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:

OZ/PE4BAS


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.
 

Dimensions
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.
 

Clamping
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


HOW TO FOLD AND UNFOLD THE HEXBEAM IN THE MOST CONVENIENT WAY

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: http://www.ph0no.net/2016/10/ph0no-goes-vlogging.html
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.

FOLDING
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.

UNFOLDING
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.

FOLDING ISSUE
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


USING A CHEAP 11M YAGI TO GET A HIGH PERFORMANCE 10M YAGI

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.

Project - Cobwebb (or cobweb) antenna


A DIY GUIDE - BUILD YOUR OWN COMPACT MULTIBAND HF ANTENNA

Living in a densely populated area antennas are an issue here. Officially I can place one antenna provided it is situated at the back of my house and not higher than 5 meters above the point where the antenna or mast meets the roof line.

The challenge: how to get good results on multiple HF bands from the home QTH with an antenna that is not too much in your face. Following the official rules I could still install an enormous beam (provided the width fits my 9m wide lot). However this would create problems with the XYL, neighbours and probably the official body that has a say on the aesthetics of any change you make at or around your house.

In 2010 I worked mainly using a Ventenna dipole in my attic (inside the house) - not a real DX killer. In 2011 I started using an end fed half wave wire that I set up sloping from my attic window into the garden. This worked a bit better but I need to change the wires for different bands and I keep on getting better results when I work portable with the same end fed wire vertically on a fibreglass mast.

Reading a lot of enthusiastic stories on the Cobwebb antenna (originally by Stephen Webb, hence the weBB) and considering its dimensions I thought it would make a good compromise for my situation.

There are two main configurations for the Cobwebb: the original T-match version as developed by G3TPW and the 1:4 balun version as developed by G3TXQ.
Comparing the two versions it appeared to me that the G3TXQ version was easier to build and tune with no apparent disadvantages.

A few good sources I used:



Parts
After soaking in all the information I set out to get components that would make the antenna less visible, sturdy enough to keep the antenna in one piece in windy conditions and that would allow me to use the antenna as a portable antenna if I would choose to do so.

The following are my main building blocks (click on the pics for a larger version):


1. Support poles 2. Antenna wire 3. Center plate 4. Metal tube (cut)

FT-240 toroids,
RG-316 coax,
SO-239

5. U-bolts 6. Steel angle 7. Balun box 8. Balun parts


  1. Support poles - looking at the various fishing poles used by people building this antenna I was not too enthusiastic. The fibreglass tubes used in fishing poles are rather thin. This means you have to either choose a large diameter or accept drooping poles. It turned out however there is a fibreglass producer in the Netherlands that sells tubes through a webshop. I visited them to find the best diameter versus stiffness. It turned out to be a 16mm diameter tube with 2mm thick walls. I bought 4 x 2m + 1x 1m of the stuff.
  2. Wire - I chose to get me very thin yet very strong wire from DX-Wire in Germany. Aiming at low visibilty yet flexible wire (for portable use) I selected the UL version of their wire that has an outer diameter of 1,5mm. I was already familiar with DX-Wire through my various end fed wire antennas.
  3. Center plate - after looking for some sort of plate - preferably aluminium - I came across the plate shown in the picture. It is a very thin metal plate called a "nailing sheet" over here. The way I was planning to connect the support poles the thickness of the plate is not very relevant. The advantage of this plate is that it holds a lot of holes that can be used to affix parts and that it is very light (good property for a portable antenna).
  4. Fixture for the support poles - I found a 50cm (20") metal axis with an inner diameter of 16mm. This suited me nicely as the fibreglass poles were just under 16mm outer diameter. The idea was to fix the metal tubes on the center plate and insert the fibreglass poles into the metal tubes.
  5. U-bolts for the metal tubes - not having any u-bolts of a convenient size handy I decided to take a length of M5 (metric) wire and cut and bend that to form U-shapes
  6. Steel angle - to be able to attach the center plate to a mast I included this piece of metal. My idea is to use the vertical strip for holding a u-bolt. For a more sturdy (permanent) setup I can extend the strip adding a plate the same width (that allows for more u-bolts) or adding a strip that is wider (that allows larger u-bolts).
  7. Junction box - the antenna needs a 1:4 (12.5 : 50) balun. The picture shows the box already prepared for the balun. You will find more info on how to construct it below - after the center plate construction info. I chose a junction box of  110mm x 110m x 60mm (4.3" x 4.3" x 2.4"). If you are looking at different sizes of boxes: the minimum I would recommend is 110mm x 100mm x 50mm. Note that I am constructing a QRO balun and therefore use large toroids.
  8. Balun parts - for the QRO balun you additionally need: an SO-239 chassis connector, two toroids (FT-240) and 2.5m (8') of RG-316 coax.
..and a hand full of washers, nuts, bolts and tie wraps.

