Basejumper.com - archive

I have been looking for thread i saw some time ago about am and fm antennas. if the thread is gone can any help me to understand what i have to consider before i jump one.

Thanks.

Consider finding something else to flik...

but it is 1250 feet

Climbing 1250 feet of transmitting antenna is going to fry you.

I'd be sure I knew what the radiation level was, and what the safe exposure time is for that level.

I swore off AM towers after landing, retching, and laying in the landing area vomiting for 20 minutes under an AM tower I thought would be in the "safe" range.

Something that tall is typically an FM antenna, most of the hazard is associated with the top stinger, and with the directional side transmitters (pods, drums, or dishes), or with any secondary stingers (omnidirectional transmitters). The antenna body (girderwork) is just a platform providing heighth to maximize signal strength over distance. Much of the climb shields you from much of the radiation because you are behind and beneath main transmission elements.

Am Transmitters tend to be smaller,and tend to occur in groups of 2,3, or 4 identical antennas with the same light scheme flashing simultaneously. The hazard traditionally is two-fold; one, the entire body of the antenna framework is used to transmit a signal, not just a stinger or whip on the top, hence exposure to electromagnetic radiation occurs uniformly from the ground up, exposing you for the duration of the climb (where an fm concentrates exposure only around transmission elements (top stinger, side mounted arrays, pods, dishes, drums, and whips) the intensity of which increases the closer or higher you get to these points.) And two, for an AM transmitter to put out its signal, it modulates the amplitude of a "carrier wave" with the signals "intelligence" (music, sports, christian nonsense, etc.). To produce the "carrier wave" the entire body of the antenna is literally electrified, when attenuated by the top, an echo of the signals modulation folds away in the electromagnetic spectrum radiating from the entire body of the antenna. Long story short, if you touch the antenna while standing on the ground or in contact with anything uninsulated you will be electrocuted. These are not necessarily popular BASE destinations.

Both Am and FM antennas come in two major forms: guy wired and freestanding. Or an antenna body which is held up by cables versus a pylon or pyramid shaped structure which supports its own dimensions internally. Typically the AM antenna that is guyed will always have multiple little black or grey "balls" or insulators visible on the cables. So there will be an antenna, then cable, then a little black ball connector then cable, then black ball, then more cable. This is a dead giveaway for the FM guyed tower. Dont mistake orange beach balls for insulator balls. Many guyed towers have these big colored beach balls on the wires to make them visible for crop dusting low flying pilots, and also because Tom Aiello is mesmerized by large orange things and will typically forget about jumping when confronted with evil orange. The freestander is a little less obvious. Small, probably unjumpable heights in this category can occur by itself (a single antenna), but very typically Am antennas of a jumpable height have a strong tendency to be in groups (like elephants or whales or prostitutes, or Tom Aiellos). They are all of the same type and height, with an identical light system which flashes all the antenna's lights simultaneously. These groups in the US tend to be in two's, three's, or four's all in the same area. Examined up close AM antennas will usually have a black insulator at the base (guyed and freestanding) although the freestander may be difficult to see. Also the freestander will have odd things at the bottom on one or more of the legs of the pylon, including massive magicians ring thru a ring perpendicular to each other, or wand like whips extending up from near the base. Also, because AM stations have smaller audiences and are less profitable, they have a tendency to have small, crappy, wooden fences around them, or even no fence at all, compared to their wealthier cousins the FM's which tend to have "cyclone" link fences with barbed wire, metal poles, etc. The AM towers fence can be as ridiculous as a three foot high white picket fence with no barbed wire. Or a Tom Aiello in a wingsuit.

The general philosophy of jumping both antenna types involves "get up, get off, and get away" to minimize exposure time, but because of the risk of electrocution on AM towers, typically people just say "stay away". To jump these you must get on the metal tower without ever touching the ground or anything in contact with the ground at any time in the process, requiring jumping on to the tower from some insulated base and grabbing non grounded antenna without flailing, stepping off, steadying yourself with anything grounded or the like due to imbalance or error. And yes, I drew a white arc off one freestander long ago by bending a grounded part of the antenna close to an electrified part of the antenna.

To sum up. Use the elevator if possible to minimize exposure. Dont rest near any pods, drums, dishes, or arrays on the antenna as you ascend. Never get in front of any transmission element as some of these are putting out a focused beam pointing away from the tower. Never touch the stinger on top of the tower (if there is one) and in fact, never ascend higher than the metal dais at the base of the stinger or above ladder accessability. Tend to stay away from the very top, and exit from 50 or hundred feet beneath the top. If you suspect an AM antenna, move on to the next jump site, Or get Tom Aiello to short it out for you. Get up, get off, get away. Dont get caught.

Lastly, take the antennas registration information, or Serial number or call sign to research further information on it, particularly on www.berkana.com or with the FCC.


