Baluns (Brands, Designs, Losses, DIY Loops, etc.)

[intravino]

Great work! Do you have a picture of the insides of that box? What is the final length of your loop?

Too late sorry, It is already sealed with silicone sealer.

Look at my older rg-59 design, it similar but without ty-raps, the coax ends are closer together, the loop is tighter, shorter coax conductor / dielectric and I put 300 ohms twin lead to connect to the antenna

http://img132.imageshack.us/img132/9412/rg59coax.jpg

Now for the new design:

I used this page for the length calculation: (bottom of the page)

http://www.k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf_feed.html


Final Length: 46.8 CM tuned for CH 13 VHF-HI.

It is wired like at the bottom of Martin's page except that I put the loop the tightest I could and taped it with electric tape (it works better the ty-raps).

Then; I cut 1/4" of vinyl off the ends of the cable, mashed the shields together, and soldered them. I stripped 1/8" of dielectric off the center conductors. Be just careful not to short the center conductors to the shields.

The coax loop (also it's at the same time the width of the balun) has to be the width of a 300 ohms twin lead. The first time I was about 2-3 cm larger and I was loosing about 20 % on the signal meter of the tuner.

Finally, I put a small length of 300 ohms twin lead for connection to the antenna. I noticed also, this makes also a big difference.

So in conclusion, this is very important:

1) Use rg-59, you can do tighter loop, I tried rg-6; it is too stiff to loop tight. I used a high quality Amphenol rg-59.

2) The loop and signal output coax has to be the width of a 300 ohms twin lead. I put the signal output coax on top of one of the ends of the coax loop, that is the one you solder to the loop. Total width of balun is the width of 300 ohms twin lead.

3) Use a piece of a 300 ohms twin lead to connect to the antenna.

Intravino

[RamKat]

I have not tried it yet but an idea that I have which our cash strap folks could use to compare the performance of baluns, especially if you live area relatively close to the transmitting towers. The first idea would be to turn the antenna away from the tower in the direction that would reduce the signal strength but also away from any potential reflections in order to get the purest signal but of a lower antenna signal output . (if you have analog channels available from the same tower you could use them to check for reflections) The antenna is turned until the measurement is about halfway between a full signal strength readout and loss of lock or in such a spot where either an improvement or reduction in performance could be quantified on the readout. The antenna is locked, the reference balun is replaced and the measurement logged. There will probably be a few angles to involved to get a nice reference reading for each channel of interest. Mounting a protractor on the antenna will allow one to repeat measurements. Since received signal strength changes over time (weather etc) one will probably have to repeat the reference test afterwards - in other words:

1. get the reference point by rotating the angle
2. measure signal strength with reference balun
3. replace reference balun with test balun
4. measure signal strength with test balun
5. replace test balun with reference balun
6. measure signal strength with reference balun

If the first and 3rd readings line up then one probably have a good indication of the relative performance of the test balun.

The other alternative would be to add some attenuators to the output in stead of rotating the antenna

Would this work?

[mlord]

Originally Posted by intravino

1) Use rg-59, you can do tighter loop, I tried rg-6; it is too stiff to loop tight. I used a high quality Amphenol rg-59.

Apart from keeping the ends as close together as possible (to match with 300-ohm twinlead spacing), what you do with the rest of the coax loop is not supposed to matter. Coiling it up tight can be good, because it allows tucking it neatly inside a container.

I now just lay my own coax loops out flat and tight against the antenna boom/mast, and tape it there, so that it doesn't interefere with the antenna itself.

Cheers

[intravino]

What is weird is that CH2 analogue SRC comes in better with my CH13 loop then the CM balun with my 10y13s.

SRC ch9 and TVA ch7 Analogue from Sherbrooke are better also.

Also, I noticed with my coax loop balun that I could place my 10y13s better.

My location on my tower was bad. Just walking on the roof with my yagi, I noticed that I was getting low 70's % on my signal meter.

I never got that with WVNY.

Now, I need a better horizontal side mount for mounting on my tower or I need a wall mount or a chimney mount.

Off topic:

Does a 7 feet yagi (10y13s) have a big wind resistance?

A low noise amp is going to be tested soon (Thanks MLord).


Intravino

[mlord]

Originally Posted by intravino

Does a 7 feet yagi (10y13s) have a big wind resistance?

Barely anything, I imagine. That's a small antenna.

[distox]

Intravino thanks for those instructions, I wired one up. Does it look a bit like this: (see photo in Post #309)

I only had 1 piece of RG-59, so I used it. It is not the foam type. I used RG-6 for the output wire. I will put it in a small box when it is done.

[intravino]

Yes that is good !

Just two things:

Are the shields connected together ? Is is not clear on the picture.

Test your output wire between shield and the center connector.

No resistance, no contact between the two.

BTW, which channel are you trying to optimize ?


Intravino

[distox]

Yes, all three shields are soldered together. Zero resistance on the 300 side and infinite resistance on the 75 side.

I am trying to optimize CH13 (WVNY), on my 10y13s. I live in St. Laurent. I think the balun I have now is an RCA I got @ Reno or Rona.

stampeder, will do.

[STL]

All of the RG6 I can find around here, uses aluminium braid for the shield, which cannot be soldered. That's why I use RJ59 for the baluns, because it does have a copper braid to solder to.

I bought some 95% copper shield RG6 at Addison two weeks ago. It seems rather flexible compared to the other other kinds of RG6 I've handled. It has a solid copper centre conductor and no foil. It's v.o.p is 83%.

I'll try building a coax balun for WVNY and will report back here.

STL

[opilion]

What is the best commercially available balun that people are using? Please provide a link to buy online. I am currently using a $1.25 balun from Sayal on my GH10 with great results, but am not sure how it will hold up in the winter ice/snow and am curious how much better I could do.

[stampeder]

opilion, the testing and opinion throughout this thread says to buy several commonly available baluns ("matching transformers" as seen in many stores) and test them against each other. Even baluns in the same batch can differ. I've had good luck with a Philips, others have with RCA and other brands, and I've also thrown away many of them too.

If you want to buy a genuine CM 94444 balun you'd need to check the typical OTA: On-Line Parts, Sales sources. If you can find a balun from an old Japanese video game system they are of high quality too.

[holl_ands]

Philips Outdoor 300:75-ohm Balun was measured to have 0.5 dB Loss from VHF thru UHF.
I have yet to see any better measurements posted...

[kkoceski]

Here's the inside of the balun in the box for a 91XG :

http://img268.imageshack.us/img268/5223/img0532u.jpg
http://img88.imageshack.us/img88/9530/img0533v.jpg
http://img249.imageshack.us/img249/7820/img0535.jpg

does anybody know if the 91XG will benefit from the coax-loop balun ??? I have to wonder, since it has a nice Printed Circuit Board and all.

I'm in Florida, and my antenna is in the attic - I only have late nights and early mornings to work on things without sweating bullets. I'm not sure when I can get back up there, but I'm curious enough to make the loop and try it out.

Thanks, Kurt

[zapperman]

"Philips Outdoor 300:75-ohm Balun was measured to have 0.5 dB Loss from VHF thru UHF"

Any idea where to get these?

[stampeder]

Mall-Wart has them - see Post #128