I quickly evaluated a MCL or Mini-Circuits Labs TC1-1-13M+ transformer as a balun. Although we live in a single-ended dominant RF world (single-ended LNAs, IF amps, bandpass filters, low-pass filters, VFOs, VCOs, etc.) there are times when you want differential output. That’s 2 outputs inverted, or 180 degrees apart with hopefully equal amplitude in each arm.
It’s easy to make a homebrew balun, but I wanted to see how the MCL part compares to my home-built stuff which might be 4 or 5 twisted turns of #28 AWG on a FB-43-2402 binocular core, or something like that.
The MCL part looks tiny and its small footprint [ 3.81mm X 1.65 mm ] would well suit my hybrid SMT/through-hole build style using Ugly Construction with a few carved copper islands for the SMT parts and AC input/outputs, or DC inputs. I prefer my homebrew projects to be as small as possible.
MCL specs this part at 50 Ω port impedance from 4.5 to 3000 MHz. An amazing wide band response. I measured the inductance of each arm at 21.6 µH. This is about the same as 4 turns through a FB-43-2402 balun I had lying around in my ready-made transformer tray. Some of these transformers are really sketchy and have been soldered in out of quick bench experiments in some cases for over decades.
My current interest is for lower HF, and in particular, ~7 MHz.
URL for the TC1-1-13M+ data sheet: https://www.minicircuits.com/pdfs/TC1-1-13M+.pdf
Above — The schematic of my testing jig.
Above — The MCL output into both 50 Ω terminated channels of my DSO with a 7.039 MHz signal applied. The phase difference is perfect as shown and lies in spec at all frequencies I tested -- really amazing. The amplitude difference isn't as good at HF but was within spec at lower VHF and all the way to ~3 GHz.
Above — Tracking generator plus spectrum analyzer sweep. I terminated 1 output port with a 50 Ω RF terminator and swept the other output port. This screen shot is just an HF sweep starting at the lower limit of the MCL part @ 4.5 MHz. It's pretty flat and insertion loss is on spec on this and on wider sweeps. I'm impressed with this low insertion loss across a huge bandwidth from my measures.
Above — The sweep of my balun with identical settings.The #43 mix ferrite material rears its ugly head. ~ 3 dB insertion loss that gets worse as you move up into VHF and above. I've only got #61 and #43 material ferrites for making transmission line transformers. C'est la vie!
It's fun and humbling to compare your homebrew parts against premium industry components.
Ciao
