Saturday, June 24, 2017

First 4m QSO - getting a transverter kit working

Almost a year ago I bought a 4m transverter kit from DF2FQ (XV4-40). I have basic understanding of electronics, acquired in part through the hobby but building a project like this was new to me. With my mechanical engineering background I am more confident in building robust stuff like antennas, masts, supports, baluns, etc. Soldering loads of tiny components on a board seemed challenging. 

However the level of documentation provided by DF2FQ and some motivating words by PG8M - who was already using the transverter - pushed me to the point that I ordered the kit. When I received the package I must admit it looked daunting. 

Lots of parts..
..and rather tiny

I started building the kit sometime in August last year. I tried to work as meticulous as I could (a challenge when you are as impatient as I am). When I had completed the kit and ran the first tests, I found that I received 70 Mhz signals with the radio tuned to 29Mhz. Hurray!

However, when I tried to transmit, the transverter appeared to be dead as a dodo. No LED, no signal. A very disappointing result. I did some tests (as far my knowledge goes) and could not find the cause of the failure. So the kit went back in the box it was shipped in. Time for other projects.

The Es season is rather good this year and I have enjoyed the effects on 6m but 4m was open a lot of times as well. I really had to get back to the abandoned transverter project. PG8M had already kindly offered to help me months ago and today I took him up on his offer. We went through the error checking process step by step, finding and fixing four major issues. It turned out I had made two soldering errors and two of the smd resistors were faulty. Whatever happened to these resistors I really don't know.

PG8M trying to locate the next error

The good news is that we ended up with a transverter that delivered up to 35W on 4m with 5W drive on 10m. 

There was no one around to do an on air test so back home I hooked up the transverter and put my tri-band yagi on a pole @2m high in the garden. PG8M was QRV 30km away with his 4 ele beam pointing in my direction. That is when I made my first 4m QSO.

DK7ZB tri-band beam in action twice this week

It is a bit late in the Es season but I am sure I will get back to this band in the future. The next thing I need is an antenna I can set up quickly at home in case of any high MUF situations. For 6m I use an end fed wire that I can attach to a pole that I push through the attic window. For 4m I am going to try a slim jim vertical. More on that later.

Friday, June 23, 2017

Playing with 6m Es - compact beam versus vertical

Some time ago I built a compact beam for 6/4/2m aimed at /P operations. It is a design by DK7ZB featuring 3 elements on 2m, 2 elements on 4m and 2 elements on 6m. I tested it when I finished building it and SWR was good on all bands.

I followed the design of DK7ZB (link) with a few changes to make this a /P antenna:
  • I use wing nuts on the 4m elements and the 6m reflector to be able to remove them easily for transport
  • I split the 6m driven dipole in a short center piece connected to the boom and removable parts on both ends of the dipole
  • I added spacers for the dipoles to keep them at the right distance from each other (refer to picture below)
Spacer for the dipole elements

Apart from a short appearance in LX (2 QSOs), I had not used the beam on the air. For 6m I use an end fed half wave vertically - both when I am /P as well as at home.
It is amazing how effective a vertical wire is in Es conditions. I have worked stations all over Europe with that antenna using 100w. I was curious how the beam would perform in comparison.

We are in the Es season at the moment and there was a 6m contest on last weekend. So I decided to go out /P and test the beam properly against the end fed wire. I used one of my Spiderbeam poles with the end fed wire in the top (feedpoint about 12m high) and the beam a bit lower at about 8m high.

I used an antenna switch to be able to quickly switch between the two antennas. You need quick switching as the signals themselves vary constantly under Es conditions. The difference was significant most of the time. Of course the heading of the beam is a factor that influences the difference. With the beam heading the right way, the signal strength on rx differed multiple s-points. On the low end this meant there were stations I could only copy on the beam. I recorded a view video's while switching between the antennas. One of them is on YouTube:

With PG8M - who lives just under 30km from where I was /P - I tested the characteristics of the beam via ground wave. We found a difference of 2 s-points front to back and 5 s-points front to side.

All in all this shows me that this beam is definitely an interesting antenna to use in the field for 6m. It is light, easy to set up and relatively easy to transport. As the 6m reflector is rather long for easy transportation I am thinking of splitting the reflector in two or three parts.

