Umm, it's impedence, not resistance, that varies with frequency......

OK,.. impedance/resistance/reactance are words of a different colour. It depends which shade you are looking for.

electrical impedance

Opposition that a circuit presents to electric current. It includes both resistance and reactance. Resistance arises from collisions of the current-carrying charged particles with the internal structure of the conductor. Reactance is an additional opposition to the movement of electric charge that arises from the changing electric and magnetic fields in circuits carrying alternating current. Impedance in circuits carrying steady direct currents is simply resistance.

;) Therefore impedance is the electric charge that arises from the changing electric and magnetic fields within a conductor. I suppose ! :o

No, each term has a very specific definition. Impedance is the opposition to current flow in an AC circuit.

See wikipededia article http://en.wikipedia.org/wiki/Impedence for details.

Sorry,... I can't resist, impede or react ;)

Check out this tutorial on what the term impedance means.

General expression of Impedance
The term impedance is a general expression which can be applied to any electrical entity which impedes the flow of current. Thus this expression could be used to denote a resistance, a pure reactance, or as is most likely in the real world, a complex combination of both reactance and resistance.
http://www.electronics-tutorials.com/basics/impedance.htm

Just to add a datapoint. I just built a coax loop balun using a piece of scrap coax. (I'm not sure whether it's RG59 or RG6, it's stamped Property of Shaw Cable and was made by Beldin; aluminum mesh & foil shield.) I cut it to 17.5cm, aiming for the geometric mean of ch 14-66, but not being certain of the velocity factor.

Anyway, according to my TV's built-in signal meter I'm getting about 3dB more signal across the entire band versus the "Made in China" balun I was using. Not much of a difference to SNR except for CityTV (very low power) which improved slightly.

So... Can a coax loop balun be used for UHF? - yes. Is it better than a cheap balun of unknown quality? - yes. For those with the materials, skills, and a little patience (It took me two tries to figure out it's better to attack the dielectric instead of trying to slide it off.) I'd recommend giving it a try.

(I'm not sure whether it's RG59 or RG6, it's stamped Property of Shaw Cable and was made by Beldin; aluminum mesh & foil shield.
That would be RG6 coax. I haven't seen any RG59 with foil.

Cheers

True MIL-SPEC RG-59 will have a 1/4-in thick, single copper braided shield and the inner insulator
is slippery, tough, translucent polyethylene plastic with a propagation velocity factor of 65.9%.

True MIL-SPEC RG-6 has a THICKER double braid (not foil) shield, the inner insulator is
supposed to also be polyethylene with a propagation velocity factor of 65.9%.

Very few "RG-6" cables are built to the MIL-SPEC....most use soft, squishable FOAM with a variety of
shield constructions, the most common being inner foil and an outer (leaky) braid shield.

I've seen manufacturers slap the RG-59 and RG-6 labels on all sorts of different constructions,
such as "RG-59" with FOAM inner insulation and perhaps even a double shield (smells like RG-6).
And even within RG-59 or RG-6 types from same manu., velocity factor specs can vary quite a bit:
http://www.generalcable.com/NR/rdonlyres/DFB5EEAE-F4B4-4ED7-A6F4-51C6B44E088A/0/Pg101_108_RG59U.pdf
http://www.generalcable.com/NR/rdonlyres/55F61B9E-9619-4C50-9093-2DED4E2238E3/0/Pg059_065_CoaxCblRG6U.pdf

WRT propagation velocity, if it's slippery, tough polyethylene plastic, assume it's close to RG-59 (66%),
whereas if it's squishable FOAM, assume RG-6 (83%).

Fol. summary table may help identify that Belden cable (currently BOTH types are 83% velocity factor):
http://www.belden.com/pdfs/03Belden_Master_Catalog/06Coaxial_Cables/06.3_15.pdf
Use the catalog page number to find the propagation velocity specs.

On the balun issue...

I find that those store bought balun is useless when compare to CM4221HD's balun. I swap out one and did a test on my CM4221HD, it is like 15% signal strength (across all channels) difference on my TV meter! This is one reason I don't like to build my own antenna since I cannot find a balun that is as good as the one in my CM4221HD.
During my quest to get the most out of my 4228HD using the hack method. I have been testing various baluns. I aquired two 4221HD baluns from damaged antennas from a friend. I then attached a short 300 ohm lead to each balun and installed them. Unfortunately the 4221HD baluns did not perform as well the store bought Winegard TV-2900. Using the TV signal strength meter there was a noticable difference (5-10% decrease). I do wish there was a high quality broadband balun that covers vhf hi thru uhf out there.

My quest continues.

For my Q&D DIY GH I made a coax halfwave balun and was impressed with the results. For my "real build" the feedpoint gap is 110mm, rather large.

Anway, I had a thought this morning. What would happen if I connected one half to the other using a halfwave length of coax? As I understand it, the halfwave length of coax delays the signal so the blanaced signal combines in phase. The following picture shows what I'm thinking of:

http://www.digitalhome.ca/forum/picture.php?albumid=166&pictureid=2193

So the feedline is connected to one feedpoint, and the other feedpoint is attached via the appropriate length of coax. The shields of the two piece of coax are connected as well.

Looks good to me. And it could be a rather clever way to get rid of the wide-gap problem that plagues the GH design.

The result is a perfect 4:1 balanced-to-unbalanced connection, same as would be gotten by any other balun there. Except you've taken care of the feed gap issue as well.

Cool. Let us know how it works out for you there!

What would happen if I connected one half to the other using a halfwave length of coax?
Since balun test equipment is rather pricey, (even if it was only $30, that would pricey for testing a $3 typical item, heh) the only way to know is to try it.

