My article (How) does this balun work analysed a balun configuration sent to me by a correspondent, apparently published on Youtube channel TrxBench.
Essentially, my analysis was that it comprises two 12t winds of two wire transmission line in parallel on the ferrite ring. The potential benefit was that the characteristic impedance Zo of each transmission line is probably close to 100Ω, and the parallel combination is probably close to 50Ω.
Online experts following fashion are opining that a low Insertion VSWR balun is better made with two wire line(s) than winding a single 50Ω coax line. They make these claims without evidence, I am not convinced.
In that vein, here is a variation on the TrxBench balun above.
The designer describes it:
Wound with 18 AWG PTFE, Solid Silver Plated Copper wire. By using that specific gauge wire with PTFE insulation tightly coupled in pairs results in a 100-Ohm transmission line. Two in parallel = 50-Ohms. The advantage using the wire over coax is it flattens and widens the bandwidth. I stress it is extremely important to pay attention to the small details. The spacing, twisting, orientation, neatness, and symmetry are extremely important.
He is quite correct regarding his last point.
His claim that the each pair of wires wound on the core has Zo of around 100Ω without supporting evidence, but it is believable based on my own experience of making and measuring similar line sections
The ‘tails’ are not just two continuations of the 100Ω transmission lines (as wrapped on the core) paralleled at the connector and load resistor, they are two line sections of some other geometry and again without evidence of their Zo. I cannot call upon experience to inform me about likely Zo, I suspect it may be significantly higher than 100Ω.
Whilst the designer explained that the picture was of a test setup for measurement with a VNA, he did not give the results of such a measurement, an InsertionVSWR plot would be informative.
I wrote a series of articles that showed how a very small length of pigtails impacted InsertionVSWR of a balun:
- A low Insertion VSWR high Zcm Guanella 1:1 balun for HF;
- A low Insertion VSWR high Zcm Guanella 1:1 balun for HF – more detail #2; and
- A low Insertion VSWR high Zcm Guanella 1:1 balun for HF – more detail #3.
So, we return to claims along the lines of
If I recall correctly, that was also K9YC’s conclusion. His updated ‘cookbook’ moved away from coax to wire which of course is fallacious if it attributes someone’s personal opinion to a well known author.
Where is the evidence of the InsertionVSWR of this ‘superior’ design? It is great to see thinking and experimentation, but a bit of scientific method would make it so much more valuable… if the claims are supported.