would cause the 300ohm antenna feed impedance to be cut in half due to the baluns being in parallel. This means that the normal 300:75 transformation would instead be 150ohm impedance stepped down 4 times to 37.5 ohms at the TV, which would probably ruin everything.


Dummy me! I never once considered the ohms dropping in half by parallel mounting...I knew better. What is so bad is I do this all the time with resistors in cb radios, when I don't have the correct resistor values. Major Brain Poot!

Thanks for setting me straight, stampeder.

What is so bad is I do this all the time with resistors in cb radios, when I don't have the correct resistor values.
And you know what that does to gain when inserting a pure resistance value, heh.

If you do it just right, you can have a very good signal discarding device, heh.

I just wasn't thinking!

The reason I thought about it to start with is when I hooked up the splitter to go to both tvs, I lost my 2 distant channels. I've got to find the "sweet spot" for my antenna location or put the reflector on and add a rotor (which is bound to happen).

I have a question that maybe some of the more RF-inclined people on this forum could be able to answer.

The ARRL 4 : 1 balun diagram with a half electrical wavelength bit of coax
( On Ken Nist's site: http://www.hdtvprimer.com/ANTENNAS/TemporaryPage.html
http://www.hdtvprimer.com/ANTENNAS/DB8BalunType.jpg )

Doing a bit of research online gets me the 'velocity factor' of RG-6 75 ohm coax to be 0.659, and the center wavelength of channel 'x' is 473 + (x-14)*6 MHz

So the 'half electrical wavelength' should be 0.659 * c / (((x-14)*6+473) MHz) / 2, right?

e.g. real channel 25 is (Google Calculator: http://www.google.com/search?q=0.659+*+c+%2F(((25-14)*6%2B473)+MHz)+%2F+2 ) 18.3 cm

My question is then, how poorly would this perform for other channels?
The range of electrical wavelengths for the post-transition channels is (470 MHz, bottom of channel 14) 21.0 cm to (698 MHz, top of channel 51) 14.2 cm.

firimari, if you use the site's Search tool with the parameters "mlord coax balun" you'll see some threads in which mlord has discussed almost the same thing. :)

One day I'll get a hang of using that... And it looks like I might be very well served making one of those loop baluns. Pictures will be posted, but it will be a week, since I'm off on vacation.

Hi firimari,
as far as I know RG6 belden type has foam dielectric (PE), than the velocity factor should be 0.83 instead the 0.66 (0.659) of compact PE.
Pay attention on your cable specification.
Greetings,
john

Interestingly, Belden's eCatalog actually posts the Velocity of Propogation (aka 'Velocity Factor') for their coax products, making this an easy thing to check. Thanks for the heads up, John, and welcome to the boards

Pay attention on your cable specification.


Yep, you can get a lot just from Googling on the numbers on the cable.

Hi firimari,
as far as I know RG6 belden type has foam dielectric (PE), than the velocity factor should be 0.83 instead the 0.66 (0.659) of compact PE.
Cables vary from batch to batch. Generally, foam-core RG59 has a VF around 0.78 = 0.82, depending on who makes it and the particular batch being measured.

The stuff I bought and measured here (using a dual trace oscilloscope), came in at (I think) 0.81 or so.

As it turns out, a coax loop balun has very high bandwidth, so very small variations won't matter too much.

"Foam core" means it has white stuff inside the cable; PTFE/teflon core is more translucent in appearance.

Cheers

I've been considering Xauto's earlier post about properly matching a coaxial cable to the feed from the hentenna.

What I understand so far is that the coaxial cable needs to have the signal applied only to the center wire and not to the shield. Since the hentenna has about 75 ohm impedance, a coax cable can be directly connected to the antenna without impedance matching, but this results in half of the signal being applied to the coax cable shielding and half to the center wire that should carry the signal.

To correct this, a 1:1 balun must be used to attach the balanced antenna to an unbalanced cable. I found four methods to make a homemade balun, including the ones that Xauto mentioned.

Pawsey Stub - This involves cutting a piece of coax cable that is 1/4 of a wavelength long and attaching the outer sheath at one end to the center wire of the coaxial cable at the anntenna, and attaching the other end to the outer sheath of the antenna cable 1/4 wavelength down from the antenna. This cancels the signal running down the outside of the coaxial cable, but only works at the particular frequency it is designed for. http://www.nrgkits.co.uk/workshop/half_wave_dipole_aerial.htm
Sleeve Balun - Requires that a 1/4 wavelength long pipe be slid over the antenna end of the coaxial cable. At the antenna end, it is not electrically connected, but it is electrically connected to the coaxial shielding 1/4 of a wavelength down from the antenna. This causes the signal that is trying to travel down the coaxial shielding to see a high impedance, but also only works at the frequency it is designed for. http://www.vhfman.freeuk.com/radio/sleeve.html
Ferrite Beads - This is a string of iron beads that are strung over the antenna end of the coaxial cable. The inductive property of the beads chokes off high frequency signals that try to travel down the shielding of the coaxial cable. http://www.qsl.net/ta1dx/amator/broadband_baluns.htm
Air-Core Balun - This involves wrapping a length of coaxial cable around a form, such as a short piece of pvc pipe or a soda bottle, so that the windings are snug against each other. This causes the coaxial shielding to form an inductor that opposes current change and thus impedes any high frequency signals that try to travel down the shielding. http://www.hamuniverse.com/balun.html


