: Baluns (Brands, Designs, Losses, DIY Loops, etc.)
2011-03-15, 03:49 PM
Just wondering... anyone have plans on making a 300 to 75 ohm balun using toroidal cores? Without divulging much, I have access to a couple.
I'm working on it. There is a lot to look into such as the correct core material...the correct wire type / size and number of windings. I have thried making a low loss balun from this link: http://homepage.mac.com/kenwetzel/Low_Loss_Balun.htm.
This balun worked better on some channels but worse in others. It is designed for FM so i am trying to fiugre out how to make it work for vhf hi thru uhf.
2011-03-16, 01:56 PM
And finally, here's what our UHF PCBs (as used on DB2, 4, 8, & C4) look like. Note that this is 1 dB/div rather than the 2 dB/div on the previous plots. Very efficient on UHF, but brutal for VHF.
Wow, that's a nice UHF response. I'd love to have that for my GH. (Although it does cause me to wonder how the DB8 could have any VHF response.
2011-03-16, 04:21 PM
Wow, that's a nice UHF response. I'd love to have that for my GH. (Although it does cause me to wonder how the DB8 could have any VHF response
Here's what happened when I tested the C5 and the DB8 baluns back-to-back for insertion loss.
Focusing on the high-VHF spectrum gives this:
2011-04-08, 02:15 PM
What would be the signal loss difference between a 1/2 wave loop balun as compared to a commercial 4:1 balun? Thanks.
2011-05-04, 11:40 PM
Over time, do typical 300Ω to 75Ω transformers (baluns) decrease in efficiency? Would the 'resistance' factor increase over time? I've read here about different brands and some having more favourable signal loss characteristics, but how would one know if what they're buying at The Source is a good ferrite core balun, or something cheaper.
2011-05-20, 10:05 PM
For the love of me, I could not figure out why my reception of WQLN 54-1 RF50 was gone while reception of the other lower RF station's were being received. Then I remembered that Jase had issues with water in his balun and was loosing reception of the higher RF channel's.
Up I went and sure as crap, when I reached up to take the balun off, water started coming out.
I had a spare XG91 laying in the basement, thus I took off and transfered it. Voila, reception came back. Thanks Jase.
Jase did you try to dry it out, or just send it back to Antennas Direct for replacement?
Anyways thanks for the tip.
2011-05-27, 04:11 AM
Stampeder referred me to the Balun thread wrt to which balun to purchase. I've read the thread, but get the impression it depends on the individual balun you happen to get. Would anyone recommend which one/s is more likely to be good, ....please; promise not to sue you if what you suggest turns out to be a dud.
Or, should I make one from coax? If so, to what dimensions.
The more I read, the more scratches the head gets :confused:
2011-05-27, 10:50 AM
I've read the thread, but get the impression it depends on the individual balun you happen to get.
Thats basically it, some individual units are better than others. Try the CM balun you mentioned, its local and fairly easy to return.
2011-05-27, 12:03 PM
Or, should I make one from coax? If so, to what dimensions.I don't think there is a coax balun wideband enough for a VHF-hi/UHF combo antenna.
2011-08-18, 01:51 AM
Hello, my name is Greg, new member, read this whole thread. WOW! I'd like to share some of my findings. I recently made a DIY 4 bay antenna which is the attic and performing great. This lead me to what kind of balun to put on it. I had 4 push on baluns in the junk drawer, three were clearly different in design. So this lead me on what the best one would be. To start with this is my current performance which I am pleased with. I left off the reflector to get multi directions with out a rotor. This chart shows the stations I get solid, 17 networks and about 50 channels. There are duplicates but that is good, since programming varies from one "affiliate" to the other.
This is the antenna being tested on a stand before I cut it down.
Mounted in the attic some what temporarily.... The attic is about 30' high and the signal is excellent, I assume most coming from the ends of the attic East and West, which is just vinyl siding, particle board and non metallic weather wrap.
Part 1 of 3
2011-08-18, 01:54 AM
Here are the baluns I am dealing with.
What looks like capacitors on the right are not. The balun on the right is the one I am using now.