In response to post #569

I tried a couple of these on my antennas this past weekend. The TO facing antenna I tunned for RF40 (CFTO). The Buffalo antenna was a toss. I have two channels that are weaker compared to the rest...them being Fox and MyTV. Problem is that they are at opposite ends of the UHF spectrum. So I just went with the middle, and used RF32 (which is one of my strongest stations...go figure). I felt that making a coax balun for RF14 would glorify RF11, which comes in very strong on its own...it doesn't need any extra attention. I also thought that designing for RF49 would drop RF14...that was the reason for going for a center frequency.

After trying them out, I concluded that they just weren't as good as my RCA baluns from Home Depot. Don't get me wrong, they did work, and most likely the weather played a major role with this, but I ended up loosing alot of signal, and lost quite a few channels. Again, the past weekend was horrendous with the amount of rain we got. It was the first time since getting everything hooked up, that my attic install actually took a hit.

I decided not to muck around with something that is working, so I ended up re-installing the store bought baluns.

It's still worth a try though...just because it didn't seem to work for me, doesn't mean it won't work for others. You may have some exceptional results. As I said, the weather was really, really bad, and that may have hampered the results more than the balun's.

Hi Anyone heard of Steren matching transformers number 200-490 ?

Bought a couple and wondering about the noise level

http://www.sterenusa.com/catalog/search_desc.asp?subfamilia=&familia=0&frase=200-490&c_todos=1&c_subfamilia=1&c_familia=&item=611&mv=200-490&tot=1&pos=1


I want to replace the ones ( no name dollar store ) on my cm 4228 hack



thanks

Send an email to them. I have a few Steren cable interconnect products, and they are pretty good to deal with. They should be able to provide you the information.

I'm no authority, but here's my take after reading most of the previous 39 pages.

1. Most balun transformers are just fine, from those in dollar-store blister packs on up. Some have unacceptably big losses. Some are dead in the water (and only these can be assessed before climbing a ladder to your roof). Most companies seem variable in their quality and evaluators' posts are not in good agreement. CM might be a trustworthy brand. Like the sound of this summary so far?

2. When factors, not all of which are known clearly are in alignment, a half-wave balun will have less loss at a certain narrow of band of channels than a transformer. Almost a crap-shoot. Certain applications, such as FM-band, FM in the presence of over-powering TV signals, single-channel reception, etc. seem to be really right for half-wave baluns. But not the broader band(s) of TV for most users.

3. The differences of opinion on such matters as propagation velocity in the possibly-unknown cable in your hand are large and the range of opinion on this parameter (and other construction niceties) is too large to let anyone make a balun and install it confidently. Might be fun to try one?

4. Some tangential topics are interesting to learn about such as suppressing stray RF traveling down shields, grounding rituals, and DIY tips.

Am I glad I spent most of today reading this thread? I have an ideal application for a half-wave balun (nearby strong TV stations and a distant FM goal on my FM-only antenna). So, I just might give it a try.

Big "thank you" to the folks who contributed generously to page 39.

Could you please rephrase the last sentence in Post Numbers? Some members use a different pager than other members do, so I've learned long ago to use Post #s instead of Page #s. :)

Could you please rephrase the last sentence in Post Numbers? Some members use a different pager than other members do, so I've learned long ago to use Post #s instead of Page #s. :)
Posts before #575.

Being a terminal DIYer, I've been contemplating the "test equipment" and methods available to me. I am talking exclusive of any method that requires some fearless soul to climb to my roof a few times.

From my reading of this thread, here are some thoughts on testing. Some of the assessments on the thread seem...ummm, casual. And stuff you build yourself often "seems to" work great although a surprising amount of honest disappointment also reported.

1. As a basic indoors method, using back-to-back baluns makes good sense. But the concept breaks down when you aren't testing identical (and/or reversable) units in identical pairs. Or at least, fraught with questions if you are not.

Can anybody suggest a universal test rig into which you could drop a 300-into-75 balun and connect it between your RG6 lead and your tuner? For UHF or FM, could you take a half-wave 300-into-75 balun and connect it to the 300 ohm twin-lead input of an elderly TV or FM tuner you found at the charity store?

(Footnote: this still leaves open the question of that critical yet mysterious link between the balun and the wing-nuts on your antenna... unless it is a piece of conventional twin-lead between the two.)

2. Many TVs and tuners have useful "meters" showing signal strength or signal goodness. For OTA signals, that's OK providing the atmosphere is cooperating with some constancy of signal arriving. Otherwise, pretty elaborate balanced comparative testing and re-testing is needed. Old FM tuners had signal strength mechanical meters - far more effective for testing than the three software bars on my new super Sony tuner.

3. My local surplus store doesn't seem to get RF signal generators at DIY prices. Any ideas for availing oneself of an RF signal source?

So I'd say the main road-blocks to measurement are the back-to-back or test rigging question and simulating the antenna-to-balun wire connection indoors.

HELP me! I always feel stymied when I can't figure out how to measure something.

Given my personal assessment of the challenges in making baluns, I wonder if anybody here abouts can do the passband testing including doing it for reasonable pay?

Footnote: many of those FM tuners from the charity store have nice air-core baluns in them. Maybe TVs have 'em too.

For pure balun testing, just hook a low power transmitter to a receiver/meter/scope via your balun. Eliminate the antenna altogether.

For pure balun testing, just hook a low power transmitter to a receiver/meter/scope via your balun. Eliminate the antenna altogether.
My stock of low power transmitters is a bit low just now. But a good idea.

Actually, I forgot an obvious method: outdoor antenna set up in your living room or back yard. Cheaper to buy a spare antenna than to hire a skilled antenna person to work on the roof.

I did some fooling around since my earlier post. Hard part is finding stations (on the crowded Toronto FM dial) that are neither too strong so the signal pegs the meter nor so weak that they are only received out-of-tune due to strong nearby stations.