The pawsey stub and sleeve balun may work for my application where I'm only interested in one channel, but don't seem appropriate for hentenna's that others are designing for use across the UHF band since they must be built for use at a particular frequency. The air-core balun is the most simple to make, but I'm not sure if it continues to function as well at UHF frequencies as it does at HF and VHF frequencies.

Just wondered if anyone could enlighten me on how narrow of a frequency range something like the pawsey stub was limited to, or how well the air-core balun would work.

Thanks.

might not be the best place to post but, im look to do this improvement to my antenna, but cant find good balun. i went to raybel on N-D and they have some kind of generic brand, is it any good ? where can i find some good ones like those CM ?

thanks

hey have some kind of generic brand, is it any good ?
Maybe, maybe not. Cant really know till you use it. Even new quality name ones can be poor or defective. It boils down to the individual balun unit. OTOH, with a quality name brand you do have more of a chance of getting a good one. Ive found older, made in Japan ones found at flea markets (usually for video game consoles) to be very very good. They would need to be properly weather-proofed for outdoor use, of course.
When you do get a good one, dont break it by overtightening.

Good morning all,

Which balun brand is better, CM or winegard

I only use Channel Master baluns. I can't say if they are good/better/best, but I do know their performance has been consistant and they have a stamp on one side that assists in determining phasing.

Hi OTA,
what exactly do u mean by a stamp on one side of the CM brand?

I do believe helps is related to for two or more antennas to put together only.
When only one antenna is feeded You don't care about phase.
This is a well known phenomenon, happens when stacked two or more antenna array. Then if the phase is not the same for all antennas, You got a loss on the resulting main lobe, instead of the gain improvement.
More to say, when a balun have the phase point clearly signed in the unbalanced side, it means the phase ability is taken in account. That should be a quality balun, or at least is electrically correct, but yet never seen on baluns for OTA antennas.
The only help, in this case, come from mechanical construction, right to right, up to up, front to front, but this not prevent a plastic case reversed while assembled.

Has anyone removed the built-in balun from a ya-1713 to use at 300 ohms? I currently have a cm-4228 and 2 channel cut vhf antennas with a cm-0264 pre-amp. I'd like to replace the 2 channel cut antennas with a ya-1713, and build a DBGH or M-8 to replace the cm-4228. Also, what is the best grey-hoverman build for the uhf channels in the 40s? I'm really on the fringe with uhf at 90 miles, and having trouble holding signal lock on the digital channels. Any advice/comments are welcome and appreciated.

thanks

Let me start with some background. I am just at the end of my living room, dining room , kitchen home renovation. I decided to add to RG6 runs into the living room to different location. While pondering the location I also reflected on the total cable run... The antenna and sat are on the chimney on the outside side wall of the living room. The current cable runs are from the chimney mounted gear through the attic to the far opposite corner of the house down to the basement where teh demarcation point is. From there I have all point to point connections the rest of the house. Including the living room. The run is approx 75ft from the antenna to the demarcation point..... internall back to the living room has to be at least 50ft given teh way I ran the cable when I finished the basement years ago. It is all RG6 but still quite a long total cable run. Original the antenna and gear was mount near the bck corner of the house.
My CM4221 has a winegaard preamp on it

So.... after all that here is the question.

I would like to run the new cables directly up to the chimney. I left enought coiled up about 30ft. So I tried to search and read up on options about splitting the output off the antenna. But I did not find a definitive answer
Soooo, I am thrying to decide which of the these options is the most correct method doing this.

1) two baluns connected directly to the CM4221
- so I would leave what is currently connected as is just add an
additional balun and connect the new cable run directly to the
living room set.

2) Use a splitter after the current balun and connect one side to the
preamp and the other to the new cable run. I beleive there would be
a signal loss from using the splitter.

3) split the output from the preamp... but I am afraid of overloading of the
signal on the shorter cable run.

4) replace the preamp with something else that could accomdate an
amplified sighanl and non amplified signal.

That is all I have come with so far.....

Thoughts, suggestions, advice are greatly welcomed.

Hi Atlas2,

I understand you wish to use a 300 Ohm preamplifier for your ya-1713 antenna.
Before any attempts make sure the ya-1713 without the original balun is a 300 ohms impedance. This depends from the antenna project, then a different value from 300 ohms can be.