Basejumper.com - archive

i was hoping someone might have some info on identifing am/fm antennas, what are the visual differences so i can recognize them.
also jumping considerations ie: getting onto the tower without being zapped, radiation etc

http://www.hawkins.pair.com/...fan/cbsfan_twr14.jpg

AM tower: insulated from the ground. Base of the tower is insulated from the ground. The guy wires may have insulators linked into them. The guy wire base may be insulated. Tower is electrified. Tower is the transmitter.

http://images.google.com/...%26gbv%3D2%26hl%3Den

Go down on this page and you will see the wire configuration.

FM tower: tower is grounded. The transmitter is not the tower itself but some smaller piece of metal that has conduit (or waveguide) running to it.

AM towers can electrocute you if you touch them and you are grounded. Numerous jumpers have reported ill health effects from climbing an active AM tower.

make tin foil shoes and lick the antenna with your tongue if nothing happens you should be ok

hey thanks freedomed, sounds like good advice let me know how it goes & i'll give it a go

thanks dude, good information

Is there a such thing as a "combined" tower? And is it common place for FM towers to have lots of stuff on them?

I have a guyed 600' about 10 min from home, and was able to quickly check it out the other day from outside of it's fenced area. Outside climb it seems. It also has a ~300' freestander a couple hundred feet from it, within the same fenced in area. I assume the freestander is AM. But i've found information regarding the site as having AM and cell service.

crumbta,

Yes, there is such a thing as a "combined" antenna. These may not have all the tell-tale signs of AM-ness, so it's best to approach any antenna with suspicion and do lots of homework.

A free-stander I was researching looked like a pretty straightfoward (that's a horrible word in this context, isn't it?) project. I began measuring it and looking at it with binoculars from afar. Then one day I noticed that each of the three legs of the antenna had long, taught wires strung up from the ground to about 2/3s up, held to the antenna by insulated booms. A little more research told me those were broadcasting AM, riding piggyback on an otherwise unthreatening free-stander.

Because they were attached to the outside of the antenna with insulated booms, climbing the inside of the antenna would not have been a problem. But an object strike could have been electrifying. I chose not to jump it.

Any chance you can get better photos of your A, without all the fall foliage in the way?

~ Chris

Chris - Thanks for your reply.

Unfortunately, I don't have any better pictures, when we went, there were people doing things in their yards and such, right across the street from the site. Quiet neighborhood. Trying our best to keep a low profile.

The building at the base of the guyed tower had a couple dishes on it as well.

I'd assume, that if it's jumpable, it most likely has been jumped, but it would be pretty sweet to open an object too.

I'm gonna try to go back out this weekend, there's easy access underneath the entrance gates from years of errosion and plowing. I'll take some more pictures too, anything in particular I should look for, except insulators at the guy wire anchors or tower anchor?

I did include the two other pics I had, and then a zoomed pic of the top.

crumbta,

As you're in the U.S., you'll find most guyed AM antennas will have redundant insulation to prevent accidental electrocution. The antenna is usually built on a non-conductive base. The guy wires are usually anchored to the antenna in a non-conductive way, and along the length of the wires, another insulator is usually used to break up the continuity of the guy wire in case it, too, was ever electrified. Take a look at the attached photo. If you see any of these on the guy wires, you're probably looking at an AM antenna that happens to have non-AM appurtenances bolted to it.

If you don't see these, it's less likely to be an AM antenna. But I'm not saying the absence of these guy wire insulators guarantees it's not AM.

Also, look at the smaller, nearby antenna that you mentioned. Do you think it's an AM antenna? If you had an off-heading opening from the bigger one, is there a chance you'd smack into an AM antenna?

~ Chris

The wires don't have any insulators between the tower and the ground, that's why initially i assumed it was FM, but some of the web sites i've used to check on things suggest that at least one of the "users" of this A, are AM Radio.

I'm guessing on the shorter freestander one being AM as well, but it looked as if there were insulators between the structure legs and the concrete blocks it stood on.

Depending on the sector jumped, I think would determine object strike in the event of an off heading. I have a pic from google earth, and modified it to show guy line and fencing orientation. Did my best to not give away any kind of location data. The area has also been better cleared since this overview was captured.

Trees on the street sides are ~60-75', but the homes are quite close.

Use or borrow a DSLR camera with a big lens.
I use a 400 mm lens and sometimes a 2x extender.
Also dress like a dork. Yes really!
Have a dorky hat and a dorky scarf and people will belive you are taking artistic photos.
You can take the photos from a long distance and when you get closer to the object you obviously have to be more descrete when you take photos.

the freestander is almost definitely AM...

the guyed tower may also be "top-fed" AM as well, hard to tell from the pics, but... just from looking at them and their general proximity, i would highly suggest not climbing them.

OTOH, totally doable. but, i wouldn't. AM does weird things to your soul.

Good to know. Thanks for all the help for a new guy! I'll still go check it out and take some more pics.


A ninja stole my soul

Here's some pics from inside the fence.

First 3 are of the big guyed one. Just the structure on the concrete pad, couldn't find anything for a lightning strike to jump, maybe that loop at the base of the guy wires? Other than that, the guy wires are clean.

I'm guessing / assuming that's what the insulators look like at the bottom of the freestander.