Hi there people! I think most of this blog readers are familiar with half-wave antenna such as the 2 meter dipole I’ve built as a side project (with height about 1 meter by itself).
But do you know the height of the tallest and biggest half-wave antenna ever built in the world? is it 30 meters? 50 meters? 100 meters? Nope.. the answer is 646.38 m or 2,120.67 feet high when measured from its base on the ground.
Unlike other ordinary radio tower which is build to ensure you can put the antenna at the highest point, the Warsaw radio mast acts as a half-wave antenna itself!
It height 646.38 meter is the exact length of the frequency it was transmitting which is 225kHz, most probably using this formula
half-wavelength = 300/freq * 0.5 * velocity factor
= 300/0.225 * 0.5 * 0.97
= 646 meter.
As comparison, my homebrew half-wave antenna is only 0.996 meter in length, and is drastically dwarf by the Warsaw radio mast radiator.

Completed in 1974, the Warsaw radio mast transmit public broadcast radio station using 2 megawatts on 225kHz frequency. It was also the tallest structure in the world (recorded on Guinness Book of Records) until it finally collapse on 1991 due to maintenance crew failure.
Despite its collapse and inoperability for more than a decade. The Warsaw radio mast still remained the tallest/biggest (and the only longwave LF ) half-wave antenna ever build in the world,
Impressive isn’t it? Take a look at the antenna site in Wikimapia.
Read more about Warsaw Radio Mast in Wikipedia.
Amateur Radio Coax Cable Power Loss calculator (RG 58, RG-8)
Ham Radio, Random Facts February 21st, 2008
Ever wonder how much power is loss in your coax cable feedline? Here is a website which helps you estimate power loss in your antenna feedline according to your choice of coax cable.
For example :

If you are transmitting on 145 MHz frequency with 65 Watt of power using 15 meter RG-58 cable, the maximum effective power radiated by your antenna is just about half of the transmitting power (36.156 MHz).
But when you switch to RG-8 cable, the loss would be significantly lower, and your antenna would radiate 54 Watt of power.
Since the power loss is significant, it is advisable that you consider the choice of your feedline before setting up your station. In emergency or QRP situation, every 1 Watt counts.
If you have no other choice other than to use RG-58 cable, it is advisable to put your antenna as high as possible with the shortest amount of cable possible. This will save your rig a lot of hard work, and may actually get your signal to travel further than before
How much power loss in your feedline ? Check it at Coax Cable and Line Loss Calculator website
Tags: amateur radio, antenna, facts, hamradio, Hobbies





About



