High Power AM Broadcast Antenna Mast Feed-Point.
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- Опубликовано: 1 июл 2016
- A close-up look at how an AM broadcast mast is fed and insulated from the ground.
You can't see it in the video but at the top of the base insulator there's a ball that allows the mast to move around and not crack the insulator as it sways a little in the wind.
I suspect the plates at the bottom of each mast leg (the ones I said look like they should have bricks under them) are there to short the mast to ground and trip the transmitters off if the mast fell over. It looks like they would touch the ground if the mast got to 15 degrees or so, so there would be no energy present when it hit the ground. 
Хобби
Nice video. The legs that you talked about putting bricks under. They are for jacking the tower up. Most insulated guyed towers between 280 and 1350 feet in height have been designed with jacking plates under the tower legs for the purpose of base insulator replacement.
Pretty good rundown, Steve, ignore the silly comments.
If it's the one I used to know, all your comments are spot on.
Did you notice that the big porcelain insulator is slightly deformed by the weight of the mast, compared to the unused one?
The downpipe on our mast hut was burnt by people creating an arc between it & the fence .(both ostensibly at earth potential).
Bit safer than the Russkis----- we had a large insulator with some heavy steel wire attached to the end.
You could hear the programme from the "singing arc".(back in the days before everybody became paranoid about RF)
I also remember lying on my back at 2am in the freezing cold cleaning "gunge" off just such an insulator
with "Bon Ami" & distilled water .
Don't know if it did much good, but I remember being very aware of so many tonnes of steel above me, perched on that insulator
all hail the naughty Russians with plants
W2NAP-TV he said 'numpty'
Thank you for posting, very interesting!
Thanks for the feedback. Glad you enjoyed it.
Those pads are indeed jack points so that the tower may be lifted several inches to replace the base insulator.
How come it doesn't have one of those transformers with two interlocking rings to run the tower lights without sending RF back down the power line?
They are called Austin transformers. They can be located within the ATH and the cable is then fed inside the main feeder out to the mast. Better protects it from the elements
Am I the only one that notice that base insulator is cracked in half? It;s a good think the tower has 3 legs close to the ground in case it goes.
I just found out today that these towers have current running through the whole thing. I love to climb but good thing I respect fences and warning signs!
Yeah, if a tower light needed changing, you turn the power waaaaaay down. Our engineer would turn our 25kW transmitter down to, I think, a thousand watts omnidirectional while the light guy was up there anywhere on the tower.
Medium wave AM transmitters are almost always of this design. Known as mast radiators because the entire mast is the antenna.
@@ApartmentKing66
Υοu mean he was up there with RF power on the mast??!
One 1 kw is not a negligible amount of power by any means. I am really surprised he was allowed to work on it while 'hot'.
Work cover wouldn't be impressed with such action..
That's why I'm here because if I had lived close to one I'd be dead
well algartum sent me here
Steady on with the camera VK6CS..
Interesting video of course but a bit dazzling trying to see what's what.
How do they 'load' this structure? Is there some kind of tuning circuit between the output of the TX and the tower?
..and, why do they need to "broaden the band" (with these cables) when, this AM tower would be of a fixed frequency?
73's from a VK2 _ _ _
Because if the antenna's bandwidth is too narrow (which happens when an antenna's Q is particularly high, e.g. due to low resistance encountered at lower AM frequencies due to reduced "skin effect") then the transmitted audio will suffer from reduced treble. Treble gets reduced because that audio is carried by the AM signal's sidebands, slightly above and below the carrier frequency, and these will be attenuated to progressively greater degrees with their "distance" away from (either side of) the carrier frequency. The treble's sidebands being particularly far out (in frequency) from the carrier.
@@DavidEsp1
Good heavens!
It's more than what meets the eye..
I never thought of that but it all makes sense.
Tnx for clarifying it David.
At 02:20 what's the function of the "wire cage" transmission line inside the metal structure? Briefly wondered if it was a shunt/gamma feed but then I remembered the base was insulated - and you explained the feed going in (as expected) at the base level. So what's the cage-feed for?
Numpty russian with plants? I know exactly which video you're talking about, lol
So Glad I do not have to do Bond Wire on my Towers
KNX attempted to employ a directional antenna ... DAYS ONLY ... in order to better serve the Inland Empire, but that was way, way back when the shorter tower was southward of the main tower. However, that configuration was far from effective and was later abandoned. That would have made KNX 50 kW ND-N, DA-D.
After the site was donated as a park, the shorter tower was moved northward of the main tower.
As a Class A station, KNX protects NO OTHER stations. After the co-channel Class A station in Canada was taken dark (moved to FM), KNX became the only Class A station on 1070. That means, of course, that every 1070 station anywhere in North America protects KNX during critical hours (if necessary) and always at night.
The taller, main tower is the ideal height at 195 degrees. The shorter, auxiliary tower (used only when the main tower is otherwise out of service), is about 135 degrees tall, and was purchased and installed when the main tower was destroyed by vandalism in the 1960s, and it served in a temporary capacity until the new tall tower could be constructed.
Now, all ND-U Class As are expected to have auxiliary antennas. Class As which operate DA-N are not necessarily so required, but they are encouraged to do so, where practical.
WWL, for instance, is 50 kW DA-1, but it has an auxiliary at a co-owned station, and that auxiliary is licensed for 5 kW DA-1, but only when WWL's main site is down.
Sounds like fun. I thought you guys liked folded unipoles between 105 and 115 degrees?
The Queen will take it over.
