[TowerTalk] Lossy Traps (really long)

[jimlux]

Tony Brock-Fisher wrote:
> The issue of lossy traps is only one of a number of factors that
> enter into antenna comparison and selection. The real question is
> which antenna is best for you? And of course, there is no simple or
> single answer. Over the period of more than 20 years, I have
> considered this question many times, and I have consistently come up
> with a single answer for my station. So before I continue, let me
> admit to being a fan of the KT series of antennas - the original KLMs
> and the newer M2 version. However, that being said, I'd still offer
> the following for consideration.
> 
> 
> 
> Lossy Traps
> 
> Traps are seen to be lossy for two reasons - one is the issue of
> limited Q and thermal losses of the input power. A second issue is
> that traps inherently result in shortened elements, which results in
> slightly reduced gain.
> 
> Heat Loss
> 
> Several years ago, when this issue was raised before, I had an
> opportunity to make some measurements on the thermal (resistive)
> losses in the traps of the KT antennas. Now, the KT antennas are
> often referred to as having 'linear loading' and not traps - but this
> is not really true, as on 10 and 15 meters, the combination of linear
> loading inductance and air-capacitors does form a tuned circuit. It
> may be the lowest possible loss for a tuned circuit - but it's still
> a trap. I did some careful measurements, which I will reprint here:
> 
> 
> (Republished from 1996)
> 
> 
> <snip>

Excellent writeup!

So, the net result is that the traps result in losses of a few tenths dB.

I would assert that this is down in the noise level when it comes to 
(i.e. you might see this amount of change from the wind moving the 
elements around)

Jim