Other than explaining the slight difference between the current and voltage baluns, this really does now signify the end of my years-long work to reach perfection with my delta loop.  If only I'd bought an antenna analyser all those years ago!

Remember that your environment is probably very different from mine, and you may of course be using coax, not twin.  Your twin may also be a different length, and terminate at a different impedance.  So a 6:1 may need to be replaced with a 4:1, or even a 2:1.  If you have a go at making some baluns, which are not difficult if you can find a schematic online, then you can try different values without spending much money.

Remember, also, that with twin wire feed, you can multiband the antenna quite readily and, unlike with coax, with extremely low losses, even at high SWR.  My efforts above are simply because I use the delta for its fundamental frequency of 14MHz and the first harmonic of 28MHz, where the match is equally good.

Are Bandplans Fit for Purpose?

Bandplans mean different things to different people.  Because they are not legally-binding on operators, they are not a directive on where and how to operate on the bands, but are intended to "aid operating".

In that sense, bandplans are a good idea, if we all want to limit the amount of interference from different powers, modes and activities.

Coming from an aviation communications background into amateur radio, I have to be frank and say the standard of operating on the hams bands is extraordinarily poor.  It is little better - if at all - than the CB radio of the 1980s.  You'd think going to the trouble of studying for an exam or set of exams would make things better.  But it doesn't seem to.

Contests are one of my biggest source of concern.  The competitive, macho nature of this activity is of course worthwhile, but brings problems.  The need to gather points and win brings with it a 'couldn't care less' approach to stamping on other transmissions, notably the weak signal modes.

True, the weak signal modes have come along quite recently, and have had to pick frequencies which might suit them best.  Like any other mode, they do not have priority.  But, in keeping with any nation's operating terms, no operator has a right to stamp on ongoing transmissions, either.  The FCC have recently made this point very clear through a series of high-profile, high-consequence court cases, issuing severe penalties of the order of $20,000 for persistent stamping.

Last night, the VK9CK team were busy stamping on on-going WSPR signals, which exist permanently at 14.095.60.  WSPR isn't that new, and as a vital probe of propagation conditions, as well as informing antenna performance tests, there is no justifiable reason why they ought to have been operating highly-intrusive RTTY there.  The herds of people desperate to bag the DX, of course, only made the already bad QRM infinitely worse.

I have to say I was quite irritated by the VK9CK team.  They ought to have known better.  I left a question on the cluster to prompt them to consider whether stamping on other transmissions already underway was a breach of their licence terms?  In all honesty, the only rational answer is: yes, it was a breach.

In fairness to the VK9CK team, by design or accident, they had moved away from the WSPR frequency a few minutes later.

But the VK9CK team are not alone.  Most weekends see a contest, and an ensuing, two-day long interruption of WSPR.  Some will claim that WSPR has to compete for its place within the band.  But that is not true when WSPR is already established and transmitting on a frequency, and the single RTTY operator decides to obliterate the transmissions of perhaps several hundred WSPR operators anyway.  It is even more true when WSPR occupies a spot frequency, with a pretty wide band where other modes can operate without causing problems.

Rather oddly, whilst the RTTY operators will claim that there's nothing wrong with operating down at or very near to WSPR, the same operators don't have the guts to transmit their mode in the SSB portion of the bands - even though that is also perfectly legal, if not in keeping with the bandplan.  It seems to me, therefore, that WSPR is ranked by some as 'unimportant' or less worthwhile than SSB, and so can be stamped upon with impunity.

In practice, I suspect the real reason why RTTY operators don't transmit on the SSB portion is because they will soon end-up with lots of people shouting at them.  WSPR operating is just too gentle and unobtrusive to bring that consequence - though my patience is wearing thin!

The real problem for WSPR is that it hasn't reached any prominence within national societies and IARU, because those bodies seem often to be heavily or even solely preoccupied with contests.  The RSGB suggested to me that the whole WSPR world QSY when QRM occurs - which only underlines their total ignorance about the mode.  IARU only accept concerns from national societies.  So that means the UK won't be getting anywhere with it!