Enjoy!

Thanks truckerbase..... I will take Tom Aiello on all my antenna jumps from this day forward.

I usually bring along a long stick and roast weenies in front of the transmitters as I climb up.

Excellent post Truckerbase! Your post should be a good reference for general antenna questions in the future.

I've moved to Idaho now (Mountain Home) so let me know if you ever need anything when you roll through. The Idaho Crew (aka the Spud Huckers) are working on opening up some new objects to compliment the bridge...so look for some new stuff in the future!

C-ya,

Bryan

Thanks 758, saved that for my reference library.

thank you Tom and specially Truckerbase for your intelligent writing.

Thank you Truckerbase for the full and usefull information. Is there any good methods to check if AM-antenna is working or not?

One AM-antennas complex i knew has 6 antennas. One in the center of the field and 5 other around it connetcted with the central one by the wires wide on the top.
Every antenna stand on an isolator. There is a metall 'ball' on the metal standing directly near the antenna' foot and another 'ball' attacher to the antenna' body a little bit over the top of isolator. It's the distance like several cantimeters bethween the 'balls'. I was told there should be 'electric flash' if you put some metal stuff bethween the 'balls' on the active antenna. Is it right?

Anyways we have an another method to check if that and other antennas switshed on or not... but that info i asked about may be usefull for the possible new sites. I guess that 'balls' are the typical stuff on the such AM-antennas.

Last time I checked on some, I phoned up the Technical Director of the company that ran them, put on a geeky voice and explained I was an "antenna spotter" and could they give me some information on their set up..........

he was more than willing to go all technical and give out the information - out of the 12 AM'sthat used to be there and were running, he told me exactly which ones were live and which were dead...............

Nice one boys in opening up the dirty dozen before knock down.... may it all now rest in pieces..............

I believe TruckerBASE's method is to have a Tom Aiello grab the tower and see if he gets fried...

I jumped an antenna complex like that near Moscow (120 km north) with Den, a very rusted group of antennas in the forest near a road, that leaves your hands very red. This is near the "military complex" ? US AM antennas are usually in a line, but yes, that group was in a circle, and was visibly disintegrating. Basically if the antenna is standing on an insulator then you should assume its "on". The Balls you describe I remember, they allow a lightning bolt to find a ground without actually grounding the towers electrification, like the ring in a ring described above. Lightning hits the tower and then arcs over that short distance between the balls (or rings) to the ground, without any direct contact to the ground. The lightning is discharged, the electronics of the transmitter are isolated from the lightnings path to ground, and the antenna continues to transmit uninterrupted. Yuri, the master, and Den, the low puller, will rule your area and an understanding of local european objects; if they havent jumped it, it must have fallen down. You guys rock in the hardcore department.

Ps. I wouldnt play with am antennas to see if you can draw an arc from it, although some people suggest dragging a finger across it quickly to test it, this is like sticking a paperclip in an electrical outlet to see if its on or not. Even if it doesnt blow you to pieces, the electrical flash from such an arc has the ability to burn your retina. Please dont put metal stuff between an active antenna and any ground. Treat it as though it were live, even if it is a derelict ruins like the moscow site. Also, although that site was military (according to Den) a commercial am antenna will have listed hours of operation. The call signs or registration number should allow you to make an innocent call to the station to check on its status or to see if the broadcast day ends at a certain time, after which the antenna may be off. Still sounds like a lot of work, when you can always just go jump KGB buildings anytime!

ps. Inviting Tom Aiello over for a mushroom hunt (he loves sauteed mushrooms), and then casually and nonchalantly shoving him into the antenna body will instantly determine whether it is on or not. This has the added bonus of feeding Zennie who is perpetually trying to roast different things in different ways, and who always has a packet of hot dogs in his glove compartment for just such an occasion.

cya

Hence the smell in zee german car...

Just watched a vid on Youtube where a couple of guys jumped an AM antenna a month ago in NZ. Did a search and found this thread which strongly indicates that there are health issues which could be ongoing.
Anybody got anything new to add?

dude, have we gotten so old that weve forgotten about s'mores?
graham crackers rule

The fact that it was on youtube attests to the Darwinian dynamic at work. Knock yourselves out.

Cheers

Not mine or of me but friends of mine. As for am radiation i doubt the one jump i have from that thing will kill me before anything else will. although would have done it a couple more times if it wasnt so far. That board gets replaced each time for those who claim damage issues. As for the video on the net thing yeah i wouldnt have done that myself but on the upside at least its not just twin falls

dude i jump this 500 footer all the time and it never bothers me go big go for it

What about the guys that worked with asbestos years ago and now have asbestosis or mesothelioma which is a particuarly nasty and aggressive form of cancer caused by astestos. They probably also had the 'it can't hurt me' mentality.

I was wondering if anyone knows much about how AM towers are designed/laid out.

