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LF: Big/small antennas

To: [email protected]
Subject: LF: Big/small antennas
From: "Walter Blanchard" <[email protected]>
Date: Thu, 04 Oct 2001 09:51:29 +0100
Reply-to: [email protected]
Sender: <[email protected]>
This big/small antenna business :

Let's get this straight - what matters is RADIATED power not how big the antenna is.  Radiated power is the ONLY determinant of how far we get . An antenna is only a launching device for em energy and as long as it is capable of launching whatever power we think we need that is all that matters.  Its efficiency is irrelevant if we don't mind how big our electricity bills are and we are able to control the lost energy properly.  One watt from a tiny antenna will get across the Atlantic just as easily as one watt from a huge one.  The big difference is how easy it is to produce that one watt.

Something of a legend has grown up in the amateur community that you need a huge antenna to get anywhere. This originated in the old licensing regs that put a lid on the  DC power you were allowed to use in the final amplifier.  It was easy to measure and when we had inspectors running around they could check it quickly and simply. This put a premium on final amplifier and antenna RF efficiency and  a "big" antenna, at any frequency, was the best way of obtaining maximum ERP.  Hence the big DX names with multi-multi-element HF arrays hundreds of feet in the air. Now the limit is on radiated power which is much harder to measure (see almost any posting on this reflector for the past few years) but gives us the freedom to use any final amplifier power we like to make up for antenna inefficiency.   So if it takes a 100 kW amplifier who cares?  As long, of course, we can control all the flashovers, corona, arcing, melting insulators etc.

To say that a "big" antenna is necessarily better than a "small" one is therefore rubbish. It's only true if you're a professional wanting 100% reliability under all conditions; are prepared to go into mechanical engineering in a big way; pay lots of money and have vast amounts of real estate. Some are, but it's hardly "amateur" radio and what exactly does it prove anyway?  Only what the professionals have known for many years.  Far better to play about with Micky Mouse antennas that no self-respecting professional would dream of using and get an occasional DX contact.

Final word - the ERP rule is of course open to considerable abuse. The field strength figures produced recently on this reflector seem to indicate that considerably more than 1 watt is being radiated by some people.  Have they got a special licence like the one we got for Puckeridge?

Walter G3JKV.


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