HFU HF Underground
Technical Topics => Equipment => Topic started by: desmoface on November 05, 2012, 0218 UTC
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Hey gang, i was repairing storm damage (courtesy of Sandy) on my full wave horizontal 80 mtr loop and am considering adding either an "ugly balun," or possibly a dx engineering 1:1 balun. The antenna is abt 275 ft long and is currently just fed directly with coax, and I use it for 10-80 operation with a tuner.
It appears to work fine, but i'd like to make sure it's performing the best it can using coax (buryflex).
Obviously, i like the cost of building an ugly balun, but will it work as good as the 1:1 dx engineering balun? I'm open to any other suggestions. Thanks in advance.
Steve
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FWIW, I use a Buxcomm (9:1 in this case) balun with sky loop, and have been very happy with it. I have also used some baluns from Unadilla.
My personal preference is to use baluns to feed balanced antennas, vs directly connecting to the coax, although I honestly have not done enough experimenting to see what, if any, actual benefit there is. It's just something I've always done.
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I'm a little cornfused over what state your aerial is currently in. Is it still a loop, or now is it an end-fed length of 275' wire?
For receive, you can forget the balun altogether. Really. If, however, it makes you feel better to use one, go the cheap route and wind 10' of coax into a randomly wound coil 6-8" in diameter right at the aerial feed point.
If it's now a random wire, no balun is needed, as it is not a balanced aerial. Better to run 50' or so of a ground wire (along the ground) soldered directly to the coax.
In the end, if you don't have one already, save up your shekels and get yourself an "antenna tuner". MFJ makes some decent ones for cheap, and they can be found on Ebay and Craig's List (or your local ham fest).
Or, you could <gasp!> build your own.
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I built a 4:1 for my loop(400' sky loop)and it did seem to help.I al;so use a tuner the balun seemed like it made the antenna tune better.Just my two cents.
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If you don't want your coaxial cable to become part of the radiating antenna which can cause high SWR along with strange
radiation patterns, then use a balun. Simple as that.
No matter how well balanced the antenna is, once you connect it directly to an unbalanced cable like coax it will cause
issues with the cable radiating the signal down it's path at various points usually at a distance of the 1/2 wavelength.
Baluns choke out this common mode current and helps push all your signal out to the antenna.
For dipoles a 1:1 balun should work perfectly. The only reason you would use a 4:1 or 9:1 is if you need to convert the impedance like when using a 300ohm closed wire dipole (or loops) instead of the more common open wire 70ohm dipole most of us use.
The same goes for receiving as does for transmitting.
For receiving a balun can help for cutting down on noise that will be picked up from the coax run path like various
electronic devices near the cable.
For longwire or inverted L antennas you want to use an unun (unbalanced to unbalanced) since end fed antennas are
naturally unbalanced aerials. An unun of 4:1 or 9:1 (prefered) helps greatly for SWLing because it converts the high
impedance of your antenna down to 50 to 75ohm impedance that your radio wants to see coming into its antenna jack.
Also helps with the mismatch caused by directly connecting the unbalanced high impedance antenna directly to coax.
I use a 9:1 unun for my SWLing on the inverted L and it helps greatly reduce noise and increases signal strength on my DX398 compared to just connecting the antenna directly to it.
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I can attest to a balun.
Kage gave the reasons.
Peace!
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I am using a pendant type antenna. The Balun results in lower noise.
On a Longwire I used to run a UnUn. Again, the UnUn (a single ended input :balun...) resulted in quieter reception.
My vote----Yes use a balun
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Keep in mind that *where* you place a transformer (balun/unun) makes a difference. For example, a transformer at the aerial feed point really won't have much effect on common mode stuff picked up by your feed line.
Also, it introduces loss.
So, your aerial might be quieter because of losses. Without taking any comparative measurements with signals of known strength and looking at the numbers, you don't know for sure.
I'm not an anti-transformer kind of person. I do think, however, that a lot of $$ gets spent on things that folks ascribe magical properties to (in all facets of radio, which is weird, because it should be a scientific kind of endeavor).
My main point is that an antenna tuner will give you frequency flexibility (on both transmit and receive) that a plain transformer will not.
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Hey Billy, you seen Studebaker Hawk? That guy owes me money.
On the antenna thing,I like a random wire tuner for listening and the "Matchbox" types for transmitting.
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Hey Billy, you seen Studebaker Hawk? That guy owes me money.
He could be a narc or a lady Marine!
On the antenna thing,I like a random wire tuner for listening and the "Matchbox" types for transmitting.