Bendable conduit/gooseneck

**Variable** · 13-02-10, 08:40 AM

Gday I need a strong bendable conduit/gooseneck to get a whip antenna out from under a tin roof from the inside.

The tin extends down into a very wide rain gutter, so I need to 'thread' the whip and some sort of support to hold it there out from under the roof and into a vertical position.

I know of corrugated electrical conduit but don't think it stays in position under any load.

Gooseneck may not be good in rain due to rust.

Basically need something that can be shaped by hand but will stay in place good and proper

Any ideas what I could use please?

**mtv** · 13-02-10, 11:18 AM

I'm not following what you have and what you are trying to do with it.

Are you saying the 'whip' antenna is currently in a ceiling.. eg: under a tin roof?

Why does the antenna need to be in a conduit?

Why does a whip antenna need a bend it it...eg: gooseneck?

**Chimp** · 13-02-10, 11:41 AM

rigid electrical conduit and a conduit spring will do the job quite easily.

there is a more rigid version of flexi conduit as well, i think its called anaconda, its lined with thin metal on the inside and rubber on teh outside. may do what you want.

**watchdog** · 13-02-10, 12:46 PM

anaconda won't bend in less than about a 4" radius. You might try an automotive performance parts shop. The stainless braided hoses could do the job.

**mtv** · 13-02-10, 01:00 PM

An antenna will not work if it's enclosed in metal conduit.

This is why I'm not following what the OP is trying to achieve..... unless someone else has figured it out.

**beer4life** · 13-02-10, 02:10 PM

Originally Posted by Variable

Gday I need a strong bendable conduit/gooseneck to get a whip antenna out from under a tin roof from the inside.
The tin extends down into a very wide rain gutter, so I need to 'thread' the whip and some sort of support to hold it there out from under the roof and into a vertical position.
I know of corrugated electrical conduit but don't think it stays in position under any load.
Gooseneck may not be good in rain due to rust.
Basically need something that can be shaped by hand but will stay in place good and proper

Any ideas what I could use please?

G'Day Cobber,
I also find it difficult to understand what and why you are trying to achieve.
Let's assume it is merely to connect to a vertical antenna in the clear with your cable access inside under the tin roof.
Nothing could be simpler with one of these for a flat roof or similar for a corrugated roof.
A mounting/feed through hole with the the whip on the outside and co-ax connected on the inside.
Available from DS (DS4056) and many other retailers.
Kindest Regards, " The Druid ".

**fandtm666** · 13-02-10, 02:26 PM

run it through the corrugated plastic then make attatch a few stays ( wire ones would do like the ones to keep antenna mast upright) connected to it and then to the roof using the screws along the gutter line then just fill the top with silicon to stop the water entering

**Variable** · 13-02-10, 03:37 PM

Sorry for not providing more info.

The site is a roof 300' AGL with no outside access. I can get a rod bent correctly under the edge of the gal roof and into a rain gutter from inside, and then turn it 90 degrees to make it vertical outside.

What I would like to do is mount a VHF RX whip outside the roof, with the element starting just above the gutter.

So what I think I need is conduit or similar stiff but hand bendable material that will stay in place after I get it outside. The whip will sit in/on the conduit. Drilling holes is verboten.

Thanks.

**mtv** · 13-02-10, 04:20 PM

Getting closer, but still not enough info.

The roof is 300 feet AGL?.... so it's a high-rise building with no roof access?

Apart from the whip antenna, you still need a base for the whip to attach to, which would be impossible to poke through a gap in the iron.

You mention VHF, but not the length of the whip, which can vary considerably with frequency and gain, etc.

What profile is the roof.... pitched, flat, corrugated iron, flat cliplock, or other?

What are the dimensions of the 'gap' you have available to push the antenna through?

It sounds like the only way you could get something out from under the roofing material is to lift a section of roofing material, which you say is not possible.

**pieces** · 13-02-10, 04:29 PM

You can wonders with PVC pipe a heat gun and sand .

**tagg** · 13-02-10, 04:41 PM

Post a pic or diagram of your intention as i am lost as well as to what you are trying to do ???

Tagg

**trash** · 13-02-10, 08:20 PM

It sounds like white cocky problems. I'd take a guess at something like a fire tower.
You may find that the white antenna chewers are just as easily dissuaded by a soft conduit. Though you can get armoured conduit that is soft enough to bend.

I would suggest have a chat to some Telstra riggers if you can or at least try and have a look at a mobile phone tower through some binoculars and have a look at how their tails are protected. The conduit they use is available, but I'm not sure who the source is. It would be very easy to ask for some recovered pieces when they replace them during regular maintenance. The hard part is finding a crew

I do know that if you have particularly bored antenna chewers, nothing will stop them.
I've seen them work away armoured cable and destroy it and the cables over a period of time.

**mate** · 13-02-10, 10:58 PM

drill a hole and poke the cable through, seal the hole with silastic. Tape the cable to the mast fro protection from the elements.