WSPR must now be seen for what it is, and protected as a beacon mode.  Legal arguments aside as to whether it strictly meets the definition of a beacon mode, the principle is clear: alongside true beacons, it is the only objective means we have of assessing propagation and antenna performance.  Unlike true beacons, WSPR is, crucially, accessible to all operators at no charge, and without complexity.

If you are concerned about the care-free way in which operators simply stamp on WSPR transmissions because they are too careless or stupid to realise they are breaching their licence terms in doing so, then please consider making a careful representation to your national society.  It's about time they all did something to defend modes, and not just contests!

E-QSL, and other matters.

Time is relative, as Einstein famously quipped.

But, faced with 196 E-Qsl confirmations to process this morning, time is, I find, running very slowly!  It took me about 1 hour, 20 minutes to check and confirm them all, some of which dated back to January 2012.

I keep thinking that I have to forget E-QSL, but can never really bring myself to not confirm someone on the other end, who might be really keen to receive it.  But I have started updating LoTW daily now, in some sort of preparation for ditching E-QSL in due course.

One useful feature of E-QSL, though, is that you can see the details of an entry made by someone else.  This has allowed me to fill in the odd gaps in my log where I was distracted and didn't enter the time, or the callsign, or the report. 

On the other hand, there are quite a few people who try their luck on E-QSL.  I've had a number of people who've heard me, but I never had a QSO with them.  This often happens on 12m, where a very good antenna set-up means I can sometimes be the only one heard in the US, for example. 

Try as they might, I never confirm a QSO unless a two-way report has been put in the log at the time, or that it was obvious that there was a two-way QSO in place but couldn't entirely complete due to QRM on JT modes, for example.  It's important to be fussy, but not pedantic.

Another irritating aspect of digital modes is the automatic uploading of QSOs to E-QSL.  I've had a few stations issue about three QSLs for the same QSO - a new one issued for each time a response was issued during a standard JT contact.  This is really very silly, and wastes a lot of time if, like me, you're a fairly active operator.

So that's today's moan over with.  Here's something positive, if you like certificates (I collect them only as an incidental aspect of confirming QSOs).  100 countries on the WARC bands:

2m Slim Jim Update

It's some years now since I first put together my copper tube Slim Jim for 2m FM working.  If you are consulting this blog to find the right dimensions, this site is reliable - except the feedpoint may well be at a different position, which you will find by trial-and-error.

The Slim Jim antenna, made for pocket money, has proved to be a very good performer indeed. Contacts over distances in excess of 90 miles are fairly common with just 20W, and out to beyond 180 miles when conditions are slightly enhanced.

Recently, not satisfied with a temporary-that-became-permanent, too low mounting position for some radiating directions, I transferred the Slim Jim to a loftier height on the roof.  This has led to considerable improvement in longer-range working.

Many of us have one of these generic, cheap SWR meters.  They are accurate, if used with some thought.

My VHF SWR meter, which is one of those cheap-and-cheerful, but apparently accurate types from China, reported a good match.  Yet, the power out was about 5W lower than my new Yaesu FM rig ought to be putting out.  Leaving the meter on the low range whilst sending about 10W out also permitted the reflected needle to climb to ~2:1.

Something was clearly out somewhere.

So, armed with my trusty SARK-110 and some very calm, clear conditions at night, I climbed the ladder to pull ol' Slim down, and see what was going on.

The refurbished Slim Jim, sitting high - and with a low SWR.

I stripped the self-amalgamating and PVC tape wraps off the feed points, and un-soldered them from the antenna.  Using pipe/Jubilee clips, I sought to find the resonant point with the antenna on a temporary pipe clip mount on a shed.

Having found a perfect match at 1.1:1, I re-soldered everything and wrapped up with tape - only to find that the SARK now reported 3:1 SWR!  After a second or two of WTF? I realised there must be something amiss at the cable.

I'd left short tails on the antenna that were meant to 'take the heat' from soldering, avoiding damaging the feedline cable.  These connected via spade connectors.  One of them had either a dry joint or had broken somehow.

