Garbage Baluns

[ChrisSmolinski]

I was testing some baluns from my junk box collection to see what types (impedance ratios) they were, using a non inductive resistor and my VNA, since they're just unmarked PVC pipes and I had lost track of what was what.

I found a 4:1 and 9:1 that both behaved reasonably well. Not sure where these came from, I think Buxcomm?

Then I tested what I was pretty sure was a standard 1:1 balun I got at a hamfest. You see them there all the time, the ubiquitous white PVC pipe balun:



Very strange. Here's the SWR plot and impedance plot:





OK, this one is just bad or something. I tested another similar looking balun. Same results.  So I tested a third. Same results.

Alright, let's crack one of these open and see how it is made, how many ferrite cores are in it, etc.



Well, that explains why it doesn't work, doesn't it?  Just a few turns on a 1" diameter PVC pipe. No cores. My guess is they were aiming for "terrible but not bad enough that the user will know for sure it's the balun and will blame their antenna instead" on 40 and 20 meters. And super terrible everywhere else.

Anyone want to buy a cheap balun? 

[Brian]

Looks like the same design as an old aerial I used to use made by Diamond. A BU-50.
It worked pretty well but then again, it's quite easy to match a valve transmitter to almost anything.

[IQ_imbalance]

Sooo...would this be an OK result for a broadband HF receive only antenna (at least above 1.4MHz or so)?  Note the scale....looks like the SWR is 1.2-2.0 above 1.4MHz.  The max SWR is ~8 on about 800kHz.

[ChrisSmolinski]

Sooo...would this be an OK result for a broadband HF receive only antenna (at least above 1.4MHz or so)?  Note the scale....looks like the SWR is 1.2-2.0 above 1.4MHz.  The max SWR is ~8 on about 800kHz.

That seems quite reasonable - what type/size of antenna is it?

FWIW what I get with the Sky Loop (which I have just discovered is longer than I thought... but that is another post...). The Sky Loop is resonant at about 1100 kHz, and you see additional SWR minimums at the harmonics:




And the 120 ft T2FD:

[IQ_imbalance]

That's my ~ 40' diameter loop on ground.  Using a squid balun since my little chinese 1:9 was flooded out

Note that's the SWR reading where my feedline comes into the house, so that's the antenna plus a whole bunch of buried RG-6/U.

[ThaDood]

I have an old B&W RC-781 Balun given to me back in 1985. B&W no longer had any specs to it anymore. Anyone have any clue to the specs on that? It has an "N" connector for the input.

[N0TLD]

Well good lordy, hahaha! That WOULD explain it.

Wow. I wonder how many users of this sort/quality of product lost their hair trying to figure out why their antenna was acting so weird -- or just terrible -- when for all they knew there was a decently made balun inline.

And then, if they eventually found that things were better once they removed it (but still assumed it was the decent, properly constructed balun they thought they'd been sold), would they then be discouraged from using baluns again, in another antenna build?

Not the tragedy of the century, I know, but we all see how cheap/bad quality products can cause more damage than merely not working in a given situation -- they can cause people to distrust or entirely discount the real, proper technology.

Mike
N0TLD

[Polar Bear]

Most antenna Balun manufacturers are  Charlatans, they waste your time with inferior materials and poor workmanship.

Look at the specifications for the Guella Balun used by the Hy Power Antenna Company.

The question is - are you using this antenna just for listening or do you expect to transmit on this antenna aslo.
Impedance matching is not as important for listening as it is for transmitting - where the transmitter expects to see a certain impedance.

A better solution for a monitoring antenna would be to use 300 ohm tv flat ribbon Twin Lead cable.

https://www.amazon.com/Radio-Shack-100-Ft-300-Ohm-Twin-Lead/dp/B003AKA08O

If you need 50 / 75 ohms at the receiver you can use a simple television balun between the two at the radio receiver..

[Polar Bear]

http://www.hypowerantenna.com/products/balun-line-isolators

Hy Power Antenna Company

Balun & Line Isolators

[RobRich]

Amazon sure values its RS ladder line. o.O

Check out The Wireman, DX Engineering, GigaParts, etc. for quality ladder line.

A couple of quick notes about 4:1 television-grade transformers.

Some have inline caps that affect operation outside VHF/UHF. Open the balun and bypass them if required.

Some also might be more like ?:1 at HF and lower.  YMMV, though it is not like most common antennas are going to present the same loading characteristics across the entire HF spectrum anyway.

Alternatively, more "proper" 9:1 baluns for HF reception are affordable via eBay, and 450-ohm ladder line usually can be found for not much more than its 300-ohm sibling.

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BTW, in case anyone is curious regarding why an air-wound coaxial balun might sometimes work.... or not:

http://www.karinya.net/g3txq/chokes/