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Discussion Starter #1
One thing I just realized about the value of these antennas is the fact that there is no BALUN signal loss. According to some articles that I read they state that you can lose more than half of the signal with a bad balun!

See - http://www.kyes.com/antenna/balun.html

So my hypothesis now is that it may be better to get a preamp with 300 ohm inputs rather than a 75 ohm input because this will eliminate the need for a signal stealing balun.

For this reason my SS-2000 works better than anticipated.

I have been wondering how to best tweak antenna setups to minmize all losses and maximize signal. My assumption is that an antenna is being used in conjuntion with a preamp for GTA viewers trying to get Buffalo stations.

I guess that you need the balun if you are not using a preamp.

I was wondering why my Winegard SS-2000 was working almost as well as a CM4221 with AP4700 preamp. When I looked inside the Wingard SS-2000 - see:
http://www.digitalhomecanada.com/forum/showpost.php?p=372939&postcount=87

I noticed that there was a preamp but no balun. The preamp was connected to the 300 ohm leads!

After doing some reading I learned something that appears to be common sense but I have not seen it discussed here.

If you have an antenna that has 300 ohm output then use a 300 ohm input preamp.

This means that if you have a CM 4221 you should not be using a CM 7777. With a CM 4221 or 4228 you should be using a Channel Master CM 0264 or Channel Master CM 064 preamp!

Match the antenna output and preamp input and eliminate the balun!
 

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Ferrite-core baluns are generally about 90% efficient. If a person was trying to wring those last 1 or 2 dB from their gear they could replace a balun -> preamp pair with a 300 ohm twinlead -> preamp solution. The down side is that twin lead is much less durable than coax.
 

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Discussion Starter #3
I guess trying to go from Buffalo to Toronto then every db counts.
If the preamp is within 12 inches of the connector post on the antenna then who cares about cable durability.

Can you make your own 300 ohm wire using heavier guage wire?
Just out of curiosity can you use electrical wire? Split it and space it accordingly?

Next is low noise preamp.
Check out the noise stats on these premium preamps from the UK
http://www.researchcomms.com/hdtv.html

If you must use a balun - what is the best one to use?
 

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The Impedence of the down lead needs to be 300 ohm, so I think its best if you just go with a properly rated manufactured twin lead, which is not particularly expensive. Impedence is a form of resistance that can only be calculated, not measured, so the gauge and material of the wire is important to get right or things could get messed up.

Twin lead is not expensive, although you can look up the price of shielded twin lead if you want durability. I keep a coil of shielded twin lead in storage at home just in case I should ever need it, and it is stiffer than RG6.

Also about Baluns, when you buy an antenna from Channel Master, Winegard, Wade, or any of the other main manufacturers, a balun is usually included, and it has usually been tested and matched to the antenna's performance. You can order the appropriate one from their parts departments.

There are lots of amateur radio enthusiast sites on the web that discuss how to make your own balun if need be.
 

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stampeder said:
Impedence is a form of resistance that can only be calculated, not measured, so the gauge and material of the wire is important to get right or things could get messed up.

There are lots of amateur radio enthusiast sites on the web that discuss how to make your own balun if need be.
Actually, impedance is a combination of resistance and reactance (R and jX)and you can measure it, with appropriate equipment, of course. A signal generator, bridge and a trough line was how it was done in the old days, now they use network analyzers.

Cheaper impedance bridges, like hams use, have two meters to indicate R & X, like the MFJ-269.

If you're going to make your own balun, you need a wideband balun. I think a binocular core would be a good choice for making a wideband 4:1 balun, but different core materials work better at certain frequencies than others.
I'd use a type 67 core if using ferrite on UHF...
 

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Discussion Starter #7
My assumption was that the baluns that are included in the package are the cheapo "good enough for regular use" baluns. But when you are trying to do the Toronto to Buffalo thing you might want a better balun. A good balun might be 90% efficient. A poor balun might be 75% effective (or less).

So with a weak signal I would want to optimize and get the best balun possible (or not even use one). I thought there would have been more interest and knowledge in this topic - especially here where people are trying to tweak every last db out of their setups.
 

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z0z0 said:
I thought there would have been more interest and knowledge in this topic - especially here where people are trying to tweak every last db out of their setups.
And you have raised an interesting point: tweaking is good! Nevertheless, I think what you're seeing is that a balun represents one of those things you'd do to get all the signal that you can after you've done all the big stuff. Don't be discouraged or dissappointed if we aren't giving you the response you expected. Let us know how your work progresses. :)
 

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We were talking about port-to-port isolation for power splitters, not the transmission loss of baluns, but I don't believe those KYES balun loss numbers. I have measured the loss of many consumer ferrite baluns at 98 MHz and I consistently get 0.75 dB or so. Others whose experience and test equipment I trust get the same result. The only difference I recall offhand is for the outdoor Radio Shack balun with long leads, for which I measured 0.85 dB. I'd expect higher loss at UHF-TV frequencies and more variation among baluns.

I have found other errors in the KYES antenna information (for example, rabbit ears are NOT equivalent to a dipole) so I'd be cautious about accepting any assertions made there without further checking.

Brian

P.S.--I keep forgetting to ask: who is the Gray in Gray-Hoverman?
 

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I'm glad the discussion turned to baluns. At 88-108 MHz, where I do most of my playing around, I've always regarded these things as pesky, unavoidable components, with a nagging loss that frequently is too small to worry about. Sometimes I've bit the bullet and taken the trouble to create an antenna design that is inherently 75-ohm rather than 300. Afterward I always wonder whether I've wasted my time, since at FM frequencies the loss is just 0.75 dB or so.

