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

[bentoronto]

Here's my narrative, please correct all my mistakes:

Practical antennas are inherently balanced. You can connect them to balanced 300-ohm twin-lead which has a really low loss being two widely spaced wires (no pesky shield near the wires... but then no insulation from unwanted RF signals). That's a great way to go from antenna into your house. But single-sided RF amps are practical in tuners and so in old days, a little matching transformer (AKA balun) internal to the TV set converted from the 300-ohm connector on the back of the set to the internal amp.

Now-a-days, we like coax cable because we can run it through metal rain gutters and it is pretty durable in the out-of-doors. But it requires a matching transformer at the antenna end and has a lot more loss.

Sometimes I wonder if going back to 300-ohm twin-lead (or even shielded twin-lead, just to mix a model) would be wiser for long down-leads?

[JamesK]

Practical antennas are inherently balanced.

Vertical antennas, which typically work against ground are not balanced. You can directly connect coax to many of them. There are also unbalanced antennas, such as the Zepp, which are fed with balanced line.

[stampeder]

Please discuss technical issues of OTA cabling here:

OTA Cabling: RG-6, RG-59, RG-11, Twin-Lead, Crimping, Other Tips

and issues with traps, amps, etc. in their own threads. This thread is just about baluns.

cheers

[hkaye]

I don't know if this has been posted before. Here is a great page on baluns. Good info and lots of pictures -

http://www.ham-radio.com/k6sti/balun.htm

[stampeder]

Actually k6sti is a member here, but Brian has not visited us in quite awhile.

[bcborn]

As mentioned, I have an older discontinued RCA/Thompson VH368 mast preamplifier. This unit can only connect to an antenna via twin lead. The amplifier can operate in UHF or VHF by user settings (switch). From this mast mounted amplifier one could run twin lead or 75 ohm to the power supply. Their are two options of running from the power supply to the TV as well - twin-lead or coax.

My question; to determine if enhanced signal will allow passage through my splitter and diplexers, can I temporarily replace the 75ohm black box on my DB4 with twin lead so I can hook into RCA pre-amplifier as the preamp will not accept a coax input.

[stampeder]

Yes, your preamp is designed to take the 300Ω twin lead connection directly from the antenna, bypassing the need for a balun (the black box).

[iblackford]

Actually, the balun is simply integrated into the preamplifier, it is not eliminated. To get true 300ohm inputs requires 300ohm traces on the PCB and an impedance matching circuit or Klopfenstein taper. I'm not aware that this is done any preamps today, is it?

[stampeder]

I doubt that there are many 100% 300Ω boxes out there any more, from what I have seen, but I was clarifying that he would not need the black balun if he did what he asked about.

[bentoronto]

Has solid-state bettered the noise figures for tubes? What were those thumb-sized RF tubes called?

[JamesK]

^^^^
Yes, they're much better. Because of the way they worked, vacuum tubes generated a lot of thermal noise. I believe you're referring to "acorn tubes" or "peanut tubes", depending on the type. The acorn tube used radial leads, to reduce capacitance, permitting higher frequency operation. Vacuum tubes could never approach frequency and noise specs of modern solid stated devices.

[hkaye]

I built a 4:1 coax loop balun with RG-59 coax cable. It was 6.5 inches in length. Using the online calculators assuming a velocity factor of 0.66 it was tuned for 600 Mhz or channel 35.



The bandwidth of this loop seemed to work fine for channels 14-51. The higher UHF channels completely dropped off.

All in all, it worked quite well but I went back to my 'lucky' Chinese made balun that seems to work just fine across the 14-69 UHF channel range. Here is what's inside this balun:



Someday I'll try to find a better balun and see if I can measure any differences in signal quality. So far these seem to work just fine for me.

[hkaye]

I bought a Channel Master Balun from Save and Replay to compare to this balun. My Antenna setup -

http://www.digitalhome.ca/forum/showthread.php?t=124542

Biquad was connected to a distribution amp and I took signal strength measurements off my Sharp Aquos TV.

There was no difference in the readings. I noticed the CM balun is made in China as well.

However the physical construction of the CM balun is quite good and better than any of the other baluns I've seen to date.

[ota_canuck]

What is the branding on your China balun? It looks like the exact same board that is found inside a CM balun.
The casing on the CMbalun is insert/injection molded using a low temp PVA material. The benefit of the CM balun is that it must always be inserted in the mold in the same orientation, so you can determine same phasing according to the printing on the one side.

[hkaye]

It says Nippon America on the balun.