Is this a balun?

[fixit7]

I am trying to diagnose my FM radio antenna.

Is this a balun?

Thanks.

 

[kubeek]

Sorry, my crystal ball is in repair. So short of measuring the thing, the only possible answer hovers somewhere between possibly and likely.

 

[fixit7]

I can measure with your help.

I found out there are 2 types.

75 -> 300 and 300 - 75 ohms.

The one I need would need to work for a FM antenna.

 

[kubeek]

75 ohms is definitely on the side of the coax, and 300 is on the side of the antenna. So i guess it should work. but saying where did you get it and what was its purpose was would shed some more light onto the problem.

 

[fixit7]

I bought it years ago for a project for a tv antenna. It worked pretty good, but needed to rotated for some channels.

This is what I have for my FM antenna.

Dropbox - File Deleted - Simplify your life

www.dropbox.com

I am only interested in improving the FM reception. It picks up some channels, but is weak on most FM channels.

 

[kubeek]

Sorry that I am no antenna specialist, but your photos don´t inspire confidence. Is that a plank with pieces of wire trying to get a refflector array antenna?
What are the dimensions of the elments and everything else, and where did you get those? https://en.wikipedia.org/wiki/Reflective_array_antenna

Also, antennas dont care the least bit whether your modulation is AM or FM. What frequency band do you want to use?
VHF radio bands are most likely being blocked by a filter that is designed to be used for VHF TV bands.

 

[fixit7]

Guessing does not inspire confidence.

I will try to find an antenna forum.

 

[Ylli]

The original picture is indeed a balun. However, the antenna you pictured is typically used for UHF TV reception. The FM broadcast band is 88 - 108 MHz, and the UHF TV band starts at 470 MHz. For use on the FM band, the total length of the elements of a bowtie (end to end) would need to be a little over 7 feet.

 

[rjenkinsgb]

That looks far too small for the FM band at around 100MHz??

Each driven (electrically connected) dipole should be approximately 5% less than a calculated half wave, end-to-end; at 100MHz, 3 metres wavelength, that is 142.5cm (56 inches) end to end.

If the dimensions are wrong by more than a few percent it will simply not work well, if at all.


This is some design info and calculations for building a Yagi style antenna:

Yagi Uda Anteena Designing Steps

An yagi antenna, a narrow band antenna working for FM channel and consisting of a reflector, a driven element and two directors.

www.elprocus.com

 

[dr pepper]

You could say splitting hairs that its a unun.
Unbalanced in at 300 ohm, and unbalanced out at 75 ohm.
Being a transformer it'd work either way.

 

[Nigel Goodwin]

You could say splitting hairs that its a unun.
Unbalanced in at 300 ohm, and unbalanced out at 75 ohm.
Being a transformer it'd work either way.

Why do you imagine it's unbalanced 300 ohms?, it would be pretty unusual - more likely it's a balun - particularly in the USA where they commonly used balanced 300 ohm feeders, where Europe never did.

However, as others have said - his aerial looks to be a low gain UHF array - I've never seen (or heard of) a short back fire array for FM radio.

If he wants a nice simple (and cheap) FM aerial, just get a piece of figure 8 twin speaker cable, cut the two wires apart slightlyat one end and hold the two wires in each hand (between thumb and forefinger) - and then pull your arms apart as far as you can to the side - this gives you a dipole of 'close enough' to the correct size. Connect the other end of the cable to the balum, and you're good to go.

 

[audioguru]

On your other thread, I asked:
1) Is the problem caused by using a cheap FM radio? My cheap clock radio has the same problem as yours. It cost $1.75 on sale.
2) Is it caused by a building or mountain blocking the FM stations you want to receive?
3) Did you know that the earth is curved in a circle, not flat and a receiving antenna must be close enough to the transmitting antenna to "see" it?

 

[fixit7]

That looks far too small for the FM band at around 100MHz??

Each driven (electrically connected) dipole should be approximately 5% less than a calculated half wave, end-to-end; at 100MHz, 3 metres wavelength, that is 142.5cm (56 inches) end to end.

If the dimensions are wrong by more than a few percent it will simply not work well, if at all.


This is some design info and calculations for building a Yagi style antenna:

Yagi Uda Anteena Designing Steps

An yagi antenna, a narrow band antenna working for FM channel and consisting of a reflector, a driven element and two directors.

www.elprocus.com

It is an interesting design.

Looks like it requires a FM transmitter and need adjustment to receive a specfic station.

This gets mostly good reviews and at $9, is way cheaper than the yagi style antenna.

Amazon.com: E-outstanding 75 Ohm UNBAL FM Radio Antenna, Dipole Indoor T Antenna HD Aerial Male Type F Connector Y Tuner for Yamaha JVC Sony Bose Radio Stereo Receiver: Home Audio & Theater

Amazon.com: E-outstanding 75 Ohm UNBAL FM Radio Antenna, Dipole Indoor T Antenna HD Aerial Male Type F Connector Y Tuner for Yamaha JVC Sony Bose Radio Stereo Receiver: Home Audio & Theater

www.amazon.com

"Guessing can be quite expensive."
Thomas Edison

 

[unclejed613]

it is a 75 ohm to 300 ohm balun. they are used for connecting an older TV set to CATV, or for connecting a high impedance antenna (a folded dipole, either by itself, or as part of a yagi array) to 75 ohm coax cable. these baluns are so ubiquitous that you can often buy bags of them.

these baluns work between about 50Mhz to 600Mhz. the FM broadcast band is well within that range.

 

[unclejed613]

This is what I have for my FM antenna.

that's a phased array for UHF, not VHF. if you scale ALL the dimensions 3:1, it will be in the right "ballpark" for the FM broadcast band.

 

[fixit7]

Unclejed613,

Glad you caught before I disassembled it.

Could you give more details on how to scale it 3:1?

"these baluns are so ubiquitous that you can often buy bags of them."

I can see why.

I took my balun apart.

They used 100 gauge wire.

 

[dr pepper]

The last one I came across with an F connector was 300 to 75 ohm.
Just a bit of a guess.

 

[rjenkinsgb]

It is an interesting design.

Looks like it requires a FM transmitter and need adjustment to receive a specific station.

They are not that critical, you just work from calculated measurements for 98MHz and one would be fine.
I built one for the 2M amateur band purely from calculations and used it for years.

I believed you needed some amount of gain, as the one in the picture was an array type.
If you do not need the extra gain, a simple wire dipole may well work fine! There is no need to buy one, you can just use a decent length of twin feeder and split the end, spreading it to about 56" end to end.

That gives you a fair half-wave dipole, as Nigel said earlier.

 

[Nigel Goodwin]

Unclejed613,

Glad you caught before I disassembled it.

Could you give more details on how to scale it 3:1?

Try like I said early, a simple piece of speaker wire - it works remarkably well for an FM aerial - even without a balun, and as you have a balun (they are fairly uncommon over here) will work even better. You could have 'built' one in the time it took to type your last post!

There's no point building a short back fire array, they aren't used at VHF and are only low gain anyway - their main purpose in life was anti-ghosting for analogue TV reception.

 

[audioguru]

The Amazon wire antenna is a simple "rabbit ears" dipole with no gain. It works fine with a high quality home stereo receiver but not with a cheap FM radio.

The UHF bowties are fine for local UHF TV but will be much too large for distant or weak FM radio frequencies.