FM Antenna

[Slartibartfast]

Two points.

 

Unlike TV, FM transmitting antennas tend to be mixed or circular polarization (alignment of E plane), which means that receive antenna polarization (orientation vertical or horizontal) is usually non-critical. However, community FM stations can be exceptions to this rule, so if the intention is to receive low power community FM, vertical mounting may be necessary. 

 

Combined TV /FM antennas are usually designed for the old analogue TV channels 3-5 and are usually hybrid log periodic / yagi designs. 

[Jesco]

I am not sure the combo antennas are an advantage or disadvantage.  Also I don't know who could tell me from experience, but I do understand your sentiment.  Your antenna is in the gain region I think I am after and if it is as well made as you say, then it may just be a good thing.  Is is the only local yagi I have seen that is FM only, so maybe it is worth a shot.

 

Unless you also need another TV antenna, I think you would be better off with a purpose built FM antenna as a combo antenna like that inevitably involves performance compromises.

[davm]

I bought and installed the following FM antenna from Radio Parts:

 

http://www.radioparts.com.au/product/00442056/y3fma-fm-radio-antenna-aerial-hills

 

It's worked very well for me, but I'm in suburban Melbourne so not as far from the FM transmitters. Agree about using high quality, shielded coax.

[acg]

Thanks everyone for their input.  Antenna is now ordered...I went with @@Jesco and ordered the three gang FM only from AcademyTV in Victoria.  Freight is a large portion of the spend but it is all manageable and I doubt I will be second guessing my choice.  If I find later down the track that the 5dB gain Yagi is not enough they also have a 10dB gain model for not much more, but I did not want to overload the 75ohm input on the TU-X1 if I could help it.

 

Looks like I will be doing a second storey antenna install in a week or two.

 

Cheers,

 

Anthony

[Slartibartfast]

Thanks everyone for their input.  Antenna is now ordered...I went with @@Jesco and ordered the three gang FM only from AcademyTV in Victoria.  Freight is a large portion of the spend but it is all manageable and I doubt I will be second guessing my choice.  If I find later down the track that the 5dB gain Yagi is not enough they also have a 10dB gain model for not much more, but I did not want to overload the 75ohm input on the TU-X1 if I could help it.

 

Looks like I will be doing a second storey antenna install in a week or two.

 

Cheers,

 

Anthony

 

 

More gain will give you a better front-to-back ratio, which might be beneficial if you're being overloaded from the rear (so to speak).

 

You can also add a second 3 element yagi for 3dB of gain if necessary. All that's needed is a small length of coax to transform the impedance.    

[HUMBUG89]

Would agree with all the tech. details re yagi antennas and gain and using the right cable.  I have a three element yagi, which has been "up" for around 20 yrs although much beaten and battered by weather of all kinds it still performs very well, picking stations from Melbourne and not just those commercial ones, but stations such as 3RRR and 3PBS, 3MBS all at varying degrees of signal strength here in Ballarat. My Tuner is an old 70's Yamaha  CT800 and I am using 300 ohm balanced lowloss line from antenna to Tuner, which I brought in my Amatuer Radio days of 30yrs ago ( I still have my "Ham" licence ). Might look at replacing the old antenna with a new one at some stage. 

[Guest]

Google

Best FM antenna

You can make it yourself

This one?

http://latham.dropbear.id.au/antenna/

I looked at that for the shed tuner

Ended up making something that was nothing like that...

Two bits of pool fencing aluminium tube (one powdercoated)

Not the same lengths as described

Tek screwed some eylet crimp connectors to it

Attached some random wire

Tucked them up in the rafters away from eachother

Perfect reception

[Gee Emm]

Yep, that's it.

Without pics, it never happened.

See, I do help!

Edited May 13, 2016 by Gee Emm

[Guest]

Without pics, it never happened.

Should sort those wires out...

Edited May 13, 2016 by Dirty_vinylpusher

[jamesg11]

What are the 'symptoms' of the signal overload?

My Sansui TU-S9 always has metered full strength & say, on Classic FM, there is a slight backgound sshhh that you can hear in quiet passages. We're Melb, N mid-inner burbs, high up, antenna directed at Dandenongs. But it is a TV antenna, with splitter. No problem with signal strength & maybe there's too much?

[Guest]

@@acg have you done the installation yet? All of the FM transmitters at Mt Mowbullan have mixed polarisation, therefore it is optional whether you mount the FM antenna horizontally or vertically. See: http://fmscan.org/ml.php?r=f&t=37700083 

 

However there are several much more powerful TV channels being transmitted with horizontal polarisation from the same site: https://ozdigitaltv.com/transmitters/QLD/109-Mt-Mowbullan

 

It may be beneficial to install the antenna vertically to minimise any unwanted TV signals in the feed-in to the tuner especially as the TV transmitters are 250kW and the FM transmitters are just 100W. The input stages of the tuner may be overloaded by the combination of all RF signals presented to the antenna terminal, not just the FM ones.