While I was testing this setup I logged 25 stations, collecting 10 new grid squares on the go.

Sunday, May 14, 2017

Projects - Inverted V antennas for the low(er) bands

Choosing a /P antenna for 80m

My favourite antenna when working /P is the end fed half wave, set up vertically. It is easy to set up and works well with reasonable DX performance. It will not beat my portable hexbeam when working DX but that one requires more time, material and open space to set up.

The EFHW vertical becomes a challenge however on the lower bands. Now I did get myself the largest Spiderbeam pole - so a vertical half wave for 40m is an option - but there is a limit and 80m will definitely not fit.

One option then is to use a quarterwave vertical. However this requires radials if you want the majority of your signal to be radiated above ground. I developed a quarter wave for 80m with four elevated radials and it works but is quite a hassle to set up. Working /P you don't always have room for four elevated radials.

Another option is to use the EFHW sloping. That is a good option and I have used it on numerous occasions. If the support is tall enough to allow for an angle around 45 degrees the antenna still has a low angle of radiation but also a lobe at a high angle. That makes it a versatile antenna. It has some directivity - in the direction of the slope. 

The challenge on 80m is that the EFHW sloping still requires a tall support for a reasonable (steep) sloping angle otherwise you will end up with only the high angle radiation. 

Inverted V antenna

Another option - using a single support - is to use an inverted V dipole antenna. For 80m I find it a convenient antenna to set up and it comes with a unidirectional radiation pattern (in the horizontal plane) that fits my needs when I am "being chased" with chasers from all directions.
The inverted V has a high angle of radiation. On my 18m pole it very much resembles a sloping half wave dipole of the same length. The main difference is that the sloping wire will have 6dB F/B ratio while the inverted V is omnidirectional. It is very much up to what you are looking for.

Practically when working on 60m or 80m (or 160m) - for more than a few QSOs - I choose the inverted V antenna. When my tallest support still was only 12m I also chose the inverted V as my default antenna for 40m.  

For my inverted V antennas I developed a universal center connector that fits on the fiberglass poles I use. It is a simple component made from 40mm PVC that allows me to connect various wires to a SO-239 connector. The reason I designed it with changeable wires is that it allows me to make different combinations like 40m and 80m inverted V's on one pole fed by one coax cable. 

The tie wraps on the sides are used to keep the cable tension away from the soldered cable shoes - otherwise the shoe will certainly break in due course. The hole through the center allows it to slip over the top segment of my fiberglass poles.

I developed a couple of these center connectors so I can set up different antennas at the same time. We use them for example with the YNOMY DX Group during the PACC contest when we set up three different inverted V's (40/80/160). We then have the 80m and 160m on the tallest mast together, being fed from one coax cable.

For each inverted V I have two separate dipole legs. Each dipole leg is cut to the right size and features a cable shoe as visible in the first picture. To hold the wire I have constructed a cable spool consisting of a piece of PVC (40mm) with two end caps. On each end caps I have glued a piece of wood and through the end caps and wood I have put a piece of threaded wire. 

40m wire spool (one leg)
This spool holds the antenna wire plus a long enough end of tension string. I find it works rather conveniently in that I can just stick the spool in the ground (slightly under an angle) where it unreels while I extend the mast. Once I am happy with the position of the mast and antenna I push the spool further into the ground, stopping it from turning. This way I do not need pegs or anything else to set up this antenna. 

Below you see an impression of the antenna with four legs - dipoles for 80m and 160m - ready to be deployed.

I just stick the spools in the ground in the direction I want the leg to go. Then I extend the fiberglass pole with the spools unreeling until the mast is fully extended. Then I pick up each spool and place it where I want the end point to be. The advantage of the spool unreeling is that there is only a slim chance the legs get entangled even when you have two dipoles on one mast - the wires are kept under some tension the whole time. 

Sunday, May 7, 2017

Projects - 18m pole set-up improvements

I use a variety of antennas and poles/masts when /P. The 12m HD Spiderbeam is the most compact one I have and is easy to set up in the field without any supporting structures. The bigger ones I normally attach to the car one way or another or to any suitable construction I can find around the place I am going to be active from. My favourite and most versatile antenna pole is the Spiderbeam 18 HD fiberglass pole. I use it almost every /P activity. Preparing for a tour through LX I decided to implement some improvements that make the pole even more portable.

