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PU2YYP-L 146.580 Subtom 74.4 -SIMPLEX MAIRIPORÃ- SP

PU2YYP-R 146.470 Subtom 88.5- SIMPLEX MAIRIPORÃ- SP

Dúvidas, escreva para:


Desenvolvimento e  manutenção  PU2YYP / PX2Y-5876

Eduardo L. Castaldelli


Atualizado em:-

06- 12- 2012

Homebrew A 4 To 1 Balun


Many modern HF transceivers come fully equipped with built in tuners. While these tuners are great for changing bands, the manufacturers left out a very important accessory; the 4 to 1 balun. With out a balun the transceiver can only feed an antenna which uses coaxial cable. While this may be satisfactory for some operators, this is a real problem for those of us who prefer the super low loss ladder line. The only other alternative is to buy an external tuner with a built-in balun which is really absurd after spending the additional money to have one built into the radio. Fortunately, a 4 to 1 balun can be easily home brewed as illustrated in Figures 1 and 2.

Figure 1 shows a bifilar winding on a toroid. The toroid should be type 2 (red) material and can be any of the following sizes but the number of bifilar turns should be adjusted accordingly:

T80-2 25 60 Watts
T106-2 16 100 Watts
T130-2 18 150 Watts
T157-2 16 250 Watts
T200-2 17 400 Watts
T200A-2 13 400 Watts
T400-2 14 1000 Watts

The exact number of turns is not critical but the numbers listed in the preceding table should yield optimum results. It is possible to exceed the power ratings listed above but the performance of the balun may be degraded during high SWR causing heating of the core.

Toroids of this type are available from Palomar Engineers, P.O. Box 462222, Escondido, CA 92046 (1-800-883-7020). If enough inquires are made, the author will make a limited number of toroids available at RASON meetings for those who hate mail order. The author will even wind the toroid for the faint of heart.

The balun should be housed in a suitable metal enclosure such as those available at Radio Shack. Use a SO239 or BNC connector for the unbalanced input. Nylon binding posts such as RS 274-662 work just fine for the balanced output.




A 4:1 Air-wound Balun

Since some time I have been using the Diamond CP6 multiband vertical for my HF activities. While this antenna performs well on 6m, 10m, 15m and 20m and also does a reasonable job (for it's length) on 40m, it does not work at all - for me anyway - on 30m and 17m. The latter is one of my more favourite bands to listen on, so it was time to do something about it. Even though my LDG AT-100Pro automatic tuner keeps the IC-7000 happy while transmitting on 17m, the signal does not really get out and reception is poor.


LDG AT-100Pro My home has an attic and that was big enough to string some wire up. I decided to have a play around with a 17m long deltaloop fed with openwire feeder. The feeder was salvaged of an old G5RV given to me by a friend (thanks Hennie). Theoretical calculations show the impedance of a deltaloop cut at its fundamental frequency to be 150 Ohms when fed from the side. So using this setup, I was in need of a 4:1 balun to present the AT-100Pro with a more reasonable load and at the same time transform the balanced line back to unbalanced.


Definition : A balun is a device that joins a balanced line (one that has two conductors, with equal currents in opposite directions, such as a twisted pair cable) to an unbalanced line (one that has just one conductor and a ground, such as a coaxial cable). A balun is a type of transformer: it's used to convert an unbalanced signal to a balanced one or vice versa. Baluns isolate a transmission line and provide a balanced output.

Quite often toroids are used to make baluns with. Even a ferrite rod from an old AM radio can be used. I however have something against using ferrite materials in baluns. If you are not carefull, the ferrite can get saturated and heat up. You won't be the first blowing up a balun when using QRO. So instead of ferrite, I went with an air-wound balun.

