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Antenna Advice
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717Racer

Aug 28, 2020, 8:16 AM
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Hey guys,

I'm looking for some advice for which antennas are safe to jump based on the radiation and radio waves. My understanding is cell towers and FM towers are OK but AM are dangerous. My buddy and I are considering buying an RF Monitor that tower workers use if that will help. What do you think? We just don't want to get nuked doing a jump.

Thanks!

Flydirty

Aug 28, 2020, 8:49 AM
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Re: [717Racer] Antenna Advice [In reply to] Can't Post

717Racer,

Start searching these forums a little deeper, there's a lot of good info and experience floating around here. Secondly, I would try to reach out to local jumpers in your area that probably have experience at the particular sights you're inquiring about. Lastly, updating your profile with a location and experience level will help others understand whom they are engaging with.


(This post was edited by Flydirty on Aug 28, 2020, 8:50 AM)

TomAiello

Aug 28, 2020, 8:58 AM
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Do you know how to tell the various kinds apart from each other? If not, I can give some details on that, but as to radiation;

On AM towers, the entire structure transmits, so you're basically climbing a giant live wire. You can also be electrocuted if you touch the tower and the ground simultaneously (because the whole thing grounds out through your body). Radiation levels vary by tower, but I quit jumping AM towers around 2002, when I had a terrible (nearly incapacitating nausea and vomiting before exit and after landing) experience on one. Rating: Zero stars, do not recommend.

FM towers are generally better than AM because the radiation is coming off the transmitters themselves (not the entire structure). I've always heard that the curley-cue looking transmitters are putting off a lot of radiation, so I try to sprint past those, but I've never actually used anything to check. Rating: Three stars, definitely jump them if you're comfortable with the guy wires.

Television (UHF, VHF) towers put off much safer levels of radiation, and only put the radiation off from the actual transmitters (which are basically clustered at the top). There are sometimes transmitters lower down doing other things, but in general the radiation comes from the other stuff hanging off the tower. If you feel like the radiation level is too high at the top, you can just exit lower. Another strategy is to gear up lower and then sprint to the top and exit quickly, but that adds some additional chance to make a mistake. In general, I try to sprint by any transmitters on the way up, gear up a couple hundred feet below the stingers at the top, and then climb the last bit at a normal pace and gear check at the top. Rating: Four stars, definitely jump them--the altitude should give you lots of time to create separation and minimize the danger of the wires.

Cell towers put off relatively low levels of radiation, and again, just from the transmitters (at the top). Many cell towers have dishes lower down, but the dishes are usually directional microwave relays, so as long as you're not in front of them (not sure why you'd be there) they're safe. Plus, they're generally low enough that you can make the whole jump (including access, gear up and gear checks) in well under an hour. As an added bonus, they are _everywhere_ (pretty much every ten or fifteen miles apart along every major freeway in the USA). Rating: Five stars, this is your go-to weekday object.

If you buy an RF monitor, you could do a lot of cool research (figuring out how much is coming off which types of transmitters) that would be pretty useful to a lot of people. If you do that, please get some numbers and post them back here for everyone else to learn from. Smile


(This post was edited by TomAiello on Aug 28, 2020, 9:30 AM)

717Racer

Aug 28, 2020, 9:04 AM
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Awesome! Thank you Tom!! This is what I was looking for. Some advice on how to tell the different kinds apart would also be appreciated.

TomAiello

Aug 28, 2020, 9:29 AM
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By law, every tower structure on the ASR must have an FCC identifier (a tower number) posted such that it is visible from a public area (usually the street). So if your tower has that (compliance varies, as with most laws), you can look up the tower directly on the FCC database. That can give you a lot of useful information.

https://wireless2.fcc.gov/...gistrationSearch.jsp


AM Antennas: Big insulators (mostly ceramic disks, but there are other types) separate the tower from the ground, and the guy wires (if there are any) from grounding out as well. You can often spot insulators in the middle of the wire from a distance. Usually they are just a metal structure with no other transmitters or equipment stuck to them. They are often built in arrays, so if you have three identical free standers right next to each other, they are an AM array most of the time. Sometimes you even see big metal nets strung between them to increase the transmission area.

FM Antennas: FM towers usually have guy wires, and often have other transmitters stuck to the side of them. They're usually higher than AM, but not always (there are some pretty tall AM towers out there too--they're just less common).

TV Antennas: These are the really big towers. Usually they are inside climbs, and sometimes they have elevators. If the tower is over 1000 feet it's almost always TV. They pretty much always have guy wires too, but they are high enough that you can get away from them. Some of them also have candelabra at the top, to support multiple transmitters, because they're expensive to build (several million dollars) so they are often split between multiple TV stations.

