Unun VS Balan for Long wire antenna

Discussion in 'Ham Radio Discussions' started by KI7NPM, Aug 6, 2018.

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  1. KI7NPM

    KI7NPM Ham Member QRZ Page

    Greetings Fellow hams,

    I have had a interest in making a long wire antenna recently to use with my Yaesu FT-857d and my yt-100 tuner (might have got name of tuner wrong its a auto tuner any way) my issue is that is cannot seems to understand if i need a Balan or a Unun. I know the Coax will be a unbalanced signal and i think the antenna is a unbalanced signal (this is where i dont understand) so i think i need a Unun. Like this:

    https://www.ebay.com/itm/QRP-Backpa...0057.m570.l1313.TR2.TRC1.A0.H0.X9:1+UNUN.TRS0

    Am i correct in my research that the Unun is like the balan but with a ground terminal (ground terminal might be for counterpoise i am not sure)? Also I have 68 ft of 26awg antenna wire what antenna length would be best? Currently I mainly talk on 10m but once i upgrade my license i will probably be on 20m and 80m more.

    Thank you to all who can give me advice.
     
  2. KK5JY

    KK5JY Ham Member QRZ Page

    In theory, that's essentially the difference. In reality, any device that does impedance transformation (e.g., anything other than a 1:1 choke) is still going to require a choke below the balun/unun. In some cases, a 1:1 choke is the better device to use (instead of a 4:1 or 9:1 balun or unun), because the feedline losses with higher SWR can be much lower than a core-wound transformer. This is especially true if the antenna is still not a good match even with the balun, as is the case with many "multiband" antennas.
    For a single band, one-half wavelength is a good starting place. Insulated wire will need to be trimmed a bit once you measure, since the insulation lowers the VF on the wire slightly.

    For multiple bands, the best length for a single antenna is a trade-off between different kinds of losses in the system, and it depends on which bands you want to operate. The OCF antennas exploit certain lengths (and they assume a well-choked feedpoint) to achieve a reasonable match across several bands. If that's something that interests you, you might search for "off-center-fed dipole" to find some examples.
    That device is a 9:1 transformer. It assumes that the antenna impedance will be nine times 50 ohms, or 450 ohms. That's not going to be the case with a simple dipole antenna. A 1:1 choke will be much better for a simple resonant dipole antenna, such as one of these: https://www.balundesigns.com/qrp-model-1110-1-1-isolation-choke-balun-1-54-mhz/
     
    KA4DPO likes this.
  3. KK5JY

    KK5JY Ham Member QRZ Page

    By the way, you are going to get a lot of different feedback on your question, and some of it is going to look contradictory. Use the stuff that people give you to do some study and find the best solution. The folklore floating around on simple antennas is unbelievable, so you are going to have to vet the answers through some decent reference material.
     
    ZL4HZ, KI7NPM, KA4DPO and 1 other person like this.
  4. KP4SX

    KP4SX Premium Subscriber QRZ Page

    balun, not balan, is a shortened term for balanced to unbalanced.
    Coax is considered unbalanced because of the arrangement of the differing conductors. Open wire is considered balanced. Dipoles are considered balanced because both wires are the same. Random-wires/long-wires are unbalanced.
    Now if you need transformation ratio of the impedance, and it sounds like you do, then un-un is the route to go. Unfortunately there are many out there selling miracle gizmos and they tend to call them all baluns, balans, balums.

    Random wires are generally considered to be high impedance. If they are a quarter wave, or an odd multiple thereof, they might actually present a low impedance load. The frequency matters. What is best at 40m is quite the opposite of what is best at 20m.
     
    Last edited: Aug 6, 2018
    SA1CKE likes this.
  5. N5PAR

    N5PAR Ham Member QRZ Page

    73F240C1-A05C-468E-885D-4382503E6005.jpeg 34EBA2B4-919D-4A4E-A5C5-09AFB702C88A.jpeg I have made several end feed antennas using a 9-1 unun and about 32 feet of wire. Here is the link to the plans and instructions on building this antenna. It is from the Emergency Amateur Radio Club in Hawaii. http://www.earchi.org/92011endfedfiles/Endfed6_40.pdf

    For a small easy to build antenna it works pretty good. With a longer wire it will even tune 80 meters but it works best on 40 meters up. I use mine on field days and when I’m traveling. As I said I have built several and even have the unun in a large prescription pill bottle on one of them. Here is a photo of the pill bottle one and the one we made as a club project. Both work and were used on this years field day with pretty good success. You have to use a tuner since it unbalanced but my LDG tunes it with no problem.

    You can order the toroids for about $1.50 each. Winding them was pretty easy even for my arthritic hands.
     
    Last edited: Aug 6, 2018
    KI7NPM likes this.
  6. KA4DPO

    KA4DPO Platinum Subscriber Platinum Subscriber QRZ Page

    If the antenna you are building is truly a long wire antenna then there are some facts to consider. A long wire that is several wavelengths at some frequency will exhibit an impedance that can be semi-closely calculated based on the RF ground system, height above ground, and proximity to other objects to name a few. If the impedance is known then a transformer (Un-Un) can be very beneficial in matching to coax at one narrow frequency. As you begin to move away from resonance losses in the transformer climb rapidly.

    If it is a random wire intended for use on multiple bands, then a variable transformer is necessary, like a transmatch or an auto wire tuner like SGC, Icom, or MFJ make. A single transformer will simply become a heating element in multi band use unless the impedance is the same on every band, which it will not be. I have used multiband wire antennas for years with great success but there are some rules that must be followed in order for them to work. Best of luck, and we are all here to answer questions.
     
    KI7NPM likes this.
  7. KY5U

    KY5U Premium Subscriber QRZ Page

    I use a 4:1 balun to match a 200-300 ohm dipole closer to 50 ohms. I use a 1:4 unun on my 13 ohm vertical to match it to 50 ohms.
     

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