This balun has 22 feet of good quality RG-213 wrapped on a 4 in. ID piece of thick wall PVC pipe. The turns are spaced with 1/4 in. nylon rope. NOTE the very short stub at the bottom right, which runs directly to a high-power L-Network matchbox.
The home-brew openwire from my vertical dipole attaches at the top right.
Pictures of the rig, matchbox, balun, and antenna can be seen here.
DUAL-CORE 4:1 GUANELLA BALUN
This is my "standard" balun I use for medium power levels.
For my 40m OCF, I used -61 Cores.
For my 80m OCF, I used -43 Cores and a couple more turns per transformer.
I run 700w through the -61 and the -43 versions of this balun in SSB and CW, but I would certainly reduce power for RTTY. This is also band dependent. On bands where the SWR is not so good, I would run less.
It's hard to state a specific power level without knowing the exact antenna and the bands in use, but here are some guide lines.
- Less than 3:1 . . . . . . 700W
- Less than 4:1 . . . . . . 600W
- Less than 5:1 . . . . . . 500W
- More than 5:1 . . . . . . 250W
For RTTY or FM I would run only 50% of that.
NOTE: These are gut-feeling calls. I haven't tested this extensively. However I have used this antenna like stated above, but only in SSB and CW. I have made not tests in RTTY.
MY MOST RECENTLY BUILT VERSION OF THIS:
I built this balun for Darell, WA3OPY in Januay of 2015. He used it for his 80m OCFD antenna.
The front side is where the wires and toroids are. All connections are sealed with either heat-shrink tubing, licquid electrical tape, or Epoxy glue.
The coax connects to the back side through an L-Connector. The coax is strapped to the pole at the connectors using a cable tie. This keeps the balun securly fastened to the pole with the exposed wires and cores on the opposite side.
Special care was taken to use a matched pair of torroids whose beginning permeability was within 1% of each other. THIS IS IMPORTANT. The greater the difference in the cores, the higher the SWR will be at 30 MHz. In a balun with 16% difference in permeability between the two cores, I have measured 1.7:1 SWR at 30MHz.
According to W8JI, there can be up to 20% difference in permeabiliy in like cores when they are from different manufacturing batches.
As can be seen here, my balun exhibits lower SWR at 30 MHz than the Balun Design Model 4115t, which I consider to be an excellent balun. I use Bob's 4115t as my standard benchmark for 4:1 Guanella baluns.
DETAILS OF THE BALUN:
- Cores: Ferroxcube Model TX36/23/15-4A11 (#43 ferrite)
- Wire: 12 turns of Teflon insulated twisted pair, [about] AWG-18
- SO-239: Gold-Plated Center Connection, Teflon Insulation
This is the CMC balun (RF-Choke) I use when working with fiberglass poles. It is the lightest weight solution I know of.
For my 40m OCF, I place this at the bottom of the pole, strapping it to the pole with cable-ties to keep it from pulling on the thin coax above.
My 80m OCF has a much more lopsided feedpoint (close to one end) and I had a lot of problems with CMC. I placed this directly under the dual-core balun, and had no more problems.
My latest balun is again a simple CMC choke, but designed to be used with low band vertical antennas. I build my verticals using fiberglass poles and simply run wire up the pole. When necessary I also use top-hat loading (wire top-hats of very thin wire).
A simple RF-Choke was needed for the base. The first one was built just last weekend but I haven't made any pictures of it.
You will find a description of it here: RF-Choke
When designing these, keep in mind power levels verus the saturation temperature of different core material. For more than 500w, you will need to stack 2 or more -43 Toroids.
Many times, even -61 is enough but I've only tried it on 80. For 160m you could simply use two in series (with -61 of course).
Many more of my home-brew baluns are shown: HERE