Cell Towers: Low-ish free standers. Usually they just have metal sheds for gear (no real buildings), and you can almost always identify the name of a cell phone company on one or more of the equipment boxes. They usually service more than one company, but if you spot a 250' free stander with metal boxes that say 'Verizon' inside the fence, that's a pretty good sign it's a cell phone tower. You can usually find them right alongside major roadways because their transmission range isn't huge (which means less radiation when climbing them) so they have been built all over to provide phone service for motorists.

TomAiello

Aug 28, 2020, 9:32 AM
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Another thought:

The country is littered with old AT&T longline towers, which used to carry the microwave relays for the nation's long distance telephone service. Since the system is retired, a lot of them (not all--some have been repurposed) are just sitting around with no power at all. Those are great to jump too, if you can find one that has enough altitude and a good landing area. They're mostly freestanders as well.

https://long-lines.net/places-routes/



As FlyDirty said, don't just go blazing all the towers in your area. There may be people who've been quietly jumping them for years, and have all kinds of useful information (and often keys, access codes, and contacts). You don't want to burn all their hard work, and making friends with them is going to be a lot easier than re-inventing the wheel, and a lot more fun than making enemies as you start jumping all the old antennas in your area.

If the 717 indicates your location, there are plenty of jumpers around there who can help you out.


(This post was edited by TomAiello on Aug 28, 2020, 4:23 PM)

717Racer

Aug 28, 2020, 10:54 AM
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Thank you again Tom. This is very helpful!

kleggo

Aug 31, 2020, 12:19 PM
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717Racer wrote:
Thank you again Tom. This is very helpful!

Here is a sample of what an AM antenna base looks like.
Note the insulators at the base.
The guy wires will also be insulated where they anchor to the ground.

This is the original KFI tower.

We used to jump from the maintenance building to the tower, never grounding = never electrocuted, climb, watch the fireworks at Knotts Berry Farm and then jump.

Hoping I'm not growing some gnarly cancer after making about 90 jumps there in the early-mid 80's................

Craig


(This post was edited by kleggo on Aug 31, 2020, 12:22 PM)
Attachments: kfi_tower_base_building.jpg (42.9 KB)

Colm

Sep 6, 2020, 8:10 PM
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The energy from FM transmitters on some towers, depending on the situation, can sometimes get absorbed by certain spots on the metal tower structure. Those spots then heat up to a very high temperature. I never personally encountered that, but I have heard of people getting bad thermal burns by accidentally grabbing the wrong piece of metal railing or truss. If you stick to the ladder you should probably be OK. If you are on a deck near a transmitter, just be careful when grabbing something you've never touched before, until you know everything is cold.

A separate thing that high RF energy can do, across a very wide band of frequencies (including many common transmitters out there), is interact with your eyes in a way that can cause cataracts or other ocular problems. The effects as far as I have read (which isn't much) are cumulative and irreversible. Your nuts can get injured too. So I would climb quickly and not take breaks when going past any transmitters for this reason.

For the most part, injuries from non-ionizing RF energy are rare. OSHA recommends not exceeding 10 mW/sq. cm. of non-ionizing RF energy.

https://pubmed.ncbi.nlm.nih.gov/14628311/
https://www.ncbi.nlm.nih.gov/...articles/PMC3526913/
https://www.fcc.gov/...ety/faq/rf-safety#Q5


(This post was edited by Colm on Sep 6, 2020, 8:12 PM)

John_Scher

Sep 7, 2020, 8:35 AM
Post #10 of 14 (1117 views)
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Re: [717Racer] Antenna Advice [In reply to] Can't Post

 
regurgitation from fourteen years ago...

A Short Antenna Story


Sunday afternoon in Nairobi, Kenya; a beautiful blue, sunny day...

I load up the car with wife and child and off we go for a drive to the Ngong Hills (Karen Blixen's old farm land). Lovely drive, cruising in the Benz... when low and behold an antenna tower (pylon) comes into view. Ignoring wife’s protests I pull over and do my best to estimate its height; probably about 150ft, not really sure though. A couple of hours later we are almost back home so I call up Mark, my Base buddy and ask him to come see; of course he agrees. I drop the family back at home and go pick up Mark and his wife Annette. Mark and I are the jumpers and Annette, god bless her, has always provided ground support. She takes the videos, fantastic stills and makes the most exotic sandwiches. The three of us constitute the total Base community in East Africa.

Within the hour we are driving back to the “A” replete with laser. As we drive nearer to the antenna I ask Mark how high? He replies “about 100ft to 150ft” I think it might still be still be doable even with our limited experience. Either way this little jaunt breaks up a less than exciting Sunday afternoon quite nicely.

