New hams are often told what they "should" do when putting up an antenna, so I encourage you to read this new post about the real world - do what works, that lets you get on the radio, and kindly thumb your nose at the "rules" while you have fun on the air. It sure beats stressing over what your antenna "should" be! After all, it's better to have something to get on the air with while you build the "correct" antenna, than it is to sit looking longingly into the ether with nothing to transmit through... http://www.n3vem.com/blog/absolutely-awful-antenna
What you should do is be safety-wise. Irrespective of performance, there are two opportunites for starting a fire--with high(er) power. First, at the points of higher ohmic loss( =heat buildup) and second, with voltage max point (s) shorting, such as with rain, to ground. Why, that would be awful!
Chip, I know you've mentioned this before but I have to ask; do you have any direct or even anecdotal evidence that a fire risk exist in an antenna (besides the obvious lightning strike cause)? Ive personally never heard of one in my 47 years it's. Have you?
I know this isn't directed at me, but this is a true story. One of my Tech students wanted to have a 2 meter radio in his garage, so I went over and set him up with a 50 watt mobile with a home made j-pole, one out of TV twin lead. There is a notch cut into the lead by design. I put tape over the notch so the antenna wouldn't snag on things. We hit a couple local repeaters fine on low and medium power. Then we turned the radio up to 50 watts to try for a farther repeater and the antenna caught fire!! Actually, it was the black tape over the notch. I don't mean smoldering, I am talking FLAMES!!! We removed the tape, what was left of it, and the antenna looked fine, and seemed to work fine with no fire, so long as there was no tape.
Sounds to me as if some component of the tape was RF conductive somehow! There was no great felt when operated without the tape? You've brought back a memory... years ago I was fooling with a ten meter vertical I was home brewing. I made a coaxial sleeve capacitor out of some plumbing parts, both plastic and metal. The antenna tuned up fine at qrp so I placed it higher and ran 100w to it. The swr immediately started climbing so I unkeyed and went out to the antenna. One of the plastic parts I used had melted with 100w to it. It might have caught fire if I had left power on it. clearly that particular type of plastic (don't ask me what it was, I don't remember) was not transparent to RF. I found another type of plastic fitting and tried that and it was fine... worked for years after that. Do you still have that tape? Put it in a microwave along with a glass of water for a few seconds and see if it doesn't get hot... DONT BURN DOWN THE HOUSE!
Yes. A decade ago I tested out several antenna types , used by hams, for a defense client, to find out exactly how much power, continuous, they would deliver before smokin'.... Theres a famous photo in the W6 AM book of a guy lighting his cigar at the feed of Don Wallaces antenna. There are well known filure modes with some those current choke/tranformers that can cause fire. 50 watts of 1500 can do bad things...
We had a big discussion about antenna fires around seven years go. I cannot find the photos, unfortunately. One ham posted a photo of his charred dipole end touching a leafy tree branch which was on fire. Others recounted a number of fire incidents related to faulty insulator materials. Yes, antenna fires can happen.
This is a classic video which shows a wire attached to the end of a 40m dipole and deliberately brought to a tree trunk. Even though it is insulated by PVC piping it immediately arcs and catches fire. Voltages at peak points on antennas can be several thousand volts.
Two accounts from QST of antenna fires. SEP 2012 - QST (PG. 63) "Your Antenna Is On Fire!" (Feature) Author: Schaefer, Thomas, NY4I This item is not available for download by Members Report a problem with this entry APR 2008 - QST (PG. 77) Indoor Antennas and Fire Safety (Hints and Kinks) Author: Crutchfield, Jim, AC4WR Article: QST Archive [PDF] Report a problem with this entry
All - thanks for the safety tips! I'll have review these articals to see how my setup fits into the picture. On the good news side - I actually use this arrangement for low power digital work (no more than 30 watts, usually less). As far as ground risk due to rain, I consider it a non-issue, because I don't use it when it's raining!
Maybe I'm stating the 'not-so-obvious', but shouldn't this thread be moved to https://forums.qrz.com/index.php?forums/antennas-feedlines-towers-rotors.33/ . For those who missed it, here is K9STH's sticky on "PROPER FORUM SELECTION", for those who need some guidance in that area. https://forums.qrz.com/index.php?threads/proper-forum-selection.248289/
It is in an odd section for this topic, no question. Maybe a kind Moderator will move it out of "News" Dave W7UUU
The post actually started as a news post of a release of a new blog article - similar to the announcement of new podcast episodes etc. so the post placement is fine - it's just the disscussion that ensued that went down the antenna / feed line path.