 

BTW I don't believe you should worry about overloading the input with FM signals only with an FM antenna of 5dB gain - the 85 kilometre distance from the transmitter will ensure there is plenty of signal attenuation before it gets to your antenna. 

Edited May 23, 2016 by Guest

[acg]

@@acg have you done the installation yet? All of the FM transmitters at Mt Mowbullan have mixed polarisation, therefore it is optional whether you mount the FM antenna horizontally or vertically. See: http://fmscan.org/ml.php?r=f&t=37700083 

 

However there are several much more powerful TV channels being transmitted with horizontal polarisation from the same site: https://ozdigitaltv.com/transmitters/QLD/109-Mt-Mowbullan

 

It may be beneficial to install the antenna vertically to minimise any unwanted TV signals in the feed-in to the tuner especially as the TV transmitters are 250kW and the FM transmitters are just 100W. The input stages of the tuner may be overloaded by the combination of all RF signals presented to the antenna terminal, not just the FM ones.

 

BTW I don't believe you should worry about overloading the input with FM signals only with an FM antenna of 5dB gain - the 85 kilometre distance from the transmitter will ensure there is plenty of signal attenuation before it gets to your antenna. 

 

Thanks John.  Yes the antenna is up and I will be testing it today sometime.  It has been installed horizontally but should be reasonably easy to pull down and mount vertically in the future.  I will leave it this way for a while and get a stable listening environment in the new room and new system and then I can experiment with the antenna orientation and input into the TU-X1 et cetera.  Good information though, and thanks for posting it.

[acg]

What are the 'symptoms' of the signal overload?

My Sansui TU-S9 always has metered full strength & say, on Classic FM, there is a slight backgound sshhh that you can hear in quiet passages. We're Melb, N mid-inner burbs, high up, antenna directed at Dandenongs. But it is a TV antenna, with splitter. No problem with signal strength & maybe there's too much?

 

I don't know for certain because I have no direct experience in this regard, but according to the fellow that diagnosed this problem it just sounds worse than it should.

[acg]

Well @@johnmath, you were right, there is plenty of attenuation in that 85km.  The 5dB antenna is giving me about 70% signal strength.  If I disconnect the antenna and leave about 5m of shielded coax cabling connected to the tuner this drops to about 40% signal strength, so I think the antenna seems to be working at about the right level.  Might have to get that 10dB gain antenna after all.

 

[Kensell21]

Err. A few years ago, not knowing what I was doing, I went and asked for the biggest fm antenna that I could find.
My Audiolab tuner which I lusted after for years finally came into my possession?. Not sure if I did the right thing.. But it works...

Ended up with this. Think it cost me $90 at the time..

 

Edited May 26, 2016 by Kensell21

[catman]

G'day all, interesting subject this, and antenna gain can be a  funny thing in practice.  I have designed two yagi's for the 146 MHz VHF Amateur Radio band that both work extremely well with the expected amount of signal gain, however I actually get better results at this location, (on both transmission and reception) with the smaller of the two yagi's, a three element design. 

 

However others have built the larger (five element) version with excellent results.  So this tells me that antenna gain isn't the only consideration, with beamwidth and operational beamwidth and pattern, and it might depend on the location as well.  A complex subject!  Regards, Felix vk4fuq.     

[Jesco]

G'day all, interesting subject this, and antenna gain can be a  funny thing in practice.  I have designed two yagi's for the 146 MHz VHF Amateur Radio band that both work extremely well with the expected amount of signal gain, however I actually get better results at this location, (on both transmission and reception) with the smaller of the two yagi's, a three element design. 

 

However others have built the larger (five element) version with excellent results.  So this tells me that antenna gain isn't the only consideration, with beamwidth and operational beamwidth and pattern, and it might depend on the location as well.  A complex subject!  Regards, Felix vk4fuq.     

 

Much like a simple ¼ wave vertical for UHF CB performs better here (here being mountainous country) than a 6db collinear does...

More gain isn't always better.

[mashley]

FWIW a friend of mine in a poor reception area where only mono was possible made one of these very simple and very cheap  aerials and it worked extremely well!

[Guest]

FWIW a friend of mine in a poor reception area where only mono was possible made one of these very simple and very cheap  aerials and it worked extremely well!

Your link doesn't work

[mashley]

Oops a typo: try this link.

[Guest]

Oops a typo: try this link.

[catman]

G'day all, an interesting full wave loop design and whilst I am a bit of a loop fan myself, I have to query the gain figures quoted.  5.5 to 6 db by itself is an impossibility. 

 

The gain is somewhat dependent on the loop shape however a simple square loop will produce no more than about 1 db of signal gain (over a reference dipole). 

 

I dearly wish that my 20 m (14 MHz) full wave loop produced 5.5 to 6 db gain, but it doesn't....Sorry. 

 

It is a very good antenna, and yes the side nulls are impressively deep, but there isn't much gain in a single loop.  Adding parasitic elements to a loop improves the gain, similar to a conventional yagi antenna structure.  Regards, Felix vk4fuq.