Guying the 18m Spiderbeam pole
I have twice set up the 18m HD Spiderbeam pole on my own using an ingenious structure with all the 6 guy lines extending while I pushed out the segments. That took quite a bit of time so I looked for another option. When I set up the pole using the car or a supporting structure I find that I do not use any of the supplied guy lines - so it should be possible to find a much simpler configuration to set up this pole in the field.

I decided to try and set it up with only the lower segment guyed. That would allow me to simply set up the pole while it is still collapsed and then push out the segments without worrying about any other guying arrangement.

Borrowing from the idea behind the clamps Spiderbeam supplies for keeping the segments extended, I bought a hose clamp and applied rubber lint that I crimped in place. I cut some of the rubber away so I could add three rings. So now I have a permanent feature on my Spiderbeam pole: fixed guy rings. 

Securing the base
You also need the bottom part to stay put. Before I would use a large peg with some soft (insulation) material around it. I would just position the pole over this peg. However I have found this is not a very solid construction - e.g. it does not allow you to keep the pole standing while it is still collapsed. With the set up I just came up with, I need the collapsed pole to stay upright while I attach the lower guy lines. So I replaced the peg with this:

The center hole fits around the pole while the other holes can hold pegs that secure this little box in its place. Trying it in the field it turned out to work well - the Spiderbeam pole kept upright while I attached the lower guys.

With these two changes I can set up the pole in no time without needing any supporting structure, like so:

I used this a couple of hours with the pole extended 18m holding an efhw wire. Granted, it was not very windy that day. I will have to see if this is strong enough in higher winds.

Practical segment clamps
One last adjustment I made to the configuration is a replacement of the clamps that hold the segments in place when extended. The default clamps provided by Spiderbeam require a spanner or wrench to open and close. That is inconvenient and so I really did not use them often. I either extended the segments to the point that they stuck (with the risk that the antenna would collapse during a QSO) or I would use duct tape (that is quick to apply but not so easy to take off). 

So I bought clamps that have butterfly tightening tabs. I added rubber strip on the inside that I crimped on the clamps to protect the pole (like with the original clamps). I tried them and they work well.

Wednesday, April 26, 2017

Finding PE4BAS

Fellow blogger and radio addict Bas, PE4BAS is on holiday. To keep his followers busy he created a little puzzle to solve: where am I?

I am always in for solving puzzles.. so here goes.

As he is a WSPR user (I think our first conversation was about visualising WSPR contacts), he can of course be found in the database. 

He is being spotted as we speak:
2017-04-26 12:26 OZ/PE4BAS 7.040044 -2 0 JO56jl 5 OH2EAT KP20xw 1003 54

So, Bas is in OZ and in JO56jl to be more precisely.  That square is not that big and there is not a lot going on there. So I sneaked around and took a picture of his place while he was not looking:


Looks familiar?

I had a look around (I hope Bas doesn't mind) and it indeed is a cosy place.

Cosy place Bas has chosen as temporay QTH
I left him alone again to enjoy the rest of his holidays. Thanks for the puzzle Bas & have fun!

Monday, April 17, 2017

Spending a lot of time at PAFF-0097

Just got home from a nice activity at PAFF-0097 as PC44FF. I brought my hexbeam but the parking I had in mind when planning the activity was too crowded. Driving around I was lucky to find a nice open space to set it up. There were some rain and hail clouds around and I was just in time setting up the beam to stay dry.

/P DX antennaThe skies cleared later on
I started out on 20m with the hexbeam pointing to NA. The band was not in a very good shape so the going was slow but I did copy a lot of NA stations (relatively). I tried a sked with VK4FW but the band was just not good enough. After 2 hours mostly on 20m - I tried 17m but that was no fun - I had logged 106 QSOs. 36 of those were with NA stations from 14 US states and 3 VE provinces. Quite a lot of familiar NA chasers in the meantime.

Personally I am OK with an activity once I reach 100 QSOs. However, as 20m was rather slow and I had not copied a lot of the familiar EU chasers, I decided to stay a little longer to try 40m. I took down the hexbeam and set up a 40m vertical (EFHW) on my 18m Spiderbeam pole. In about 45 minutes I was good to go again.