These two look the same but performed slightly differently.
The one that looks like it has capacitors, does not. Those are RC components, both resistor and capacitor combined. The single toroid is a voltage balun. This link explains this very well, about 3/4ths the way down the page.
The other three look like 1:4 Guanella-Balun (Current-Balun). You can google that and find some good links...
Part 2 of 4
2011-08-18, 01:56 AM
With my new DIY attic antenna (9.5" spacing, 10" elements) I wanted to figure out how to test these baluns and pick the best one. I have some HP gear on my bench but they only go to 512 Mhz. My sweep is only good to 20 Mhz. I don't have a spectrum analyzer, so I used the TV's signal strength, SNR diagnostics to make some A/B comparison (Sony Bravia LCD 37" about 3 yrs old).
The first test was between the one with the "capacitors" (RC device) and single toroid and the one I am using now (double ferrite and big wires). I used my DIY 4 bay antenna on a stand outside, 30 feet of coaxial, direct to the TV. I did use a small indoor amp near the TV, that came with an indoor **Terk HDTVa antenna. Not sure how that might have affected results, but I'm going for relative readings. The one on the left was slightly better, than the single toroid version (with RC devices) on the right, however the latter was better on VHF Hi. I only have one VHF Hi station, Chan 11 (200 Mhz). I put that balun on the left, double ferrite big wires, on my DIY antenna, where it is working now, giving results in previous post.
I found the other two push on baluns in the junk drawer later (double ferrite, small awg ceramic covered wire). They look identical. I compared them to each other using rabbit ears. For these test I used TV rabbit ears (dipole) on a stand, 3' elements each (78 Mhz resonance), laid out horizontal and no amplifier. From the twin lead the balun, than 30' of coaxial into the TV. The rabbit ears did fine for the "local stations", even UHF. It even got some distant stations late at night.
Not bad on UHF for some broken dipole (rabbit ears).
(On this TV 80%/20 SNR is a min good solid signal, but signals down to 76%/16 SNR are viewable, however marginal and subject to dropout and pixelation.)
Since they look the same you'd expect the same results, but one was consistently one or two more % signal and SNR greater. The one with the loose windings did not perform as well. Goes to show you there are variations as people noted. I compared the "RC" single toroid version with the rabbit ears and found it was the same or less pretty much across the freqs, except again noticeably better on channel 11 (~200 Mhz).
*(BTW the Terk HDTVa is an excellent indoor antenna. It actually got all the stations but needed to be aimed and was an eye sore. One tip with indoor antennas, add on a coaxial extension so you can move the antenna away from the TV and closer to outside wall, window and higher up near the ceiling.)
Part 3 of 4
2011-08-18, 02:07 AM
Coaxial Balun on UHF... (per eariler posts)
This thread inspired me to make my own coaxial balun with some RG58 I had (VF 0.66). I know it's 50 ohms but it's what I had bulk. I did not want to cut up any RG59 or RG6 cables (yet). I was shooting for about 515 Mhz, so the matching section was about 7.6" I recall. I jury rigged it up, than compared to one of the small wired baluns (the better of the two).
These are TV station signals not a constant signal from a generator.
It is only relative results not absolute.
The little bump around 489 to 555 Mhz could be the balun peak freq, but I was not impressed nor disappointed. BUT! Before I got too excited I went straight from twin lead (rabbit ears) to coaxial and got about the same signal, or I got tad less signal on a few stations with the straight antenna to coaxial (no balun) but not much. Why?
That showed me the balun was doing a little (but very little) at least for this antenna, which may be a poor choice for this kind of testing. I was not using my DIY 4-Bay because it's in the attic working well, did not want to mess with it. It is also hot up there. Why was the straight 300 twin lead to 75 ohm coaxial working well compared to the baluns? The rabbit ears was just for ease of testing, but may be a poor choice to do balun comparisons? We shall see. I will test it on the real DIY antenna. A folded dipole might be better. I don't have any twin lead to make up a folded dipole.