We pull up in a side road and note the “A” is situated in several acres of grass land with a not very dense population surrounding it. Mark points out that it will still have to be done at night. With our limited experience this is going to be a challenge in itself. Anyway off we go, through the perimeter bush, across the unkempt grass land. Within minutes we are at the perimeter wall of the antenna. Jeez this thing seems bigger than we thought, or is it? Out comes the laser and… and… and... bingo, it’s over 400ft tall and 360ft to the small cage platform at the top of the ladder. We can’t believe our luck; we’ve got one right on our doorstep, excellent!

To be honest the realisation that this thing is actually doable changes our thoughts completely; scary and exciting but more scary than anything else.

We work our way round the perimeter wall to the wooden gate noting that the longish grass is not at all trodden down or otherwise disturbed. The gate is somewhat rickety and has cobwebs between it and the frame. No one’s been here for some time. There's no lock, just a wooden slat providing a basic latch. Inside the same feelings prevail: un-trodden grass and an apparently derelict structure. There are no antennas, reflectors, radiators or any other transmitting devices on the antenna. "I don't think anyone's been here for ages"

I see, open up and check out an electrical box which is fitted on the base of one of the legs. I have an HND in electrical engineering so no problems in that department. The wiring inside is hanging loose, the fuses are missing and it’s full of cobwebs and dead spiders. In fact the tower has rust all over it, the ground is littered with old electrical supports and other bits of metal; there’s no doubt about it, this antenna is definitely not in use.

There is a small block building situated right under the tower which we will work our way round to in a minute but for now we are overwhelmed and amazed. I climb up onto one of the concrete blocks supporting one of the legs. This leg has the externally mounted, ladder directly above it. I note and discuss with Mark some huge interlinked but not electrically connected flux rings on one of the legs. I assume that these must be part of a lightning protection system however as I am not unfamiliar with lightning protection systems I wonder why there is no direct connection to earth; no problem, I’ll look it up when I get back to the office on Monday.

Mark is standing on the ground at the base of the block and I am about 5 feet above him. We are looking straight up the ladder which has hoops going over it. It looks like an endless tunnel and really, really scary. The ladder starts about six feet above where I’m standing but I’m sure that I will be able to pull myself up if I just reach up over this shroud and ... ZZZAAAAAPPPPPP! .... Bluish flash, smell of bacon (burning flesh), fingers are burning; jeans are smoking and a sharp stinging feeling on my calf muscle.

Derelict tower? Yeah right!

I made direct contact with the tower with my fingers just above an insulator shroud. The high Voltage, because I was wearing thick rubber soles, travelled from my fingers to my leg; blew a hole in it, burnt a small hole through my jeans and jumped across a four inch air gap onto a piece of metal protruding from the concrete block.

Needless to say we have since read every forum and have studied everything there is to know on "AM" towers. We do have a plan for jumping it and the all wood ladder will be ready in a day or two but that’s another story.

(This post was edited by John_Scher on Sep 7, 2020, 8:37 AM)
Attachments: Finger & Thumb.jpg (33.5 KB)
  Leg.JPG (56.7 KB)
  Tower 2.jpg (18.3 KB)
  Tower 4.jpg (44.6 KB)

Colm

Sep 7, 2020, 4:23 PM
Post #11 of 14 (1090 views)
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Re: [John_Scher] Antenna Advice [In reply to] Can't Post

Did you ever try this? :)

John_Scher

Sep 8, 2020, 9:37 AM
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listening with grass haha funny and scary



We went back to the AM tower a week or so later, at night with a dry wooden ladder and some rubber sheets nailed to the back of it to act as a sort of shroud/insulator. There was a lot of moisture, actually mist, in the air and we could hear the Tower sizzling like a sausage frying, from 100yards away. It put us off as I was worried about it arcing across to us thru the damp air as we got near it.

My buddy left the country so I don't have anyone to help carry the ladder other than my staff at work or my domestic staff at home and I sort of think that electrocuting one of them might be considered "poor form".

(This post was edited by John_Scher on Sep 8, 2020, 12:56 PM)

717Racer

Sep 9, 2020, 5:19 AM
Post #13 of 14 (967 views)
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I appreciate the help guys! John, that's a pretty crazy story. I'm glad you're alright. The antenna we climbed the other day was definitely FM and we can spot the differences between them. We'll stay away from the AM ones for sure.

NimblyDuck

Nov 12, 2020, 6:31 PM
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Re: [TomAiello] Antenna Advice [In reply to] Can't Post

Tom,
I've been trying to find what levels of effective radiative power (EFP) are considered (safeish), or at what EFP should you avoid an FM tower?
thanks


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