oh dear,,,,

Discuss UK-based Radio outside the South East of England
e.g. Birmingham, Bristol, Leeds & Manchester
'Legal' radio topics often go here too.
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mixfm
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oh dear,,,,

Post by mixfm » Mon Jun 26, 2017 12:01 pm

seen this in the press last week... zoom in & tell me wht you can see,
.jpg
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pirateaddict
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Re: oh dear,,,,

Post by pirateaddict » Mon Jun 26, 2017 12:33 pm

Nowt... The size of the pics that you're allowed on this site is wank...Just tell what we can't see mate..

mixfm
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Re: oh dear,,,,

Post by mixfm » Mon Jun 26, 2017 1:54 pm

dipole on middle block...

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thewisepranker
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Re: oh dear,,,,

Post by thewisepranker » Mon Jun 26, 2017 1:57 pm

Image

wazza
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Re: oh dear,,,,

Post by wazza » Mon Jun 26, 2017 6:20 pm

Which station(s) used d**** h****? Can't recall anything from over that way.

SOTS 87 7
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Re: oh dear,,,,

Post by SOTS 87 7 » Tue Jun 27, 2017 11:55 pm

My other half recognised that location straight away from the picture. :D

Giggles

Re: oh dear,,,,

Post by Giggles » Tue Jun 27, 2017 11:57 pm

I was also getting distinct 99.7 as well actually all strong in birmingham

SOTS 87 7
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Re: oh dear,,,,

Post by SOTS 87 7 » Tue Jun 27, 2017 11:58 pm

Probably,
all I seem to get in the car when we are in the area is either Hot92 or Distinct 99.7.

mixfm
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Re: oh dear,,,,

Post by mixfm » Mon May 27, 2019 10:56 am

some pretty pics..... enjoy
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Albert H
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Re: oh dear,,,,

Post by Albert H » Mon May 27, 2019 11:38 am

I have never understood the average pirates' obsession with dipoles. They have no gain, are not truly omnidirectional (the mast has a nulling effect) and they require unbalanced to balanced conversion to get them to work properly. Most pirates throwing up their silly dipoles are wasting as much as half their (expensively generated) power!

Even a basic ¼-wave vertical with four ¼-wave grounded radials will work better, not require match conversion, and actually radiate the signal outwards in all directions rather than downwards into the block! Your average pirate couldn't believe that a cheap aerial made from still wire soldered to an SO239 socket would work so well.

Just for amusement, I demonstrated the difference between a quickly thrown-together ¼-wave groundplane and a dipole a few years ago. We put a little 40 Watt rig on a well-known block near Shepherds Bush and two aerials - a dipole and a wire ¼-wave groundplane, both at the same height. We fired up the dipole and drove around the area checking the field strength on a calibrated receiver. We swapped aerials and did the same test, following the same route. The ¼-wave was much weaker near the block, leading to the station operator sneering "I told you it wouldn't work"..... A mile away, the field strength from the groundplane aerial was 8dB better than the dipole!

The chaps trying to find your transmitters and take them off the air - whether from OFCOM or just bastards trying to steal your gear - are generally pretty stupid. They'll get close to your site using field strength readings from their receiver in the car, possibly attenuating the input as they get closer. Then they go dipole-spotting! If you use an aerial that gives weak signal near the block, and looks like a CB aerial or PMR installation, they're lost. We used to have the RIS guys going up every block in East London because they couldn't understand the field strength readings and couldn't see an obvious aerial..... They'd waste days trying to find a site. At one time, one station I engineered had three sites set up - two south of the river, and one north side - and when the DTI RIS guys were spotted near to one of the blocks, they'd switch to another site. They stayed on for months before they finally lost some gear!

A little bit of creative thinking, and some basic constructional skills can give you a cheap aerial that will better than double your radiated output power. Stacked dipoles work - I've used them myself on occasion - but they still require matching conversion and a phasing harness if they're going to be useful. My favourites are the ⅝ and ⅞-wave with groundplane for simple verticals (I always found Stephen's ½-wave to be a PITA to match), and I really liked the slim vertical colinears, like the Bandtex and J-Beam ones that were in fibreglass tubes. They were quite expensive to get hold of, but they paid for themselves in the reduction in power of the rig needed to get good coverage.

The simple J-pole is a good place to start for a beginner - easy to build and to match, and it's effectively a ½-wave vertical with a ¼-wave matching transformer at the bottom. Set up properly, it'll always out-perform a dipole with the same power put into it. We used to make them out of plumbing pipe, and paint them pale grey with acrylic paint or car spray paint so that they weren't too obvious from the ground.
"Why is my rig humming?"
"Because it doesn't know the words!"
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mixfm
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Re: oh dear,,,,

Post by mixfm » Mon May 27, 2019 11:51 am

weve had few end feeds in our time our tech guy used to build us. also j folded pole. u got any photos of the aerials your mentioned....

Albert H
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Re: oh dear,,,,

Post by Albert H » Mon May 27, 2019 3:43 pm

Here's a few to look at:

http://sm0vpo.altervista.org/antennas/6dbvhf0.htm from Harry's Homebrew Homepage. It's easy to calculate the dimensions for other frequencies.

http://users.marktwain.net/aschmitz/ant ... tenna.html shows a number of antenna designs. The "copper cactus" is especially good.

http://www.hamuniverse.com/vertbazooka.html - a quick and easy stealth antenna that'll get you on the air in a hurry. It's made from bits of coax and parts from your local hardware store.
J_Antenna_Variations.png
Some variations on the basic "J" - some of these get really big at Band II, but their gain is amazing.

https://m0ukd.com/calculators/slim-jim- ... alculator/ - enter your frequency and the Velocity factor of the materials that you're using, and it will give you all the dimensions!

https://m0ukd.com/calculators/quarter-w ... alculator/ - another calculator, but for groundplane aerials.

https://www.qsl.net/w4sat/five8th.htm - a basic calculator (and a bit of a write-up) on the ⅝-wave groundplane aerial - one of my favourites.

These should give you a few good ideas!
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thewisepranker
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Re: oh dear,,,,

Post by thewisepranker » Mon May 27, 2019 9:21 pm

You can't always transmit from the middle of where you want to cover. You can exploit the vertical mounting pole to shape your radiation pattern. When you take the time to tune them with some nice gear, they work really well.
dbl1.png
That's a double-stacked Gamma, using the mounting pole as a reflector, arbitrary lengths of 50 Ohm coax (no 75 Ohm coax used) and a 1/4 wave splitter. All connectors are N type. :tup

I quite like how you've included the correct J pole diagrams, Albert. I have built them before with mast decoupling stubs and well to be honest I've never found out whether they really did any good or not because I don't live in any of the blocks we used! I've also used a stack of clip-on ferrites before, again, no idea.
With anything bigger than a Super-J, it's going to be hard to get the thing strong enough to not fail in high wind. The J's wobble around enough as it is. To be honest, I think it's beyond most people to build a Super-J strong enough to withstand winds of a few MPH.
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Albert H
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Re: oh dear,,,,

Post by Albert H » Tue May 28, 2019 3:57 am

I built Super-Js using fibreglass rods and wire for the elements. Those things withstood anything that the weather could throw at them - short of a lightning strike!

You're right about shaped coverage - I used to use a pair of stacked vertical "H"s at Addington to get the signal northward into London, not southward to a load of sheep and farmers, for example.
"Why is my rig humming?"
"Because it doesn't know the words!"
;)

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