The two 4 bays are connected in parallel and the mean appears to be around 150 ohms

snowman,
http://www.hdtvprimer.com/ANTENNAS/TemporaryPage.html
ken nist uses a 2.5:1 balun made from two 120-ohm quarter-wave segments

the popular approach is to use a 4:1 balun on each 4-bay and join the 2 together

Oh, so to know that, you must have either measured it or simulated it, right?

For example, each of those 4-bay halves, is itself four dipoles, combined together. Depending upon *how* they are combined, a particular output impedance is produced.


I have no idea what it really is, only that the NEC model shows approx 150 ohm mean over the 470 - 700 band, which makes sense with parallel transfer lines.

Thanks

In my search for a 2:1 balun, I came across this 2.25:1 coax design. I figure that's close enough, so I have built one.

The question I have is; other than hooking it up and seeing if there is a picture, how does one test it?

http://www.innovative--concepts.com/downloads/2_25 to 1 Balun.jpg

Thanks!

Here is what I understand so far:

--->>>
I'd like to tinker with a homemade yagi antenna. If I use a folded dipole for the direct element I'll need a 4:1 balun and if a use just a dipole I'll need a 1:1 balun. I think I get the basic understanding of a coax balun - delaying one side of the balanced input by a half wave length creating a 180 degree phase shift.
<<<------


However, I'm at a loss to understand the difference between these 1:1 balun and a 4:1 balun designs:

1:1 coax baluns:
http://www.southgatearc.org/techtips/coax_balun.htm
http://www.arisanremo.it/index.php?name=Content&pid=195

4:1 coax balun (the basic 1/2 wavelength U)
http://www.n-lemma.com/calcs/dipole/balun.htm

Maybe, I don't need to. I want to use a dipole and just want to make sure the above 1:1 baluns are indeed correct (and not just misinformation on the net).

One nice thing about folded dipoles, is that they are mechanically simpler (oddly enough) to construct than the plain dipoles. Much easier to attach to a yagi than a plain dipole.

Sounds weird, yes, but I've built a lot of antennas, and that's my experience.

Cheers

Hi Guys,

I was doing some fine tuning before winter and Sunday was maybe my last time on the roof before April.

Anyways, I upgraded my coax on the 4228 in August but I also made the mistake of installing a generic outdoor balun from Raybel ( they have been out of CM baluns for months ).

I was having dropout with that balun even at 100 % signal. Previously, I had a cheap Addison interior balun.

So, I made this test of 4 baluns.

WFFF-DT, Tivo HD tuner, CM 4228, this was done in 3 minutes:

1) Generic exterior balun Provo (from Raybel) with bare wire: 76 % signal
2) Winegard exterior balun with lugs: 78% signal
3) Philips interior balun (Walmart) with lugs: 78% signal
4) Generic interior balun (Addison) with lugs: 82 % signal.

So they clear winner is the generic interior balun. I had no dropout since I installed back the generic balun.

DHC user KRO made this discovery last year and I remember him saying that the baluns with bare wires are more noisy.

It looks like he was right, I sure did miss my cheap 99 cents balun.

I build a DBGH with NARODS, so I need a balm designed for VHF-HI and UHF. I also have a kitz amp installed about 20 feet from the antenna.

I am trying to maximize 7-1, 7-2 and wwti 50-1 and 50-2 (real channel 21)

I get these stations 7-x most of the time and 50-x starting about 4-6pm and getts better as the evening goes on. They are also still avaialbe till about 10:30 to 11am... so alot of the time.

I want to maximize my availability of these channels.

As posted before this is my tvfool http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d8ecdfaaddf5d47

Currently I have a Balun from the source on the DBGH I built.

Thanks for the help,
Bruce

I get these stations 7-x most of the time and 50-x starting about 4-6pm and getts better as the evening goes on. They are also still avaialbe till about 10:30 to 11am... so alot of the time.
Thats heat layer fading. http://www.hdtvprimer.com/ANTENNAS/glossaryA.html#fading

Youre doing fantastic to get those 2.8 and -7.5 NM 2 edge stations from 77 - 83 miles away. Im not sure a different balun is going to change things. Moving the antenna up or down when you lose signal may, but in most cases thats impractical.

...Im not sure a different balun is going to change things. ....

I'm not too sure about that 300ohm. I have a very similar situation - I built a DBGH (well, a few...:)) and the choice in baluns was the difference between constant reception vs nothing. I have two 2-edge stations at -12NM that I receive - using the exact same (noisy) balun as bitterman, I didn't get the stations at all, other than registering some activity on the signal quality meter. I experimented a lot, and found that using the Philips (or Magnavox) 61009 balun increased my reception to the point where I received both channels 95% of the time (about 40-50% on my TV meter). My DIY coax balun was even better, getting a reading of usually 50-60%.

I would just target your weakest channel (21 in your case) - you'll find that it should cover your band of channels well. It worked for me anyway!