I believe the UHF-TV balun loss numbers at AVS Forum are more realistic than the KYES numbers. The larger losses are troubling.

I test baluns by placing two in series so I can use 75-ohm unbalanced test equipment. I have 50-ohm test gear, but I use resonant 50:75-ohm networks to match everything. I'll have to get some wideband matching networks to test baluns at UHF-TV frequencies. I have a homebrew, wideband, minimum-loss 50:75-ohm resistive pad, but the other day I tested it at UHF and I wasn't impressed with its transparency. I made its resistor lead lengths very short, but evidently not short enough. Chip resistors should work though.

What I mainly wanted to mention is that I've noticed that the input impedance and transmission loss depend on exactly how I couple two test baluns. Sometimes I have just touched the spade lugs together. This works if you can get a reliable connection. But the impedance characteristics depend on the spacing between the spade lugs, as you might expect. The impedance of a transmission line is a function of the conductor spacing and the dielectric constant of the material in between. If the twin-lead that exits the balun is really 300 ohms, when the dielectric is split and carved out and the resulting dielectric becomes mostly air, the impedance is no longer 300 ohms. Essentially you have inserted a short section of transmission line of higher impedance. This can degrade a good match. You really see the effect for antennas that have several inches between their 300-ohm feed terminals. Although I haven't measured it, the impedance at the 75-ohm end of a balun is not likely to be the same if you use the full balun lead length and gradually fan out the conductors to the terminal distance, or you shorten the lead length and feed with wires at right angles to the intact twin-lead portion. The latter case mimics the usual feedpoint computer model, which is a straight wire between feed terminals. I think the dimensions involved are large enough to make quite a difference at UHF-TV frequencies. This issue deserves its own thread.

The other thing I've done is to couple two baluns with a screw-terminal mount, the kind of thing that vacuum-tube FM tuners used for their 300-ohm antenna input. I made a 300-ohm load for testing baluns using one of these terminals. I soldered a resistor very close to 300 ohms across the terminals using extremely short leads. It works fine at 88-108 MHz, but when I tried it a few days ago at UHF-TV frequencies I was surprised how much reactance it had, way too much to be useful as a 300-ohm load.

Anyway, balun loss is important because it is unrecoverable--it comes before any low-noise amplification. If it gets to be several dB you're going to notice its effect on weak signals. But I haven't found balun loss simple to measure.

Brian
 

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For the benefit of others, here are some of the Balun-Loss numbers from the balun-loss comparison at avsforum:
Code:
Maker          Model            Typ. Max.
-------------- ---------------- ---- ----
Channel Master Model 3075       1.7  2.2 dB
RCA            VH101            2.5  4.2 dB
Philips        PM61009          3.0  4.7 dB
Radio Shack    15-1230 Goldstar 3.5  6.2 dB
Radio Shack    15-1140B         4.5  6.2 dB
The baluns I'm using here are mostly RCA/Magnavox ones, though I don't know if they are the exact VH101 model listed above.
 

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What an interesting outfit. I'll bet they make great stuff. But it's all custom, made to order, and it looks like prices begin at $30 Canadian. That's a lot for a balun. I don't know the typical return loss of a UHF-TV balun. A return loss of 16 dB is equivalent to an SWR of 1.38, and yields a mismatch loss of 0.11 dB.

I know an RF engineer who has developed a very low-loss balun for 88-108 MHz. He offers plans for free and he will sell you a partial kit of parts to make your own. I'm going to see if I can interest him in making a low-loss balun for UHF TV.

Here's his FM balun:

http://homepage.mac.com/kenwetzel/Low_Loss_Balun.htm

Note that this is a current balun, which has some advantages over the common voltage balun. Google "current balun" for the full story.

Brian
 

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If you're interested primarily in UHF, then a very simple coax-loop 4:1 balun costs only a buck or two to construct, and will show about 0.5dB insertion loss across much of the the UHF television band.

That kind of proposition is hard to beat!

Speaking of which.. can any of you hams enlighten me further on the gamma match feed for a dipole? To me, it looks very much like a 1/2 wavelength loop balun in disguise. :)

Cheers
 

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I know an engineer in Sweden who uses a half-wave balun for his UHF-TV antennas. Although it is exactly a half-wavelength long at only one frequency, he said he was surprised how well it worked over the whole band. I think he made some measurements and I'll see if I can get more info. It surely is the easiest and cheapest way to go if it works decently. It is not nearly as small as a ferrite balun, but usually that's not a concern.

Think of a gamma match as tapping down on a dipole until you find the impedance you want. It is a matching device and does not perform a balancing function. But if you shunt-excite one half of a dipole with current, the current will flow into the other half as well. If the feedline uses a perfect current balun, the excitation current has nowhere else to go.

Brian
 

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At that price range, just get a CM0064 or CM0264 300ohm in 75ohm out preamp and kill a couple of birds with one throw.
Good point! Sort of an amplified balun. I'm using the old model 0064C (or something like that). I found it in an orchard. A few years later I found the proper power supply / injector at a garage sale. I just held on to them until recently, when I coupled them with my Radio Shack UHF zigzag. I checked the preamp last week. I get 24-30 dB gain over 470-700 MHz (includes an unknown amount of loss for the balun I used to feed the preamp input). It has LOTS of coils inside, with separate steep-skirted passbands for low-VHF/FM, high-VHF, and UHF. It has a removable plug that engages/disengages a tunable FM trap. I discovered that if you remove the plug entirely, the VHF passbands disappear leaving a UHF-only preamp. Since it is only connected to a UHF antenna, I removed the plug to reduce any intermod.

Brian
 
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