Friday, 29 August 2014

0% Compliance for USB Chargers.

During ongoing discussions within the radio community about EMC issues arising from the flood of Chinese USB chargers, my attention was drawn to this important article.

Given that most of us have several of these damned things around the house, this is certainly worth a read:

http://www.electricalsafetyfirst.org.uk/electrical-professionals/product-safety-unit/plug-in-chargers/

Suprisingly Useful Tip of the Day

The other day, I accidentally soldered a PL259 to the free end of a roll of RG-8X.  This proves to be surprisingly useful, because I'm always chasing a brainwave when I am connecting-up coax, usually a brainwave in bad weather, or when there are other things to do as well!


By making sure I always have a PL259 nicely finished off at the end of the reel, I can just cut the right length needed for the job, connect-up at the antenna, and pass the other end through the wall for some comfortable indoor soldering to finish the job!

Thursday, 28 August 2014

SIM 31 Mode

No sooner had you managed to twiddle all your settings than another digital mode arrives!

Yes, folks, SIM-31 is here.



Fair play, it's a good new take on PSK, seemingly much more robust in the face of poor conditions than plain PSK-31.  There aren't many using it as yet, but it's very early days.

What SIM-31 doesn't have is charisma!  Whilst it has a chat mode, its set macro offerings are very 'Spanglish' in nature, and the whole package feels just a bit sterile.

That is pushed even further in that SIM-31 includes a fully automated setting that can initiate and complete a QSO without any operator input whatsoever.  I mused on that type of 'amateur radio' in yesterday's post, and the distinct feeling you get when you see an automated 'CQ' call is one that highlights the pointlessness of 'conversing' with a machine with no human at all on the other end.

I'm not sure if SIM-31 will take off in the community.  For my money, I much prefer the quirky but very robust ROS mode for when conditions are poor (ROS was developed for this purpose.)  Despite the powerful benefits of ROS, very few use it.  I suspect SIM-31 will discover the same ground.

You can download SIM-31 from this site

Wednesday, 27 August 2014

Philosophy of Radio

Oh dear!  It's serious when it comes to philosophical matters!

The prompt for this post is the discovery that my FT-450, a lovely acquisition from a famous internet auction site, allows the recording of 10-second messages - typically 'CQ' calls - for later playback.

Now, I've often developed sore throats from calling 'CQ', so this facility is really useful.  But, it does beg the question: if we can automate 'CQ' calls, and automate most of a QSO via the various digital modes, are we as operators simply reduced to button-pressers at the appropriate moments?

The point being that, whilst most modes need us to click a mouse or press a button, that's only from kindness of a sort; it's pretty obvious from modes like WSPR that the whole experience of radio can be fully automated, with no need for an operator, other than being the licence holder for the transmitter, at all.

Now, I love WSPR.  It's a phenomenally useful mode.  It's also fully automated.  You can even exchange valid QSLs based upon it.  So, is full automation a future for radio?  Yes.  But not the full future.  Automation where it's appropriate and useful.

Otherwise, it's clear that real humans love real involvement in the sending and receiving of transmissions, and I see little evidence that what we have today is going to be much different from what we will have tomorrow.  You only need to spend a couple of days on faceless digital modes to realise the truth of this!


Friday, 22 August 2014

Ten.

Ten.  That's the global total of operators, including me, that are currently active on 60m WSPR.

Admittedly, I only just came to 60m this week.  But really, only a handful of stations across the globe?

This is a real shame, and rather contrary to the spirit of allowing access to 60m, which is meant to be largely for the purposes of experimentation.  Surely, figuring out the propagation system using the invaluable resource of WSPR is a lynchpin of such work?

Come on, guys and gals!  Get active on WSPR.  If it weren't for the couple of ZS stations active on 60m WSPR, there would be no stations outside the EU. 

This really is a sorry state of affairs, dear ops!

Thursday, 21 August 2014

Fitting PL259 Plugs to RG8-X

Like many operators, I'm a regular user of the relatively low-loss RG8-X coax.  It's a lot nicer than using the very bulky, stiff RG-213, which has much the same loss characteristics.

It's always a bit of a question as to how best to connect coax to a plug.  Soldering to the braid through the plug holes is always prone to heat-damaging the inner insulator - damage that you can't assess because it's largely out of sight.

An old, dismantled RG8-X plug to coax connection.  The screw thread provides very good physical and RF coupling.
 
But it's very easy with RG8-X.  First, I use coarse aluminium oxide sandpaper (or a metal file/rotary tool head) to rub away a key to the base metal all the way round the outside of the bit that attaches to the outer sheath of the coax.  I then carefully heat the plug and add a thin layer of solder all the way around.  If you melt a blob of solder onto the tip of the iron and simultaneously let it touch the plug, this is a very good way to quickly transfer heat to the plug.

After the fairly long time it takes the plug to cool down, I strip the coax as usual.  I pull the outer braid back over itself, so that it faces away from the plug.  You can then screw the plug directly onto the braid and PVC sheath, which fits very snugly, without the need for excessive force.  This makes a very stable, secure and sound RF connection with the plug, as you can see from the years-old example recently disconnected.

To make doubly-sure of a good connection, I then wrap the remaining short length of braid around the tube of the PL259 that fits over the braid/sheath, and then apply solder, which attaches itself very easily to the plug due to the earlier pre-soldering.  Once it's cooled, add a layer or two of self-amalgamating tape to add some mechanical strength and weather tightness (if needed.)

You now have a bomb-proof RF connection to the plug!  I'll add some more photos of the process when I get a chance...






When ATU Bypass Isn't Necessarily So.

A long time ago, when I was even more ignorant of ham radio set-ups than today, I tried to create a well-matched delta loop by using an ATU's SWR meter, with the matchbox set on 'bypass'.  I remember trudging backwards and forwards so much in that exercise that I'd worn a very muddy path in the garden!

Beware stray currents - and false SWR readings - on ATU 'bypass'.


I never did achieve a low SWR with the ATU meter, and wondered why that was.  The answer, it seemed, was that, even when switched to 'bypass', there is some kind of interaction between the RF and the ATU circuitry, leading to strange and usually meaningless SWR meter readings. 

This phenomenon made itself known again the other day, when I switched over to an extremely reliable 2-ele quad for 6m that has a 1:1.05 SWR at worst.  It went via a coax switch to the ATU on 'bypass', and then to the rig.  I keyed-up to check the antenna, and the rig SWR meter was reading 1:1.5!  I scratched my head a bit and thought about what had changed recently.

It turned out that the changed item was the position of the inductor switch on the ATU.  I'd been using an inverted-L on 60m, this antenna design necessitating the use of a matchbox.  I turned the switch back to its earlier position, and the problem 'high' SWR on the 6m quad vanished.  I connected to the quad directly via a separate SWR meter, and that also reported the expected, 1:1 SWR.   It was the same with the delta loop; only by using a standalone SWR meter and direct connection to the rig, rather than via an ATU on bypass, was I able to cut the right wire length with ease.

Some ATUs might be OK in this regard.  But seeing as many of us use relatively cheap units by the well-known producers, it's a salutary point to note next time you want to check what your antenna is doing!