Friday, 21 November 2014

TS480 Box for /P

[Standard Health and Safety advice applies - use brain, and wear eye goggles if you feel so dangerous you might damage your eyes!]

My TS480sat became rather redundant after a couple of years of faithful service, largely as a result of frustration with its tendency to drift when used with digital modes.

But the Kenwood is a good rig, and not one to dispose of lightly.  It has remarkably good audio both out to the world and from the internal speaker, which in itself makes it a keeper.

The basic layout for my box design.  The transverse arrangement allows for both good cooling throughput and easy accessory connections.

The problem with the TS480 is that Kenwood seem to have conceived of it mainly as a car-mobile transceiver, so it's a bit cumbersome, to say the least, to use it as a standalone field-portable unit.  If you want to connect digital interfaces, then things become even worse, because the radio body will be so far back that it can't be attached to the carrier.

There are no base screw holes in the supplied TS480 carrier, so I drilled four on each corner (see text for important comment about this!)

So, because I operate from windswept beaches where airborne sand is a real problem, I decided to build a box for the darned thing!  I used lightweight, exterior grade plywood of 1/4 inch thickness for the sides, with 21mm x 21mm timber to secure the panels and add some stiffness.

 The carrier has no base screw holes as standard, so using some standard oil and a sharp metal bit on a slow speed hand drill, I cut four holes.  This is perfect, but there is a problem that becomes apparent later - the screws make the side panels bow out slightly when screwed into the wood, so they no longer properly line-up with the 480's screw holes!  It would thus be better to make the holes at the base of that 'U' section to the right of the image, and either side of that panel mounting, on the left.

To allow for efficient air throughput to cool the 480, and to permit easy connection of other equipment, I placed the body of the radio lengthwise, with hinged doors to both sides, closed simply by magnetic door fixings, which have an ample 4Kg strength.

Do remember to drill a small pilot hole for all your screws, because if you don't, softwood timber will show a strong tendency to split.  

Use flush hinges to make small doors for air circulation and accessory connection.  I put the magnetic latch on the top of the box because it's easier to fit and adjust that way; you can put it inside, for a neater finish.

The power cables of the 480 are quite long and stiff, and tangle into a mess.  So I just tied them up into a bundle, removed the banana plugs and soldered the wire to panel-mount terminals bolted onto the plywood side.  I added a third terminal to permit earthing of the rig.  Now the rig is entirely enclosed, with only the need for two shorter, more manageable cables to the battery.  Remember to use heavy-duty cable of about 25-30A rating for that.

Banana panel terminals attach to the 480's power cable, allowing the cumbersome wires to stay inside the box.

I reused the 480's carry handle by screwing it into the box, which works well.  If I had longer ones, I would have preferred to us bolts, for peace of mind. A lick of exterior varnish is finally applied, to keep it all neat and tidy.

Nearly finished!  The rear, showing the power and earth connection terminals.  Rememeber to fit runners to prevent the connectors being damaged!

All done!  You could also fix an SO239 panel connector for the antennas, for added convenience.

Thursday, 20 November 2014

RadCom - It's Been a While...

Now, this blog is primarily aimed at encouraging amateur radio on a pocket-money budget.

For example, if you look up the 'I-Am' end-loaded vertical antenna I wrote about here some time ago now, you will save yourself about £200 over the commercial version and have significantly lower losses in the feed system. More importantly, you will learn more about antennas, and even be a little less frightened to experiment with non-established designs; there's little to get wrong, if you follow the basics.

So, it's disappointing, to say the least, to find RadCom, as so many other hobby magazines, reviewing equipment within its pages that doesn't so much save money as encourage you to spend more of it.

Turn to the Christmas 2014 edition, page 32.  Here's a review of the 'Whizz Whip' - a simple telescopic whip antenna currently primarily aimed (given its direct male coupling) at the smaller Yaesu mobile transceivers.

Now, there are people who can use most types of equipment, and the 'Whizz Whip' is probably useful in some circumstances.

What I wonder about is whether any situation makes the 'Whizz Whip' a good antenna choice, given that it costs - wait for it - 5p short of £100!  As the review diplomatically asserts, a whip like this needs a counterpoise to reduce RF feedback from the I3 current, and help make the situation more stable altogether.  It doesn't come with one!

Which kind of brings any sensible operator to ask: why not just use a simple homebrew inverted-L, vertical dipole or something like that?  Total cost for one of those can be pennies, maybe a couple of quid if you buy a new SO239 connector (not that you in fact need one of those!)

RadCom repeats the sin, rather, when it moves, at page 61, to review what's ambitiously called a "quarter size" G5RV.  At least this only costs £24.99, giving the maker a pretty low margin all in all.