Construction of the center plate


2. adding u-bolts 3. adding the metal angle (mast support) 4. adding tubes and center bolt



  1. I cut the metal axis in three pieces: 2 x 20cm (to hold 2 support poles each) and 1 x 10cm (to hold the support pole for the balun). 
  2. I started adding my home made u-bolts through the right holes in the nailing sheet. I had to enlarge the holes slightly (from 4 to 5 mm).
  3. I added the metal angle that would go under one of the metal tubes, using two small bolts to keep it in the right position.
  4. I added the two larger tubes, drilled a hole through the whole stack and put a bolt through it - this is not really necessary to keep the tubes in place (the u-bolts will do that) but the center bolt marks the end of the insert for each of the four main fibreglass poles.
  5. I added the fifth metal tube. To attach that one I used one u-bolt and one bolt through the end of the tube. I chose this configuration as there was not enough room for two u-bolts
Construction of the balun
The G3TXQ version of the Cobwebb requires a 1:4 balun. I mistakenly grabbed a commercial 4:1 balun I had from an abandoned antenna project. Although called a "1:4" balun it was meant to be used to transform a high impedance antenna feed point down to 50 Ohm. Browsing the web I found that 1:4 and 4:1 are frequently used to describe the same balun - not the one you need for this antenna (you need one that is going to transform the low - 12 Ohm - impedance of the antenna up to 50 Ohm). Time to build the Guanella current balun described in detail in G3TXQ's website...

Note that G3TXQ describes a 100w balun. If you are building a QRO version like me you will need different toroids. Luckily NH7RO built one as well and shared the info.


3. RG-316 on toroid 6. stacked chokes 8. tube clamps 10. balun in box


  1. Cut four pieces of RG-316 of 540mm (21.25") each and strip the ends
  2. Lay two pieces along side each other (use heat shrink tubing or tape to keep the two pieces together) and connect the ends braid to braid and center to center
  3. Wind the double RG-316 with 7 turns onto one of the toroids, creating a choke
  4. Repeat step 2 and 3 for the remaining two pieces of RG-316 and the remaining toroid
  5. Stack the two newly created chokes in such a way that the coax ends of both chokes are aligned and bind the chokes together (using tie wraps)
  6. Connect the coax ends in two different ways:
    1. On one end connect the two combined coaxes (or 4 coax ends) braid to braid and center to center. This end will be used to connect to the antenna wires ("the antenna end").
    2. On the other end connect the braids of one choke to the center of the other choke. The two remaining "free" ends (center and braid) will be used to connect to the SO-239 connector ("the feedline end").
  7. Add two short pieces of wire (of equal length) to the antenna end of the balun - so you will be able to bring these connections to the side of the balun box.
  8. Prepare the balun box: add the SO-239 connector, two bolts to opposite sides that will hold the antenna wires and any clamp to the bottom of the box that allows you to attach the balun to the fibreglass tube later on (refer to picture 8 for a suggestion).
  9. Solder the feed line end of the balun to the SO-239 connector 
  10. Attach the two wires of the antenna end of the balun to the bolts in the sides of the balun box (I used cable shoes) 
This concludes the balun construction. I found connecting the tinned center braids the most challenging part as they tend to break off easily.

Putting it all together
Adding the fibreglass poles is very far from rocket science once you have the center plate. So I will refrain from going into detail. I chose to let the antenna wires keep the poles in place - so I did not affix the poles to the metal tubes.This way I should be able to take it apart relatively easily if I want to use this antenna /P. Time will tell if this is sturdy enough to withstand a storm.

The frame for the antenna wires is now ready: a cross of fibreglass of 4m each side and a fifth shorter leg (1m in my case) holding the balun. Now it is time to add the wires.

