Spacing 6m/2m/70cm - and a scanner - and a cb... and my TV antenna

[rjvalenta]

as the title says... i'm trying to figure out an antenna setup for my home... i have a large attic under a slate roof, i considered just putting all my antennas up there... but that's where my TV antenna is, and i'm fairly sure ramming 30w of VHF/UHF into my TV antenna will be bad.

the TV antenna is a few feet back from the attic vent, i'd like to put my MLA30 in front of it to catch some SWL... and maybe a scanner antenna in the attic...

but the CB and ham antenna concerns me. SSB CB is up to 12w and some VHF rigs can put out 50w, some 6m rigs 100w... so i'm fairly sure that's not something i want in the attic with my MLA30, TV, or scanner antennas.

then i started to wonder about spacing. it's a topic you can find online, some say a quarter wavelenth, some say 2.5 wavelengths... and i'm over here wondering if 2.5 wavelengths.... 6ft... is going to make a difference when i'm ramming 25w of UHF into my TV antenna.

i can run cable out the vent on to a part of the roof that's over an addition to the house - but then i have the issue of keeping these antennas from hurting each other as well - AND - part of that roof has a thick tree over it.

my best idea so far is to get a 10/6/2/70 quad antenna, go as far out as i can from the vent, in to the tree and maybe even attaching the mast to the tree. i'm not doing HF here yet, just want to get in some local coms, SWL, and scanning. it is my understanding the VHF/UHF are less impacted by trees, and this could give me 25ft from the MLA30 / TV / scanner inside the vent under the roof.

i realize this isn't much to go on without pictures, but until i can find a way to get a drone over here my questions are this:

- how far would you separate your UHF/VHF TV antenna from a 50w 6m/2m/70cm transmitter?
- how far would you separate your scanner antenna from a 50w 6m/2m/70cm transmitter?
- how far would you separate your scanner and TV antennas from a 12w CB antenna?
- how far would you separate and ML30 from a 12w CB antenna? (assuming the MLA30 won't get overloaded by the VHF/UHF, correct me if I'm wrong)

and, just because it could make things easier - does anyone know if a slate roof may offer some kind of RF protection?

love to hear any thoughts... i just got my license back after years of not using it, so i'm re-learning a lot... and even back then everything was on a dual band HT or a mobile rig.

thanks,

Richard
N0TZC

 

[Lauri-CoyoteFrostbite]

Hello Richard

I read over your post a few times, and I must say you have quite a project on your hands. If I understand it correctly, you want to put all those antenna's together up in your attic ?

...... Regardless of the separation issues, I don't think that's a good idea, even though a slate roof may not be an issue as an RF attenuator.
I will say, and re-enforce what you know already- that separation of antennas is important- though you will not be able to get them all far enuff apart in an attic to do much good. They will interfere with each other, I am afraid. The good news- unless they are in such close proximity (ie: almost touching) there isn't much danger they will cause RF damage to each other at the power levels you listed.

In the light of all this, i would suggest you re-engineer this design..... figure out what antennas are really important and then how to get them outside and away from each other.

I am sure others here will have ideas that may be helpful..... good luck !


Lauri

 

[GlobalNorth]

A slate roof? You may have other problems with more than signal saturation due to antenna power levels and proximity.

That may well present problems with RF transmission and reception. Slate is composite sedimentary stone that is made up of microclastic particulate minerals and rock. Some may be localized [to the quarry] clays, quartz, iron, cobalt, various non-metallic/metallic minerals, and there is no predicable way of guesstimating the transmissibility of RF energy without sampling every tile individually and as a mapped coherence to determine pattern suitability. Some tiles may have significant levels of metallic microclasts and some may not.

RF energy from OTA TV towers is considerable and the VHF/UHF frequencies can penetrate/reflect their way into many structures. A 50 watt 6 meter signal from miles away may well be below the power threshold to overcome a quality antenna behind some metallic slate tiles.

You can try to see if you are lucky, but I'd avoid the headaches of trying to install, move, adjust, and then possibly redo your antenna array to an outside location if it doesn't work for you.