But, come on!  Why would you buy an antenna like this?  Can't you cut some wire and solder?

Let's imagine you have little space, which is the justification, it seems for the review.  You can build your own twin-fed dipole for maybe £15 if you bought all the stuff, a lot less if you have an established junk box.  You don't have to give it a name - it's not really a G5RV at all, more a doublet.

What really annoyed me about the '1/4 size G5RV' review was its use with 30m - that's 100 feet - of Mini-8 coax.  Whaaaaat?  30 metres?  If you mounted the antenna at 10m, and your garden is meant to be small (the justification for the antenna and review), that gives you 20m of coax to eat up somewhere on the ground, remembering that the height is covered by the twin line!!

I think a realistic assessment ought to have been made with no more than 15-20m of coax.  Of course, the SWR figures would be somewhat worse under that condition, due to coax losses being reduced.  Even then, it's a question as to why you wouldn't simply build a shortish doublet fed only with twin to a 4:1 current balun and a tiny section of coax to make it to the ATU - far lower losses even at very high SWR - and cheaper. At 5m a side (2m longer than the commercial unit), you could work 20m and up efficiently.

Quite why RadCom is reviewing a quadcopter (p68-69) is anyone's guess.  But that guess might be related to the advertising income, given that it featured prominently - read expensively - on the back of last month's RadCom.

And then we come to some stuff about propagation beliefs being wrong.  I tossed the magazine aside when I read that one-way propagation might be down to higher noise at one station over another.  Tsch!..

Wednesday, 5 November 2014

Ampro Mobile Antenna - 12m Variant

The higher HF bands have been wide open during the past couple of months, and activity is very high there.

As regular readers may recall, I sold my G-Whip Pro Mobile antenna during last spring, as it was just a little too much fuss to change bands with it.  Much better, in my view, to have a handful of monoband whips tuned-up and quickly screw in and out as bands dictate.

Mobile whips are much of a muchness, really - there's not an awful lot of latitude for one to be better than the other, being simply helically-wound verticals, the lower HF ones with loading coils, the upper ones without.

The Ampro-12 atop the radio car(!)
I love 12 metres, so opted for an Ampro 12 from Nevada, for £19.95.  Nevada charge a very reasonable standard delivery rate, and their service is very good, fair play.  The antenna arrived essentially next-day.

The Ampro, a very slimline design, has a standard 3/8" male screw fitting, which will see it attach to the vast majority of magmounts without any fuss.  The whip has a stiff lower section, and then a very lively stainless steel top section which is the part you raise up and down to get the right match to the transceiver.

The top whip is held in place very securely by two small set screws.  The only problem is that the supplied Allen wrench is made to a very poor quality, such that it is more round in profile than hexagonal! Accordingly, it doesn't work.  But Allen keys are so common that this is not a problem worth worrying about.

The top whip is kept firmly in place by two set screws.

Matching is very easy, and remains stable with changing environments.  Nearby metal sheds and power lines do affect mobile whips quite a lot, so if you do encounter any difficulty, it's best to take the car somewhere clear of development to match the antenna.

Performance-wise, the Ampro is, in essence, just a piece of wire on a stick, so it works as well as any other wire on a stick would!  My first QSO was with a 7U station in Algeria, who was hearing me well enough.  A TO station (Guadeloupe) was coming in extremely strongly at well over 59, but I didn't get a chance to have a QSO.

So, yes, this Ampro whip works as you would expect, is a really good price, and robust enough to last many years.  I was impressed by the way it shirked-off an encounter with a height limiting barrier at my local supermarket.  The springy upper section came into its own, merely whipping back into verticality on clearing the barrier!

Just remember that, whilst your car looks a bit silly with a huge antenna on top, it will typically give you 3dB - that's twice the input and output - over one installed on a tow hitch or eye.  It's also easier to match, due to the lack of complicating matters such as heating elements in the rear screen.

Blog's rating 

on price: 10/10
design: 9.5/10
performance: 10/10

Monday, 29 September 2014

Twisted Gamma Match

Attention has turned again at this station to the wonderful and intriguing magnetic loop.

Having been doing some more technical reading, I thought I'd try out a twisted gamma match, brought to our attention by Prof. Mike Underhill probably more than anyone else.

Now, most people who make a magloop use a primary 'Faraday' loop, which couples to the secondary, larger loop.  This works well, especially if the Faraday loop is squashed into an oval, which tends to yield easier matching.

But I was curious whether the gamma match would work as well as - or better than - the two-loop system, although the overall efficiency of the antenna was already superb.

Solder shield to one side of the loop, and the gamma wire to the centre..

So, out came the blowtorch and solder, and off came the Faraday loop!

