Antenna mounting question(s)

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Captain Fantastic
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Antenna mounting question(s)

Post by Captain Fantastic »

I've been pleased with what my home made horizontal dipole achieved so far - 900km from Zurich to Exeter or to Swidon.
However, with local contacts it is hit and miss, and likely depends where they are in relation to the wire, or something technical like that!

So now it's time for me to think more seriously about a proper antenna. This is likely a 1/2 wave vertical at biggest. Also not another dipole, even a vertical one as I'd need a pole anyway. It could be one of these T2LT things, I could even make it, but again I need to put it up on a pole which might be an issue. Or a smaller mini-boomerang thing.

I really don't want to put anything on the side of the house sticking up 5m over the roof, as I'll be asking for trouble. I don't rent, and we do have a garden. We also live at 650m elevation facing SW on the side of a hill 300m above a lake. There is about another 150m of elevation (hill) behind us NE.

The current dipole is on an upper terrace, which is technically about 5 or 6m above ground. I don't know if that counts, or if the terrace itself counts as the ground? I could put a vertical up there, but that is going to stick out like a sore thumb as it faces the road.

Behind the house we have a trampoline. It's got a very heavy frame, pretty much scaffolding for the base and slightly slimmer for the verticals to hold the net. It is so heavy and also out of the wind that we never had any issues with it moving etc. The verticals are about 3m long. If I put a 5.5m vertical antenna it will be about as tall as the house + 0.5m

Questions:
1. I'm assuming that if I get a 1/2 wave vertical I can still manage 900km answering someone DX'ing - yes or no?
2. Could I mount a 5.5m vertical to the trampoline? Is this a really bad idea, and why? (Assume nobody is on the trampoline in wet or stormy weather!)
3. If 2 is 'no' go, then how might a mini-boomerang perform - locally and DX? (I could possibly put that on either the terrace or trampoline since it is smaller in height - about 1/2).

Thanks for any input!
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Alan Pilot
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Re: Antenna mounting question(s)

Post by Alan Pilot »

I would give it a go and dx can be a funny thing you might get even further away contacts.
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Re: Antenna mounting question(s)

Post by MrWeetabix »

Could you post a photo of your garden for us and we can maybe suggest some ideas for mounting an antenna :thumbup:
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InTheClouds
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Re: Antenna mounting question(s)

Post by InTheClouds »

If it is safe to do so I would try mounting a 1/2 wave Sirio GPS 27 to the trampolene. That might be tricky you will have to see how robust the trampolene is around the edges and how the Sirio mount with it's U bolts will attach in a strong way. It won't win an award for "lowest angle DX" antenna of the decade but it is likely to work strong Sporadic E DX and F2 layer DX. Just for the record when the conditions are very intense I have worked S. Africa with a 1/2 wave ground Silver rod (5 years ago) mounted 2ft off the ground on a concrete post upon first key up when demonstrating what DX is to someone. It was a great way to show them.

You have a great height ASL and this will definitely help you. However even on a mountain a 1/2 wave clearance above ground would be the ideal. It reduces ground losses and will allow a lower take off angle (and again your great height ASL will also assist that low angle take off). The rule is that below 1/2 wave from the earth below and your lowest angle of radiation will also be lower than typically optimal.

A 1/2 wave horizontal antenna actually has significantly more gain (albeit at a higher angle of radiation) than a vertical at exactly the height you have it.... i.e. 5.5m. (at least in 2 directions) How you have it mounted on a balcony is likely to be stopping the antenna from having its natural figure of 8 pattern. It will be distorted.

You may find greater noise levels with a vertical as much noise from electronic devices is vertically polarized. Something to listen and check for.

An alternative option and possibly your first and best.... is to purchase a 10 - 12m fibre glass fishing rod (€50 - €70) make sure 100pct it is fibre glass (and not carbon fibre which may cause SWR issues) and attach a T2LT either permanently or temporary when you want to DX. They are very quick and easy to slide out, lock and attach a T2LT to.. and you get your antenna 5m + up from earth. This will work fine for DX.. in my experience they are not the best antenna in the world but they work OK and on a mountain 650m ASL in the open in your garden it will probably work well to very well.

A T2LT will not work on the trampolene as it is a balanced antenna and the radiation pattern and likely the SWR won't be good. (i.e. the lower element , the negative element will be too close to metal)

Sporadic E is now dropping off for 11m, there will be more openings but the trend now will be less frequent and less strong openings as time goes on.

Good luck with it. For reference the longest contact I made this year on the Sporadic E (must have been double hop Sporadic E from the UK) was Cyprus and Greece on the same evening, using a vertical, circa 3,000 kms. Verticals are great for summer skip. (when optimally set up)
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The Collector
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Re: Antenna mounting question(s)

Post by The Collector »

My honest (and most likely useless) opinion ;) -

1: you could possibly get 900km on a wet piece of string... SSB can be a funny old thing, but it'd be crap for local "ground-wave" contacts. A half-wave, decent quality silver rod thingy without ground-planes may be ideal.

2: As mentioned, a silver rod - without ground-planes as it offers less wind resistance - hopefully means your trampoline stays put unless it's sucked up by an F3 tornado :)

3: Anything that says "Boomerang" on it is probably a bit pants, so stick with the silver rod type thing. I would however say mount it on a 3m aluminium pole that's in turn, attached to the trampoline. That way, the pole will flex slightly, taking some of the strain off the aerial in high winds and hopefully meaning it'll be less likely to snap.
Captain Fantastic
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Re: Antenna mounting question(s)

Post by Captain Fantastic »

Thanks for the excellent advice. On my list was the Albrecht GPS 27 1/2 - which I believe is the same as the Sirio - since it's readily available at a reasonable price.

