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643 posts

Ultimate Geek
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Topic # 84377 29-May-2011 21:28
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Can anyone recommend a cost effective outdoor (roof mount) FM aerial for radio?

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Uber Geek
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  Reply # 475654 30-May-2011 08:42
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I use a short piece of wire on the end of a length of coax tied to the TV pole with a bit of string. Works fine and cost nothing as I had heaps of ocax in the junk box.

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Ultimate Geek
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  Reply # 475656 30-May-2011 08:46
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Still got your old VHF TV aerial? Connect that to your radio, most times is more than adequate.

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  Reply # 475847 30-May-2011 18:09
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I concur with illicit - our combo VHF/UHF aerial picks FM up with no problem.



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Ultimate Geek
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  Reply # 475891 30-May-2011 19:22
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illicit: Still got your old VHF TV aerial? Connect that to your radio, most times is more than adequate.


mm1352000: I concur with illicit - our combo VHF/UHF aerial picks FM up with no problem.


Does this not need some kind of filter? Does it need to be at a 45 degree angle? (I have a feeling I've asked these question before...)

I do have a VHF aerial, and it's in really good nick. 

If the VHF fails, I'll try the wire idea.

EDIT: ah yes, it seems I've repeated my own thread: http://www.geekzone.co.nz/forums.asp?ForumId=34&TopicId=76670

So the VHF at 45 degrees then. I'll try it tomorrow. 

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  Reply # 475905 30-May-2011 19:46
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Interesting - never knew about the 45deg thing. Our aerial is pretty much vertical as its purpose is to pick up DVB-T and analog TV signals. It looks like this...although it may not even have that many short pieces. The FM + analog TV + DVB-T is amplified, then combined with satellite signals by a multiswitch, then split 8 ways and 4 ways again on one of the 8 way feeds. All modes work fine. Smile

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  Reply # 475916 30-May-2011 20:01
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Technically mainline FM transmitters use slant polarisation this means they work well with a mixed receive antenna, ie does not matter if H or V there is only a 3db penalty unless slanted 90deg out.

So as others have said a BandI/III TV antenna will typically do a good job.

Oh and if you do go for slanting your antenna when standing behind the antenna right side down.

Cyril

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  Reply # 476035 30-May-2011 23:42
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VHF antennas work OK so long as they are pointing the right way for FM, but watch out as most amps have an FM trap in them as it us usually way stronger so overload things, so as a result with the trap, they are attenuating the FM not amplifying it.

I got the biggest that there was and it was cheap as, as I wanted to see if I could get one of the LPFM stations. It worked, for about 2 weeks before some bloody ethnic mob started up 0.2 away and overmodulating.




Richard rich.ms

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  Reply # 476082 31-May-2011 09:07
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mm1352000: .Our aerial is pretty much vertical as its purpose is to pick up DVB-T and analog TV signals. It looks like this...although it may not even have that many short pieces. Smile


If its the same as in the picture then no its not. Its two horizontall polarised antennae stacked one above the other.
If rotated 90 degrees it would be two vertically polarised antennae side by side.

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Geek
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  Reply # 476107 31-May-2011 09:53
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Most of the Large Transmitting sites are using Circular Polarisation, so rotation of the antenna will not make too much difference.. 
Some are Vertical, but I havent seen any Slant for a while.. There were some in the 80's so they could well still be around.

On the fringe it's definitely worth trying all options of polarisation even with circular as its not often perfect in all directions and objects in the path can reduce one component more than the other.
I've always wanted to try making a circular receiving array with H and V antennas 90° combined for deep fringe testing..

My experience is mostly with Skytower Akl where the large FM1 array is circular and the FM2 is vertical. Within a few kms it can be useful to use a horizontal antenna to reduce the FM2 signals which are quite hot on the ground from the less directional small array..

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  Reply # 476380 31-May-2011 20:35
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which ones are on fm2?




Richard rich.ms

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  Reply # 479968 11-Jun-2011 04:49
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if you have an exising vhf tv aerial buy a wallplate with fm/vhf splitter - most radios have a 75ohm coax aerial plug - just connect to the fm outlet of the wallplate - easy

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Ultimate Geek
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Chorus NZ

  Reply # 480063 11-Jun-2011 15:09
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richms: which ones are on fm2?


Hi techricky, yes which ones are on fm2?

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