::NEC guidelines are based on wire strength, not conductivity, and I agree a lot of hams are using antennas that wouldn't fall within the rules. Although, since I don't like replacing wire antennas when they break, I pretty much follow section 810-52 without even thinking about it.
Originally Posted by K9STH
Regarding towers being good antennas, sure they are. But galvanized steel's a way better conductor than stainless steel is. I'm sure you're familiar with the popular conductivity scale where copper is "100." Based on copper having 100% conductivity and being the standard, other materials are:
Stainless steel 5
Stainless is only about 5% as conductive as copper. However, galvanized steel has a high zinc content and ranks at about 28%, which isn't bad. It's about half as good as aluminum, which is excellent.
::Just did, and it's hocus-pocus for antenna wire.
Originally Posted by VK2AKG
Depth at 10 MHz for Cu = .0008"
Depth at 10 MHz for Al = .0009" ...
Less than 1 mil depth either way
The difference between using galvanized fence wire and copper wire of the same size for a dipole on 160 meters is about 1 dB or less. The difference between #17 aluminum wire and #17 copper wire on 160 is about 0.13 dB. The difference is less on the higher bands.
Galvanized fence wire is usually 17 ga, hot dipped galvanized, plated with about 43 microns of zinc (if it is the high quality thick plating). That's about 0.0017 inches thick. The skin depth of zinc on 160 meters is about 0.0036 inches (compare to copper which is about 0.0019), so for RF purposes the wire looks like steel, or maybe iron, depending on what you buy. You can get iron (low carbon steel), medium carbon steel, or high carbon steel.
Wire size also makes a difference. On 160 the difference between #17 copper and #12 copper is about 0.2 dB. Since loss is a function of current and the distribution of that current on the antenna, you can't accurately extrapolate this to other types of antennas. The best method would be to use NEC to calculate it.
There isn't any significant difference in loss between solid wire and stranded wire if the stranded wire is twisted. If the stranded wire is braided there still isn't a difference, unless the braided wire becomes corroded because of water intrusion or some other reason. If water enters the braided wire it will have loss of contact with overlapping strands, and current will resist following the strands into the center of the braided wire, resulting in a lot of loss. Same thing happens with coax when water gets inside it. This is one of the bad features of building an antenna out of coax (like a double bazooka). A crack in the jacket (which can be assisted by birds and wire tension) will allow water in. Although some may consider that an advantage since the extra loss will increase the bandwidth and that is the only reason for using a double bazooka anyway.
This thread is geting ALMOST as out of hand (yet remaining ON topic) as the one about SWR, coax and tuners a few weeks ago.
Use the type of wire conductor that best suits your NEEDS, to allow for maximum life of the antenna.
IF your antenna is going to whip around in the wind, flexing all over the place, and is less than 150 feet total, use copper, stranded, 14 ga.
Easy to work with, doesn't kink, lasts a long time.
If longer than 300 feet, get stronger wire.
Copperweld STRANDED is strong, BUT the copper can be THIN in places, and it will rust in those places very quickly, even just a few years, those thin wires will break when rusted, flexing in the wind. Kinks easily when installing.
Solid copper IS strong, but streaches in time, I ONLY use #12 or larger when using copper, pre streched, hardend copper is better.
I have NEVER, EVER had a SOLID copperweld antenna break.
IF you are going to put up an antenna where there is a chance of a heavy branch breaking and falling on your antenna, USE SOLID copperweld.
I use #12 solid copperweld, have had MANY, HEAVY branches fall on it, some STAYING there, swaying in the wind for days, one side had a TREE fall against it, for over a week before I discovered it, NEVER broke. Has been up, no repairs, for over a decade so far, 200' each leg. Has survived ice, serious winds, trees, and yanking to shake off branches over the years!
VERY difficult to keep the kinks out of the solid copperweld (when installing), however, carefull handling, unwinding and days of prestreching all help.....
Bottom line, ANY WIRE will work, some work structurally in some situations better than others, but electrically, they ALL work just fine.
Just MY $.02,
Last edited by WA9CWX; 07-29-2008 at 06:37 PM.
"Clear intent is the best predictor of experience"
For "permanent" antennas, I use Copperweld #14 for 80 & 40 Meter antennas, and #18 for 20 and above. The Wireman has them in stock. Split-bolt connectors facilitate adjustments.
When tinkering, it's whatever is at hand, including electric fence wire.
Last edited by W4HAY; 07-29-2008 at 07:20 PM.
“There are two ways to conquer and enslave a nation. One is by the sword. The other is by debt.”
"The penalty good men pay for indifference to public affairs is to be ruled by evil men."
Broadcast towers are NOT made from plain iron! Iron is generally way too soft and does not have sufficient strength to be erected at the height of even a quarter-wave in the AM broadcast band. They ARE made from steel. Remember that steel can be considered an iron alloy. Even if wrought iron was used to make the broadcast antennas it is way too brittle to withstand the elements including wind forces.
Now every broadcast tower that I have ever seen definitely was galvanized. Now years ago many towers were painted to reduce the effects of weather on the tower. However, the paint was generally applied over the galvanization. Now, somewhere, there may be a really old tower that was not galvanized (just painted). But, these days, tower sections are routinely galvanized for rust prevention.
Since most AM broadcast towers need only to support themselves (of course the vast majority of these are guyed towers) the tower sections are often hollow although solid steel towers are also used in many cases. I have seen Rohn 25 tower used for the antenna at many low to medium powered stations and Rohn 45 used in many other cases. Of course many of the high powered stations (i.e. the 50 kW types) use Rohn 55 or even Rohn 65 tower or equivalents.
However, iron just is not used for towers. Even the "iron" beams used in skyscrapers are made from steel if, for no other reasons, than steel is considerably stronger than iron and steel generally is slightly lighter for any particular size. To get the same potential strength from plain iron the cross sectional area of the item would have to be substantially greater.
BC towers I've seen up close are all galvanized too. Sometimes also painted alternating white and red going up to make them easier to spot for low flying airplanes, I guess, but they're still galvanized.
The guyed ones are often Rohn 55 or 65. The self-supporting ones all taper a lot and have very wide bases, Rohn SSV or whatever. Still galvanized.
Wire for dipoles can be any thickness, within common sense. If the wire is too thin it will not support its own feeder in the centre unless it is supported by a suitable length of cord. Incidentally, 2/16th in most circumstances is known as an 1/8 of an inch, not an unusual diameter for antenna wire.
::Pretty thick for antenna wire, but I've seen it used. AWG #8 ("8 gauge" wire) is .1285." Pretty heavy stuff.
Originally Posted by G0GQK
While being an elmer for a ham radio class the one presenter stated that he used very thin wire for several months in his novice days. He did this so he would not get face to face type QRM about his hobby. The wire was so thin that the birds hit them and got decapitated. After several months he went around and asked his neighbors about TV interference, when they said they had none, he THEN stated that he was a ham. Effective antennas can be very thin, but the code says otherwise.