I think the protection radius was 750 miles in every direction. There's a station in Houston on 1070 (DA-N, I'm sure). Maybe it varies for different license classes, I don't know. When I was at KNBA in Vallejo, CA (1190 kHz), our engineer told me that because we were within a 750-mile radius of Portland, we had to shut down at sunset to protect KEX. We wouldn't have had to do that if we were south of Monterey Bay. KEZY in Anaheim broadcast at night.
There seems to be a lot more going on here. what about those series of wires inside the mast area? So, you're saying the tower itself is the antenna? ...and what about the circle of wire at the top of the tower? You say the tower is 600ft. or ~750khz? the rest of the area looks pretty dilapidated and is in need of attention for more efficiency. What do you think?
How much pressure can a bace insulator take?
Hi, how much KV is the power supply on this transmitter feeding into it? Just curious. Any concerns of arcing at the base of the mast where that insulator is, especially when raining or flooding? Are there any safety hazards for unauthorized personnel loitering about the vicinity of the antenna? Thank you.
Very interesting, but where are these masts
Thanks. Western Australia.
We have a similar mast on the north side of Brisbane called the bald hills radiator.
I assume if you touched it, you'd glow like a neon bulb ?
Yeah, from the inside. Your insides would start to cook first, then the RF radiation would work its way out...if you were able to hold on long enough before dropping dead.
@@vk6cs456 What's the purpose of the unmodulated 20kW carrier?
Towers usually have legs fixed to the ground, and no guy wires, ie self supporting, Masts on the other hand have guy wires to keep them upright. Just thought I would clarify this for those of you who may be wondering what the difference is.
You have no clue what in the hell you are on about. Search "guyed tower." Nobody calls them "masts" certainly not the people who manufacture them.
I guess they don't call 'em "towers?"
Nope, maahhsst
would it be possabelto move the camera NON STOP ??
Dear Sir,
May I suggest another reason for the legs and feet ?
What is more likely is that the feet are used when they replace the insulator and they need a way to jack it up.
Any other bright ideas ? I'm not a broadcast guy although I have a secret plan to one day have my own AM broadcast station with giant diesel generator, just so I can see and smell the black smoke when I do full carrier double side band......
As Jeremy Clarkson says "POWER"
I must ask the ACMA the cost for a single frequency AM license, say upto 5000 watts.
You may suggest anything you like Sir. They wouldn't be able to get jacks under those plates as they're too low to the ground/copper sheeting. You're probably right though, that's what they're on the ends of the mast legs for, they probably expect there to be more to the mast structure at the bottom, like the four corners going to a point, then sitting on the insulator. That would put the plates about 2m above the ground. it was probably modified, it is quite old. The mast with the capacity hat weighs around 58 tons so it would need some significant jacks to lift it.
As for your AM station, why not do a Wolfman Jack and go for 250KW.
VK6CS I want to talk over radio china.
Why should they have a monopoly on pollution and RF radiation spurious emissions ?
As for the tower : I tell you what, Why not ask the guy and find out ? It's one of those things that I have to know but I really don't need to know.
I am fascinated by engineering.
So, Question : What are the leg ends for ?
NB : Hydraulic plate jacks are flat and can easily lift 100's of metric tonnes. If the whole things weighed 1000 tonnes then flat faced lifting jacks could easily fit between the leg ends and the ground.
Or could it all be to do with electrical length, capacitance and ground-effect or whatever ??
But thanks anyway for the video. I have only been in NTA re-broadcast sites and never into a main transmitter. I bet when they switch her on that she'd be humming.....
Q : What is the safe distance when she's running full power ?
I'll ask the questions when I see him.
Steve,
The 3 "feet" are the jacking points to change the insulator. We used to use 3 Enerpac hydraulic jacks piped to a single pump so all the jacks took the same weight. The jacks were only 3-4 inches high when collapsed. They only had to lift about 2 inches to get the main insulator out. I remember doing one of them in WA but cant remember if it was Dalwalinu, Wubin or Hamersley. They were all the same type of mast.
Arrr, That should read Wagin not Wubin.
Tried climbing up an AM tower once... but hey, I'm still here so there's that 😅
One of my hobbies used to be climbing tall structures like smokestacks and lattice towers. I had no idea this particular tower was actually a mast radiator and that it was electrically charged like that. When I reached up and grabbed the bottom rung I got an instant shock. Needless to say it was quite unpleasant however I've been shocked once before installing a light blub and that was actually worse. The AM tower was more superficial and I got a bit of a burn on my finger tips while the light blub shock I felt across my entire body.
Anyone know why that is?
Rf skin effect. High frequencies don't travel as far into the body
@@phillipsfilms8023 That effect only applies to good conductors (such as copper), which your body certainly is not (skin depth in tissue is something around 20 cm). The reason you don't feel 'electrocution' by RF is because your nerves can't react fast enough to the high frequency electricity.
Do you remember that characteristic smell of burning flesh ??
@@maverick5117 I don't remember the exact smell anymore, but yeah I do recall that it smelt pretty bad.
Jittery filming
That doesn't look like cornila
??
He has to learn how to use zoom on the Camera:)
Oh, c'mon. It's only You Tube.
Certainly did not sound as if you knew a thing about which you were speaking.
Thanks for the feedback.
Russians with their plants 😂
Brush up on 'Antenna Theory 101' before attempting another video....
Why, where do you think I went wrong? Let's see which one of us needs 'antenna theory 101'.
"Nice video?" No it's NOT. This is a TERRIBLY done video. Please learn to SLOWLY move and pan the camera.