18m Spiderbeam pole with an EFHW for 40m

40m was very noisy where I was. It was due to splatter (a combination of a good rx antenna and poor filters in my FT857d) but also QRN. I changed frequencies a few times but then decided I would have to just bear the noise. It was really busy though. As signals were rather strong I could copy a lot of stations above all the noise. As chasers kept on calling there was no way for me to leave. It was getting dark and far past my negotiated return time but you can't just ignore a pile-up of chasers (well, I can't).

After 2 hours the pile up thinned and the signals dropped below the QRM level. By then I had logged 238 QSOs on 40m - apart from 4Z and SU all of them EU chasers. This makes for a total of 344 QSOs for this activity with 6 park to park contacts. A lot more than I had anticipated. 

Driving home in the dark I saw a lot of huge bonfires and remembered that in this part of the country it is tradition to make large Easter fires. It made it a magical drive home with my ears still buzzing from all the noise.

Magical views driving home

Sunday, April 9, 2017

YNOMY LX-pedition planned for May

In preparation of our expedition to BS7 or P5 sometime in the future, YNOMY DX group has planned its first group expedition. So far we have all been active from various places outside of PA individually. As a contest team we have shown to be able to work together for a couple of years already with rather acceptable results.

So now we are off to our first team expedition on May 20 and 21. We chose LX as a convenient location and we chose WWFF as the focus of our operation. Working together with the LXFF coordinator, Mill LX1CC, we have made some draft plans and acquired a special callsign to be used for this expedition: LX44FF.

Our goal is to work as many chasers as we can from Saturday morning till Sunday evening using multiple stations both on phone and CW on whatever band is open between 80m - 2m. We will also issue an award to the most active chasers - check out: LX44FF Award

Really looking forward to a whole weekend of LXFF. Let's hope conditions are acceptable or better.

Project - Mast support for heavy masts

For my portable endeavors I have built an aluminum push up mast and I have bought various fiberglass poles from Spiderbeam. I actually started out with a 10m pole from Spieth. That was rather thin, so I went for the 12m HD version from Spiderbeam.
To get my inverted v's for the low bands up higher I then bought the 18m version and recently I went even further and got myself the tallest pole they sell - 26m.  

Heavy masts present a challenge when working /P. I can manage to set up the 18m pole in the open field on my own but it is quite a bit of work and it would be a really daunting task with the aluminum mast and the 26m pole.

When I built the aluminum mast I went looking for a proper mast support that I could use with my car. Typically this would mean a drive-on support. The ones I found on the internet however were too light for my sturdy (and heavy) mast.

Not having any welding tools available to me at the time (I now have an arc welding machine), I decided to build something myself out of wood. After some experimentation I went for a design where I attach the support to the wheel using lashing strap, instead of driving on the support.

If you are reading this to try something yourself, keep in mind this design only works if you have spoke rims on your car.

I never got around to write something about this support, even though I got questions about the design. After buying the 26m pole I had to build a new support - for a much larger diameter mast - so I decided to take some pictures in the process.

The end result looks something like this (showing my first version):

The tried and trusted version from different angles - note the rubber pads that go between the support and the car tire:

I constructed the old one for my aluminum mast that has a diameter of [--- mm]. It can also hold the 18m Spiderbeam fiberglass pole. Conveniently the tall vertical wooden beams are the same width as the bottom segment of the mast. This means that the only spacing that is critical when you build it, is the spacing between the two vertical wooden beams.

Now for the 26m I built the same support but I could not find wooden beams of the desired width, so I used the nearest (smaller) width and added planks to end up with the correct width - as you can see in the picture below.

Wooden parts cut to desired lengths 
Now that the vertical beams are of the correct width, the only spacing you have to worry about is the one between the two vertical wooden beams. I used the bottom segment of the Spiderbeam pole to define the space, as shown below.

The length of the horizontal wooden beams is not critical. They define the space between the car tire and the mast / pole. I use [--- mm] to leave enough room for my shoes - so that I can use the support to position myself higher when I push out the mast segments.

The height of the upper horizontal beam is critical in the sense that you need to make sure it stays within the height of the car tire (more about that later).