I envy you guys. I cant get a consistant lock on my 6.6 NM 2 edge stations from 60 miles away at 25ft, heh. But I have tons of signal obstructions in that direction. Height over the tree tops is the only answer for me. Two edge stations are tricky. Its like trying to figure out where a baseball, thrown in a junk yard, will land on the second bounce , heh. A lot of people cant get 2 edge stations that are in the high teens NM-wise.

My DIY coax balun was even better, getting a reading of usually 50-60%.
What specific dimension did you use ? RG6 or other ?

How much of a decrease will a coax balun optimized for 512-518 Mhz (Channel 21) decrease performance of real channel 7 (7-1 and 7-2)

Based on the below link and 515 Mhz I need about 21.8 CM of rg-6 for the loop of the balun
http://www.k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf_feed.html

Thanks,
Bruce

I envy you guys. I cant get a consistant lock on my 6.6 NM 2 edge stations from 60 miles away at 25ft, heh. But I have tons of signal obstructions in that direction. Height over the tree tops is the only answer for me. Two edge stations are tricky. Its like trying to figure out where a baseball, thrown in a junk yard, will land on the second bounce , heh. A lot of people cant get 2 edge stations that are in the high teens NM-wise.


What specific dimension did you use ? RG6 or other ?
I use RG59 - pretty much mandatory given the tight bend radius required, especially for my Ch 58 baluns (13.4cm length, bent 180)! Convenient that I have a truckload of RG59 that I don't need/ want for anything else...

For the 2 edge stations, I'm probably fairly fortunate - my signals (80km/ 48 miles away) have to travel through (well, over) two mountains before reaching me, but I have pretty much flat, unobstructed view to the last mountain, approx 20 km (~12 miles) distant. Lots of room for diffraction! (see pic below)

http://www.digitalhome.ca/forum/picture.php?albumid=314&pictureid=1771

How much of a decrease will a coax balun optimized for 512-518 Mhz (Channel 21) decrease performance of real channel 7 (7-1 and 7-2)



Actually Bitterman, I'm sure there are all sorts of formulas, theories and calculations out there to answer your question, all valid, all beyond me, but I would suggest just trying a couple. I've actually never tried a coax balun in the VHF Hi band (mlord could probably help you out there...), but I have found in all my testing, nothing beats just trying them to see what works for you. For example, for whatever reason, the baluns that worked best for my situation to receive channel 58 were ones that I optimized for channel 33 - go figure!

Your coax lengths will be much different though, since your channel 7 loop will be 55.9 cm (RG59) vs your channel 21 at 19.2. For the few minutes it'll take to throw together a rough balun, I would try both, then something in between to see your best fit.

Thanks, I'm not sure what to do now. Winter is setting in and our steel roof is very slipery from frost... So may no be able to do anything now till spring depending on the weather. I would like to get a good comercial balm and try it if I get the chance but I am also interested in how well a coax balm will work also and I'm not sure were to aim at for vhf-hi 7 and real channel 21.

Thanks,
Bruce

If it were me, I would shoot for your weak one, build a balun using 19.2 cm unshielded section of RG59, connect it, and cross your fingers. At least this will give you a good indication of how coax baluns will perform for you at the targeted channel. I suspect you will see an improvement and also that you will also likely retain channel 7. But I am an optimist....:)

For the 2 edge stations, I'm probably fairly fortunate
Yeah. A few miles to the left and you would have no chance at all with those stations, heh.

Yeah. A few miles to the left and you would have no chance at all with those stations, heh.
...to the right as well - that mountain is fairly large and would also put me in a signal shadow. That being said, "fortunate" is a relative term - my extensive target OTA digital lineup originates there and consists of all of 3 stations, 1 of which broadcasts with the strength of your toaster...(and sadly enough is one of this country's big three broadcasters...)

I envy you guys. I cant get a consistant lock on my 6.6 NM 2 edge stations from 60 miles away at 25ft, heh. But I have tons of signal obstructions in that direction. Height over the tree tops is the only answer for me. Two edge stations are tricky. Its like trying to figure out where a baseball, thrown in a junk yard, will land on the second bounce , heh. A lot of people cant get 2 edge stations that are in the high teens NM-wise.

300omh, If you can't get those stations at your location I don't think anyone could... Well manybe with a 100 foot tower it might be possible :)

Maybe I can find a philips balum locally and compair it to a diy coax balm on the m4 I built for testing before climbing the slipery roof. Would this be a good test?

Thanks,
Bruce

Maybe I can find a philips balum locally and compair it to a diy coax balm on the m4 I built for testing before climbing the slipery roof. Would this be a good test?
Phillips outdoor baluns can be found at Lowes or Walmart. They are fairly common. $3.95 here, so theyre cheaper than the crappy RS ones.
Of course, build quality can vary from balun to balun, so if you get one thats worse than what you have now, take it back.

If you can't get those stations at your location I don't think anyone could...
Besides the trees, I have a powerful FM farm with 6 high transmit towers and their associated guy wires, 1.5 miles away directly in the signal path, heh. Im not sure of the exact effect of that, but it cant be good.

Ouch on the transmission towers, that would be nasty, if not impossible to deal with.

Bruce