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Antenna Separation On Mast


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#1 spinner

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Posted 24 April 2005 - 02:32 PM

Does anyone know the recommended separation between antenna's on a mast? I am going to have 3 (VHF, UHF, and DY14 for digital). Or should I use a seperate mast for the digital?

#2 Topdog

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Posted 24 April 2005 - 06:15 PM

I know a lot of people will have a different opinion, but I have two on my one mast, a KMart(Hills) and a Frecarro seperated by only about 6- 9 inches and have no trouble whatsoever. Of course it would be a different kettle of fish if I were transmitting.

#3 Chicken Man

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Posted 24 April 2005 - 06:26 PM

Generally 1 metre of separation on the same mast is the usual spacing.

C.M

#4 mtv

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Posted 24 April 2005 - 06:42 PM

I know a lot of people will have a different opinion, but I have two on my one mast, a KMart(Hills) and a Frecarro seperated by only about 6- 9 inches and have no trouble whatsoever.

<{POST_SNAPBACK}>

Just goes to prove that theory isn't always correct. Whatever works! Having said that, I agree with C.M. 1 metre spacing, also this would be measured from the bottom of the longest element in the case of vertical polarisation.

Col

#5 alanh

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Posted 24 April 2005 - 07:59 PM

All,
The theory is at least 1/2 wavelength separation. This would be around the length of the element which has the cable connected. If it is a log periodic, that will be the longest dipole.

All separations in the list below are in mm. For the lowest mounted antenna it is the roof particularly if it is metal.

Lowest edge of Band 3, Channel 6: 862
Lowest edge of Band 4, Channel 28: 285
Lowest egge of Band 5, Channel 35: 258

Channel 0: 3 333 mm
Channel 1: 2 679
Channel 2: 2 381
Channel 3: 1 765

FM radio: 1 714

If vertical polarisation is used I would double these figures.

For further explaination see Antenna Design Basics http://www.dtvforum....showtopic=12098

See also Get the best reception
Which transmitter and which antenna

in your geographic strand for the real channels in use.


AlanH

#6 poidahl

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Posted 25 April 2005 - 07:29 PM

When I was an installer I added a lot of band 4 UHF antennas to VHF. Whilst 1m separation is a rule of thumb I accept, I let my meter be my guide. Putting the antennas closer than 24" (3 lengths of my 8" shifter) seriously compromised the UHF signal, in other words one antenna de-tuned the other. Doing a similar test with 2 channel 2 (B1) antennas gave an even more amazing result. More than 6' was necessary to avoid 1 antenna sucking the life out of the other.
Conclusion 1/: you need a meter.
Conclusion 2/: you still need to use a meter on every job.

#7 Topdog

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Posted 26 April 2005 - 04:36 PM

See I told you., but I will take it on board and if I have problems it's up the ladder I go and move them at least 1M apart..