Radio Antenna On Chimney ?

[the_constructor]

Being a white stick radio operator, I have to find someone to put the antenna up on the chimney stack for me, but before I do, I need some advice please.

Obviously, a small pole needs to be attached to the chimney stack so that the antenna which is a glass fibre aerial weighing 0.9Kg can be fitted just above the stack itself. Neither I nor my neighbour have chimney pots.

I would estimate that the pole would be overall about 3 feet long and then the antenna fitted at the top of the pole to clear the stack.

Should I use 1 or 2 lashing kits to hold the pole. The pole will be 2" alli scaffold, already obtained, curtousy of the housing refurbishment contractors.

I have written consent from my neighbours because the chimney stack belongs to both of us.

I asked on another group but advice not forth coming.

Kindest regards,

Jim

[dave]

At this point, I have to ask is the antenna for V/UHF, or HF use? If the latter, I would advise a double lashing kit.

Have you gone for the thick walled stuff, or the zip up type?

Dave

[Andrew Gabriel]

If you get an aerial installer to do it, get the advice from them.

That seems quite small compared with many TV aerials, although I have no idea what shape, and more importantly, wind resistance the glass fibre aerial has, but providing it's not large, one lashing kit should be fine.

Make sure your brackets will take a 2" mast, as 1.5" is a more common aerial mast size (although 2" masts do exist).

[dave]

If he is a radio amateur as I am, our aerials demand different mountings than do TV ones. Lightening and static during a storm can take out the front end of a receiver in a flash. Pun intended

This is one of the unknowns. For amateurs, wind resistance calculations are well known. A TV aerial installer will have no knowledge of this. Our aerials that work from 50 Meg to 70 centimetres can be quite wide and bulky. Thus giving a much higher wind resistance than expected.

Dave

[dennis]

I have seen amateur radio aerials on the ground, still attached to the chimney, they can be rather large compared to a TV aerial.

[David WE Roberts]

I put up an alloy scaffold pole as a TV aerial pole a few years back. However it was a lot more than 3' long - taller than me so 2-3 metres.

I used a couple of very large lashing kits to hold the pole.

The aerial is still up there, and well above any others around it.

If it is only 3' then one lashing kit might do - although you don't say how long the aerial is. Short and stumpy will exert less lateral pull than a very tall one. If there is any doubt I would use 2 - the cost of a lashing kit will be small compared to the cost of someone going up there and fixing it.

HTH

Dave R

[the_constructor]

Yes, I am a licensed radio ham. Jim G1SSO located in County Durham.

The bracketry I was thinking of is something like this:

is the spec of the antenna:

Compact white fibreglass dual-band base antenna for 2m and 70cm.

Frequency Bands 2m/70cm Max Power 200W Length 1.7m Radials 3 Gain (2m) 4.5dB Gain (70cm) 7.2dB Weight 0.9kg Type (2m) 3 x 1/4 wave Type (70cm) 3 x 5/8 wave

The alli tube that I have is 2" dia and roughly 3/8" wall. As I say, I would imagine all I need is about 3 feet.

I was thinking of running a 10mm green earth cable from the mounting brackets down to a ground spike, but someone commented that it may upset the antenna. Also I want a termination box with an N socket attached, on the wall in my shack and to run a similar cable to ground.

All comments gratefully received.

Jim

[tony sayer]

In article , the_constructor scribeth thus

Thats not that much of a load but its more of a load that I'd feel happy with the bract chosen for what your trying to do!.. Put it on a decent lashing, a competent aerial rigger if you have one round your away can advise. Or if you have one a decent couple of wall brackets on a gable end might be better.

It should be able to clamp to a standard 50 mm dia pole we use similar aerials for PMR applications and don't have problems usually they come with their own brackets sometimes we have to supply them but it shouldn't be rocket science.

The bit about earthing sounds duff info!, you won't upset the aerial at all at those frequencies. Very very few aerials on domestic premises are earthed with a view to lightning protection, this does require more than a bit of Green earth wire a solid lump of Ally or copper and earthing plates or driven electrodes are required.

An "N" type outlet shouldn't be a problem either and earthing that and disconnecting the aerial lead in thundery weather might be better then nothing. If your belted by a direct strike expect that to be vaporised and an insurance claim!. What it will help with is small induced current side swipes..

73's

[zaax]

Stick a pole in the ground it much easier to take down when you need to put up another type of ariel. The ariel can be 15M from ground level. A tempory wind up / down one can be as high as needed.

[the_constructor]

Many thanks for the suggestion, but unfortunately, this is not an option.

Jim

[dave]

and it has been up over ten years now without a problem at all.

Just popped up to the shack to check on a dual bander that must be very similar to yours and that came with 4 foot 25 mm or one inch diam aluminium pole about 4 foot long.

Very similar to the one I have in storage.

Or just enough to get the radials above the chimney pot. But this is where length matters ;-)

It won't upset the aerial at VHF and above, but it won't do anything to prevent lightening striking either. You will only need an earth for HF. and that is only for ballancing the antenna system.

A good choice and make sure you un-plug when there is static (warm dry weather and high winds.) or thunder in the area. I once lost the front end of a UHF rig through that.

Dave g6khp

[dave]

You didn't declare what the aerial style or size was. Are you saying that you are an expert in this field as well?

Dave

[dennis]

No one has said how big the aerial is, yet! Lots have advised how to fix said unknown aerial. Are you psychic now? PS I do know a bit about aerials but I wouldn't dream of advising anyone on how to fix an unknown aerial in an unknown location on an unknown chimney, which as you may note I didn't.

[fred]

In article , the_constructor writes

Compared with a moderate TV aerial, that is really quite a light load as far as windage is concerned. I would be happy to use a single lashing kit but would use a 9" bracket instead as that will spread the load over

3 bricks. The style of bracket you chose is fine, I have use the same to good effect. 9" bracket: I assume it's galvanised, it looks it, find another if it isn't.

[<me9]

I'n not far south of you, about 400 metres out of Co. Durham, G3V..

That's a handy site, I've been looking for 2.5 inch V brackets at a price without exhorbitant postage. I put up a TV aerial on a 10ft pole on T&Ks on my side wall recently. I've been since inundated with marauding crows, whose early morning antics managed to loosen the brackets (mounted with 8mm expanding bolts into bodger Ba**et's finest bricklaying) due to the whip in the (too thin wall) 10' ali pole. I've replaced the expanding bolts with 10mm resin fix ones (in different bricks) and the pole with a 2" dia ali 8' scaffold pole surmounted with a cranked pole for the aerials, to get them away from over the path so they can use the gutter for what birds do over cars.

So far this had done the trick, but I had to bodge the u bolts to fit the larger pole. I now have the correct size on order.

[dave]

The OP did.

It isn't an unknown aerial to anyone who is competent, or familiar with the frequency and specifications.

No, but...

I know the exact aerial he is talking about, having had them for quite a number of years.

I have over 30 years experience of erecting amateur antennas and never once has one been blown down.

Dave

[dave]

For the obvious reasons that a pole would be subject to much more wind loading, that could result in it coming down in a storm and putting next doors windows through.

Dave

[dennis]

After I replied!

Well lucky you. How many have you done? Do you want me to send you the addresses of some I have seen blown down so you can go and tell them what they did wrong?

[dave]

I have totally lost count of the numbers, but as a radio amateur, you experiment with antennas very regularly. In the past, I have built as many as 4 in as many days.

I don't like to communicate with stupid people.

Dave

[Mark]

He did

Length 1.7m Radials 3 Weight 0.9kg Type (2m) 3 x 1/4 wave Type (70cm) 3 x 5/8 wave

LOL