This air-core balun is wound using the following components :
  • 40mm diameter grey PVC pipe with a length of 9.5cm
  • 2 endcaps 40mm PVC
  • Simple zip cord (multi-stranded core insulated wire)
  • 8 turns bifilar wound
  • 2 banana type chassis connectors
  • 1 SO239 socket
When fed with the 50 Ohm coax from the AT-100, the balun transforms this impedance to 200 Ohms which is close to matching 150 Ohms. The image below shows how to wire the balun :

Terminals B and C are wired to the banana chassis connectors for hooking up the feedline. The SO239 terminal center pin is wired to C and it's shield to D. Make sure to connect D and A together. As can be seen on the image at the top of this page, the wiring enters the PVC pipe and all connections are made internally. In my case - since I am using the balun inside - I did not glue the endcaps to the pipe but used a couple little screws instead. This way the balun is easy to service should the need arise.

Good luck constructing yours !



How to Make a Great 9:1 RX Transformer
for your Beverages or K9AY Loops


by Gary Breed, K9AY

There are lots of good designs for matching transformers for receiving antennas. Here is how I make mine it's cheap and easy, and very high performance. This is the design used in the TRX-9 transformers.


(2)  0.375" x 0.410" ferrite beads, 77 material (Fair-Rite 2677006302or Amidon FB-77-6301)

(8") #22 AWG enameled wire

(19") #24 AWG enameled wire

Small dab of super glue


The sketch below describes most of the process, but I'll list the steps anyway:

1. Glue the two beads side-by-side into a single "binocular" core assembly

2. Wind a 3-turn primary through the core using the #22 AWG wire. A wire passing through both cores and back to the same end is one turn. Be careful to avoid scraping the insulation off the wire as you pull it through the core — the edges of the core can be rough.

3. Wind a 9-turn secondary in the same manner as the primary, using the #24 wire. It may be easiest to bend the wire in half — into a "hairpin" shape. Insert the two end through the cores for the first turn, then alternately wind each end of the wire until you have a total of nine turns.

4. When I'm finished, I apply a generous dab of Duco polystyrene glue to each end — to hold everything solidly together.

5. The result should look something like this:


1. Why use two different wire sizes?  Well, it's not really needed, but it sure makes it easy to identify the primary and secondary windings after the transformer is completed. I have also made these transformers using only #24 wire, but with two different colors of enamel.

2. Do I really need enameled wire?  No, but when you nearly fill the hole in the core, and place the windings very close to one another, the efficiency (loss and accuracy) of the transformer is best. Enameled wire does this well, but I admit that enameled wire can be a bit of a nuisance to work with for inexperienced homebrewers. Good results can be had with Kynar-insulated "wire wrap" wire or other insulated wire that is small enough diameter to fit the required windings through the cores. It is also possible to make this transformer with larger wire, using 2 turns in the primary and 6 turns in the secondary. The resulting transformer will be quite acceptable for most hams, but the loss will increase somewhat.

3. Why 77 material, since it's harder to get than 73 material?  Simple — it's the optimum material for the job! It has lower loss than the more common 73 material and a permeability that places the "sweet spot" of performance between 1 and 2 MHz. But go ahead and use 73 material if it's available to you — it will make a transformer with fine performance

4. How well does the transformer perform?  This number of turns results in lowest loss in the frequency range of the 160M and 80M bands. Measured loss is 0.2 dB using the standard method of connecting two transformers back-to-back and dividing the result in half. Loss is 0.25 to 0.3 dB from the AM Broadcast band through the 20M ham band. With a 450 ohm resistor across the secondary, the primary will have a VSWR of 1.2 maximum from below the AM Broadcast band to 30 MHz. Note that neat and tidy winding results in the best performance, although more "casual" winding techniques will not add enough extra loss to make a practical difference! Unlike toroid core transformers, this type of transformer is very forgiving of the builder's technique.

5. What if I want to match to 75 ohm line?  The winding ratio can be changed accordingly. A secondary (high impedance) winding of 7 or 8 turns will work well with 75 ohm coax feedline. However, if you just go ahead and use this transformer as-is with 75-ohm line, the extra loss due to mismatch is so low that you will never detect the difference anywhere but on the test bench.