I also found that the gap I had on my Slim Jim was too big.  I followed some online design which was in agreement with others in terms of length.  But the gap was about 4 inches, whereas it needs to be an inch, perhaps slightly less.

The way I adjust for minor inaccuracies like this is to solder a bare copper wire that's thick enough to be dimensionally stable, yet bendable by hand.  Craft wire is often ideal for this.  Wrap the joint in self-amalgamating and PVC tape to keep water out, and then just bring an 'L'-shaped arm down to a point where the SWR lowers to perfection.

A wider-than-ideal gap is adjusted simply by a stiff, bare copper wire, soldered to the top pipe.

The SARK finally reported a 1.09:1 SWR at 146MHz, and an impedance around 53 +j4.9Ohms.  The Chinese analogue SWR meter now also agreed, showing the correct rated power outputs when keyed. It's a remarkably broadband antenna, yielding well below 1.5:1 SWR over a span greater than 6MHz!

Near-perfect matching across the band.

Another 30 minute task that took 3 hours, but with a productive outcome.

Delta Loop Matching

As I've often written, my proper DX career on radio began one, wet Christmas week morning, when I decided my long wire really wasn't good enough any more.

I recycled the LW into a 15m delta loop, and never looked back.

I have three delta loops now, having moved away from the usual desire at the beginning of operating that one antenna must do the whole damned lot!

Now, if you connect-up a delta, using twin wire and a 4:1 balun, then a delta will match-up on several bands.  However, its radiation pattern gets progressively higher as you move up the bands, and it really isn't much of a performer above its cut band.  This, of course, does not equate to not being able to make QSOs.  Far from it.

The problem with the 4:1 arrangement on a monoband delta, though, is that the impedance doesn't work out properly.  You can spend many a happy hour looking at various opinions about what a delta loop's natural impedance is, and a figure of anything between 100 and 200 Ohms is often bandied around.

Now, for a very long time, I had to rely on software models and implied impedance by simply 'feeling' how the antenna was matching at the ATU.  Although the SWR can be brought down from something like 2:1 to a perfect match very readily, it's clear that the matching is a bit odd, in that there is little change in SWR from one end of the band to the other.  In other words, it's got impedance issues!

Just remember, though, as we move on in this post, that the delta loops in their present configuration of twin-feed wire and 4:1 current or voltage baluns, have worked entirely satisfactorily for several years, have never generated any RFI or other problems, and have brought in a couple of hundred DX entities.  They have only needed a very slight tweak by my simple external ATU to bring a perfect match, and only then for higher power use.

So, if you have a delta in this configuration and don't want to change that which is already working fine: don't!

But, for those seeking a bit more natural antenna performance, and newly armed with my trusty SARK-110 analyser, I set to work to examine just what is going on with the delta system I have.

I looked at the less-used 17m delta first, to avoid hassles with my mainstay, 20m delta for the time being.  If the 17m worked out OK, I could then apply the insights gained to the 20m loop.

Here's how the SARK saw the 17m delta when connected up to the 4:1 voltage balun:

17m delta loop attached to a 4:1 voltage balun.

That SWR is fairly high, at about 2.5-ish across the whole 17m band.  There is no sign of a resonant dip, and my intuition that the impedance was off is dramatically shown to be correct!  At the lower end of 17m the impedance is about 25-ish Ohms, with a fair bit of imaginary component.

So this impedance result shows the delta loop doesn't have an impedance of 200 Ohms, but nearer 100 Ohms - the 4:1 is reducing 100 Ohms to 25 Ohms, resulting in the ca. 2:1 SWR.

Modelling using MMANA-GAL yields an impedance for the delta of about 130-160 Ohms, and this appears to be reasonably correct.

Now, having switched out the 4:1 and switched in a 2:1 balun, which ought to cut somewhere around 100 Ohms to something near 50 Ohms. This is how the SARK reports:

17m delta on a 2:1 voltage balun.

This now looks more like the expected curve to resonance!  The impedance is floating around the 50 Ohms mark, and the SWR curve dips beautifully to a perfect match - albeit in need of some minor shortening on the basis of this curve.

Once shortened both curves should look almost perfect.  That will have to wait for a sunnier, drier and less windy day!

Just remember that a 4:1 balun remains your best option if you want to multiband your delta loop, because it will generally allow you to match-up the antenna across more bands.

Update 1.

I tried the 2:1 balun on my 20m loop.  This didn't work!  The SWR climbed to 3:1 or so. The answer to this problem is addressed in a new post, which you can find here.

Spring is Here!

If you are a frequent operator of radio, you'll soon become linked to the subtle, but constant changes in propagation that mark the advance of Earth in its orbit - and our seasons.

Over the past week or so, as we see the start of meteorological spring, the upper HF bands have seen a renewal in activity. 

On most days, there is a 30 minute period on 12m where Japan comes through very strongly.   Stations in India, China and far eastern Russia have also featured prominently, as have a couple of stations in VK-land.

Last night, on firing-up using WSPR, I found a strange 'flattening' effect on the 14MHz map in where my signal was being received - essentially along a line of about 45 degrees latitude and not above it.  The WSPR traces were also beginning to spread out, indicating a strong geomagnetic disturbance.  On opening the front door, I was welcomed by a sky alive with aurora to high elevations, with prominent streamers. 

Time to reconnect the 2-ele 6m quad, quickly!  If you want to build one, which has an ideal, wide azimuthal pattern for auroral working (and is great for Es and meteor work, too), you can find instructions here.  For a lasting antenna (mine puts up with severe gales to hurricane force during our winters), use fibreglass spreaders attached to metal brackets, not timber, because timber rots quite quickly.

This simple 2-ele quad has given me some magical moments on 6m over the years. 

Because the weather wasn't clear everywhere in the UK, and that it takes time for other operators to realise it's worth trying 6m out of the summer Es season, a minor engagement with self-spotting on the cluster is required to attract attention.  Even when word gets out, there are only ever a handful of aurora operators in the UK, and even fewer will be in view of a given display and so able to make use of it.

After a couple of calls on 50.150MHz, I was delighted to hear Martin, GM8IEM, in the far northwest of Scotland coming back to me.  Nice and stable, there was relatively little garbling by the dynamic aurora, allowing a pretty easy QSO at roughly 57 both ways.

Last night's aurora, permitting some interesting radio!

Sadly, nobody else came on 6m, partly explained by the passing of the most active auroral period, though it remained strong at lower elevations throughout the night.

I then switched to 12m, pointing my 3-ele LFA due north, to find quite strong signals coming from an LA4 station, chasing after some DX in the Pacific over the north Pole.  The second sound file records that there was also an EA8 station coming in, very stable, via an auroral backscatter path.  The sheer stability of the EA8 signal probably indicates auroral E, rather than direct aurora backscatter.

No matter how jaded one becomes through years of radio working, working aurora always fires up the spirits, thinking that radio - already an almost miraculous phenomenon - is letting you talk to someone through bouncing your signal off the northern lights.  That really is quite magical.

SARK 110 Antenna Analyser

After years of not knowing much other than SWR and implied impedance values for my antennas, I've finally opted for purchasing an antenna analyser!

I thought long and hard about which unit to choose; there are now quite a few on the market.

The three that made it to my shortlist were:

(1) The widely reported as very accurate, Array Solutions units, enjoying excellent Eham reports.
(2) The SARK-110, also reported as very accurate and with excellent Eham reports.
(3) One of the RigExpert units, which are in widespread use, also enjoying good Eham reviews.

The Array Solutions units are the reference standard by which the ARRL tests in QST are compared.  So there is no doubt at all that these are top-of-the-range units, comparable to industrial analysers costing an awful lot more.

Two reasons went against the Array Solutions units: cost and the need to have a computer running alongside.  This latter aspect can be overcome with a laptop, but it's not ideal for me.

The RigExpert units are very fine, very well thought-out analysers with a long and good reputation.  A review in the latest QST magazine showed the 'Zoom' unit, the latest offering, to be accurate and reliable.  However, it is quite expensive, and some have commented that the features offered, whilst more colourful on a new screen, are not that different from earlier, cheaper models like the AA-30 and AA-54.

The SARK-110 is very small - but extremely capable.

Because one is often out in the cold and good-sized buttons built onto a battle-ready case such as enjoyed by the RigExperts are essential, I was very close indeed to selecting an AA-54. 

In the end, I opted for the diminutive SARK-110.  With its tiny dimensions and buttons, this has all the wrong features for me!  Except that a QST review recently found it to return values almost identical to the Array Solutions reference unit.  That, and the fact very many people - myself included - have found the maker to be very responsive to requests and questions.  The firmware is regularly updated for free to accommodate not only bug fixes, but entirely new features as well.

Given that one can subtract the feedlines from the SARK-110 calculations and end-up with a virtual feed point measurement, the ability to use it inside, where it's warm and clean, means its unsuitability to extreme outdoor use isn't such a drawback.

UPDATE.

The SARK duly arrived at a local delivery point yesterday afternoon.  The package is very small, so if you've spent money on this that your XYL preferred you hadn't, you can blandly pretend it's 'just a cheap SWR meter' inside the package!

I found myself thinking that the SARK is so small that I really ought to have stuck with the RigExpert models.  But that feeling was washed clean away when I switched it on and saw firstly how intuitive it is to use - I've yet to resort to reading the manual - and secondly, how cleanly everything is displayed.

The frequency sweeps are very quick - maybe 2 seconds or so, so there's no hanging around, waiting for readings to be taken.  Even the multiple HF sweeps are just as fast.  The sweep can either be run continuously or as a 'single shot'.  The continuous mode is very useful for watching in real-time as any changes are made.

The main question people will have before buying a SARK is: just what connector does it come with?  I've read a lot about the SARK, including a very recent QST review where the supplied connector was an MCX (on the body of the SARK) to BNC female type.  This meant that, for that review, adapters (BNC male to SMA female) were bought, albeit cheaply, to allow the SMA male calibration loads to be fitted.

The calibration loads you need are: an Amphenol SMA shorting cap, part number 523-132331 and an Amphenol SMA 50 Ohm termination cap, part number 523-132360.  In the UK, from DigiKey, these tiny bits of metal and plastic will set you back an astonishing £25 or so.

You'll be glad to know that my production model came with an MCX to SMA female connector, with about 30cm of cable in between, which means the expensive calibration loads fit directly, making life much simpler.

The supplied SARK-to-outside world connector is currently an MCX to SMA female.  You need an SMA male to SO239 or N-type connector for HF/VHF analysis.

The calibration process is directed with simple 'connect this, connect that' on-screen instructions, which takes just two minutes or so.  A comparison of factory calibration with my subsequent calibration shows this system works perfectly, with no evident anomalies.  Do remember to keep your caps in the original, labelled bags, or lightly etch a label onto their tops, so that you don't confuse which is which - they both look identical!

Don't worry, as some have done, about the longevity of the MCX connector onto the SARK.  True, the rated lifetime is about 500 connect/disconnect cycles.  But you simply keep the MCX to SMA adapter permanently connected, and add a SMA male to SO239 or N or whatever.   This really is no problem at all!

A photo of the SARK's screen (not a screen grab), showing the very clear layout.  The results are for my 14MHz vertical delta loop, with a tiny tweak from my ATU.

The SARK connects up to your PC easily; I found there were no driver headaches when installing onto a standard, elderly Windows 7 machine.  The drivers were found from online sources, automatically.

After a few hours' use, I have to say I'm really, really glad I bought the SARK.  I think the protective case might be a wise use of money, as it might be prone to knocks and bumps owing to its size.  Data from measurements transfers across easily as CSV files, opened without fuss into any standard database program.  Bitmap images can also easily be grabbed by the SARK.