 

[n2nov]

Living in an urban environment where my small house on a small piece of property makes me look at a similar situation with this suggestion.
Let's take a rectangular attic running from left to right and the TV stations are to my left.
- place the TV antenna as close to the left wall of the attic thereby having the antenna coverage go to the left and not the right
- put your transmitting antennas to the far right of the attic behind the TV antenna, but also space them out from each other by at least 1/4 wavelength of the lowest transmitting signal
- try to use as many multiband antennas as possible with duplexers to match the bands at the radio room end of the single coax coming down
- keep in mind double and triple harmonics of any transmitted signal getting into a signal that you are trying to simultaneously receive

 

[rjvalenta]

Lauri -

i would love to put all the antennas in the attic, but i've come to terms with that not being reality...

so this morning i started to re-engineer things just like you suggested, and realized that my satellite dish is behind me when i look out the vent - and above, on a part of the roof that does not have shingles on it, which i can easily drill through and seal.

with this in mind, my new plan is to get one of Comet's 10/6/2/70cm mobile antennas, mount it to a standard dish mount with a radial kit (and possibly some wire radial extensions) - and place that behind (about 12ft) and above (about 10ft) from where the MLA30, scanner antenna, and OTA TV antenna are.

with a duplexer i can separate out the CB and keep my ham VHF/UHF from possibly damaging the CB... i think.

i remember hearing that separation by elevation was worth more than vertical spacing, and the layer of roofing should help as well...

so - the end result will be... INSIDE the attic, MLA30 at the vent, Tram 1410 Scanner antenna next to it, OTA TV antenna behind it... then behind all that by 12ft and above everything by 10ft OUTSIDE on the roof will be a Comet UHV 4 10/6/2/70cm antenna that will split via duplexer to my CB and VHF/UHF mobiles on my desk.

love to hear any other thoughts you have.

rjv

Hello Richard

I read over your post a few times, and I must say you have quite a project on your hands. If I understand it correctly, you want to put all those antenna's together up in your attic ?

...... Regardless of the separation issues, I don't think that's a good idea, even though a slate roof may not be an issue as an RF attenuator.
I will say, and re-enforce what you know already- that separation of antennas is important- though you will not be able to get them all far enuff apart in an attic to do much good. They will interfere with each other, I am afraid. The good news- unless they are in such close proximity (ie: almost touching) there isn't much danger they will cause RF damage to each other at the power levels you listed.

In the light of all this, i would suggest you re-engineer this design..... figure out what antennas are really important and then how to get them outside and away from each other.

I am sure others here will have ideas that may be helpful..... good luck !


Lauri

View attachment 129707

 

[rjvalenta]

i have the same suspicions and was replying to Lauri with similar thoughts when you sent this reply, so it's time to start to engineer a plan for an outside antenna.

rjv

A slate roof? You may have other problems with more than signal saturation due to antenna power levels and proximity.

That may well present problems with RF transmission and reception. Slate is composite sedimentary stone that is made up of microclastic particulate minerals and rock. Some may be localized [to the quarry] clays, quartz, iron, cobalt, various non-metallic/metallic minerals, and there is no predicable way of guesstimating the transmissibility of RF energy without sampling every tile individually and as a mapped coherence to determine pattern suitability. Some tiles may have significant levels of metallic microclasts and some may not.

RF energy from OTA TV towers is considerable and the VHF/UHF frequencies can penetrate/reflect their way into many structures. A 50 watt 6 meter signal from miles away may well be below the power threshold to overcome a quality antenna behind some metallic slate tiles.

You can try to see if you are lucky, but I'd avoid the headaches of trying to install, move, adjust, and then possibly redo your antenna array to an outside location if it doesn't work for you.

 

[rjvalenta]

yes! from the front of my home, the vent is on my left - AND - the majority of the TV towers would be to the left...

when you sent this reply, i was in the process of replying to Lauri (see above), but i think i came to the same plan! a quad band antenna, not just separated as much as possible, but also outside and ABOVE, with the roofing material as an added barrier. i can feed that down with one line of coax, then split that with a duplexer...

after that you lost me, i am not familiar with double or triple harmonics.

Living in an urban environment where my small house on a small piece of property makes me look at a similar situation with this suggestion.
Let's take a rectangular attic running from left to right and the TV stations are to my left.
- place the TV antenna as close to the left wall of the attic thereby having the antenna coverage go to the left and not the right
- put your transmitting antennas to the far right of the attic behind the TV antenna, but also space them out from each other by at least 1/4 wavelength of the lowest transmitting signal
- try to use as many multiband antennas as possible with duplexers to match the bands at the radio room end of the single coax coming down
- keep in mind double and triple harmonics of any transmitted signal getting into a signal that you are trying to simultaneously receive