Once all the horizontal beams have been added the support looks something like this:

What is left, is adding the frame that you can tie to your car rim. I use 44x44mm wooden beam for this frame. The height and width for this last rectangular frame have already been defined by the structure you have created so far. It is therefore important that the upper horizontal beam I referred to earlier, is positioned at a height that puts the top of the frame we are now going to add right against the rubber of your car tire.

When I completed this stage I took two more steps: a piece of (ply)wood on the bottom of the support - this keeps the mast / pole from getting stuck in the ground (e.g. in case of a muddy underground). And I add pieces of rubber that go between the car tire and the wooden frame (refer to the pictures above of the old version).

Now you have the lower support for your mast. This might be enough to keep your mast straight up. In my case I added a second support on the roof of the car. This helps keep the heavier masts (like my aluminum mast and the 26m Spiderbeam pole) straight up without guying. 

This roof support is nothing magical. It is simply a wooden beam (44x44mm) that is longer than the width of your car + the distance to the mast. At one end I add two pieces of wood at a distance that equals the width of the mast. Through these pieces of wood I put a threaded rod (M8). This rod is positioned at such a distance that it keeps the mast in place. I use some pvc pipe to keep the keep the sharpish threads from damaging my mast / pole. This roof support looks like this:

I use lashing strap to attach the support to a roof rack on my car.  

Project - DIY aluminium push up mast

Working portable a lot I was looking for a set up that could help me work the DX that I could mostly copy on my vertical end fed wire antennas but that I had a hard time working - especially in a pile-up situation.

I bought the CB yagi first and changed that into a 4 element 10m yagi. Later I bought the folding hexbeam. Both are very nice antennas to work DX.
Of course I could not put these antennas up with the fiberglass poles I use for the end fed wires.

So I set out to find a portable mast that was sturdy enough to set up without guying (under low wind conditions) and could reach at least 10m high.
This turned out to be a challenge. There is not much out there that is strong enough to set up without extensive guying or it is outrageously expensive.

DIY decision

After a while I decided to build a mast myself from aluminium tubes. I could not find the right material around where I live. The challenge is that you need a nice series of diameters with 1-2mm in between the sections. The other challenge is that you do not want to buy 6 meters of each section (which is the default "industry length"). Luckily it turned out there is a webshop for aluminium stuff in The Netherlands that stocks almost all diameters and sells custom lengths.

What would be the dimensions to choose if you want a sturdy but still portable mast?
After some experimentation I decided to go for the following series (diameter x thickness in mm): 70x2 - 65x2 - 60x2 - 55x2,5 - 48x2 - 42x2 - 35x2,5

The widest tube is 2 meters long - running up to 2,4 meters length for the last tube. I did this to make sure they collapse together nicely with each narrower tube sticking out the previous one.

Okay. So far, so good.

Now how do you clamp the tubes together when you want to extend the mast?
For this I used my angle grinder to grind slits into the top of each section. In the most narrow tube I used 4 slits (the gap between the 42 and 35 is larger), for the other sections I used 2 slits. Note: be sure to carefully file the metal afterwards or you will find that the tubes "stick" when you want to extend the mast.

Tube clamps - right one is the new and more durable version
Over this upper part of each section I slid a heavy duty tube clamp. I started using a version I found in a boat shop but they are made of stainless steel. As this is slightly softer the threads of the bolt used to open and tighten the clamp tend to damage quickly. Now I am using a different kind that seem to be more durable (see the picture above).

The end result: mast of 7 aluminium tubes with 6 cable clamps (5 old types, 1 new type)

Proof of the pudding

How does it work in practice?
Well, the mast is a fully manual operation version :)
Extending the tubes can be hard work, especially under windy conditions. In those conditions the mast tends to bend putting a force sideways on the tube you want to extend. This increases the friction.
The best way to extend the mast is to make sure you position yourself on top of anything practical that brings you on a height where the top of the mast is just above your waist. That way you can extend the mast  

Does it need guying?

In conditions of low winds the mast can be extended completely without guying. It needs to be on a level surface though.
When the wind is somewhat stronger I do not extend the last section and still use the mast without guying. At some point it will need guying, either to compensate for not setting the mast perfectly upright or for windy conditions. For this I added a simple and low cost guy ring out of PVC (as can be seen in the picture). It does what it needs to do: act as an attachment point for the guy wires and stay in place while the mast rotates.

