JER

spokybob

Cheapies. I have made many YouTube antennas for folks. I bought a whole sackful of baluns on Ebay. I compared a couple with a CM. Performance wise, I did not detect any difference. As far as durability I don't know. I never intended these to be used outside.

ProjectSHO89

There's a huge difference between testing baluns with lab equipment (VNA) vs. a youtube coat hanger.

The balun's performance with a coat hanger antenna will only characterize those that are grossly deficient and those that are not. For that antenna, any balun that is not grossly deficient will suffice.

The VNA allows the tester to characterize the complete performance of the balun by displaying the device's performance characteristics as a function of frequency.

Perhaps JER has some VNA plots for baluns he can share that demonstrate this analysis.

Piggie

It's not a matter of touching the pipe, shorting, or anything like that.

The wires out of the balun are to come close to 300 ohm twin lead. So actually in a sense, the separate wires alone cause an impedance bump unless they are are exactly the right distance apart. Since a CM balun is more like open wire line being two wires.

The impedance of open wire line depends the wire size (gauge) the distance between the wires and the dielectric constant of the material between the wires. So considering a metal pole is not a dielectric, on test equipment it should show a huge bump.

I noticed this weeks ago, but just got around to posting it. This is the sort of thing you spot from decades of building ham antennas.

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The more I understand, the less I know.

EscapeVelocity

Jim in Seattle, I scraped the CM 3075 lead wire and it is indeed copper. Its tinned copper wire and the tinning continues down the wire under the insulating jacket. Very nice.


Got ya, Piggie. I will read up on transmission lines. Also, how do you run your 4 bay balun away from the feedlines then down through the screen?

In my reading the lightly insulated feed lines coming close to a large metal object affects the wire....that is why old school lightly insulated twinlead is recommended to be kept away from large objects (especially metal). I think that keeping the wires 1" away from the mast helps.

What say you?

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Piggie

I don't know how far away to say from the pole. Back in the day when I used twin lead all the way from the antenna to the TV, I used the standard spacers. I think they were 2 to 3 inches from the pole.

Open wire or twin lead there is an external EM field associated with each wire. The interaction of the two wires in a simple explanation is what makes twin lead work. For a given impedance like I said before the distance has to be precise. The size of the wire also affects it, just like in an antenna, hence why tapered elements work in the CS and part of why like your antenna or any whisker antenna has a broader response, as the whiskers simulate what the antenna you sold me does with filled in butterfly wing elements (can't remember the number of that antenna).

If you go through the history of balance feed lines, open wire came first. Quickly radio engineers and hams figured that home made spacers between the wires, maintained a better consistent distance between the wires. Then came twin lead that eliminated the need for spacers as the insulation for each wire also extended across to the other wire keeping them at the correct distance. This made it possible for anyone to install "open wire" line now in twin lead form.

The only thing then a homeowner or installer had to do correctly was keep the wire away from the mast, not penetrate the wall near other wires (hoping it wasn't a metal wall), and not turn a corner to sharp or the impedance was then greatly effected.

But still most people didn't run twin lead right and with the advent of inexpensive amps, coax with it's lossy characteristics became the default, as it can be routed just about any old way.

Twin lead routed the wrong way gives much worse than just an impedance bump, but it ceases to be transmission line not transferring but a small percentage of the signal. Routed correctly, most people in near fringe would not need at amp to a single TV. Is it worth being that picky with it? I don't think so, and run an amp and coax.

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I would say keep twin lead 3 inches from other metal to be safe, if you want a definitive answer.

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How do I wire my CM4221A? The balun is on the front side of the antenna. I take the balun wire straight out as possible from the feedpoint. Then I turn the balun down, so I am not out in front of any elements and run the coax back through the screen.

Is it absolutely the best way? I don't know.

If you figure at the most a baluns open wire side is 1/8 of a wavelength at channel 51, most attachment methods work to a large degree. But yours with the metal between it would have to show up on test equipment as a no no.

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Jim In Seattle

The discussion about twin lead made me wonder if I still had any twinlead standoffs, but then I remembered I tossed them away many years ago. However, I have a quart milk carton full of standoffs for coax. Several varieties including the typical eye-bolt with wood-thread and plastic 'grommet', as well as those that 'clamp' around antenna masts.

Is there any reason to use these in the UHF world when using good RG-6? Thanks in advance,
Jim

PS The last time I saw twinlead was under the carpet in a used car I bought 20-some years ago. Speaker wire!

ProjectSHO89

Using coax makes standoffs unneeded. You can use them if you have them and the job will look neat, but there's no performance benefit.

Piggie

Well twin lead is the superior transmission line for loss. But it has so many drawbacks it's no longer practical since masthead amps became so inexpensive. It's also very hard to deal with though a splitter. Between having to route it perfectly and it's tendency to age fast, it would only be good in very specific installations by a very few people.

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The more I understand, the less I know.