Bloody trampoline

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NightProwler
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Bloody trampoline

Post by NightProwler »

I got my Sirio GM on the line post at the end of my garden as a temp instalation. We got a 12 foot trampoline in the garden which was about 10 foot away from the GM. The SWR was never the best but useable. I had to move the trampoline the other day so it is now closer to the GM and the SWR has shot up. I presume the trampoline is messing wirh the GM as the base of the GM is on the same level as the top of the trampoline with is all metal. Could it affect it that bad?
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ch25
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Re: Bloody trampoline

Post by ch25 »

Any metallic object in close proximity (2 wavelength) affect antenna.
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Buick Mackane
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Re: Bloody trampoline

Post by Buick Mackane »

It'll work fine richie, The signal will bounce off it :) Joking aside as lemmy above says
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InTheClouds
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Re: Bloody trampoline

Post by InTheClouds »

Even worse than SWR having risen is the pattern of the antenna will highly likely be negatively effected in a rather unpredictable but surely negative way. The GM is a dipole of sorts and as such is a balanced antenna.. so any parasitic capacitance near by... i.e. metal will make the pattern worse than it is meant to be. This is why software models are just a best case scenario and never realized in 99pct of set ups unless you have a metal pole in the middle of a field. They are a computers best case guess, that is not 90pct of people's QTH.

Models are about as much use as a chocolate teapot, motor bike ashtrays, farts in space suits, t*ts on a bull etc. for most people. They do not denote a great antenna in very average setups.

It sounds like the right time to make the GM work like it is meant to. Get it up properly 20 feet or more and you will experience vastly superior
DX and local performance.
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Re: Bloody trampoline

Post by The Collector »

Reading the title, thought you badly cut yourself whilst doing a triple somersault :)

As above, it's obviously messing with the field. Can you not move it back to its originally space? Or, if it met with an "accident", you could get shot of it altogether ;)
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Re: Bloody trampoline

Post by InTheClouds »

The GM is in the top 3 11m band vertical DX antennas that exist. It all comes down to installation quality and height. When you have GM at 8m high
and ideally in the clear it is a DX force to be reckoned with. In my personal opinion it will give a poorly installed and operated beam a run for its money.

If you get it high enough it will have a lower angle of its main beam width, some gain and is faster to TX/RX than a beam as you TX/RX all round instantly. Spurting all your juice in one direction is not the be all and end all.

One of the best 11m DX verticals ever made. If it is not working out in your install/QTH try the Vector or an 827.
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Re: Bloody trampoline

Post by NightProwler »

I wish something would happen to it so I can have my garden back but the kids and the dog love it. The GM is going to be replaced soon with a Sirio 2016 and mounted away from the trampoline but it will only be about 8 feet off the ground until I can get my hands on another scaffolding pole.
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InTheClouds
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Re: Bloody trampoline

Post by InTheClouds »

Get an ATU and load the trampolene 2 birds one stone
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NightProwler
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Re: Bloody trampoline

Post by NightProwler »

Yeah and chuck a few KW into it when the kids and dog are bouncing on it.
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InTheClouds
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Re: Bloody trampoline

Post by InTheClouds »

It will probably work better for DX than some of the stuff hams use, some put up with some real shonky sub par antennas. I am sure trampolenes model well for "a low angle radiation which is great for DX" :lol:

It is no wonder some CB'ers blow hams out of the water with their DX. Really good dx antennas are just that, really good operators are just that, ham or cb whatever.

Is it a bit of metal ? Is it non horizontal and non diagonal ?.. Then it absolute without doubt is great for low angle radiation and dx'ing !

Just having a laff really. Just imagine what a Gain Master designed for ham bands on 20m/40m would do for DX. Totally impractical of course, too long and too high a mounting necessary but if you could make and support such and antenna for ham bands - now that is a good antenna with low angle for DX :o

2016 will do a good job for you but not likely better than a GM. It might work better than a GM if you cannot get it as high up and in the clear... low vertical dipoles don't work very well for long distance DX in my own experiences (actually not much does, although there are a few exceptions). The pattern goes bad, proximity to ground for the lower element unbalances it somewhat. Where as a 5/8 wave is a form of ground plane so metal directly under it won't do as much harm and might do it good... metal to the sides though is not good... that just become a weird parasitic element with unpredictable effects.

There are always exceptions to the rule but they are few and far between.

We all have to make the best of our situation.
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Re: Bloody trampoline

Post by InTheClouds »

The crux of the issue is CBers are on one band, you don't have the fannying (MUFfying? :lol: ) around hams do wondering about what band to be on just to get the oft underwhelming 5/9 stamp collecting thing done. So if you have a well designed, well made, well installed antenna for that sole band you would have to be doing something seriously wrong to not DX when 11m is open. 11m is very efficient prop when the F1/2 layer is ionized sufficiently well enough to create a path somewhere....It does not suffer as much absorption through the D layer (below the F layers) compared to lower hams bands 15-20m etc. Hams often use a wire or 2 of some sorts that is jack of all trades master of none. They often don't even work very well for the main band they are cut for.

11m prop can seem miraculous at times for the above reasons.

There is a lot to know and none of us know it all. And you cannot know about how the sun, atmosphere and magnetosphere are interacting at any given second in time so a lot of prediction is a waste of time. Some right ham jokers about mind you giving it large online.

Anyway veered off a bit there sorry good luck with your antenna, either way I am sure you will make some DX.
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Re: Bloody trampoline

Post by 26mb04 »

Have you tried tuning up the trampoline and seeing where it works? It should tune somewhere, alternatively it'd make a pretty decent groundplane.
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