I've been looking at some nearby antennas and I'm 99% certain that they're all for the one station (so just the 1 freq), but the strange thing is that there are 4 towers in 2 pairs. The towers in the pair are about 200 - 250 m apart and the pairs are about 1 km apart. From what I can tell from the ground, they're identical and about 150 m tall. The station is 891 kHz and I've seen the power listed as 5000 W although I don't know how reliable that is.

So... does anyone know why there would be 4 towers for just the one station? I can't imagine it would just be for redundancy (seems like an expensive way to do it). It's a national station so could it be some sort of re-trans configuration and one of the towers in the pair is only receiving? Any other ideas?

Is there anyway of finding out if a tower is live without becoming crispy or glowing green and spewing?

The towers are in a sweet location and 1 1/2 hrs closer than my current 'local' A so I'm hanging on to the dim hope that at least one won't be active.

PM sent

Oh yeah. Just realised I should've added this is in Australia so the FCC website isn't applicable.

Edit: I've made a little bit of progess and also found this WRT exposure to RF radiation. I haven't read through it properly yet (pretty geek-heavy stuff) but if anyone's got a knack for physics...

http://www.acma.gov.au/...lerts/guidelines.doc

Just in case anyone's vaguely interested, I've found out what's going on with these towers. I put this up on the ABA site a while ago, but figured I'd share the info here too.

Turns out there are 2 stations after all. After a few emails to random people which gave me a start point, I finally found a very small, obscure sign with the 2nd station's name and just sent them an email asking why they used 2 towers. The station engineer was really helpful and didn't mind answering any of my questions.

Turns out, having AM towers in pairs is used to make the signal more directional by reinforcing the wave in one axis and cancelling in the other. So if you see a couple identical looking towers within a few hundred metres of each other, this is probably what's going on and they'll both be active. Bummer.

It's also possible that there will be more than that, for the same reason. I've seen arrays as large as 7 antennas.

Think any of these could be of any use to detect type of radiation and safe exposure levels?

http://www.norad4u.com/monitor/home-emr-meters

 
http://www.norad4u.com/monitor/home-emr-meters

Although I'm pretty inexperienced, I recently talked frankly with an antenna rigger and I have a few relevant notes:

* The radiation is non-ionising (but various frequencies can cook flesh really well)
* The damage done to your body could be immediate, or could take years to manifest.
* Antenna riggers have to wear EMR meters but often turn them off because they're always beeping. (I would like to get one, I'm considering this one). But the meter that is designed to go off when you point it at your WiFi router might be too sensitive to take up a tower.
* Just don't jump AM towers unless you really know what you're doing: Not all of the towers in an array are active at a time but you can never know which ones are inactive.
* AM towers have shitty wooden fences so that there isn't spikey metal nearby to ground the antenna.
* AM Towers sometimes have well cut grass around the base reaching out the antenna's height away - the exact height of the antenna is important and grass growing can affect the transmitted wavelength.
* Even if an AM tower is off, it is a big ungrounded piece of metal and will pick up EM radiation from the air (like a regular receiver radio) and this could still electrocute/shock you. I haven't tried grounding one with Tom Aiellos though
* For this reason, tall towers (AM, FM, anything) may have insulating blocks breaking up the longer guy wires.
* Some non-AM antennae can have an AM wire just away from the structure that runs up the length of the antenna. If you're grounded on the antenna and you touch this: game over
* Clusters of transmitters can create radiation pockets on the antenna
* Tower riggers are allowed to work on cellphone transmitter towers while the transmitters are on because they're really low power.
* There are 'lobes' of radiation directly behind and to the sides of transmitters as well as the main one in front.
* If you're in the US, you can look up any antenna and find out what it transmits.

I hope if anyone sees any errors/inaccuracies in this that they correct me. My understanding is that one should avoid AM; I know people jump them but I don't know if they have mitigated all the EM risks. I guess grounding a powered-off AM antenna would work but I wouldn't want to be the one to do it just because I lost at rock-paper-scissors

interesting info, thanks.

no offense, but this is the part i hate about forums.

gotta love the telephone game.

shirley you cant be serious..........

None taken. Antenna rigger was a BASE jumper (no he didn't just get a few at the Perrine) for many years. Perhaps his advice was more conservative to me because I'm new, that's why I suggested not to jump AM if you don't know what you're doing - the part I love about forums is that some people here know more than me and can give more direct advice.
Anything I wrote that you disagree with? Or are you being healthily skeptical?

haha. I think I know what happened here.

Somewhat related question here. Does anybody know anything about FM Translators? To be honest I have no clue if these things are your typical AM tower that is pretty much untouchable or if it's something that could be done? There's a nice 400' a few miles from me but I've always thought it was just a regular AM tower until I did some digging through the FCC sites.

I am serious. And don't call me Shirley.

Couldn't resist...