I connected the shield of the coax directly to the bottom of the large loop, and then soldered about 2 metres of relatively heavy duty (30A) insulated equipment wire to the centre conductor.  I twisted this, with no idea what might work and what might not, until the wire wrapped up half one of the bottom pipes, up one whole side, and a few inches along one half of the top pipe.  Prof. Underhill seemed generally to do much the same, loosely wrapping one whole half of a circular loop with the gamma match wire.  I used a crocodile clip to connect the end of the twisted gamma match to the top rail of the magloop; you eventually solder this in place.

I tuned-up by ear with the magloop's 0-200pF air-spaced capacitor, to pleasantly find the SWR a perfect 1:1.  Running on WSPR at 5W in poor daytime conditons on 20m showed the system was working as expected.  Comparison of my received signals by US and Canadian stations showed I was level-pegging with other transmitting stations known to have very efficient beacon systems.

More tests needed, but the twisted gamma is very easy to do, seems non-critical as to design, and is less prone to being disturbed when knocked or moved than a Faraday loop.  You can find lots of information about loops and matching systems here. 

Update: I've rebuilt the magloop in wider-bore, 28mm copper.  This has slightly changed capacitor requirements, but works perfectly well.  Using the twisted gamma match, I've been particularly pleased with its performance on 40m, where nightly PSK on 10W and WSPRing on 5W reveals an efficient antenna, more especially considering it is working indoors!

Friday, 19 September 2014

RSGB: Up The Swanny?

The latest edition of RadCom just dropped through the letterbox.

Fair play, the editorial team are making what is a fairly obvious attempt to change the content so that it appeals to mere mortals as well as career engineers.

On page 7, half-yearly and unaudited accounts are presented.  They make for troubling reading, indeed.

Having ridden a significant but very short-lived wave of sales during the centenary year (2013), 'normality' is now coming home to roost.  This month's RadCom heavily promotes the new Handbook, whilst trying to get members to boost the society's income with a £5 book token. 

Whilst I could go through a lot of detail, the bottom line is that the RSGB has taken a huge, 9.2% drop in income as compared with the half-yearly results for the same period last year.  Its income from interest has halved in one year.  The RSGB states it expects a "roughly break-even" position for the full year.

Now I don't know much about business, but when faced with a situation like this, a subscription fee hike would appear to be wise, if unwelcome.

One detail that I think the membership ought to severely criticise the Board for is its continued operation and financial support for its ill-conceived National Radio Centre at Bletchley Park.  This accounts for an overhead of £18,414 - or a staggering 25% of the RSGB's total non-activity overheads.  I've said it before and I'll say it again - the NRC has no meaningful worth to the society or its membership, and is entirely unaffordable.  It has been the focus of much criticism and needless expense.  Why it isn't being closed down as an expensive luxury is something that will become a louder cry in coming months, I think.

Urgency should be setting in amongst the Board members and all members of the society alike.  If the society maintains its current, quite static line of activity, then it has only a few years left before hitting the hard rocks of financial unsustainability.

Many have commented in the recent past that the RSGB has only "about ten years left."  On the latest results, that would seem to be rather optimistic.  Membership, and so income, is still falling, and the realisation that nobody's been doing anything to attract newcomers to the hobby has come way, way too late.  Many of the RSGB's members have been only too enthusiastic to play their part in the downfall, in their attempts to keep radio an exclusive man's club.

The RSGB now runs, unless it shows exemplary management direction, the potential risk of making mistakes in an effort to improve its future prospects.  With a break-even outcome, it has no latitude to invest in improvements to services to its membership, many of whom seem simply to join "for the magazine".  It has reached a point where it can only - just - keep its head above water.

The time for a total revamp of the society, how it does things, what it throws money at, and what services it provides, is now.  Not tomorrow.  Not the next time a new Board is appointed. Now.  If not, then during the next couple of years, we'll be seeing accounts with little more than increasingly red numbers.

On the positive side, we can take a glass half-full approach and say that the RSGB's time may have passed, and that a new kind of representative for the radio community should come into existence.  Many would welcome that, and I would be one of them.

Friday, 12 September 2014

Switch Mode Power Supply RFI

Just when you thought we had enough QRM on the bands, I seem to have found a new culprit yesterday - domestic CCTV systems.

Now, before we begin, CCTV isn't rare.  It's used by a large swathe of the neighbour-harassed population, so there will be one near you.

Because of their popularity, and developing HD technology, CCTV is subject to huge competition and cost pressures.  As a result, so is the quality and design of the various components.

The facts:

I bought a 'Home Guard' CCTV system with a 1TB HDD and 2 cameras.  It cost £189 at Argos, a very popular UK retail outlet.

After a full and careful installation (well, there are only a couple of basic BNC and PSU connections, after all!), I powered up to see whether there was any RFI.

