Great graphics; I love that knot to stabilize the twin lead!
Are you recommending a balun at both points – the transciever input and the other end of the feedline where it feeds into the antenna?
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Of course, you only need a balun to get from the balanced antenna to the unbalanced coax cable or the unbalanced coax socket…
The current balun would not be mandatory for qrp /p applications… however, the vagabonding RF can also do stupid stuff there…
With the IC 703, for example, the paddle no longer worked for me.
73 Armin
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OK. So if I’m using twin-lead for the feed line and the antenna, I don’t need a choke or anything at the “split point”, only at the transciever end of the feed line?
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Correct… this would then be a solution for installing the balun, for example, in order to get from the parallel wire to the antenna socket.
73 Armin
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I like it. If I’m making my own balun, can I just choose a toroid based on the size of the box?
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Of course you have to adapt your toroid and the wires to the power. … and then you choose a suitable box…
This can be very small. Here is an example from me… up to about 50 watts.
For the parallel line you need of course 2 sockets. …or you take something like that
73 Armin
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That makes sense, but I don’t know anything about the sizes and types of toroids. How can I determine which ones are suitable for my power levels? FYI, I intend to use 20W or less on the HF bands between 80m-10m.
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the outer diameter of Amidon 114 - XX (I recommend the 114 - 43) is about 30mm … then a little space for the wire (22 AWG)… it ist ok for 20 Watts
If the housing has inside 40mm space it is enough
The toroid in the film can is a 114 - 43
73 Armin
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So: If you like to test this with a dipole and parallel wire…
Then just take a thin two-wire line (e.g. speaker cable) and find the dimensions for the respective band… leave it a little longer on each side and bend the wires at the end of the dipole legs and fix them with cable ties. You can then tie a string to the loop at the end.
Make a knot as above so that the dipole keeps its length. Take the mechanically suitable length of the parallel line and clamp it to the sockets of the 2:1 balun.
With the SWR meter (you may even have one in the TRX?) between the TRX and the balun, you can then adjust the length of the feed line and / or the dipole.
BTW: You can test the balun before if you connect a 100 Ohm resistor instead of the antenna. If the SWR is ok… then the balun fits.
Have fun building the antenna - Armin
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You should keep zip cord feeders short, and just use them on the low bands. It is likely high loss because of the pvc dielectric.
I like twisted pair from CAT5. It is PE dielectric, and a nice low loss feeder.
Zip cord KE4MD test: 5dB/30m@10MHz = 1.1dB@7m
Cat5 spec: 2dB/30m@10MHz = 0.5dB@7m
KE4MD tested some
And as usual Owen has something to say on the subject
Something important with thin antenna wire, twisted pairs, and zip cord is using a figure 8 winder or you will enter the tangle zone.
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I have a Xiegu G90 and yes, it does have a built-in SWR meter. It’s not the rig I want to carry up a high mountain (again), but it can be very useful as an antenna analyzer!
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You’re right, of course… here is a comparative measurement from DL2LTO… for 30m feed line in this way.
With 20m it is just about possible…if the line is not too long
73 Armin
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I always build my antennas down in the yard or park… and when they work I go with them to the summit 
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…by the way do you know the great video from Ingacio @EA2DB
Armin
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As promised earlier I follow-up with some fotos.
Here are some dipole centerpieces made from strips of plastic.These are all recycled lids of food containers. Philadelphia cheese and Pringles chips come with suitable plastic lids.
This is the most fancy one built recently. It has a real strain relief to the dipole legs. I have used pieces of silicone tubing pushed over the feeder to prevent it from breaking. Not shown here is a final layer of heat shrink tubing on the crimped connectors.
In my experience these dipole centerpieces last at least for 100 activations. If they get older the wire might break. It is a good idea to use a cold winter evening to refurbish your dipole antennas once a year and replace centerpieces, shorten the wires by a few inches and make all connections new.
This is my connection of the feed line to a KX2.
Plenty has been discussed if a balun is necessary or if it offers any advantage. I have decided to go without a balun. After all, where is the unsymmetry? One side of the dipole is connect to the enclosure of your rig via the ground connection, the other isn’t. Does not look like a big assymetry to me. It would be different if the rig was operated from a mains power supply. But this is anyway not the case for a SOTA activation.
73 Heinz
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Scabbing covers the full range of procuring without payment from begging to dumpster diving, but stops short of doing something likely to result in a conviction, if anybody is watching.
In some quarters there is a spiritual aspect as scabbed objects have mauri that is lacking from bought and new objects
also noun: The pull tag or crown seal on a beer . “Pick the scab off another Lion Red”
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In some cases two maybe ok.
For your case the 4:1 Transformer (first of the three) is not relevant.
73, Ludwig
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There is one more question. Do you use an ATU (matching unit, extra device or part of your TRX)?
case 1 - no, case 2 - ATU only usable for lower antenna SWR (up to 3 or 4 or so) or case 3 - for higher antenna SWR (up to 10 or more).
case 1: you have to tune your antenna (mechanical) together with the feeder by using a SWR meter or better an antenna analyser.
case 2: a well calculated antenna may work well without tuning by the cutter.
case 3: nearly all random wires are usable.
73, Ludwig
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Hi Armin,
At the risk of confusing Joe and being labelled a PITA, your 2:1 balun isn’t accurately named It is a 1.5:1 current transformer and matches a 112 5 ohm load to 50.0 ohms source. It is more elegant than the 2:3 turns ratio voltage transformers I have used in the past.
Thanks for posting it.
73
Ron,
VK3AFW
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That’s the fantastic thing about the KX2’s tuner… it matches almost anything: whether it’s open lightning rods, cut aluminum foil, or just a long wire with a counterpoise…
In general, without a tuner, (when you have tuned the system) you will have an SWR of 2 - 3 without balun.
But: Normally this does not kill the power amplifier.
But as I explained above, I’m not a fan of using dipoles on summits anyway…:
- In my experience dipoles are much more sensitive than endfeds as far as ambient influences are concerned. (especially if you don’t have a tuner, you are quickly in the border area of SWR). And there are different conditions for each summit.
- A Balun 2:1 transforms here also the influences and lets them become a little smaller.
- I can set up the endfed more diversely (Slooper, L, Inv V. …).
With a balun 49:1 to 64:1 the influences become even smaller. - And since I’m lazy, perhaps the most important argument for me: for a band change on a linked dipole, I have to get up and lend a hand … maybe even lower the mast.
But that is my philosophy… 
73 Armin
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