G3TXQ has a very handy table of wire lengths he needed to get his antenna tuned (including the center to wire fix point length along the fibreglass pole). I repeat it here adding the metric numbers in as well:


Band Wire length Wire length (metric) Centre-to-corner length Centre-to-corner (metric)
20m 201" 510,5cm 72.25" 183,5cm
17m 157.5" 400cm 56.75" 144cm
15 135" 343cm 48.25" 122,5cm
12m 114" 289,5cm 40.25" 102cm
10m 100.5" 255,5cm 34.75" 88,5cm

Note that you use 2 wires for each band - the numbers represent one leg of the folded dipole. I added a few centimetres when cutting the wires making sure both dipole ends were exactly the same length. It is always easier to tune upwards cutting the wire than it is to tune downwards (never found an easy way to lengthen a wire ;-)

With 10 wires of the right length you can start affixing them to the fibreglass cross, one tube after one tube, one wire after the other (starting at the 10m wire and working outwards kinda makes sense). I used the centre-to-corner lengths specified above and marked them on the fibreglass tubes. That way I knew where to (approx.) wrap the tie-wrap around the wire and tube.

I then added cable shoes to each of the wires at the balun to make for a neat connection of all the wires to the balun:
Balun with all the wires connected

The other end of the wires are the ends of the folded dipoles. They need to stay some space apart. The length of the wires and (therefore) the amount of space in between will change during the tuning process. To keep the ends at an adjustable distance I tried several things but finally went for electrical strip connectors (single pieces) and tie wraps.


Dipole ends connection before and during tuning

For every end of wire I folded over a piece of the wire, slid the connector over it and screwed it tight. That way I created small wire loops on all wire ends that could be connected using long tie wraps. By folding over too much wire at the beginning of the tuning process I knew the wire ends would only get closer to each other during the tuning. That is what you want if a tie wrap is keeping the ends together (as a tie wrap is easily tightened but not so easily loosened).

After the tuning I removed the electrical strip connectors and replaced them by heat shrink tube and a small tie wrap, like so:
Dipole ends connection after tuning

Whatever you select as the material to keep the wire ends apart be careful that the material does not soak up water and influence the SWR of the antenna.

Tuning the antenna
I tuned the antenna today (April 22, 2012) using only the built in SWR meter of my FT-857d (very doable). I started with the 10m band dipole. I read about different results people got when changing the effective wire lengths either by folding over more or less wire or by cutting of wire. On the 10m dipole I cut most of the extra length. On the other bands I left most of the excess wire. I think the latter approach is the best as you can always tune down the antenna if you ever need to.

Note that I found the antenna can be tuned by only folding over more or less wire (no cutting).



The Cobwebb during tuning
From 10m I went outwards to all the other dipoles. I did not find a noticeable change in the resonance of the dipoles I already tuned when tuning the other dipoles.


First live tests
During the tuning process I tried to get some signal reports and did some comparisons to my tried and tested half wave end fed wire I set up vertically. My mast was not sturdy enough to carry the Cobwebb on a height above 6m (18ft). Therefore I focused on 10-12-15m to at least have some relative height.

Conditions were rather poor on the higher bands with deep QSB. Three Italian stations came back to my calling on 15m but either the signals or their fluency in English was just not good enough - anyway there was no opportunity to get different reports on the two antennas. On 17m I heard and was able to work EY7 (5000km) using the Cobwebb. The first DX on this new antenna!

10m came slowly alive but I had to pack up soon so I just compared the signal levels on the Cobwebb and the vertical end fed wire (using a handy antenna switch). The QSB made it difficult but switching quickly back and forth I found that both antennas were most of the time very close (not even 1 S unit apart), sometimes 2-3 S units apart with no clear winner - sometimes the vertical was stronger, sometimes the Cobwebb. There was not enough time to find a pattern (like distance or antenna used by the other side). I will need to do more testing to establish that.

What this first test shows me is that the Cobwebb is a very practical multi-band antenna (my end fed wires need to be changed to cover the 5 bands) with a very acceptable performance. It also shows me that for a quick portable setup the end fed wires set up vertically on a fishing pole are hard to beat.


Cobwebb in action during and after tuning