I have been using this mast now for more than a year and I am happy with it. When I set it up, I secure it at the base (I built a mast foot from wood that attaches to the wheel of my car) and at the roof of the car (again using a wood construction) I am still considering changing the base I use. I will write about that one another time.

Tips - Setting up the Hexbeam by Folding Antennas


As blogged before I got myself the 6 band portable hexbeam by DL1ELU. His manual is very detailed so there is no way that I can add anything useful to that. There are however some tricks to learn about the folding and unfolding of the antenna once you have built it from the kit.

What I want to do here is add my experiences with the setting up of the antenna hoping it will help others who like myself did not really get it right first time. If you have tips that speed up this process, please let me know.

I have added a short YouTube video in which I set up the hexbeam:
Assuming you have put the hexbeam together for the first time, your first challenge is to fold it for storage. So let's start with the folding process.

One important tip: do use a stand of some sort so you can keep the beam upright when folding. I tried it without and ended up with a big wire mess. If you're lucky and your mast goes low enough than leave it on there (mine doesn't - it doesn't go lower than 2m, which means I can't reach the top of the beam). I bring a parasol stand just for the (un)folding.
Folding 1: Hexbeam unfolded with all wires attached
 Now the first thing I do is to loosen all the joints of the spreaders and fold them down, like so:

Folding 2: Loosening the joints and folding the support elements one by one
I start with the two spreaders where the driving wires run towards the centre post. I try to keep the wires together by guiding them through the nearest joint, like so:
Folding 3: Keeping the wires together
If all joints have been loosened I fold the inner spreaders up and keep them (inner and middle spreaders) in place with a Velcro strap. Like so:
Folding 4: inner and middle spreaders fixed
The parasol stand does a very important job at this point: it keeps wires from ending up on the wrong side of the antenna. If that happens you are in for a nice untangling job later.
The next step I take is folding up the outer spreaders and fixing them with another Velco strap. If you do that you will have something like this:
Folding 5: all spreaders folded
The wires still look like a mess but that will turn out all right. The next step I take is to secure the bottom of the antenna with a Velcro strap. I use this lowest secured point to fold all the wires over and up. Then when I got all the wires up (you would like to have 4 hands at this point, dropping wires all the time) I secure the wires with another Velcro strap somewhere half way up. Now I have a package that looks like this:
Folding 6: wires secured using to straps

Important to check is whether all wire loops are clear from the bottom end of the antenna. If they are not, you will certainly find that a wire has ended up at the wrong side of the antenna, the next time you try to unfold it. So the bottom end of the antenna should look something like this:

Folding 7: no wire loops near the bottom end of the antenna
Okay, now you can put the antenna in the handy bag Christian provides and leave it there till the next activity.

So how about unfolding the antenna?

I use the parasol stand as described above. It keeps the wires nicely on the right side of the antenna. When unfolding I unstrap the first two Velcro straps and loosen the wires a bit, making sure they hang freely.
The I unstrap the outer spreaders and let them fold downwards. Like so:

Then I remove the last Velcro strap and fold the inner spreaders down, pushing the outer spreaders outwards. It takes a bit of walking around the antenna and freeing wires that are stuck in joints but in 1 to 2 minutes the antenna looks like this:

The next thing I do is to close the joint between the outer and middle spreaders. Again you need to walk around to free any wires that are stuck in joints or on wire clamps. You end up with a large spider looking structure if you do it like this:

The last step is closing the joints between the inner and middle spreader and moving the completed Hexbeam on to my push up mast. As the antenna weighs next to nothing this is not a very difficult move. It is like walking around with a rather large umbrella.

This process took 15 minutes including taking the pictures. If I solve the folding issue described below I think it can be done faster.

I still need to address one issue. I have not fixed the position of the wire clamps. With the folding and unfolding they tend to move a bit. This distorts the delicate balance I created when I first put on all the wires. So now all spreaders bend in different shapes (see the picture below). It is difficult to rebalance the whole antenna and straighten all the spreaders. So in the near future I will remove all the wires and put them on again one by one making sure I fix the wire clamps when I am done (Christian remarked btw that it is wise to fix the wire clamps when you use the antenna for portable operations regularly).