**Variable** · 14-02-10, 07:42 PM

Thanks everyone, will go with conduit and spring bender

**mtv** · 14-02-10, 07:56 PM

Originally Posted by Variable

Thanks everyone, will go with conduit and spring bender

It would be nice if you could resond to my questions though, so I and others can fully understand more about the structure and how you hope to mount the antenna and in particular, how you get the mounting base for the whip ouside the roof.

**Variable** · 15-02-10, 09:50 PM

Originally Posted by mtv

I'm not following what you have and what you are trying to do with it.

Are you saying the 'whip' antenna is currently in a ceiling.. eg: under a tin roof?

Why does the antenna need to be in a conduit?

Why does a whip antenna need a bend it it...eg: gooseneck?

Ok M here goes.

There is no antenna there yet.

Conduit only mentioned as its cheap, strong, easy to bend and won't rust.

The whip will be vertical, just need a mounting bent the correct way to thread out from under the tin roof. The site is on top of a highrise...

**Variable** · 15-02-10, 09:55 PM

Originally Posted by mtv

Getting closer, but still not enough info.

The roof is 300 feet AGL?.... so it's a high-rise building with no roof access?

Apart from the whip antenna, you still need a base for the whip to attach to, which would be impossible to poke through a gap in the iron.

You mention VHF, but not the length of the whip, which can vary considerably with frequency and gain, etc.

What profile is the roof.... pitched, flat, corrugated iron, flat cliplock, or other?

What are the dimensions of the 'gap' you have available to push the antenna through?

It sounds like the only way you could get something out from under the roofing material is to lift a section of roofing material, which you say is not possible.

Yes no outside access.

There is a gap under the tin roof, in a big rain gutter. I can get a coat hanger bent correctly up through that gap.

The quarter wave length of the whip is 22"

The roof is pitched and inter locked, no holes allowed.

There are only an inch or two gap between the edge of the roof and the rain gutter, like working blind on the other side outside.

**Variable** · 15-02-10, 10:01 PM

Originally Posted by mtv

It would be nice if you could resond to my questions though, so I and others can fully understand more about the structure and how you hope to mount the antenna and in particular, how you get the mounting base for the whip ouside the roof.

Hope to solder a piece of 3mm soft iron rod, that muffler shops use to trace a template for bending exhaust pipes, as the whip in to a PL259.

Then screw that on to a female to female SO238/9 adaptor and screw PL259 terminated coax on to that.

I was hoping to mount the the plugs/adaptor inside and at the top end of a suitable diameter electrical conduit, sealed with silicone. But the plugs/adaptor could easily be cable tied to the side of the mount.

Thanks for all your help.

**tristen** · 16-02-10, 12:13 AM

Originally Posted by Variable

Hope to solder a piece of 3mm soft iron rod, that muffler shops use to trace a template for bending exhaust pipes, as the whip in to a PL259.

Then screw that on to a female to female SO238/9 adaptor and screw PL259 terminated coax on to that.

I was hoping to mount the the plugs/adaptor inside and at the top end of a suitable diameter electrical conduit, sealed with silicone. But the plugs/adaptor could easily be cable tied to the side of the mount.

Thanks for all your help.

I can see a problem with the method you propose.

An antenna comprises the actual radiating element(s) and a ground-plane.

The inner conductor of the co-axial cable must be connected to the driven element of the antenna, while the shield of the co-axial cable must be connected to the antenna ground-plane. The latter is an essential part of any antenna system.
MTV alludes to this in post #9, where he says, "Apart from the whip antenna, you still need a base for the whip to attach to".

If I understand you correctly, the method you describe makes no allowance for a ground-plane, so presumably your intention is that the metal roof will form the antenna ground-plane. This procedure is perfectly acceptable as is demonstrated in antennae installed on the roof or body of a vehicle.

My question is, how do you intend to connect the coaxial-cable shield (ground) to the roof at the base of the driven element?
Whatever the method used, it will affect the resonant frequency of the antenna system and hence its efficiency.

It will also affect the antenna impedance and while this might not be a great problem if the antenna is to be used solely for reception, it will be a serious problem if the antenna is to be connected to a transmitter.
If the antenna is to be used for transmission, the resulting high VSWR due to mismatch will not only cause spurious emissions resulting in interference to nearby services, but can also be disastrous for the output stage of the transmitter in use.

**mtv** · 16-02-10, 12:34 AM

tristen,

In post#8 variable said "What I would like to do is mount a VHF RX whip outside the roof" so it's receive only, but it will still have limitations in regard to the ground plane, or lack of it.

There are still several questions I asked that Variable has not answered in relation to the structure, the pitch of the roof and the construction of the roof, all which are relevant to antenna performance.

eg: if it's a pitched metal roof and the antenna is intended to be mounted just above the gutter, then the roof itself will act as a shield, blocking signal from the direction of the pitched roof.

Variable still hasn't said what length the antenna is required to be. Just saying VHF doesn't mean much as antenna length for VHF can vary considerably, depending on frequency and gain.

If he can manage to push a curved conduit through an opening of unknown dimensions, then rotate it, then my suggestion would be to use a ground-independent VHF whip. eg: