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Topic # 245360 31-Jan-2019 08:10
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I have a spiky uhf antenna. Also on my aerial I have a massive long antenna around 2.5m - 3m high and a shorter long one about 0.5m high. I know the spiky uhf is the only one used with freeview, are the other two both different forms of vhf? Are they good for anything else? or are they scrap


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  Reply # 2170539 31-Jan-2019 08:12
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The VHF ones are redundant, could still be useful if you have poor FM reception.


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  Reply # 2170547 31-Jan-2019 08:27
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VHF analog TV covered bands 1 (called low band), 44 to 68 MHz (channels 1 to 3), and Band 3 (called high band), 174 to 230 MHZ (channels 4 to 11). FM radio, band 2, 88 to 108 MHz. Higher the frequency then the shorter the elements.


 
 
 
 


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  Reply # 2170566 31-Jan-2019 09:22
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DjShadow:

 

The VHF ones are redundant, could still be useful if you have poor FM reception.

 

 

This is the only reason mine is still up in the roof.  Works a treat for Radio


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  Reply # 2170567 31-Jan-2019 09:25
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If there is a masthead amp then they usually have a filter to block FM since its generally a lot stronger than TV.

 

Also they're really only useful for FM if they come from the same location, all my VHF got for FM when I cared was a whole lot of multipath distorted mess, I had to put a proper FM antenna up aimed off towards the city to get usable FM here. But then there is streaming which gives almost as good sound as FM for most stations but is a hell of a lot easier, and its not like they sound any good to start with. Once I fix the deck that the ladder has to go on to get up to the roof I will be pulling everything off the roof antennawise since its all redundant now.





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  Reply # 2170569 31-Jan-2019 09:30
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Our vhf is long gone. When I needed an external antenna for FM I just made a half-wave dipole out of wire and tacked it along the eve. Worked a treat but we haven't used it for ages.

 

 





I reject your reality and substitute my own. - Adam Savage
 


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  Reply # 2170633 31-Jan-2019 10:43
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A 3 meter high antenna doesn’t sound like vhf tv. Some other comms more likely

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  Reply # 2170641 31-Jan-2019 10:57
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Full wave?

 

 





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  Reply # 2170645 31-Jan-2019 11:07
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Band 1 half wave would be 3 metres.


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  Reply # 2170721 31-Jan-2019 13:17
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Old TV antenna's can be very useful for making low power FM antennas - its an easy option for getting LPFM stations on the air where the operators have limited funds.  I've made a few over the years, a half wave dipole is all that's required - 300/freq gives you the wave length in meters then you multiply by the velocity factor which for most TV antenna elements is 0.935. (93.5% the speed of light) and divide by 2 to get a half wave length.  It's fed with RG58 coax and a balun made from the same coax - the balun is a quarter wavelength, the VF of RG58 is usually 66% the speed of light.


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  Reply # 2170728 31-Jan-2019 13:32
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RunningMan: A 3 meter high antenna doesn’t sound like vhf tv. Some other comms more likely

 

He's probably talking about a vertically polarised antenna and 3m is about right for Ch1 - 3 analogue.


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  Reply # 2171034 31-Jan-2019 22:00
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Old VHF antennas are horizontal or vertical polarisation.  FM is diagonal polarisation.  So while a VHF antenna will work for FM, if you really want the best reception (for Concert FM, for example, where they really care about transmitting good quality sound), then you need to get a proper FM antenna.


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  Reply # 2171035 31-Jan-2019 22:10
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fe31nz:

 

Old VHF antennas are horizontal or vertical polarisation.  FM is diagonal polarisation.  So while a VHF antenna will work for FM, if you really want the best reception (for Concert FM, for example, where they really care about transmitting good quality sound), then you need to get a proper FM antenna.

 

 

 

 

A proper FM antenna pointed at the transmission source will also reduce the effects of multi path distortion - signals reflecting off buildings etc... and causing a distorted stereo image, the same as ghosting on analogue TV.


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  Reply # 2171039 31-Jan-2019 22:27
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"Diagonal polarisation" is actually circular, Auckland FM stations come from the SkyTower, there are multiple stacks of 8x circular polarised transmit antennas wrapped around the tower - most of the stations are fed into this one antenna system through an RFS combiner which is a combination of 3db couplers and band pass filters to prevent RF getting back to the transmitters while keeping everything at a 50ohm impedance.  There are 4 stations which are *not* circular, 96.6, 95.8, 103.8, 106.2 because they run on a stack of 4x vertical polarized dipoles mounted on the north west facing side of the tower - a vertical polarised yagi would be best for receiving this group.

 

Click to see full size

 

 


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