The issue of the bending spreaders

Project - Changing a CB beam into a 10m beam


As blogged before I got myself a cheap 11 meter 4 element yagi (Sirio SY27-4). I am now in the process of making a manageable yet strong and high enough mast to use in a portable set-up as well as optimising the antenna itself.

Today I started using a modelling program called 4nec2. It took me some time to figure out how to use it but in the meantime I have modelled a few different configurations of the Sirio.

This is what the antenna radiation pattern looks like when used in its original configuration on 27.2Mhz

Horizontal pattern (original) 3d pattern (original)
The main figures for this original configuration @ 27.2Mhz: Gain: 8.39dB, F/B: 18.5dB and beamwidth: 60 degrees.

Paul MM0ZBH advised me to shorten all elements by moving all sections in by fixing them with only one screw (they are normally held by 2 screws per section). This means a reduction of the elements lengths by 8cm. This slightly changes the relative size of the elements (relative to eachother). So I was wondering what would happen to the radiation pattern. It looks like this:
Horizontal pattern (one hole shorter) 3d pattern (one hole shorter)
The main figures for this shortened configuration @ 28.45Mhz: Gain: 8.59dB, F/B: 13.9dB and beam-width: 60 degrees.

Gain is up a bit but F/B ratio suffered from this change. F/B ratio is however not a main concern for me in the portable set-up. To be sure that this configuration would be a good one I also compared this to a completely scaled down version of the antenna - changing the element lengths and boom position by x% based on the higher target frequency. The outcome of this exercise:
Horizontal pattern (scaled down) 3d pattern (scaled down)

The main figures for this scaled down configuration @ 28.45Mhz: Gain: 8.41dB, F/B: 18dB and beam-width: 60 degrees.

The F/B ratio is back up to 18dB. Gain is roughly the same. To me this does not seem like a worthwhile change as it involves adding new holes to the elements. It might be a good step when F/B ratio is relevant.

While researching antenna models I also came across a model designed by DF9CY. Christophe apparently also changed an 11m beam into a 10m one. The radiation pattern of his antenna also looks very good. The position of the elements along the boom is a bit different: the dipole is much closer to the reflector.

The radiation pattern of the DF9CY yagi:
Horizontal pattern (DF9CY) 3d pattern (DF9CY)
Christophe's version performance @ 28.45Mhz: Gain: 8.64dB, F/B: 16.3dB and beam width 60 degrees.
The performance looks a lot like the scaled down version of the Sirio. Christophe achieved a bit more gain while opting for a bit lower F/B ratio.

All in all this tells me that taking the Sirio and changing it by just moving all sections in by one screw hole leads to a very acceptable 10m beam that is hard to beat by any other configuration (if you take the 4m length of the boom as a given). The sigma match for this configuration needs to be 22cm extended for the SWR to be flat around 28.4Mhz.

Another advantage of taking the "one screw hole"-approach is that you can use it the other way around and create a rather decent 12m antenna. If you keep the boom positions as they are and move all sections of all elements out by one screw hole (from the original two screw connection) you get a 12m antenna that works as shown below.
Horizontal pattern (one hole larger, 12m) 3d pattern (one hole larger, 12m)
The performance @ 24.65Mhz: Gain: 7.61dB, F/B: 9.02dB and beam width 60 degrees.
This is not brilliant - especially the F/B ratio is low - but compared to my vertical wire this should deliver a better performance. The question is whether I will be able to tune this antenna using the standard gamma match. Will have to find that out later.

Note that all models above are based on an antenna in free space. If you take the chosen configuration for 10m ("one screw hole shorter") and put it on 6m height (what I am aiming for). You get the following performance:

Horizontal pattern Vertical pattern
The performance @ 28.45Mhz: Gain: 12.58dB (at 25 degrees), F/B: 15.4dB
At 15 degrees elevation (more relevant for DX) the gain is still 12dB. This should help me to get in touch with some DX.

Update November 2012: In the meantime I built the portable alu mast to hold this antenna. The mast goes up to approx. 13m (43ft) without the need for guying (even with the beam). I used this combination during CQWW SSB 2012. The beam was at that time around 11m (37ft) high. It then has a theoretical gain of 13.6dB at 15 degrees. Perfect for DX-ing on paper but also in practise. Check out my experiences here.