Based on what you said, I think I'll order that with some new RG213 and throw it up on the trampoline. It'll probably take a few days to get here and then I need to faff around with it, but when done I'll let you know!

Worse case is that I end up using that for a static-mobile antenna :-)

Tonight it's the local CB round on SSB and I will go out mobile in the hope that I can get better contact from the top of a hill using my Wilson Little Wil and Jackson II.
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InTheClouds
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Re: Antenna mounting question(s)

Post by InTheClouds »

First re-think about how you you are going to "throw it up" on the trampoline.... you need to mount it solidly using the bracket and U bolts to something metal for it to have a ground plane/counterpoise, at the very least 1.5M of pole I would say. (i.e. complete the second part of the antenna) or you may find the SWR is higher than ideal.

Also the T2LT on a 10m-12m fibre glass rod is the ideal static mobile antenna. The 5m off the ground will likely also give it a performance edge over a Silver Rod 1/2 wave mounted down low. Lower angle of radiation and less ground losses (i.e. your RF energy will penetrate/be absorbed and reflect off the ground surrounding the antenna reducing your RF output and lowest angle of radiation)

None of this will break the bank though and experimenting can be fun so do what you feel suits you best and come back and let us know how you got on with photos if possible. :)

You may wish to think about this as well.. where you mount any 1/2 wave end fed vertical on the trampoline it may start to have a slight directionality.. so if you favour a specific direction for contacts then mount it in the opposite side of the direction you wish to radiate slightly more.. a little like the position of an antenna on a car. In my experience this effect is around 1-3dB, I have a noticeable directionality with my car tank whip.

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Captain Fantastic
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Re: Antenna mounting question(s)

Post by Captain Fantastic »

I have put some thought into mounting on the trampoline - it's 40mm galvanized steel and very robust, fortunately it is not a £50 Toys-R-Us job. Attached is a photo of the location. I drew a silver line to show approx where I may start with it. As was said, I can experiment, and even take it around onto the front terrace to see what difference that makes.
antenna location draft.jpg
I do like the idea of a T2TL as well, so mabye I make one out of the current RG58 I am using and see how that fairs after messing with the vertical. Then I would have 3 different options (vertical, dipole, T2TL) and can choose the one for the right moment.

Anyway, the order is placed, and I'll let you know how it goes!
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Re: Antenna mounting question(s)

Post by MrWeetabix »

If you get it fixed to the Trampolene, you could always buy some tent pegs or U-pegs to go over the legs and secure the trompolene to the ground more too. Also if you have a direction which the prevailing wind comes from, then make sure the antenna is facing towards the wind and the trampoline behind it to minimise the chances of it toppling.

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Captain Fantastic
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Re: Antenna mounting question(s)

Post by Captain Fantastic »

Fortunately the wind comes over that roof from the SW so my intended mount point would be pretty much as you suggest. The trampoline is well protected from the wind being on the NE side of the house there, probably why we never had an issue in 15 years. The antenna is going to protrude about 0.5m over the roof line so will get some direct wind and some spillover from the roof. I'm thinking the antenna base will be between 2.0 - 2.5 m above ground but will need to get it up to see exactly.
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Re: Antenna mounting question(s)

Post by The Collector »

Question time.

1- Are those trees yours?

2 - Are you any good at climbing?

3 - Can you buy more co-ax? ;)
Captain Fantastic
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Re: Antenna mounting question(s)

Post by Captain Fantastic »

LOL I see where those questions are leading...
1. no, the neighbour's
2. yes.
3. of course!

So the answer could be a stealth operation late at night?

I do have a couple of trees but not as tall as those. Actually another neighbour has his own flagpole (it is a 'thing' with the Swiss, trust me...) so maybe I need to get on best terms with him!
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Re: Antenna mounting question(s)

Post by The Collector »

Shame...although if yours are at least 20ft, there's nothing to stop you putting an aerial up inside it to hide it, especially if it happens to be a conifer :)

I've had 2 aerials up inside a 30ft Leylandii conifer for years now, a 17ft Antron and lately a 24ft Imax. The aerial didn't grow upwards as the actual conifer the aerial was bolted to was a dead one that was enveloped by its neighbouring ones. They were both sprayed green and brown to help hide them and even my wife had no idea I'd had an aerial up until she saw the Imax lying on the shed roof the other day after I'd araldited one of the joints together after it'd come loose. She saw it out of the bedroom window and said "What's that?" lol. The co-ax was run along a power cable from the house that feeds my wife's "gym" in a nearby shed, so she'd never seen that either ;)

I don't use CB's to talk on (although I have usually got one wired up), but I use an aerial for testing the distant receive on any radios I buy off ebay etc. I can usually test the transmit works by listening with my handheld.
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Re: Antenna mounting question(s)

Post by original45 »

Trampoline I have used too and they work very well. Our tramp poles are swaged so when extra height is needed I Rob couple others to raise height.
I tend to test and swr my base antennas on the tramp.

One consideration is when the kids get on jumping about it does cause the poles to bounce about shaking the antenna.for a silver rod type no problem I guess.A99 could be a problem .
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InTheClouds
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Re: Antenna mounting question(s)

Post by InTheClouds »

Looks like it will work out great. Although a silver rod on a pole wave will be rather larger than the line drawn. So don't be overly surprised when it is much larger in real life. Good luck with the installation, we shall speak soon, maybe next summer : )
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