Sadly, there was.  A lot of it.

The 12m band went from a totally quiet, noiseless environment to one with a S5 hash.

Here's the evidence:

So, if you buy one of these, which are probably the same kind of unit sold under endless branded guises, then chances are it will have a cost-cutting PSU, and RFI as a result.

I'm taking mine back as not fit for purpose, and a breach of European Directive 2004/108/EC, the material part for consumers being Article 5 (hat tip to UKQRM for this):

"Equipment shall be so designed and manufactured, having regard to the state of the art, as to ensure that:

(a) the electromagnetic disturbance generated does not exceed the level above which radio and telecommunications equipment or other equipment cannot operate as intended".

Argos were exceptionally good with me - they accepted the complaint and refunded me with no quibble whatsoever.  They even called me back the same day when I told them about the wider issues with selling this product. 

But, many other shop assistants will look at you with a blank face if you present them with this complaint as a basis for returning and claiming your money back.  It's understandable, but not acceptable.  It's probably best to ask for the manager, if there is one, and explain it is a piece of equipment that is probably illegal due to its RFI-generating nature, and that the problem of power supplies like this generating RFI is very well known and the reasons for it understood (omission of isolating components.)

Tell the shop you are also the holder of an OFCOM radio licence, and that you will be reporting the product to both OFCOM and the local trading standards office.

DO NOT ACCEPT the shop telling you to contact the manufacturer, even if the manufacturer asks you in their instruction leaflet to contact them 'in the event of a problem'.  This is not an operating problem for the maker to help you with, it's a basic manufacturing flaw.   It is the seller's legal obligation to deal with complaints and refund you (a replacement isn't appropriate here, because it's likely all their CCTV systems will use the same PSU - you should tell them this if they dig their heels in.)

If the shop, as often happens, really digs their heels in, you can try and ask the manager to write down their reasons for refusing to accept the return and/or refund you, and then go to ask for help from your local trading standards office at the Council.  Inevitably, these are rather stretched and much less able to help than once was the case.

Saturday, 6 September 2014

Antenna Switch

Like most hams, I accumulate antennas over time.  I have one commercially made antenna switch, which can handle QRO operating, and so has some pretty robust switching.  However, it only has three antenna ports, and I never use more than 100W, usually much less.

Here's what my commercial unit looks like.  You may wish to note that a four port switch sells for anything from £60 - £90, depending on maker.  That's a lot of money for what is actually an extremely simple device.

Knife switch on a commercial, higher-power 3 port antenna switch.  Simple, but expensive.

As I have five antennas in active use at the moment, and always a couple under experimentation, I decided to make my own, seven port switch.

Now, a note of caution: if you use more than 100W output, you may want to select your switch unit with consideration to how robust the contacts are, and whether their arrangement might be too close for higher powers.  At 100W or below, the following should be more than adequate, but it's up to you and your training to check!

I obtained my 11-position, single pole switch from a well-known online auction site for about £2.50 each.

At the same time, I bought a smallish aluminium box from RS Components, who seem to have a more sensible size range than other outlets.  This was about £12.  I bought a lot of twenty SO239 panel-mount connectors for £8 - all the way from Texas - via the same online auction site.  They took a mere week to arrive.

The 11-position, single pole switch, and all the connections.  The SO239 on the left is attached to the common pole, to which the transceiver is connected.  The remaining seven are antenna ports.  Don't forget to add a grounding post as well.

I then bought a reamer, which cuts larger holes in metal to allow the SO239s to fit through.  This was a one-off tool outlay of £11.

Making the switch is easy-peasy, lemon-squeezy.  Just drill a number of modest sized holes where you want the connectors, and then use the reamer to widen the holes until the SO239s sit snugly against the box.  Then drill some smaller holes for attaching the SO239s to the box using M3 or thereabouts bolts and Nylok nuts.  Two is enough for each connector.

Drill a hole in the bottom of the box (NOT THE LID!), which is where you stick the switch through to attach it to the metal case.  The lid goes on last, and becomes the bottom of your antenna switch box.

The rest is just a case of connecting each antenna port to the switch.  You also need to attach a bolt through the lid somewhere out of the way so that you can ground the box directly (and not to another piece of equipment like an ATU, etc.)

And as I can hear the purist elders ask: "Ah!  But what about the inter-port isolation, my boy?", I ran a test using two rigs, one on a connected port, the other on a disconnected port.  According to this simple test, the isolation is very comparable to the commercial unit, being of the order of 60dB.

So there you go.  Apart from the fact that you rarely see antenna switches with more than four ports, this project saves you a lot of money.  Sure, you can do a nicer, less hurried soldering job than me, and maybe use a chunkier switch, but that's another story!