Your TV antennas look a bit different to ours!  On the other hand, I guess the whole of the UK would fit in your back yard - so you need a BIG antenna!

After a bit more reading (while I should have been working!), about the only compact antenna nobody has much bad to say about is a HexBeam - so maybe that's the way to go.  Decisions Decisions!

Si

Thanks Dale - that's a fantastic & comprehensive response!

I can see that some modelling software might be on my Christmas List!

Out of interest, do any of the apps allow you to import an antenna from a CAD drawing - just taking the line segments as wires?  I'm a design Engineer by trade and use Solidworks all day.  Drawing even complex antennas is easy & quick (Solidworks allows parametric, equation driven drawings) whereas the drawing interface in the modelling software I've seen is a bit clunky!

Are there any decent books / resources to get me going with modelling?  It finally struck me last night writing the post that not using software is daft!

Si

I'm interested in these because I would like a rotatable antenna for 20m, but don't have the space (or friendly enough neighbors) for a beam or cubic quad - and was looking for a more compact alternative.

I've read Pfeiffer's paper about the antennas - which (perhaps obviously) is very enthusiastic about them.  But most of what I've read (mostly on QRZ) has been negative - many suggesting that it's the feed line that is transmitting and it would work better without the antenna at all!

I don't have any simulation software - nor know how to use it.  I'm more practical, build it & see if it works then modify to make better (or worse).  But I'd like an opinion, is this a turkey? - before I start cutting up hundreds of feet of wire!

Thanks in advance,

Si

Another quick video which shows how fast it will move an antenna weighing about 10 Lbs and 5' diameter supported on a push-up fibreglass mast about 30' in the air.

http://www.youtube.com/watch?v=FrVEHKQdra0

Today I've been playing with a HexBeam type thing which weighs about the same - but obviously the mass is further from the centre so has more rotational inertia.  However it seems to move with similar speed & acceleration.

I'll post up a video of that once it's finished & transmitting.

Si

The limit switches on jacks normally work by the switch being normally closed with a diode across the terminals and the two limit switches connected in series with the motor.  When the jack reaches the end of its travel, the switch opens such that the diode is now connected in series with the motor.

The diode is polarised such that it stops current flow in that direction.  However, if you reverse the current, it flows through the diode running the motor in the opposite direction (until it reaches the other limit switch).

Thus, all you need to control it is a switch which reverses the power to the motor.

If you need a limit switch which operates before the built in limit, just fix a microswitch in an appropriate position such that the contacts open when the jack reaches the desired location.  Connect a diode (rated for the motor current) across the normally closed contacts and connect the NC contacts in series with the motor (or with the wire going in to the jack).  If it does not work, reverse the polarity of the diode.

Si

This one, for the time being is going in the attic above my workshop.

Here's todays project:
http://www.youtube.com/watch?v=jVnCmJu49jw

I had a micro-controller from a company called ByVac which has a 4" touch screen - which I thought would be useful.

I now have it controlling both the direction and tuning of the loop by touching the screen.

Seems to work pretty well and is silent RF wise on HF up to 21Mhz, then you can hear the rotator moving - but it's quiet.  Maybe the servo needs a choke or something.

At the bottom of the screen there is a compass display with a red dot showing the direction the antenna is pointing.  you just touch the display to move the dot to where your finger is - or drag it to move slowly.

The buttons at the top are to fast & slow tune the VC.

There are another two buttons on the left which calibrate the rotator - you point the antenna north, click N then south & click S and it works out the calibration for the dial.  This bit doesn't actually work yet - but there's always tomorrow!  I didn't bother as it seemed to be spot on with my initial values, by chance.

Longer term the plan is to put it on the mast with a 2m Yagi - but I've not built the Yagi yet.

Si

It was just a test with the bracket zip-tied to a bit of metal.

If you use a couple of U bolts - it will not move at all.

The hole in the centre of the big pulley is 30mm which fits over the support for the antenna.  This sits over the top of the mast which is 1" diameter, sleeving over the top 3' or so.  Bracket will bolt to mast below that with the pulley on the very bottom.

The weather is too horrible today to install it - but you get the idea.

Si

OK, just for Chris.....
http://www.youtube.com/watch?v=D1DMO98Xuy0
I've uploaded a quick video of construction and operation.

The actual winch servo I have is a Hi-Tec HS-785HB.

The whole rotator weighs just over 1/4Lb and produces plenty of torque and will rotate the antenna 360 deg in 6 seconds - so not too bad.  It will also give better than 1 degree positional accuracy.

Si

OK, I'll see if I can get into the attic at the weekend and take a photo.

The pulleys & belt came from eBay - something like this:
http://www.ebay.co.uk/itm/HTD-5mm-Pitch-Timing-pulley-for-15mm-belt-20-tooth-CNC-ROBOTICS-/221012709019?pt=UK_BOI_Industrial_Automation_Control_ET&hash=item3375624e9b

I bored a hole in the bigger pulley which the bottom of the antenna would fit through tightly - then glued it in place.

The servo came with an circular 'horn' (plastic bit which screws on to top of servo shaft).  I glued the smaller pulley to this and secured it with a couple of small self tapping screws in to pilot holes.

Bracket for servo was just made out of folded Aluminium sheet held to mast with a U bolt.  Nothing fancy!

I'm going to make another one for a new loop - so maybe I'll just take photos of that as I make it!

Si

Best of luck with your build.  DIY antennas are much more fun than bought ones, and even if one doesn't work as well as you hope, you have at least learned something from the experience and hopefully the next one will be better!

It gets quite addictive - chasing weaker and weaker signals or more distant contacts and the fact that you've made it yourself makes it all the better!

Si

It does look nicely made - but it still looks a lot of hassle to get it up & running compared to a loop for example.

Anyone know how the 'solid state match' works?  Assuming it works, it's a lot easier than the tuning coil thing which looked every bit as much bother as tuning a loop.

In the video the guy says that the combined length of the whip and all the radials is 128' = 1/4 wave on 160m.  Is it reasonable to add up the lengths of ALL the radiating elements to give the wavelength it's tunes at?  I'm not totally convinced.  That's not to say it doesn't work well on 160m though.

Si

I agree - you could make the same thing (or something as good) for almost nothing!

For the mast, what about using the poles used for 'feather flags' - you know the kind of thing they use at outdoor exhibitions.  They are usually a composite construction and disassemble in to short lengths.  The companies who sell them usually supply bases / mountings - and you can get them very tall!

Search eBay for "Pole Windsock"

For example:
http://www.ebay.co.uk/itm/Brookite-7m-Telescopic-Windsock-Flag-Pole-BRAND-NEW-FAST-SHIPPING-/281080445981?pt=UK_Toys_Games_Outdoor_Toys_ET&hash=item4171b33c1d

This one even has an eye on the top to attach your wire!

Si

I just fill the connector & threads with general purpose grease!  It's a bit messy - but seems to do the trick, and they're easy to unscrew when you need to!

In the UK, it does nothing but rain!  No amount of wrapping seems to keep it out long term - but grease seems to work OK.

Si

That's a clever idea!

Si

I had a similar problem - but running a cool box which kept melting plugs & sockets!

I machined this:
http://www.x-eng.co.uk/images/forum/lighterplug.jpg
(Is there a way of embedding images on the forum?)

With a socket to match!  It would be much easier just to use a better connector, such as an Anderson however!

Si