Playing with baluns/ununs

[majoco]

I always thought my antenna was not doing very well once it got past the 19metre band - 16metres was very flat. It's an OCFD, 45ft one end and 15ft the other, a homebrew 9:1 unun at the junction and a braid breaker in the same container. The toroid was a FT140-43, 11 quadrifilar wound, one winding was the secondary and the three all in series the secondary going to each leg of the OCFD. A bit of googling more or less explained that the 43 mix didn't go much above 15MHz so was prompted to make a simpler unun with a 61 mix binocular core - much easier to manufacture and supposedly a better performer as there is less leakage as nearly all of the winding is inside the core.

A fine afternoon and I was up the ladder after measuring the signal from my local interference in the IMS band at 13.560MHz - gave me -60dBm -ish. Back to the bench and took the cover off my pillbox enclosure - all very dry - pic attached of all the bits. Fitted the new unun and used the old braid breaker - up the ladder again and reconnected - all good. (PS - I don't use anything fancy to keep everything dry - a couple of layer of plumber's teflon tape around the lid of the pillbox and the PL259 connector at the bottom is shrouded by another pillbox as an umbrella!)

Back to the SLM and the signal has increased by about 3dBm which is alright, a search around the 16m band found a few stations, Radyo Filipinas on 17820kHz had a very good signal, 1530pm/0230UTC. As a bonus the background atmospherics around the lower bands seems to have decreased, just hope the signals haven't done the same! Now for some late nights and early mornings just to see how it goes.

The "SLM" is a Hewlett-Packard 3586A - I'm not going to question its accuracy!

 

[prcguy]

Type 43 ferrite should have been just fine for your balun, are you sure there are not too many windings causing too much inductance? I've built a few 9:1 types and dozens of 49:1 transformers on FT-240-43 single and dual cores and they work very well across a few MHz to 30MHz. I recently made a dual core 49:1 using FT-240-61 cores and with the same winding arrangement the usable low end moved from about 3MHz to 6Mhz.

The typical offset center fed dipole using various wire length ratios like 67/33% or 75/25 (as yours), 81/19 and so on generally use a 4:1 current balun and a 9:1 might degrade things. Using an Amidon BN-61-002 binocular core you can make a great 4:1 current balun and two of them tested back to back have less than .1dB insertion loss and under 1.2:1 VSWR over 500KHz to 55Mhz. And this balun will handle up to about 150 watts continuous. I've also made the same balun using type 43 material with only a slight shift in frequency response.

If your curious, here is the 4:1 winding arrangement I use for the BN-61-002 core, borrowed (purloined) from Elecraft:
https://www.nonstopsystems.com/radio/pdf-ant/antenna-artile-balun-elcrft-bl1.pdf

I always thought my antenna was not doing very well once it got past the 19metre band - 16metres was very flat. It's an OCFD, 45ft one end and 15ft the other, a homebrew 9:1 unun at the junction and a braid breaker in the same container. The toroid was a FT140-43, 11 quadrifilar wound, one winding was the secondary and the three all in series the secondary going to each leg of the OCFD. A bit of googling more or less explained that the 43 mix didn't go much above 15MHz so was prompted to make a simpler unun with a 61 mix binocular core - much easier to manufacture and supposedly a better performer as there is less leakage as nearly all of the winding is inside the core.

A fine afternoon and I was up the ladder after measuring the signal from my local interference in the IMS band at 13.560MHz - gave me -60dBm -ish. Back to the bench and took the cover off my pillbox enclosure - all very dry - pic attached of all the bits. Fitted the new unun and used the old braid breaker - up the ladder again and reconnected - all good. (PS - I don't use anything fancy to keep everything dry - a couple of layer of plumber's teflon tape around the lid of the pillbox and the PL259 connector at the bottom is shrouded by another pillbox as an umbrella!)

Back to the SLM and the signal has increased by about 3dBm which is alright, a search around the 16m band found a few stations, Radyo Filipinas on 17820kHz had a very good signal, 1530pm/0230UTC. As a bonus the background atmospherics around the lower bands seems to have decreased, just hope the signals haven't done the same! Now for some late nights and early mornings just to see how it goes.

The "SLM" is a Hewlett-Packard 3586A - I'm not going to question its accuracy!

 

[nanZor]

While you are at it, consider making a 1:1 balun (common mode choke) if you don't want your coax to be part of the antenna, and the resulting change in directionality. Unless of course you DO want a bit of vertical interaction.

UNbalanced antenna fed with Unbalanced coax, is a virtual guarantee of braid common-mode coupling. Many amateurs find this out the hard way with either an increase in noise ingress from the shack, or perhaps undesirable directional characteristics. Either that, or burning lips on the mic, turning lights and other gadgets on and off at high power etc.

Just saying - while you are in this mood, wind a 1:1 with enough choking impedance to do some good, and place it near the feedpoint. Obviously you won't have the "hot mic" issue, but may cut down on shack-noise traveling up the coax and back down, and/or preserving what the antenna patterns are supposed to be without any vertical coupling.

 

[majoco]

That's what the thing still in the pill box is - a braid breaker, about 12 turns of the small coax through a another FT140-43 toroid. Down the other end before the cable is connected to my multicoupler it goes through a load of smaller toroids around the cable. I won't be doing any transmitting through it anyway, my only HF transmitter is a TS120V and thats been in the cupboard for years! It gets hauled out occasionally for a signal source rather than anything else!