I looked into a non folded dipole, aka rabbit ears, 180 degrees apart horizontal. The impedance may be only about 75 ohms at it's half lambda resonance Freq, in this case 78 Mhz. Since I was many times over 1/2 lambda, who knows what "impedance" it was? Who knows what my DIY antenna is, 150 ohms impedance? So may be 2:1 balun is better as discussed in this thread and some links. It seems some of the commercial 4 bay antennas have "air core" PCB baluns that may be much less than 4:1. Of course some baluns only lend their self to even multiples, 2:1, 4:1 and so on. More test....
I ordered some transformers from Coilcraft and Mini Circuits... These are RF transformers for the communications industry. They have excellent specs. I am going to experiment with three of them, on my DIY antenna in the attic. They are all 4:1, but two of the three models have taps for 2:1. I will see if a ratio other than 4:1 is better, at least for my antenna. I'll let you know.
Conclusion so far:
Balun performance is antenna dependant and Freq dependant.
Not all antennas are 300 ohms impedance, theoretical for folded dipoles.
Baluns are like a box of chocolates, you never know what you will get, China.
A good Balun may be bad for your particular antenna, feed line and Frequencies.
If you have only UHF channels, a balun optimized for VHF may not hack it, vice verse.
Go buy a bunch and try them, see which one is best, a good balun can make up a dB or three. A bad one can cost you many dB's. At least make sure you don't have a really bad one. After that the best you can do is get a bigger, more directional antenna higher above ground.
Part 4 of 4
2011-08-18, 01:25 PM
gmcjetpilot thanks for the great contributions and welcome here. :)
2011-08-18, 01:45 PM
Wonderful to see experiments and data. Thanks much.
Yes, a bit of a bump at 549 but not dramatic.
My hope is to fashion a fractional-wave coax balun which is tuned as sharply as possible to pass 94.5 FM and discriminate against everything else around. (Or figure other ways to tune my antenna feed.)
I have the means of quantitative measurement and evaluation for most of my other hobbies, connubial bliss excepted, but RF eludes me... so far.
2011-08-18, 02:02 PM
Would a shorted quarter wave stub or a (helically) tuned cavity do what you want?
2011-08-18, 02:56 PM
Would a shorted quarter wave stub or a (helically) tuned cavity do what you want?
It certainly looks like a good solution for receiving far-away FM signals when you live not far from the CN Tower. But you have to assume some good agreement among theory, design, and construction... which I rarely find and I can't measure when it is done.
I say "good" agreement because we are talking of a band where being off, say 10% (a pretty small tolerance for DIY) changes the 94.5 MHz into 85.0 or 104.0.
Is there somebody who can build or measure other DIY constructions?
What are the bandpass characteristics of such a balun? If centred on 94.5 MHz, where is it down, say 6 dB?
2011-08-18, 02:59 PM
Can you take one of gmcjetpilot's nice coax baluns, just smother the exposed wires in silicone caulk, and be done?
2011-08-18, 10:08 PM
Not to be picky....ok I am. The coax connector could be improved using the compression type. Not sure if the loose crimp connector is affecting anything in the way of signal.
2011-08-18, 11:59 PM
peano wrote: Not to be picky....ok I am. The coax connector could be improved using the compression type. Not sure if the loose crimp connector is affecting anything in the way of signal.
Yep this was THROWN TOGETHER as I sat in front of the boob tube with an exacto knife, beer and a hunk of raw RG58 (I use for SW radio stuff). I had some el cheepo RG6 fittings I would never use. Clearly RG58 is smaller. So I just took the braid, made a pigtail and wrapped and stuffed it in the outer ring of the fitting. :o I made the center insulation so not short out, but it is flopping around in the to big fitting. It's just sitting in there, very crude but better than nothing (barely). It's not crimped at all. It will pull out without any force. I do have a very nice (expensive) AMP tool and BNC connectors for RG58. I make my own antenna and test cables. I have 400' or RG58. Should last a lifetime.
I don't think I will use a coaxial bulun any more than testing. If I do I'll cut up an existing RG59 or RG6 coaxial cable assemblies with fittings already on it. I have several I can sacrifice.