One thing that strikes me about the whole concept of analysers is that, especially for beginners, they can provide far too much information.  There is nothing wrong with - and was the only way possible for decades for the vast majority of hams - cutting a wire to the correct length and, through just a little pruning, getting a good match at the rig.  This is how I made my delta loop, and it's worked without fuss, both with and without a matching unit, across the world.

There's little point being over-fussy about small antenna imperfections.  This shows my 12m LFA Yagi's driven loop could do with a very minor lengthening.  But with the SWR below 1.3:1 for the sections of the band I use, I won't be rushing to make changes - especially as I'm often the only one heard on 12m in the US.

The danger is that a beginner might cut a wire, fire-up an analyser, and start obsessing over getting a perfect SWR and a perfect impedance.  Just about all of us have antennas that are a little way off perfection, often due to environmental effects of surrounding cables, tin sheds and cars, and we live with it - with an ATU if it's that much out.  There is leeway in antenna construction, and I hope some perfectionist types don't spend weeks banging their heads against brick walls because they just can't get that last bit of imperfection eliminated.

The dramatically-sharp tuning of my magnetic loop antenna (homebrew), at the 60m WSPR frequency.

I love this plot.  Just a simple elevated vertical, two elevated radials.  Or, three wires up a fishing pole!  That match is just beautiful for data modes, especially knowing the simplicity of the antenna - and also that it's pretty close to other antennas!

If you think I'm being defeatist about small antenna imperfections, have a look at the specification of some really expensive commercial antennas.  Quite a few can only claim an SWR "below 1.5".  It's worth reflecting on that.

My score for the SARK?  10 out of 10.  Absolutely brilliant piece of kit.

WSPR - More and More Questions.

Last night was the second 14MHz WSPR run, looking specifically at the propagation around the time of 'setting' of the sunlit F2 layer locally.

Bang on time, and with a couple of minutes' delay from the previous evening (superficially consistent with lengthening daylight), all US stations,all east or mid-southern states, took a dive in signal strength, promptly vanishing altogether at around 22:36UT.

That was the expected situation.  So far, so good.

Then the complications began.  After a few minutes, I started hearing - and was sometimes heard by - a station way, way out west in Alaska - AL7Q.  A couple of other west-coast stations were then heard - VA7UBC and N6RCD.  A station in the extreme west of Montana, right on the border with Washington state - WK0I - also was heard, and was also hearing me.  This is not the first time I've noted something special about WK0I.  There were only two EU stations also 'seeing' the same thing. and indeed the only ones in connection with the US at all from the EU.  One an ON station, the other a LA station, in the far north of Norway.

Whilst the rest of the US was silent both ways, these three, and one in Alaska, just kept going, long after the theory of propagation indicates it should have stopped.  The magnetic pole is a suspect...

 
Rather bizarrely, there was a short period earlier in the evening but after the disappearance of the F2 layer, where three, tightly clustered stations in or very near to Dallas, Texas, were the only ones hearing me.  These were K5XL, KE7A, and KD6RF.   I have absolutely no explanation why that was, especially when one considers, at a visual guess, that there were maybe 60 or more US-based WSPR stations active at the time, and with a good geographical spread across the country.

This bizarre, tight cluster were the only US stations hearing me for one, post-F2 layer period.

I suspect the late evening development of a path between me and the west-coast US had something to do with the magnetic field, given the northerly latitudes and proximity to the pole of all stations involved.  That said, whilst the LA station is in a special magnetic location, I'm not especially so, nor was the ON station.

Auoral conditions were quiet, with a very small increase in activity but still at very low levels.  I remembered something about paths tangential to the auroral oval, and something called the mid-latitude trough (of low ionisation), and one or both of these might have some importance for last night's path out west.

I need to read a lot more, but that often leads to more questions - and a realisation that nobody, really and truly, fully understands propagation under more esoteric situations.


As we move into spring and summer, this kind of exercise won't be possible much longer on 14MHz, so I'll keep going on this for a while, and later in the year.

If you've any insight, please leave a comment!  After a few nights of more activity, I can see that this strange reception of signals from out west is not a regular occurrence, with the whole of the US shutting down entirely on a typical night as the sunlit F2 drops below the horizon.