Ugly is a valid adjective to describe random/higgledy-piggledy winding.
I recently made a linked dipole for 40 / 30 / 20. It is fed with RG174 coax, and does not include a balun.
Whilst trimming it, using an MFJ antenna analyser, I noticed that the SWR changed if I walked a pace or two to one side or the other, along the axis of the dipole (carrying the analyser with coax connected). This suggests that there was common mode current flowing on the coax outer, interacting with the field from the legs of the dipole. The effect was much more pronounced on one side than the other - I didn’t check whether it was the side connected to the inner or to the outer of the coax.
The SWR variation was not enough to worry about, but I may repeat the experiment with a balun included, just for interest.
People say after Plato that “beauty lies in the eye of the beholder”, and if so then the same goes for ugliness. You cannot define ugly, it is a personal response, so I would argue against it being a valid adjective.
c.f. ugly construction!
I’m familiar with the term, but “Ugly” is just an aesthetic response and inappropriate because it describes nothing except the individual values of an observer. Indeed it could be argued that the “Manhattan” style of construction is beautiful because if done well it reduces wasted space!
To return to the topic, I would avoid using a balun if possible because a balun increases the windage of the antenna.
Perhaps we should add some maths to the current balun. From the ARRL handbook a long time ago before we had fets and pentaflops a rule of thumb was that the impedance of the choke should be 10 times the feed impedance. So 500Ohms reactive at the lowest frequency. I have found that the red iron dust cores are the best solution. About 30mm od wound with 10 turns of rg174. To satisfy yourself measure the inductance of the coil (screen) at the operating frequency and use xl =2pi f l to determine the coil impedance. Aim for 500Ohms. Note that the apparent inductance changes with frequency because of inter turn capacitance. Rg174 will happily carry 100watts in this situation.
David in dl
Just my almost 50 years experience as an SWL and licenced ham - with resonant dipoles I have never used a balun until I found it was essential on the home station using an off centre fed dipole (Carolina Windom) to match it close to 50 ohm. 6:1 is used and it prevents feeder radiation and RF in the shack. This setup I have been using at home on the 80/40/30m bands for the last 2.5 years.
Otherwise with an asymetric resonant dipole I have never used a balun, and never on a portable link dipole I use for SOTA. Made 1000s of contacts without one, contest and DX work also, so why add extra weight to the top of a lightweight fishing pole with ferrite when it plainly is not needed.
Instead of opinions why not consider how things work? Yes personal experience is valuable but not every persons situation is the same and YMMV.
A balanced antenna that is a 50 ohms resistive source does not need a balun if fed with 50 ohm coax that is at right angles to the antenna wire. The feeder and antenna are matched and any induced current on the outside of the coax from one half of the antenna is cancelled by an equal and out of phase from the other half of the antenna. Bliss.
If there is a mismatch and or the antenna and coax are not symmetric in their arrangement then some rf will flow on the outside of the coax. This is called common mode current.
A matching balun or transformer at the feed point will help confine most of the rf inside the coax and allow more efficient power transfer into the antenna. But an asymmetric arrangement with the feed line may still cause problems due to common mode current.
If the length of the coax is such that you get a voltage maximum on the outside of the coax you have the highest probability of getting RF feedback. A 1:1 balun (or rf choke if you prefer) will be a big help if installed at the atu/tx end of the coax.
A choke made from coax will be as efficient as one with a magnetic core but may have less effective bandwidth and will be larger. It will also be cheaper. An earth connection at the TX would also help but usually you can’t do that on a peak. A quarter wave of wire is a good ground substitute.
Proper bonding of ATU and ground connections oc coax, key, mic screen in the rig is also important especially if there is some residual rf on the outside of the coax and rig case… A piece of #28 gauge wire does not cut the mustard.
Just because you use QRP and no smoke issues from the balun or coax does not mean you are not wasting power. A 3 dB loss is a 3 dB loss and power independent. Indeed there is a case for having lower loss systems for use at QRP. If you run 100 watts dropping to 50 watts erp won’t matter as much as dropping from 5 watts to 2.5 watts erp. Every dB above the noise is important and for QRP you will be closer to the noise than the big boys.
A balun at the top of the mast needs to be light weight and efficient. It will then ensure the lowest received noise and best signal. Common mode current and extraneous noise are correlated.
Adding a 1:1 balun at the bottom of the coax is likely to be the only way to kill off persistent common mode currents.
I use no baluns on my link dipoles, a 1:2.25 balun at the antenna for OCF dipoles and a 4:1 balun or 1:1 balun at the botton end of the feeder for my 300 ohm ribbon fed dipoles and doublets.
Thanks for the nice clear appraisal, it helps!
The two statements I’ve highlighted, though, seem to be somewhat contradictory - or are you saying that in some circumstances a choke at each end of the coax would be beneficial?
A balun at the bottom sounds a better idea due to the weight up a fiberglass pole , also the antenna would be set out in the inverted v fashion.
Yes, if you can run the coax down the mast and the antenna is symmetrical about the mast you should not need a balun at the base.
Matching and balancing at the feed point is better than at the bottom of the coax from an efficiency point of view. However, poor feed line dress can of course introduce common mode currents in spite of the balun at the top. And an asymmetric antenna may do the same.
That’s when a balun at the base will be needed as well. So yes sometimes two baluns are needed.
The balun at the tx or atu is there to “choke off” or isolate the “hot” outer of the feeder from the case of the atu/tx.
I hope that helps.
My dipole feed arrangement includes connections for the dipole legs, a BNC female for the feeder, strain relief, a choke balun (120mm diameter 6 turns coax) and a fitting to attach it to a fibreglass pole and the lot weighs just under 100g. I suppose if you use depleted uranium in your balun, the weight may become an issue.
Well yes, when u compare it with the anvil in your trouser pocket, it is as light as a feather. I always chuck the top 2 sections of the pole away so the end at the top is a sturdy 10mm dia.
It ain’t arf ot mum
Regards David in dl
We are making a batch of baluns here today so I weighed one. An effective broadband 100 Watt balun weighs in at 20 grams (0.7 Ounces). According to the internet that’s the same weight as a mouse or 1/10th or the weight of a hamster.
That sounds reasonable. 2x 4mm binding posts and a female BNC weigh in at 40g leaving 60g for 2.2m of RG174 for mine.
Damn EU and their hot and sunny WX in the Shengen Area We don’t want any of that foreign sillyness here, it’s why we had a referendum don’t-cha-know!
Its nice to know that in fact there was one sensible reason!
Is that with rg174 coax and how many turns Richard?
Balun or no balun, don’t forget to consider the weight of the entire system; including coax feeder. There is a reason why end-fed antennas are very popular with activators. Here is a picture of an end connected Windom I made:
It weighs 184 grams in total, including the spool (a Gelert washing line reel). That is not the lightest antenna possible, but connecting at the end saves carrying a long length of RG174. Also, the [current] balun is at one end of the antenna, and so it can be supported by a trekking pole or hung from a tree, thus, it does not weigh down the main mast. It is extremely quick to put up and take down; works on every band 40-6m, and is ideal for use with auto ATUs. Don’t get too fixated on one aspect of antenna design. If your overall antenna weight is low and it works fine, well then your winning. Perhaps a better investment for someone who likes making their own antennas is a vector network analyser. This seems like a good value kit:
73 de OE6FEG
73 de OE6FEG